Effects of Season of Breeding on Reproductive and Weaning

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					Effects of Season of Breeding on Reproductive and Weaning
 Performance of Beef Cattle Grazing Seleniferous Range

           C. A. Dinkel, J. A. Minyard and D. E. Ray

                J Anim Sci 1963. 22:1043-1045.

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           AND W E A N I N G P E R F O R M A N C E OF B E E F C A T T L E
                     GRAZING SELENIFEROUS RANGE 1
                           C. A.   DINKEL,   J. A. MINYARD AND D. E. RAY
                                South Dakota State College, Brookings

   LEN U
S Ecient Ito M content10ofp rangeor grassesofsuffi-
             make up        pm       more      the
                                                               resistance and susceptibility to selenium poi-
                                                                soning. Within each selection line were early-
total ration has been shown to be deleterious bred and late-bred cows; all cows within a
to beef cattle (Moxon et al., 1944). While line were bred to the same bull.
much of the research concerned with counter-                      The experiment was initiated in 1957 and
acting the effects of selenium poisoning has has progressed for 5 years. Since this repre-
dealt with growth, the effects on reproductive sents about one generation in beef cattle and
performance appear to be of much greater since selection has been primarily for exter-
economic consequence. Studies with swine nal symptoms, rather than reproductive
have indicated beneficial effects on growth performance, the two selection lines were con-
 (Wahlstrom et al., 1955, 1956) and somewhat sidered as replicates of the season of breed-
limited benefits for reproductive performance ing study for this analysis. The data were
from feeding arsanilic acid (Wahlstrom and summed over replicates to facilitate report-
Olson, 1959). This same compound has not ing the results (table 1). In order to avoid an
proven to be effective in growth studies with error term with one degree of freedom, all in-
beef cattle (Minyard et al., 1960) and no teractions involving replications were pooled
other feed or feed additive has been reported to provide an error term for the percent born
effective in protecting beef cattle.                           and percent weaned analyses. These interac-
    The selenium intake of range animals is tions were pooled with the residual in all other
highest from preheading to maturity of the tests. The number of cows in each of the two-
range grasses (Olson et al., 1942). This would season-of-breeding groups has varied over the
occur from early June to mid-July in normal years from a low of 10 per group to a high of
years on ranges in good condition with both 29. Bulls were placed in the early breeding
cool and warm season species present. Under pastures about M a y 1 each year and in the
the usual management systems in South late breeding pastures about July 18. The
Dakota the period of high selenium intake oc- breeding season extended for 10 weeks in each
curs simultaneously with the breeding sea- case, with a 1-week interval between breeding
son. This study was initiated to determine if groups to rest the bulls.
breeding prior to this period would be                            The calves remained with their dams with-
beneficial to the reproductive performance of out supplementary feed until weaning, which
beef cattle grazing selenium ranges.                           occurred during the last 2 weeks of October.
                                                               At this time the calves were weighed and
             Experimental Procedure                            scored for conformation, condition, and symp-
                                                               toms of selenium poisoning. Visible symptoms
    A group of grade and purebred cows at the in weaning calves are principally lameness,
Reed Ranch Substation were divided into two horizontal denting of the hoof, and in some
groups, one to be bred early and the other to cases longer than normal hoof growth. In a
be bred late. Division was random except for few extreme cases there is a decided lack of
cows which had not calved early enough in condition and thriftiness.
the season to allow breeding at the early                         Conformation scores had a possible range
period.                                                        from 17 to 0, with the high score indicating
    This experiment was superimposed upon a more desirable conformation. Condition scores
selection experiment initiated at the same had a possible range from 14 to 0, with the
time in which selection was directed toward high score indicating the fatter animal. Selen-
- 1 Contribution from the Animal Science Department in co-      ium symptom scores had a possible range
operation with the Animal Husbandry Research Division,
A.R.S., U.S.D.A. Approved for publication by the Director       from 13 to 1, with the high score indicating
of the South Dakota Agricultural Experiment Station as Jour-   no symptoms. Weaning weights were adjusted
nal Series No. 598.

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 1044                                        D I N K E L , M I N Y A R D AND RAY
                            YEARS FOR EARLY AND LATE BRED GROUPS
                                 1958             1959             1960            1961            1962          All years       Overall
Item                        Early    Late-    Early   Late    -Early   Late    Early   Late    Early   Late    Early   Late       or av.
No. of matings               15      14        10      10      11       12      12      12      27      29      75      77        152
Percent born                 46.7    14.3      90.0    90.0    45.5     33.3    66.7    25.0    59.3    37.9    60.0    37.7 H     48.7
Percent weaned               40.0    14.3      90.0    80.0    36.4     25.0    58.3    25.0    48.1    31.0    52.0    32.4 ~     42.1
Weaningwt.~                 436     334       468     394     434      362     416     383     437     383     440     380 ~      417
Adj. weaning wt, b          420     447       443     419     412      376     387     407     399     393     411     405        409
Conformation                 10.3    10.0      10.4    10.9    10.2      9,7     9.6    11.0     9,5    10.1     9.9    10.4       10'.1
Condition                     7.7     7.5       7,0     7.6     7.0      5.0     6.3     6.7     6.8     6.9     6.9     6.9        6.9
Se. symptoms                 12.7    12,5      11.6    11.5     9.2     11,0    12.8    13.0    12,1    12,5    11.9    12.1       12.0
       ~" P<.O1.
        a Adjusted for sex and age of dam.
        b Adjusted for sex, age of dam and age of calf.

in two different ways prior to analysis. Sub-                           management system weaning would be accom-
sequent reference to weaning weight indicates                          plished on most ranches on one day and prob-
weights adjusted for sex of calf and age of                             ably within a month of the time the calves
dam only, whereas adjusted weaning weight                              were weaned in this experiment. Among the
is used to denote the weight adjusted for age                          advantages to calving early are the additional
of calf differences in addition to sex and age                         grazing period available and especially the ad-
of dam.                                                                vantage of larger calves at the time of in-
                                                                       creased milk flow from the dam.
               R e s u l t s and Conclusions                              While there was no significant difference
                                                                       between the breeding groups for adjusted
   The number of matings made and the per-                             weaning weight nor was there a significant in-
formance of the calves produced in each of                             teraction between year and breeding group,
the breeding groups in each year are presented                         the year by season means seem to indicate a
in table 1. In all, there were 152 matings, 75                         trend. If one uses the selenium symptom
in the early and 77 in the late breeding group.                        scores as a measure of the extent of selenium
The average calf crop born was 48.7%, with                             poisoning in a year, it can be seen that in
the early breeding group averaging 60.0%                               years of only slight to moderate selenium
and the late group 37.7%. The difference of                            poisoning the late group averaged heavier in
22.3% was highly significantly ( P < . 0 1 ) . The                     adjusted weaning weight than did the other
average calf crop weaned was 42.1%, with                               group. In 1959 and 1960 when selenium
the early breeding group averaging 52.0%                               symptoms were more extreme, the early group
and the late group 32.4%. The 19.6% differ-                            averaged heavier for adjusted weaning weight.
ence was highly significant ( P < . 0 1 ) . Differ-                    Further data will be required to establish if
ences between years for both calf crop born                            this is a chance occurrence.
and calf crop weaned were highly significant                              No significant differences were found be-
(e<.005).                                                              tween breeding groups for conformation, con-
   Analysis of the weaning data indicates a                            dition or selenium symptom score at weaning.
highly significant difference between the early                        There were significant ( P < . 0 5 ) differences
and late groups for weaning weight but a non-                          between years for weaning condition and
significant difference for adjusted weaning                            highly significant ( P < . 0 0 5 ) differences be-
weight. Weaning weights without age adjust-                            tween years for selenium symptoms. These
ment favored the early group by 60 lb. over                            differences reflect the extreme variation that
the late breeding group.                                               has been observed from year to year in sever-
   Considering the combination of the in-                              ity of selenium poisoning.
creased calf crop and increased weaning                                   These results indicate that producers ex-
weight, breeding the cows early resulted in                            periencing a selenium problem as severe as is
229 lb. of calf at weaning per cow exposed                             present at the Reed Ranch Substation would
compared to 123 lb. in the late g r o u p - - a dif-                   do well to convert from a cow-calf operation
ference of 106 lb. Since all calves were weaned                        to a steer program. Most of the private
on the same day, this method of analysis                               ranches in the trouble areas do not contain as
penalizes the calves born in the late breeding                         high levels of selenium as the Reed Ranch
group. A producer calving late in the season                           Substation. Many of these producers are stay-
would probably wean later than one calving                             ing in a cow-calf program, and the trend in
early in the season. However, under either                             most areas in recent years has been away

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                  BEEF CATTLE GRAZING S E L E N I F E R O U S R A N G E                             1045
from a yearling steer operation. The results         1) and 77 in the late group (bulls turned out
indicate that producers who continue in the          approximately July 18).
cow-calf operation could increase their re-            The early breeding group averaged a
turn by breeding earlier in the season pro-          22.3% higher calf crop born, with the early
vided they are prepared to take care of              group averaging 60.0% and the late group
February and March calves. While this                37.7~o. The advantage to the early breeding
recommendation is based on relatively few            group in percent weaned was 19.6, with the
matings per year, the consistent advantage of        early group averaging 52.0~ and the late
the early group throughout the 5-year period         group 32.4%.
lends support to the recommendation.                    Weaning weight unadjusted for age of calf
   Although the experiment was designed to           averaged 60 lb. in favor of the early group,
study the advantage of breeding early to             but after age adjustment no significant dif-
avoid the period of lush growth of the range         ference existed between the two groups. No
grass, it is recognized that other factors may       season effect was found for conformation,
be confounded with the rate of growth of the         condition, or selenium symptoms at weaning.
grass during the two periods studied. For            The results indicate an advantage to calving
example, the temperature difference during           early if selenium poisoning is a problem and
the two breeding seasons would be consider-          early calves can be properly cared for.
able, and this difference might influence the
results obtained. Stott and Williams (1962)                           L i t e r a t u r e Cited
in a study conducted in Arizona observed a           Minyard, J. A., C. A. Dinkel and O. E. Olson. 1960.
decline in pregnancy rate from 61.5% in May            Effect of arsanilic acid in counteracting selenium
to a low of 17.1% in August. In addition, the          poisoning in beef cattle. J. Animal Sci. 19:260.
early group would be grazing principally cool        Moxon, A. L., M, A. Rhian, H. D. Anderson and
season grasses during the breeding season              O. E. Olson. 1944. Growth on steers on seleniferous
                                                       range. J. Animal Sci. 3:299.
while the late group would b e grazing princi-       Olson, O. E., D. F. Jornlin and A. L. Moxon. 1942.
pally warm season grasses. Any species differ-         The selenium content of vegetation and the map-
ence between the two kinds of grasses in their         ping of seleniferous soils. J, Am. Soc. Agron.
rate of selenium uptake could influence the            34:607,
                                                     Stott, G. It. and R. J. Williams. 1962. Causes of
results. These are questions which are left un-        low breeding efficiency in dairy cattle associated
answered by the present study.                         with seasonal high temperatures. J. Dairy Sci.
                                                     Wahlstrom, Richard C., Leslie D. Kamstra and Oscar
                  Summary                              E. Olson. 1955. The effect of arsanilic acid and
                                                       3-nitro-4-hydroxyphenylarsonic acid on selenium
  The effect of season of breeding on repro-           poisoning in the pig. J. Animal Sci. 14:105.
ductive and weaning performance was studied          Wahlstrom, Richard C., Leslie D. Kamstra and Oscar
                                                       E. Olson. 1956. The effect of organic arsenicals,
over a 5-year period in which 152 matings              chlortetracycline and linseed oil meal on selenium
were made. The numbers of matings made in              poisoning in swine. J. Animal Sci. 15:794.
each breeding group were 75 in the early             Wahlstrom, Richard C. and Oscar E. Olson. 1959.
                                                       The effect of selenium on reproduction in swine. J.
group (bulls turned out approximately May              Animal Sci. 18:141.

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