A-description-of-the-findings-from-bull-breeding-soundness-evaluations-and-their-association-with-pregnancy-outcomes-in-a-study-of-western-Canadian-beef-herds

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                                               Theriogenology 74 (2010) 871– 883
                                                                                                                   www.theriojournal.com




          A description of the findings from bull breeding soundness
          evaluations and their association with pregnancy outcomes
                  in a study of western Canadian beef herds
                     Cheryl L. Waldnera,*, Richard I. Kennedyb, Colin W. Palmera
      a
          Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, 52 Campus Drive, Saskatoon SK,
                                                            Canada S7N 5B4
                                                 b
                                                   Pincher Creek, AB, Canada T0K 1W0
                          Received 16 January 2010; received in revised form 9 April 2010; accepted 9 April 2010



Abstract
    The primary objectives were to describe beef bulls considered for use and those reported as used in 205 beef herds in western
Canada, and to determine whether factors typically assessed during breeding soundness evaluations were associated with
reproductive success. More than 100 veterinary clinics reported 2990 breeding soundness evaluations for bulls considered for
natural service in client’s herds. Differences among clinics explained 5.2% of the variation in scrotal circumference (SC) and 6.9%
of the variation in percentage of morphologically normal sperm of all bulls considered for use (after accounting for age, breed,
body condition, significant physical abnormalities, month, and year). The percentage of morphologically normal sperm was lower
in bulls with an SC 34 versus 34 cm (P 0.006). This study included data from 1384 and 1370 bulls used for breeding in
2001 and 2002, respectively. Most (80%) of the bulls used were Simmental, Black Angus, Charolais, Red Angus, or Hereford,
and 80% were 4 y of age. Before the breeding season, a veterinarian evaluated 89.5% of all bulls used in these herds. Of the
bulls subjected to a breeding soundness evaluation and subsequently used, 93.1% were satisfactory. In 2001 and 2002, injuries
were reported in 2.5 and 2.1% of bulls and in 16.6 and 11.4% of herds, and necrobacillosis of the foot was reported in 2.5 and
1.2% of bulls and 11.2 and 6.5% of the herds. The average number of cows exposed to each bull was 26 (both years). Cows
exposed to bulls with a smaller SC were less likely to be diagnosed pregnant (P 0.047) and had a longer median interval from
first bull exposure to calving (P 0.016) than bulls with a larger SC. In conclusion, our findings emphasized the value of breeding
soundness evaluations, including measurements of SC, in fertility management of beef cattle.
© 2010 Elsevier Inc. All rights reserved.

Keywords: Beef bulls; Breeding soundness evaluation; Herd fertility




1. Introduction                                                            sold for breeding in western Canada are subjected to a
                                                                           breeding soundness evaluation prior to sale. The utility
   Reproductive success is one of the most important
                                                                           of breeding soundness evaluation in predicting bull
factors affecting the profitability of the cow-calf herd,
                                                                           fertility has been reviewed by Kastelic and Thundathil
and livestock producers recognize the importance of
                                                                           [1]. Most organized bull sales in western Canada re-
bull fertility in overall herd performance. Most bulls
                                                                           quire that all animals offered for sale have passed a
                                                                           breeding soundness evaluation; however, not all pro-
 * Corresponding author. Tel.: 1-306-966-7168; fax: 1-306-966-7159.        ducers subject their bulls to evaluation before subse-
   E-mail address: cheryl.waldner@usask.ca (C. Waldner).                   quent breeding seasons. Despite an apparent lack of

0093-691X/$ – see front matter © 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.theriogenology.2010.04.012
872                                 C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883

recent information regarding the percentage of produc-             and only herds with a winter/spring calving season
ers in western Canada that routinely evaluate their bulls          were enrolled. One of six project veterinarians regu-
for breeding soundness, 27.9% of Alberta producers                 larly visited each herd to collect herd data, including
reported having their bulls evaluated by a veterinarian            reports from the local veterinary clinic, and to monitor
between 1986 and 1989 [2]. More recently, 18.3% of                 the quality and consistency of on-farm records.
US beef producers reported having their bulls semen
evaluated in 1992/93 and 17.0% in 1997 [3]. Also many              2.2. Bull inventory and breeding soundness
producers evaluate only the herd bulls suspected of                evaluation results
having a fertility problem (e.g. based on pregnancy                    An inventory of all bulls intended for use in the
rates or calving history or obvious physical defect),              participating herds was completed before the start of
rather than evaluating all bulls in the herd.                      breeding season in 2001 and again in 2002. This infor-
    A large on-farm study of factors affecting the pro-            mation included herd identification, bull identification,
ductivity of cow-calf herds in western Canada provided             age, and breed. Producers were asked to record any
a unique opportunity to obtain complete breeding                   purchases as well as any losses from inventory, includ-
soundness evaluation data for bulls from commercial                ing the date and reason (death, sales of breeding stock,
herds and to evaluate associations among bull at-                  culling, or missing).
tributes, management, and herd fertility [4,5]. Produc-                Before the breeding seasons in both 2001 and 2002,
ers were given incentives to encourage them to have all            herd owners were asked to have all bulls intended for
their bulls evaluated and to have a veterinarian deter-            use in natural service pasture breeding evaluated for
mine pregnancy status of all cows. This minimized                  breeding soundness by a private veterinarian chosen by
potential bias resulting from a less complete and rep-             the herd owner, using the criteria and forms established
resentative sample of animals or herds. The first objec-            by the Western Canadian Association of Bovine Prac-
tive of this study was to describe the results of breeding         titioners (WCABP) [6]. When possible, pre-purchase
soundness evaluations for all bulls considered for use             breeding soundness exam reports using this protocol
and those used in a large sample of cow-calf herds. The            were obtained and those results were then included for
study considered associations among commonly re-                   bulls that were not re-evaluated after purchase.
ported measurements from breeding soundness evalu-
                                                                       Briefly, the WCABP Bull Breeding Soundness Eval-
ations and factors that potentially affected these mea-
                                                                   uation form consisted of data entry cues for the follow-
surements. The second objective was to determine if
                                                                   ing: bull owner; history; identification; age (months/
the breeding soundness evaluation results for the bulls
                                                                   years); breed; body condition score (BCS) (scale 1–5);
used in commercial herds were associated with repro-
                                                                   physical abnormalities involving eyes, feet, legs, and
ductive performance in this group of beef herds. These
                                                                   the internal reproductive tract; scrotal circumference
data also provided an opportunity to assess differences
                                                                   (SC); method of semen collection; semen quality; and
among veterinary clinics regarding how they used and
                                                                   classification of the bulls breeding potential. Semen
reported the tools for breeding soundness evaluation,
                                                                   quality assessment varied slightly among practitioners,
while assessing the utility of this information in the
                                                                   but consisted of series of measurements potentially
context of a real-world setting.
                                                                   including assessment of volume of the ejaculate, semen
                                                                   density, gross and progressive motility (percentage of
2. Materials and methods                                           motile sperm), percentage of morphologically normal
                                                                   sperm and those with specific morphologic defects, and
2.1. Herd selection
                                                                   the percentage of sperm staining alive. Only the SC,
   Herds were recruited as part of a comprehensive                 percentage morphologically normal sperm, percentage
study of factors affecting beef cattle productivity in             of sperm staining alive, and percentage of motile sperm
western Canada [4,5]. Private veterinary clinics across            were entered into the database for further analysis.
Alberta, Saskatchewan, and north-eastern British Co-               Bulls were classified as satisfactory, questionable, de-
lumbia were invited to participate. Within each prac-              cision deferred, or unsatisfactory breeders. The deci-
tice, herds were enrolled based on selection criteria that         sion deferred classification was used for bulls which
considered herd size, completeness of animal identifi-              were expected to show a substantial improvement in
cation, calving records, presence of animal handling               semen quality before the coming breeding season,
facilities, and a relationship with a local veterinary             thereby warranting a re-evaluation within a few to sev-
clinic. Herds with 50 breeding females were excluded               eral weeks [6].
                                    C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883                               873

   Data were also collected on whether the bull was                pastures, the bull to cow ratio, and the percent of bulls
reported as used after evaluation, and if so, the identity         purchased and lost from inventory.
of the cows each bull was exposed to during the breed-
ing season, the duration of bull exposure during the               2.4.1. Data from all bulls considered for use and
breeding season, and whether the bull was used in a                evaluated
single- or multi-sire breeding pasture. Producers were                In the initial step of the analysis, data from all bulls
also asked to record any problems with the bulls during            considered for use was included to describe the full
the breeding season, e.g. lameness and other illnesses             range of breeding soundness evaluation results ob-
or issues (including death) that may have affected preg-           served in these herds, differences among clinics in how
nancy outcomes.                                                    these results were reported, the association between
                                                                   important semen characteristics (e.g. percentage of nor-
2.3. Cow inventory, pregnancy outcomes, and
                                                                   mal sperm cells and SC), and the differences in breed-
breeding-to-calving interval
                                                                   ing soundness evaluation results between bulls used
   Early in 2001, the project veterinarians worked with            and those that were not used.
herd owners to establish an initial inventory of all                  Generalized linear mixed models (GLMMs; PROC
breeding females. Using a 9-point scale [7], veterinar-            MIXED, SAS for Windows Version 9.2; SAS Institute,
ians determined body condition scores on all cows                  Cary, NC) were used to examine the proportion of
before breeding and when assessing pregnancy status.               variation in the SC, the percentage of morphologically
Individual cow condition scoring also provided an op-              normal sperm (percent normal sperm), the percentage
portunity for the project veterinarians to verify herd             of sperm that stained alive (percent live sperm), and the
inventory. Herd veterinarians determined pregnancy                 percentage of individual progressively motile sperm
status by transrectal palpation in the fall of 2001 and            (percent motile sperm) for all bulls examined that could
2002, when cows were expected to be between 2 and 6                be explained by differences among veterinary clinics
mo of pregnancy. Herd risk of nonpregnancy was de-                 ( 2v/( 2v      2
                                                                                    h    b
                                                                                           2     2
                                                                                                  )). This was estimated after
scribed by dividing the number of nonpregnant females              adjusting for the age and breed of the bull, BCS, sig-
by the number of females examined for pregnancy. In                nificant physical abnormalities, and the month and year
addition to herd risk of nonpregnancy, the total number            of testing, and then accounting for variation associated
of cows exposed to each bull and the risk of nonpreg-              with herd ( 2h) and repeated measures on individual
nancy for each bull was also determined.                           animals ( b2) using random intercepts.
   The breeding-to-calving interval (BCI) was calcu-                  The association between the percent live sperm and
lated for each cow where the calf was born alive as the            the SC was also examined using GLMMs in all bulls
lesser of the difference between the first date of bull             considered for use. Scrotal circumference was classi-
contact in the spring of 2001 and the 2002 calving date,           fied into six categories based on 2-cm intervals above
or the difference between 21 d after the 2001 calving              the 10th percentile for SC ( 34, 34 to 36, 36 to 38,
date and the 2002 calving date. This was done to                     38 to 40, 40 to 42, and 42 cm). The analysis
account for situations where the cow was exposed to                accounted for variation associated with veterinary
the bull in 2001 before she had delivered her calf for the         clinic, herd, and repeated measures on each bull, using
2001 calving season.                                               random intercepts and adjusted for bull age at testing,
                                                                   breed, BCS, and month and year of testing. Similarly,
2.4. Data management and analysis
                                                                   associations between percent motile sperm, percent live
   Herd bull and cow inventories, records of breed-                sperm, and SC were also examined.
ing management and bull problems, breeding sound-                     The difference in SC, percent normal sperm, per-
ness evaluation data, pregnancy outcomes, and calv-                cent motile sperm, and percent live sperm between
ing dates were entered into a commercial database                  bulls that were evaluated and used, and those that
program by project-employed veterinarians (Mi-                     were evaluated and not used, were determined using
crosoft® Access 2002, Microsoft Corporation, Red-                  GLMMs, adjusting for the age and breed of the bull,
mond, WA, USA). Data summarized included age and                   BCS, and the month and year of testing, and then
breed of bulls considered for use and used in these                accounting for variation associated with herd and
herds, the frequency of reported injuries and other bull           veterinary clinic, as well as repeated measures on
problems, the relative use of single and multiple sire             individual animals.
874                                 C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883

2.4.2. Data from bulls used for breeding in study                  els also considered the potential for confounding by the
herds                                                              following risk factors: bull age, breed, and BCS; year of
   In the second step of the analysis, researchers sum-            testing; whether the bull was ever the only bull on a
marized the breeding soundness evaluation results for              breeding pasture; whether the duration of bull contact
bulls reported as used in these herds and considered               was less than 63 d; and the proportion of cows that had
differences associated with the characteristics of the             a BCS of less than 5 out of 9 (equivalent to 2.5 out of
bull and time of testing. The breeding soundness eval-             5.0) prior to the start of the breeding season.
uation results, month of testing, and BCS were sum-                   A similar analysis using a normal distribution and
marized for all bulls evaluated and used, as well as the           identity link function was conducted to determine if a
proportion of breeding soundness evaluation reports                record of a BSE, SC, the percent normal sperm, or
with complete information on SC, percent normal                    breeding soundness evaluation test status before the
sperm, percent live sperm, and percent motile sperm.               breeding season in 2001, were associated with the me-
Then GLMMs were used to describe differences in SC,                dian length of the interval from the start of breeding in
the percent normal sperm, the percent live sperm, and              2001 to the calving date in 2002 for all of the cows to
the percent motile sperm associated with age, breed,               which each bull was exposed.
and BCS for bulls used in these herds, as well as to                  For each question, manual backwards elimination
describe differences between bulls used that were de-              of variables was used to achieve a final model con-
termined to be satisfactory and those that were not,               taining only the statistically significant variables of
after accounting for variation associated with veterinary          interest and any other potential risk factors that were
clinic and herd.                                                   either significant (P        0.05) or acted as important
                                                                   confounders. After establishing the final summary
2.4.3. Association between breeding soundness                      main-effect model, biologically reasonable first-or-
evaluation results and reproductive outcome                        der interaction terms were added and assessed for
    Finally, the breeding soundness evaluation out-                their association with the outcome.
comes from each bull were examined to determine if                    The adequacy of the models was evaluated using
any were associated with the proportion of the cows,               plots of residuals compared with predicted values. Plots
which had been exposed to the bull, that were not                  were used to assess the importance of outliers and to
pregnant at the end of the breeding season. These fac-             examine the impact of any influential data points.
tors included whether the bulls were or were not re-
ported as evaluated, SC in cm (continuous) and classi-
fied into categories ( 34, 34 –36, 36 –38, 38 – 40,                 3. Results
   40 – 42, and 42 cm), percent normal sperm ( 50,                 3.1. Breeding soundness evaluation results: All bulls
50 – 69, 70 –79, 80 – 89, and 90 –100%), and breeding              considered for use and evaluated
soundness evaluation status (Satisfactory or Not Satis-
factory). Scrotal circumference was examined as a con-                There were a total of 2990 breeding soundness
tinuous and then categorical variable, to test whether             evaluations reported from 1988 individual bulls con-
the association between SC and odds of nonpregnancy                sidered for use and evaluated in either 2001 or 2002.
suggested a linear or monotonic relationship that was              The age of the bulls reported in these evaluations
potentially consistent with a causal association. Where            were as follows: 22.3% yearlings (666/2990), 26.0%
there was more than one evaluation per bull before the             2 y olds (778/2990), 19.4% 3 y olds (580/2990),
start of breeding season in either 2001 or 2002, then the          13.6% 4 y olds (408/2990), 16.2% 5 y (483/2990),
best result for that bull was included in the final anal-           and 2.5% age not reported (75/2990). Five breeds
ysis examining association with reproductive success:              represented more than 80% of evaluations of bulls
maximum SC, maximum percent normal sperm, and                      considered for use: Simmental (21%), Black Angus
best final classification.                                           (19%), Charolais (16%), Hereford (13%), and Red
    Models to evaluate the proportion of the cows, ex-             Angus (12%).
posed to a bull but not pregnant at the end of the                    The data included 1550 evaluations reported by 102
breeding season, used generalized estimating equations             veterinary clinics in 2001 and 1440 evaluations by 90
with a logit link function and binomial distribution to            clinics in 2002. Veterinarians reported that the bull was
account for clustering associated with repeated mea-               a satisfactory potential breeder on 2541 evaluations
surement of pregnancy status within herd (PROC                     (85.0%); 80 (2.7%) were classified as questionable, 166
GENMOD, SAS for Windows Version 9.2). The mod-                     (5.6%) were unsatisfactory, and the decision was de-
                                     C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883                                       875

ferred (decision deferred category) on 203 examina-                 SC that was 0.7 cm (95% CI, 0.2–1.1; P           0.007)
tions (6.8%).                                                       greater and a percent normal sperm value that was
   Scrotal circumference was recorded in 2931 of 2990               12.5% (95% CI, 10.7–14.3; P         0.0001) higher than
reported evaluations (mean, 39.1 cm, SD, 4.8) and the               bulls that were not used, after accounting for repeated
percent normal sperm was reported for 2894 tests                    measures, herd, veterinary clinic, age, breed, BCS and
(mean, 82%, SD, 16). After accounting for differences               month and year of testing. Similarly bulls that were
in bull breed, age at the time of testing, BCS, significant          used had an average percent motility that was 8.9%
physical abnormalities, the month of testing, and the               higher (95% CI 6.0 –11.7; P 0.0001) and percent live
year of testing, differences between herds accounted for            that was 6.6% higher (95% CI 1.9 –11.2; P        0.006)
2.7% of the total remaining variation in the SC data,               than those that were not used.
repeated measures on individual animals accounted for                  In this study, 11.4% of all evaluations (342/2990)
29.7%, and differences between veterinary clinics ac-               had comments regarding physical abnormalities. The
counted for 5.2%. Similarly, herd differences ac-                   most common problems were reported to involve the
counted for 1.4% of the remaining variation in the                  scrotum (4.2%, 126/2990), feet and legs (3.6%, 107/
percent normal sperm, repeated measures on individual               2990), penis (2.0%, 60/2990), seminal vesicles or other
bulls accounted for 27.6%, and the veterinary clinic                accessory glands (1.7%, 50/2990), prepuce (0.4%, 13/
reporting the results accounted for 6.9%.                           2990), epididymides (0.4%, 13/2990), and eyes (0.3%,
   The percent motile sperm and percent live sperm                  8/2990). Included in the scrotal abnormalities were
were only reported for 57.7% (1724/2990; mean, 70%,                 1.3% of all bulls with reported frostbite lesions (40/
SD, 27) and 52.6% (1574/2990; mean, 71%, SD, 36) of                 2990). Of the 342 reports where physical abnormalities
evaluations of bulls considered for use, respectively.              were noted, 237 (69.3%) of these bulls were classified
After accounting for the factors listed above, differ-              as satisfactory.
ences between veterinary clinics accounted for 47.3%                3.2. Description of bulls used for pasture breeding
of the total remaining variation in the individual sperm            in study herds
motility data; herd differences accounted for 4.4% and
repeated measures on individual animals accounted for                  Breeding activity was reported for 1879 individual
3.8%. Similarly, the veterinary clinic reporting the re-            bulls; 1384 bulls were used in 205 herds during the
sults accounted for 41.6% of total remaining variation              2001 breeding season and 1370 were used in 201 herds
in the percent live sperm; whereas, herd differences                during 2002. Several breeds of beef cattle were repre-
only accounted for 2.8% and repeated measures on                    sented in this study with the five most common breeds
individual bulls accounted for 0%.                                  (Simmental, Black Angus, Charolais, Red Angus and
   After accounting for the factors listed above, bulls             Hereford) comprising 80% of the bulls (Table 1). Ap-
with a SC that was below the l0th percentile ( 34 cm)               proximately one quarter of all bulls used were yearlings
had percent normal sperm that were between 3.4%
( 34 –36 cm) and 6.3% ( 42 cm) less than bulls with                 Table 1
larger SCs (P 0.006). Bulls with a SC 42 cm also                    Summary of breed information for 1879 beef bulls reported as
had between 2.1 and 2.9 higher percent normal sperm                 used in 205 herds in 2001 (n 1384 bulls used) and 201 herds
                                                                    2002 (n 1370 bulls used).
than bulls with SC 34 – 40 cm (P 0.05).
   Similarly, bulls with a SC 34 cm had a percent live              Breed               No. bulls with       No. herds with at least
                                                                                        attribute            one bull with attribute
sperm that were between 8.8% ( 34 –36 cm) and
                                                                                        (n 1879) (%)         (n 205) (%)
15.9% ( 40 – 42 cm) less than all bulls with larger SC
                                                                    Simmental             386 (20.5)                88 (42.9)
(P     0.008). Bulls with a SC 40 – 42 cm also had a
                                                                    Angus                 367 (19.5)                87 (42.4)
percent live sperm that was between 5.5 and 7.1%                    Charolais             305 (16.2)                61 (29.8)
higher than bulls with a SC 34 – 40 cm (P            0.03).         Red Angus             229 (12.2)                77 (37.6)
Finally, bulls with a SC 34 cm had a percent motile                 Hereford              223 (11.9)                59 (28.8)
sperm that was between 4.8% ( 36 –38 cm) and 5.5%                   Gelbvieh               78 (4.2)                 24 (11.7)
                                                                    Limousin               65 (3.5)                 16 (7.8)
( 40 – 42 cm) less than larger bulls (P 0.03).                      Salers                 54 (2.9)                 12 (5.9)
   Of the 1436 bulls evaluated in 2001, 1255 were used              Maine Anjou            41 (2.2)                  9 (4.4)
for breeding and 181 were not. Of the 1356 bulls                    Beef Booster           28 (1.5%)                 6 (2.9)
evaluated in 2002, 1211 were used and 145 were not.                 Tarentaise              9 (0.5)                  1 (0.5)
                                                                    Other                  94 (5.0)                 34 (16.6)
Bulls subsequently used for breeding on average had a
876                                         C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883

Table 2
Age distribution and breeding soundness evaluations reported for 1384 beef bulls used in 2001 and 1370 beef bulls used in 2002 (n      2754
bull-use records).
Age (y)              No. in age       Proportion BSEa     Proportion            Proportion            Proportion           Proportion decision
                     class (%)        with records (%)    satisfactory (%)      questionable (%)      unsatisfactory (%)   deferred (%)
1                     637 (23.1)        511/637 (80.2)      478/511 (93.5)         8/511 (1.6)            4/511 (0.8)          21/511 (4.1)
2                     716 (26)          646/716 (90.2)      600/646 (92.9)        13/646 (2 )            11/646 (1.7)          22/646 (3.4)
3                     529 (19.2)        501/529 (94.7)      471/501 (94)           6/501 (1.2)           10/501 (2)            14/501 (2.8)
4                     367 (13.3)        350/367 (95.4)      328/350 (93.7)         8/350 (2.3)            5/350 (1.4)           9/350 (2.6)
5–10                  422 (15.3)        401/422 (95)        363/401 (90.5)         3/401 (0.7)           13/401 (3.2)          22/401 (5.5)
Age not recorded       83 (3)             57/83 (68.7)        55/57 (96.5)          0/57 (0)               1/57 (1.8)            1/57 (1.8)
All bulls             n 2754          2466/2754 (89.5)    2295/2466 (93.1)       38/2466 (1.5)          44/2466 (1.8)         89/2466 (3.6)
 a
     Breeding Soundness Evaluation.



(Table 2). Producers also reported using bulls up to                         euthanized, and 0.7% (10) were reported as missing or
10 y of age, but 80% of the bulls were 4 y.                                  were lost from herd records. Of the 1370 bulls used for
   During 2001 or 2002, 42.5% (1172/2754) of bulls                           breeding in 2002, 24.7% (338) had been purchased in
spent at least some time as the only bull on a breeding                      the previous year.
pasture and 31.7% (874/2754) of bulls were exposed to
cows or heifers for less than 63 d. The average number                       3.3. Breeding soundness evaluation results: Bulls
of cows exposed to each bull was 26 in 2001 (SD, 13)                         used for breeding in study herds
and 26 in 2002 (SD, 11). The two most commonly                                  Prior to the 2001 and 2002 breeding seasons, a
reported problems during the breeding season were                            veterinarian evaluated 89.5% (2466/2754) of all bulls
necrobacillosis of the foot and injury (Table 3).                            used in these herds; 288 bulls were not tested before
   Of the 1384 bulls used for breeding in 2001 and                           use. Of the bulls subjected to a breeding soundness
present in these herds on June 1, 28% (387) were sold                        evaluation and then used, 93.1% (2295/2466) were re-
or culled before May 31, 2002, 1.6% (22) died or were                        ported as satisfactory and 6.9% (171/2466) were not.
                                                                                Of the 1384 bulls used on 205 ranches in 2001, 1184
                                                                             (85%) were classified as satisfactory potential breeders
Table 3
                                                                             and 71 (5%) were classified other than satisfactory; 129
Problems with health, temperament, and breeding performance
reported by the herd owners for beef bulls used during the 2001 or           bulls (10%) had no record of a breeding soundness
2002 breeding seasons.                                                       evaluation. In 2002, 1370 bulls were used on 201
                                          Number         Number of           ranches, of these 1111 (81%) were classified satisfac-
                                          of             herds (%)           tory, 100 (7%) were classified other than satisfactory
                                          individual                         and 159 (12%) had no record of breeding soundness
                                          bulls (%)                          evaluation. In 2001, 87 bulls were evaluated twice and
2001 breeding season                     n 1384          n 205               two bulls were evaluated three times; in 2002, 61 bulls
  No problem reported                   1286 (92.9)      205 (100)
                                                                             were evaluated twice and five bulls were evaluated
  Injury                                  35 (2.5)        34 (16.6)
  Necrobacillosis of the foot             35 (2.5)        23 (11.2)          three times.
  Dead during the breeding season          5 (0.4)         5 (2.4)              Almost all of the breeding soundness evaluations
  Temperament                              4 (0.3)         4 (2.0)           were completed from February to June (94.5% in 2001
  Lack of libido                           5 (0.4)         4 (2.0)
                                                                             and 98.6% in 2002). The most intense period of eval-
  Illness                                  2 (0.1)         2 (1.0)
  Other                                   12 (0.9)        11 (5.4)           uation was between March and May, with 83.4% of the
2002 breeding season                     n 1370          n 201               evaluations completed during these 3 mo in 2001 and
  No problem reported                   1302 (95)        201 (100)           76.0% in 2002 (Fig. 1).
  Injury                                  29 (2.1         23 (11.4)             Herd owners were least likely to provide a written
  Necrobacillosis of the foot             17 (1.2)        13 (6.5)
  Dead during the breeding season          6 (0.4)         6 (3.0)
                                                                             breeding soundness evaluation report for yearling bulls
  Illness                                  3 (0.2)         3 (1.5)           as compared to older bulls (Table 2). However, 36%
  Lack of libido                           3 (0.2)         3 (1.5)           (105/289) of the bulls with no written breeding sound-
  Temperament                              0 (0.0)         0 (0.0)           ness evaluation record were reported by the herd owner
  Other                                   10 (0.7)         9 (4.5)
                                                                             to have been evaluated prior to the breeding season.
                                          C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883                                       877

                                                                         0.02). Neither the percent motile sperm (P      0.27) or
                                                                         percent live (P 0.61) differed by bull age.
                                                                             Bull breed was associated with differences in SC
                                                                         (P     0.005), percent normal sperm (P       0.005), and
                                                                         percent live sperm (P 0.005), but not with the percent
                                                                         motile sperm (P 0.41) after accounting for age, BCS,
                                                                         month and year of testing (Table 6). Limousin bulls had
                                                                         SCs which were more than 2 cm smaller (P           0.05)
                                                                         than bulls that were Angus, Beef Booster, Charolais,
                                                                         Gelbvieh, Hereford, Red Angus, and Simmental. Maine
                                                                         Anjou bulls had SCs that were more than 2 cm smaller
                                                                         (P 0.05) than Beef Boosters, Charolais, and Simmen-
                                                                         tal. Salers bulls had SCs that were more than 2 cm
Fig. 1. Comparison of the proportion of yearling () and mature (●)      smaller than Beef Booster and Simmental bulls from
beef bulls used for breeding that were evaluated during each month       these herds. The percent normal sperm for Beef Booster
of the study.                                                            bulls evaluated was more than 5% greater (P        0.05)
                                                                         than for Hereford, Angus, Red Angus and Maine An-
                                                                         jou. The percent live sperm for the Gelbvieh bulls
Seventy-four percent (78/105) of these were either                       evaluated was more than 10% greater (P 0.05) than
yearlings or 2-y olds, and 73% (57/78) of these were                     for Angus, Beef Booster, Charolais, Hereford, Limou-
recently purchased.                                                      sin, Red Angus, and Simmental. The percent live sperm
    In 2001, 2.5% of bulls that were evaluated and then                  for the Red Angus bulls evaluated was more than 10%
used for breeding had a BCS of 2 out 5 at the time of                    less (P     0.05) than for Charolais, Salers, and Sim-
evaluation, 52.3% scored 3, 32.6% scored 4, and 0.3%                     mental.
scored 5. In 2002, 3.3% scored 2 out of 5, 61.6% scored                      Bulls with a BCS of 2 out of 5 had smaller SCs than
3, 21.7% scored 4, and 1.5% scored 5. Body condition                     bulls with BCSs of 4 out of 5 (         1.0 cm, 95% CI
score was not reported for 12.2% of the bulls evaluated                    0.1 to 1.9, P 0.03) after adjusting for age, breed,
and used in 2001 and 11.9% in 2002.                                      and month and year of evaluation. Both SC (P
    Scrotal circumference (2420/2466) and percent nor-                   0.0001) and percent normal sperm (P 0.01) differed
mal sperm (2430/2466) were recorded for more than                        by the month the test was completed after adjusting for
98% of bulls evaluated (Table 4). Percent motile sperm                   age, breed, BCS, and year of evaluation; the percent
was reported for 58.5% (1443/2466) and percent live                      motile sperm (P      0.29) and percent live sperm (P
sperm was recorded for 54.0% (1330/2466). However,                       0.10) did not. Bulls evaluated in August had SCs that
either percent motile sperm or gross wave motion of a                    were 3 cm less (P         0.05) than bulls evaluated in
drop of semen (gross sperm motility) was reported in
98% (2414/2466) of the breeding soundness evalua-
tions. Of the 52 bulls with no indication of sperm
                                                                         Table 4
motility, 39 were classified as satisfactory.
                                                                         Summary of reported results for the 2466 breeding soundness
    Scrotal circumference increased in association with                  evaluations reported (n 1255 in 2001 and n 1211 in 2002) for
age of the bulls used in these herds (P 0.0001; Table                    1707 beef bulls evaluated and used in 205 herds.
5), after accounting for breed, BCS, month and year of                                           Scrotal         Percent   Percent   Percent
evaluation. The SCs for bulls whose age was not re-                                              circumference   motile    live      normal
ported were similar to bulls that were either 3 (P                                               (cm)            sperm     sperm     sperm
0.95) or 4-y old (P 0.11), and bulls that were 4 y of                    No. bull records with      2420         1443      1330      2430
age were not significantly different than those that were                   result
   5 y (P 0.10). The percent normal sperm also varied                    Mean                         39.5         72.7      73.1      84.7
                                                                         SD                            3.50        25.8      28.1      11.2
with age of the bulls used in these herds. The percent                   5th percentile               34            0.0       0.0      70.0
normal sperm in 2-y old bulls was greater than that of                   25th percentile              37           70.0      75.0      80.0
either yearling bulls (P 0.0008), or bulls 5 y or older                  Median                       40           80.0      80.0      87.0
(P      0.0005). The percent normal sperm in 3-y olds                    75th percentile              42           86.5      90.0      92.0
                                                                         95th percentile              45           95.0      95.0      96.0
was also higher than in bulls 5 y of age or greater (P
878                                      C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883

Table 5                                                                 (P     0.05) than for bulls evaluated in August. Bulls
Summary of breeding soundness evaluation results for beef bulls         evaluated in January, February, May through July, and
of all breeds (n 2466 reports from 2001 or 2002 for bulls tested
and used).                                                              November had a lower percent normal sperm than those
                                                                        evaluated in March or April.
Age                         Scrotal       Percent Percent Percent
                            circumference normal motile live               In bulls used for breeding, SC (      1.0 cm, 95% CI,
                                          sperm cells                   0.5–1.5, P     0.0001), the percent normal sperm (
1 y (n 511)                                                             24.4%, 95% CI, 22.9 –25.8, P        0.0001), the percent
  Mean                          36.2       83.4    73.3    74.1         motile sperm (        15.1%, 95% CI, 12.3–17.8, P
  SD                             2.5       10.6    23.6    26.4         0.0001), and the percent live sperm (        12.6%, 95%
  5th percentile                32.0       70.0     0.0     0.0
  25th percentile               34.0       79.0    70.0    70.0
                                                                        CI, 7.5–17.8, 0.0001) were all greater in satisfactory
  Median                        36.0       85.0    80.0    80.0         bulls than in non-satisfactory bulls (includes bulls clas-
  75th percentile               38.0       90.0    85.0    90.0         sified as unsatisfactory, questionable and decision de-
  95th percentile               40.0       95.0    90.4    95.0         ferred) in models accounting for bull age, breed, BCS,
2 y (n 646)
                                                                        and month and year of evaluation.
  Mean                          38.8       85.5    71.9    72.0
  SD                             2.8       11.4    27.4    29.9
                                                                        3.4. Association between bull breeding soundness
  5th percentile                35.0       70.0     0.0     0.0
  25th percentile               37.0       81.0    70.0    75.0         evaluation results and pregnancy success for
  Median                        39.0       88.0    80.0    80.0         in-contact cows
  75th percentile               40.5       92.0    90.0    90.0
  95th percentile               43.0       96.0    95.0    95.0            The average herd pregnancy rates were 93.1%
3 y (n 501)                                                             (SD, 3.9%) in 2001 and 91.4% (SD, 4.9%) in 2002.
  Mean                          40.4       85.0    72.6    74.8         Whether a breeding soundness evaluation result was
  SD                             3.0       11.6    26.8    26.3
  5th percentile                36.0       70.0     0.0     0.0
                                                                        provided for the bull (P 0.74), the percent normal
  25th percentile               38.5       80.0    70.0    75.0         sperm (P      0.59), and whether or not the bull was
  Median                        40.0       87.5    80.0    80.0         classified as satisfactory breeder (P 0.38) were not
  75th percentile               42.5       92.0    89.8    90.0         associated with the odds of non-pregnancy in the
  95th percentile               45.0       96.0    95.0    95.0
4 y (n 350)
                                                                        33,551 cows exposed to this group of bulls in 2001,
  Mean                          41.5       85.1    71.0    71.5         and the 32,676 cows exposed in 2002.
  SD                             2.9       10.6    27.3    29.8            However, pregnancy status for the cows exposed to
  5th percentile                37.0       70.0     0.0     0.0         each bull was associated with SC (P 0.016) after con-
  25th percentile               40.0       81.0    70.0    75.0
                                                                        sidering other risk factors. Cows exposed to bulls with a
  Median                        42.0       88.0    80.0    80.0
  75th percentile               43.0       92.0    85.0    90.0         SC 34 cm were less likely to be pregnant, than cows
  95th percentile               46.0       95.0    95.0    95.0         exposed to bulls with a SC of 36 –38 cm (OR, 1.25;
5–10 y (n 401)                                                          95% CI 1.05–1.48; P 0.011), 38 – 40 cm (OR, 1.27;
  Mean                          42.1       83.8    73.9    73.2
                                                                        95% CI 1.07–1.49; P 0.005), 40 – 42 cm (OR, 1.37;
  SD                             2.9       11.7    24.2    27.9
  5th percentile                37.0       69.2     0.0     0.0         95% CI 1.13–1.65; P 0.0025), and greater than 42 cm
  25th percentile               40.0       79.0    70.0    74.5         (OR, 1.42; 95% CI 1.15–1.77; 0.001).
  Median                        42.0       86.0    80.0    80.0            Models of whether cows exposed to individual bulls
  75th percentile               44.0       91.0    89.3    90.0         were not pregnant were adjusted for whether the bull was
  95th percentile               47.0       96.0    95.0    95.0
Age not recorded (n   57)                                               ever the only bull on a breeding pasture (OR, 1.27; 95%
  Mean                          40.0       86.7    77.5    71.4         CI, 1.11–1.46; P 0.0006), whether the duration of the
  SD                             3.7        9.6    17.2    27.5         bull’s exposure to the cows was less than 63 d (OR, 1.18;
  5th percentile                34.0       70.0    48.5    22.0         95% CI, 1.01–1.38; P 0.03), bull age (P 0.22), and
  25th percentile               36.0       83.0    70.0    69.8
  Median                        41.0       89.0    85.0    80.0
                                                                        the study year (P 0.05).
  75th percentile               43.0       93.0    85.0    87.8            The average interval from first bull exposure to
  95th percentile               45.0       97.0    90.0    92.3         calving was 304 d (SD, 17 d) for the 22,544 cows with
                                                                        calving records exposed to the evaluated bulls from
                                                                        2001 with the necessary calving data (1239/1255).
January to July, September, and November. Similarly                     Whether a breeding soundness evaluation result was
the percent normal sperm for bulls evaluated from Jan-                  provided for the bull or not (P        0.21), the percent
uary to July or in November was more than 5% greater                    normal sperm (P 0.35), and whether or not the bull
                                           C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883                                     879

Table 6
Scrotal circumference results (cm) classified by age and breed summarized for all breeding soundness evaluations from beef bulls evaluated
and used in 2001 or 2002 (n 2420a with scrotal circumference data).
Age                                              Reported bull breed information
                                                 All breeds    Hereford        Simmental   Charolais   Black Angus   Red Angus      Other
1y
  Suggested minimum standard (12/14 mo)b         —             30/32           32/34       31/33       31/33         —              —
  Count                                           502           30               130         77           109            68          88
  Average                                          36.2         36.1              37.3       36.4          36.0          36.3        34.8
  SD                                                2.51          2.95             2.4        2.31           2.30         2.33        2.36
  5th percentile                                   32.0         32.23             33.5       33.0          32.7          33.0        31
  25th percentile                                  34.0         34.0              36.0       35.0          34.0          34.5        33
  Median                                           36.0         35.8              37.0       36.0          36.0          36.0        34.8
  75th percentile                                  38.0         37.8              38.0       38.0          37.5          38.0        36.6
  95th percentile                                  40.0         41.1              42.0       40.1          39.6          40.0        38.8
2y
Suggested minimum standard (21–30 mo)b           —               34              36          35            35        —              —
  Count                                           637            72             130          94           130            92         118
  Average                                          38.8          38.3            39.8        39.6          39.1          38.6        37.3
  SD                                                2.8           3.6             2.6         2.3           2.5           2.4         2.8
  5th percentile                                   34.9          33.6            36.0        36.0          35.0          35.0        32.0
  25th percentile                                  37.0          36.0            38.0        38.0          37.0          37.0        35.1
  Median                                           39.0          38.0            40.0        40.0          39.0          39.0        37.3
  75th percentile                                  40.5          39.6            42.0        41.9          41.0          40.0        39.0
  95th percentile                                  43.0          44.5            44.0        43.0          43.6          42.0        42.0
3y
  Count                                            489           61             100          97            90            58          83
  Average                                           40.4         39.7            41.5        41.1          40.2          41.0        38.6
  SD                                                 3.0          2.9             2.7         2.8           2.7           3.0         2.9
  5th percentile                                    36.0         36.0            37.0        36.8          36.0          36.9        34.0
  25th percentile                                   38.5         38.0            39.4        39.0          38.0          39.0        37.0
  Median                                            40.0         39.0            42.0        41.0          40.0          41.0        39.0
  75th percentile                                   42.5         42.0            43.0        43.0          42.0          43.0        40.3
  95th percentile                                   45.0         44.0            46.0        46.0          45.0          45.0        43.0
4y
  Count                                            347           56               62         68            61            34          66
  Average                                           41.5         40.4             42.8       41.7          41.9          42.5        40.0
  SD                                                 2.9          2.7              2.82       2.8           2.5           2.77        2.9
  5th percentile                                    37.0         37.0             39         37.0          38.0          38.0        36.0
  25th percentile                                   40.0         38.0             40.6       40.0          40.0          41.0        38.0
  Median                                            42.0         40.0             43         42.0          42.0          42          41.0
  75th percentile                                   43.0         42.0             45         43.1          43.0          44.0        42.0
  95th percentile                                   46.0         46.0             47         46.0          46.1          47.2        44.0
5–10 y
  Count                                            388           72               77         72            59            34          74
  Average                                           42.1         41.8             44.3       42.1          41.2          43.0        40.3
  SD                                                 2.9          2.2              2.5        2.6           2.4           2.9         3.0
  5th percentile                                    37.0         37.9             40.8       38.0          37.0          38.7        35.7
  25th percentile                                   40.0         40.4             42.0       41.0          40.0          41.3        38.0
  Median                                            42.0         42.0             44.0       42.0          41.0          43.0        40.5
  75th percentile                                   44.0         43.0             46.0       44.0          43.0          45.0        42.0
  95th percentile                                   47.0         45.5             49.0       46.0          45.0          48.4        45.0
 a
     Age was not reported for 57 bulls (they were excluded from this table).
 b
     Barth, 2000 [6].




was found to be satisfactory (P       0.36) were not                          After adjusting for other risk factors, the length of
associated with the median breeding to calving interval                    the interval from first bull exposure to calving was
of the cows exposed to each bull.                                          associated with SC (P 0.047). Cows exposed to bulls
880                                 C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883

with a SC 34 cm had longer breeding to calving                     sible. Associations of both age and breed with SC
intervals than cows exposed to bulls with a SC of                  reported here were also consistent with previous studies
  38 – 40 cm ( , 3.2 d; 95% CI 0.1– 6.4; P         0.04),          [6,9].
  40 – 42 cm ( , 3.5 d; 95% CI 0.6 – 6.3; P 0.02), and                 The percent normal sperm was greater in 2- and
  42 cm ( , 3.4 d; 95% CI 0.2– 6.6; P       0.04). Cows            3-year old bulls than either yearlings or bulls 5 y old.
exposed to bulls with a SC 36 –38 cm also had a                    Many of the younger bulls likely had not yet reached
longer breeding to calving interval than cows exposed              sexual maturity and it also seems plausible that many of
to bulls with a SC 38 – 40 cm ( , 4.2 d; P 0.03).                  the older bulls had passed their sexual peak. Apparent
   Models of the median breeding to calving interval of            differences among breeds in the percent normal sperm
cows exposed to each bull were adjusted for whether a              have not been previously reported, and were not con-
health problem or injury was reported for the bull ( ,             sistent with breed-average SCs.
7.4 d; 95% CI 0.5 to 14.3; P         0.03), whether the                This study is unique in that the work was done by a
duration of the bull exposure to the cows was less than            large number of private veterinarians under a variety of
63 d ( , 6.2 d; 95% CI 9.3 to 3.0; P 0.0001),                      field conditions. The study population is also unique in
and bull breed (P 0.23).                                           that the data provided a picture of bulls actually used in
                                                                   commercial beef herds and not just a subset of bulls
                                                                   intended for sale or suspected of fertility problems.
4. Discussion
                                                                   Most of the bulls used in these herds were 4 y old,
    This is the first field study in western Canada to               and represented a range of British and continental
examine associations between the results of breeding               breeds common in western Canada. Compliance by the
soundness examinations in beef bulls by private veter-             study participants was good, giving us a uniquely com-
inarians and pregnancy success. In this study, there was           plete picture of the bulls used in these herds. However,
no link between reproductive outcomes and the re-                  despite the fact that the cost of the breeding soundness
ported semen characteristics measured under field con-              evaluation was covered by the study, approximately
ditions, percent normal sperm and percent motile                   10% of the bulls were not evaluated. Also interesting is
sperm; or whether the bull was classified as a satisfac-            that producers sometimes chose to ignore the results of
tory potential breeder or not. Because less than 7% of             the breeding soundness evaluations; approximately 5%
the bulls tested and used were classified as less than              of the bulls used had been reported as not satisfactory.
satisfactory and that many of these bulls were used in                 Compliance by the private veterinarians was also
multi-sire pastures, this study did not have adequate              very good, although there was substantial variation
statistical power to address the question of whether               among veterinary practices in the detail recorded on the
classification as satisfactory is a useful predictor of             breeding soundness evaluation forms. Scrotal circum-
pregnancy status.                                                  ference and the percent normal cells were reported on
    However, there was a consistent link to the SC                 almost all forms, whereas the percent live sperm and
measurement. Kastelic and Thundathil [1] concluded                 percent motile sperm (individual sperm motility) were
that a breeding soundness evaluation could usually de-             not. Sperm motility can be difficult to evaluate in field
tect bulls that were grossly abnormal, but accurate                conditions, as it can be influenced by changes in tem-
prediction of fertility required a comprehensive ap-               perature, or a prolonged interval from semen collection
proach that would exceed the capability of non-institu-            to evaluation. Sperm concentration can also influence
tional practices. In the present study, increasing SC was          the perception of gross and individual sperm motility.
associated with a higher frequency of cows diagnosed               Ideally, semen should not be exposed to cool temper-
as pregnant by transrectal palpation and to a lesser               atures or equipment and sperm motility should be eval-
extent with shorter intervals from first bull contact to            uated immediately after semen collection; however, in
calving.                                                           many cases in the field this might not be possible,
    Scrotal circumferences 34 cm were also associated              especially on cold days in outdoor facilities.
with a decrease in the percent of normal sperm. Bulls                  Percent motile sperm was reported for only approx-
with significantly smaller SC had a higher proportion of            imately half of all evaluations, whereas one of either
abnormal seminiferous tubules [8], or may be pubertal              gross motility or percent motile sperm was reported for
and are not yet capable of producing a mature spermio-             98% of evaluations. Typically, gross motility was eval-
gram. Since the majority of the bulls with small SCs               uated by private practitioners by placing a 5–10 mm
were in the yearling category, the latter was very plau-           diameter drop of semen on a slide and observing the
                                    C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883                              881

wave motion using bright field microscopy at a suitable             tions. Many clinicians report that the proportion of
magnification, 40 –125 X as suggested by Barth [6].                 bulls having a satisfactory classification frequently ex-
Gross motility is a reflection of both sperm concentra-             ceeds 90 percent within groups of pasture breeding
tion and individual sperm motility. If adequate wave               bulls that routinely undergo a breeding soundness eval-
motion is present in the sample, further examination of            uation on an annual basis (unpublished data).
the sample is considered unnecessary [6]. An accurate                 Most of the breeding soundness evaluations were
assessment of individual sperm motility in raw undi-               performed between March and May. Similarly, the per-
luted semen requires the placement of a coverslip over             cent normal sperm was highest in bulls tested in March
a much smaller 2– 4 mm drop and evaluation of 10 –15               or April. In western Canada, most bull sales are con-
fields, preferably with phase contrast microscopy at 400            ducted during the months of March and April and
   ; a much more time-consuming procedure. Given the               generally the best fed, highest quality bulls are offered
proportion of bulls with adequate motility ( 60% mo-               at these sales. In the Barth and Waldner [10] study,
tile sperm cells) [6], it appeared that some veterinarians         semen quality improved with the approach of spring
preferred to evaluate both gross and individual sperm              and summer; however, there were fewer sale bulls
motility.                                                          represented in that population. Semen quality also de-
    While the determination of the percent live sperm              clined, as in the present study, in the late summer which
was performed on only 54% of semen samples from                    may be a result of diminished feed quality or the pre-
bulls tested and used for breeding, the impact on the              sentation of bulls for testing that were suspected of
results was likely negligible. Barth and Waldner [10]              having problems. It is not unusual in western Canada
reported that percent motile sperm and percent live                for bulls to lose weight and body condition during the
were highly correlated (r       0.84) and both were cor-           breeding season; this can be due to either breeding
related with percent normal sperm (r 0.60); however,               activity with or without deteriorating pasture conditions
   2% of the bulls were classified as questionable breed-           as the season progresses. Also, it is not unusual for
ers in that study and only a proportion of these may               livestock producers to re-test suspect bulls after breed-
have been because of low numbers of live sperm. An                 ing season if they notice an unusual number of cycling
advantage of assessing percent live sperm, however, is             cows. In this study body condition was not evaluated
that it is less likely to be influenced by ambient tem-             after the breeding season; therefore, no comments can
perature than sperm motility.                                      be made with respect to observed weight loss amongst
    Although only 85% of all bulls considered for use              these bulls. Seasonal effects associated with tempera-
and evaluated were classified as satisfactory potential             ture extremes and photoperiod could also contribute to
breeders, 93% of bulls evaluated and then used for                 the decreased semen quality at the end of the summer.
breeding were satisfactory. This is considerably higher            Barth and Waldner [10] cite several early references
than the results reported by Barth and Waldner [10]                which indicate that there are both endocrine and semen
where 66% (n         2110) of all bulls evaluated over a           characteristics that appear to be seasonally associated.
13-y interval were classified as satisfactory. In another           Pasture conditions, temperature, rainfall and photope-
study where client bulls were evaluated, Carson and                riod changes (herds were located from 49 °N to 55
Wenzel [11] reported that 63% were classified as sat-               °N) varied amongst the herds. Given the limited num-
isfactory. Both previous studies and the present study             ber of repeated measurements on individual animals
included bulls of all ages, and not just young bulls               within this study that included late summer data, the
intended for sale. However, the present study may have             specific cause of this seasonal difference could not be
differed from the other two in that the bulls described            determined.
were not targeted by paying clients for examination                   Herd owners occasionally question the consistency
because a problem was suspected. Some of bulls would               with which breeding soundness evaluations are re-
have been evaluated prior to purchase or many would                ported among veterinarians. Although the identity of
have been selected for breeding in the current season              the veterinarian performing the evaluation was not part
based on breeding soundness evaluation or pregnancy                of the available database, the present study provided a
rate results from the previous year. Palmer and Barth              unique opportunity to look at differences among private
[12] reported that 81% of 105 mature bulls were clas-              practices. In this study, only 5.2% of the variation in SC
sified as satisfactory breeders using the same criteria as          and 6.9% of the variation in percent normal sperm
the present study. In that study, nearly all of the bulls          could be explained by differences among clinics after
had been evaluated previously, with some new addi-                 accounting for other known risk factors. Substantially
882                                 C.L. Waldner et al. / Theriogenology 74 (2010) 871– 883

more of the variation in SC and percent normal sperm               problems in the earlier report, the 26.1% average cull-
was explained by the differences between subsequent                ing rate for bulls in the Ontario study [21] was compa-
measurements in individual bulls, emphasizing how                  rable to the 28% rate in the 2001 season data from
bulls, especially those that are still maturing, can               western Canada.
change over time. Some of the variation in SC mea-                    This was a unique opportunity to examine the utility
surements was explained by the body condition score of             of breeding soundness evaluations for breeding bulls
the bull. There was an average 1.0 cm difference in the            from commercial herds under field conditions. Al-
SC of bulls that scored 2 out of 5, as compared to 4 out           though there appeared to be some variation among
of 5. There was a much greater variation among clinics             veterinary clinics, SC was an important tool for opti-
in the reported percent motile and percent normal                  mizing herd fertility. This observational study also em-
sperm. Although there was no difference in pregnancy               phasized the importance of early detection of illness
rates between bulls that were classified as satisfactory            and injury in breeding bulls and the necessity of careful
or those that were not, there were significant differ-              monitoring performance in single-sire breeding groups.
ences in SC, sperm motility, and the percent normal and
percent live sperm between bulls that were or were not             Acknowledgements
satisfactory.
    Rapid change in breeding soundness evaluation re-                 Data reported in this paper were collected as part of the
sults occur in bulls between 11 and 15 mo of age                   field research activities for the Western Canada Study of
[13–19]. The yearling bulls in this study, had in most             the Animal Health Effects Associated with Exposure to
cases, been evaluated and found to be acceptable for               Emissions from Oil and Natural Gas Field Facilities.
inclusion in the herd as a breeding bull before entering           Funding support was provided in part through the Western
into the study. For this reason and because the age in             Interprovincial Scientific Studies Association (WISSA).
months could not be determined for all bulls, the results          The authors acknowledge the invaluable contribution of
for these bulls cannot be directly compared to earlier             the participating herd owners and private veterinary clin-
studies.                                                           ics to this study.
    For bulls 2-y of age and older which were already in
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