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Residual feed intake in beef steers II

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									                              Proceedings, Western Section, American Society of Animal Science

                                                          Vol. 53, 2002

          RESIDUAL FEED INTAKE IN BEEF STEERS: II. CORRELATIONS WITH HEMATOLOGICAL
                              PARAMETERS AND SERUM CORTISOL1

    C.M. Theis1, G.E. Carstens1, R.J. Hollenbeck1, M.W. Kurz1, T.M. Bryan1, L.J. Slay1, R.D. Randel2 and T.H. Welsh1

                           Texas Agricultural Experiment Station, 1College Station and 2Overton, TX

ABSTRACT: Selection against residual feed intake (RFI)             more efficient cattle have been based on measurements of
has the potential to improve feed efficiency without               postweaning FCR, which is the amount of feed consumed
affecting growth performance or body size, but measuring           divided by ADG. In growing animals, FCR is negatively
this trait in cattle is costly. Identification of physiological    correlated with ADG, and selection for ADG in growing
indicators of RFI may facilitate early detection of more           animals has been associated with increases in mature cow
efficient calves. The objective of the study was to examine        size. Consequently, selection for FCR in growing animals
correlations among RFI, feed intake (FI), ADG,                     will not likely improve efficiency of feed utilization in
hematological parameters, and cortisol secretion.                  integrated beef systems as feed requirements for the cow
Braunvieh-sired crossbred steers (N = 169) were                    herd would increase (Archer et al., 1999). Residual or net
individually fed a roughage-based diet (ME = 2.2 Mcal/kg;          feed intake is an alternative measure of feed efficiency that
15.7% CP, DM) using Calan feeders. Following 30 d of               quantifies the variation in feed intake of animals beyond
adaptation, weekly BW and FI were measured for 77 d.               that needed to meet maintenance and growth requirements.
RFI was calculated as the difference between actual FI and         Residual feed intake is calculated as the difference between
FI predicted from linear regression of FI on mid-test BW.75        actual feed intake and the amount of feed an animal is
and ADG. RFI ranged from -2.4 to 2.7 kg/d but was not              expected to eat based on its size and growth rate.
correlated with ADG or BW. On day 5 of the adaptation                   Recent studies have demonstrated that RFI is
period, blood samples were obtained prior to and 30 min            moderately heritable in growing cattle, and that RFI is not
after i.v. infusion of ACTH (0.1 IU/kg BW) and serum               phenotypically or genetically correlated to ADG or BW
analyzed for cortisol. Serum cortisol was also analyzed            (Arthur et al., 2001a; 2001b). However, measuring RFI in
from samples collected on d 0, and white (WBC) and red             beef cattle is expensive and inconvenient due primarily to
blood cell (RBC) parameters determined from samples                the cost of using current methods (e.g., Calan gates,
collected on d 0 and 70 of the RFI determination period.           Pinpointer feeding systems) to measure individual feed
Pre- and ACTH-induced cortisol concentrations were not             intakes. The identification of physiological parameters
correlated with RFI. However, d 0 cortisol concentrations          predictive of RFI would be useful as early screening tests to
were negatively correlated with FI (r = -.18, P < .05) and         minimize the number of animals that would need to be
ADG (r = -.24, P < .01), and positively correlated with feed       subjected to a complete RFI evaluation protocol.
conversion ratio (FCR; r = .16; P < .05). WBC counts and           Richardson et al. (1996) found that steers with low RFI
differentials were not correlated with any growth or               (more efficient) had significantly lower mean corpuscular
efficiency parameters.          On day 70, RBC counts,             hemoglobin (MCH; hemoglobin:RBC ratio) values and
hemoglobin and hematocrit were negatively correlated (P <          lower total plasma protein concentrations than steers with
.001) with FI (r = -.36, -.34, -.34) and ADG (r = -.37, -.44, -    high RFI (less efficient). Serum cortisol concentration has
.44) and positively correlated (P < .05) with FCR (r = .16,        been shown to be correlated with stress responsiveness and
.25, .24). These results demonstrate that serum cortisol and       growth performance in animals. Nikolic' et al. (1996)
RBC parameters were correlated with ADG, FI and FCR,               found that serum cortisol concentrations were negatively
but not with differences in feed intake independent of BW          correlated with growth rate in growing calves. The
and ADG (i.e., RFI). Additional studies are warranted to           objective of this study was to characterize the relationships
identify physiological indicators of RFI.                          between RFI and various physiological parameters (e.g.,
                                                                   hematological parameters, serum cortisol concentration and
Key words: Residual feed intake, Cortisol, Hematological           ACTH-induced cortisol response) in order to determine
parameters                                                         their status as potential physiological indicators of growth
                                                                   and feed efficiency in beef cattle.
                        Introduction
                                                                                    Materials and Methods
    Significant reductions in the cost of producing beef
could be achieved if selection programs were targeted to               An experiment was conducted to characterize RFI in
improve feed efficiency independent of growth traits               growing steers and to examine correlated responses with
(Archer et al., 1999). Traditional attempts to select for          performance traits and ultrasonic measures of composition.


1
    This research was supported by the Texas Agricultural Experiment Station, Texas A&M University, College Station, TX.
A description of the steers and the procedures used to           P < .001) and FCR (r = .49; P < .001), but was not
measure performance traits, RFI and ultrasound measures          correlated with final BW or ADG (see Carstens et al.,
of body composition were provided by Carstens et al.             2002). The less efficient steers that were identified as
(2002). Briefly, Braunvieh-sired crossbred steer calves          having high RFI (steers that were > 0.5 SD above the mean)
(initial BW = 233.7 ± 25.6 kg; mean ± SD) were adapted to        consumed 21% more DM feed per day and had 23% higher
the experimental diet and trained to eat individually from       FCR (DM feed/gain) compared to the low RFI steers that
Calan gate feeders over a 30-d period at two feeding             were < 0.5 SD below the mean. There were no differences
locations (College Station; n = 57 and McGregor; n = 112).       found in ADG (1.02 vs 1.02 ± .03 kg/d) or final BW (323.7
Thereafter, steers were individually fed for 77 d and full       vs 325.0 ± 5.4 kg) between the high and low RFI steers
BW measured at weekly intervals. The roughage-based              (Carstens et al., 2002). Ultrasound measures of rump fat
diet was pelleted and formulated to meet or exceed all           thickness revealed that the low RFI steers were slightly
nutrient requirements for growing steers (2.2 Mcal/kg;           leaner than high RFI steers (3.89 vs 4.24 ± .13 mm,
15.7% CP, DM basis). Growth of each animal was                   respectively), but there were no differences between RFI
modeled by linear regression of weekly BW against time           groups detected in longissimus muscle area or
(SAS, 1996), and the regression coefficients used to             intramuscular fat percentage.
calculate individual steer mid-test BW.75 and ADG. For                It has been suggested that regulatory factors involved
steers within each feeding location, average daily feed          in controlling growth of animals are inversely related to
intake was regressed on ADG and BW.75, and RFI                   those involved in controlling an animal's ability to tolerate
calculated as the difference between actual feed intake and      stressful conditions. Consequently, selection for increased
feed intake predicted from the regression model. Ultrasound      growth in animals may eventually lead to an increase in
measures of 12th rib and rump fat thickness, longissimus         stress susceptibility (van der Westhuysen, 1973). Nikolic' et
muscle area and intramuscular fat percentage were obtained       al. (1996) found that serum cortisol concentrations were
on day 70 of the experiment.                                     negatively correlated with growth rate in male Friesian
      Sample Collection and Analysis. On day 5 of the 30-d       calves. In the current study, both pre-ACTH and day-0
adaptation       period,   cortisol    response     to    an     serum cortisol concentrations were negatively correlated
adrenocorticotropic hormone (ACTH) challenge was                 with feed intake and ADG (Table 1). However, ACTH-
measured. Blood samples were collected via coccygeal             induced cortisol secretion was not correlated with feed
venipuncture from all steers prior to and 30 min following a     intake or ADG. Red blood cell counts, hemoglobin
bolus intravenous infusion of ACTH administered at a rate        concentrations and hematocrit values obtained on days 0
of 0.1 IU/kg BW. Blood samples collected via jugular             and 70 were negatively correlated with feed intake and
venipuncture were also obtained from steers on days 0 and        ADG. Additionally, these day-70 RBC parameters were
70 of the 77-d experimental period. Serum from blood             negatively correlated with 12th rib fat thickness.
samples collected prior to and following ACTH infusion                Cortisol, hemoglobin, hematocrit and MCH values
and on day 0 were analyzed for cortisol using RIA                measured on day 0, and all RBC parameters measured on
procedures as described by Carroll et al. (1996). Blood          day 70 were positively correlated with FCR, reflecting the
samples collected in EDTA blood tubes on days 0 and 70           negative correlations of these physiological indicators with
were submitted to the Texas Veterinary Medical Diagnostic        feed intake and ADG. However, none of the physiological
Laboratory for complete blood cell count and differential        indicators measured in this study were correlated with RFI
analysis.                                                        (Table 1), or found to be different between RFI groups
      Statistical Analysis. To examine the relationships         (Table 2). In contrast to these results, Richardson et al.
between RFI and hematological parameters and pre- and            (1996) found that steers identified as having low RFI (more
post-ACTH serum cortisol concentrations, partial                 efficient) had significantly lower MCH values than the
correlation coefficients were determined using the               steers identified as having high RFI (less efficient). There
MANOVA function of Proc GLM (SAS, 1996), with                    were no significant correlations found between WBC
feeding location and ranch origin of steers included in the      parameters and growth and efficiency traits (Table 1).
model as class variables. To further examine the
relationships between RFI and these physiological                                       Implications
indicators, steers were ranked by RFI within each feeding
location and separated into low, medium and high groups               Results from this study found that serum cortisol
that were < 0.5 SD,  0.5 SD, and > 0.5 SD, respectively,        concentrations as well as RBC parameters measured at the
from the mean RFI of 0.0 ± .82 kg/d (mean ± SD). The             beginning of the experiment were moderately related to
hematological parameters and cortisol data were analyzed         feed intake, ADG and FCR. However, there was no
using the GLM procedure of SAS (1996) with a model that          indication that these physiological parameters were
included RFI group, feeding location and ranch origin as         predictive of variation in feed intake independent of BW
class variables.                                                 and ADG (i.e., RFI). Given the potential value of RFI to
                                                                 improve feed efficiency of beef production, additional
                  Results and Discussion                         research is warranted to identify other physiological
                                                                 indicators as well as genetic markers that would be
     In support of previous research on RFI in cattle (Archer    predictive of RFI in cattle.
et al., 1999; Arthur et al., 2001a; Arthur et al., 2001b), RFI
in this experiment was correlated with feed intake (r = .59;                               Literature Cited
                                                                    Carstens, G.E., C.M. Theis, M.B. White, T.H. Welsh, Jr.,
Archer, J.A., P.F. Arthur, R.M. Herd, and P.F. Arthur.                 B.G. Warrington, R.D. Randel, T.D.A. Forbes, H.
   1999. Potential for selection to improve efficiency of              Lippke, L.W. Greene and D.K. Lunt. 2002. Residual
   feed use in beef cattle: A review. Aust. J. Agric. Res.             feed intake in beef steers: I. Correlations with
   50:147-161.                                                         performance traits and ultrasound measures of body
                                                                       composition. Proc. West. Sect. Amer. Soc. Anim. Sci.
Arthur, P.F., J.A. Archer, D.J. Johnson, R.M. Herd, E.C.               53:(current proceedings).
   Richardson, and P.F. Parnell. 2001a. Genetic and
   phenotypic variance and covariance components for                Nikolic, J.A., J. Begovic, V. Resanovic, I. Dankovic, and
   feed intake, feed efficiency, and other postweaning traits          S. Filipovic. 1996. Serum hormones and insulin-like
   in Angus cattle. J. Anim. Sci. 79:2805-2811.                        growth factor-1 in male and female calves and their
                                                                       possible relation to growth. Acta Veterinaria-Beograd.
Arthur, P.F., G. Renand, and D. Krauss. 2001b. Genetic and             46:17-26.
   phenotypic relationships among different measures of
   growth and feed efficiency in young Charolais bulls.             Richardson, E.C., R.M. Herd, P.F. Arthur, J. Wright, G. Xu,
   Livest. Prod. Sci. 68:131-139.                                      K. Dibley and V.H. Oddy. 1996. Possible physiological
                                                                       indicators for net feed conversion efficiency in beef
Carroll, J.A., S.T. Willard, B.L. Bruner, N.H. McArthur and            cattle. Proc. Aust. Soc. Anim. Prod. 21:103-106.
   T.H. Welsh, Jr. 1996. Mifepristone modulation of
   ACTH         and     CRH       regulation   of    bovine         van der Westhuysen, J.M. 1973. Relationship of thyroid and
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              Table 1. Partial correlations between growth and feed efficiency traits, and serum cortisol
                                     concentrations and hematological parameters
Parametersa                      Day-77 BW          ADG              FI           FCR           12th-rib fat      RFI
Cortisol Parameters:
    Pre-Cortisol, ng/mL        -.14 (.06)        -.20   (.01)     -.16   (.04)    .11   (.18)   -.13   (.10)   -.009 (.92)
    Post-Cortisol, ng/mL       -.01 (.93)        -.07   (.36)     -.01   (.91)    .09   (.26)   -.02   (.76)    .04 (.63)
    Post-Cortisol:Pre-Cortisol .10 (.20)          .04   (.65)      .14   (.07)    .08   (.32)    .07   (.36)    .11 (.16)
    Day 0 Cortisol, ng/mL      -.11 (.14)        -.24   (.002)    -.18   (.02)    .16   (.04)    .00   (.97)   -.10 (.19)
Day 0 Hematological Parameters:
    RBC, 106 cells/L         -.21    (.01)      -.19   (.01)     -.27 (.0004)    .01   (.94)   -.11   (.14)    -.08   (.30)
    HB, g/dL                  -.13    (.11)      -.34   (.0001)   -.27 (.0005)    .16   (.05)   -.15   (.06)    -.07   (.37)
    HCT, %                    -.09    (.22)      -.31   (.0001)   -.20 (.008)     .18   (.02)   -.10   (.18)    -.03   (.68)
    MCH, pg                    .11    (.17)      -.20   (.009)    -.01 (.93)      .19   (.02)   -.06   (.47)    -.01   (.94)
    WBC, cells/L              .11    (.14)       .12   (.13)      .08 (.29)     -.07   (.37)    .00   (.95)    -.08   (.30)
    NEUT, %                   -.01    (.86)       .09   (.22)      .003 (.97)    -.15   (.06)    .03   (.67)    -.06   (.41)
    LYMPH, %                   .03    (.74)      -.07   (.39)      .02 (.78)      .12   (.13)    .01   (.90)     .02   (.77)
    MONO, %                   -.04    (.60)      -.09   (.23)      .00 (1.00)     .10   (.18)   -.01   (.93)     .12   (.13)
Day 70 Hematological Parameters:
    RBC, 106 cells/L           -.35 (.0001) -.37 (.0001) -.36 (.0001)     .16 (.04)   -.18 (.02)     -.03 (.74)
    HB, g/dL                    -.29 (.0002) -.44 (.0001) -.34 (.0001)     .25 (.001) -.21 (.007)      .01 (.93)
    HCT, %                      -.32 (.0001) -.44 (.0001) -.34 (.0001)     .24 (.002) -.19 (.01)      .00 (1.00)
    MCH, pg                      .10 (.19)      -.12 (.11)      .04 (.63)  .14 (.07)   -.05 (.48)      .04 (.62)
    WBC, cells/L                .08 (.28)       .08 (.33)      .14 (.07)  .02 (.79)   -.06 (.45)      .09 (.26)
    NEUT, %                     -.03 (.67)       .11 (.17)      .06 (.47) -.09 (.23)    .00 (1.00)     .06 (.44)
    LYMPH, %                     .06 (.40)      -.06 (.42)     -.02 (.83)  .08 (.32)   -.02 (.79)     -.05 (.52)
    MONO, %                     -.04 (.57)       .01 (.93)     -.06 (.48) -.07 (.34)    .04 (.57)     -.05 (.56)
     a
       RBC = red blood cell; HB = hemoglobin concentration; HCT = hematocrit; MCH = mean corpuscular hemoglobin
(HB*10/RBC); WBC = white blood cell; NEUT = neutrophils; LYMPH = lymphocytes; MONO = monocytes; FI =
feed intake; FCR = feed conversion ratio; RFI = residual feed intake.
       Table 2. Least squares means of serum cortisol concentrations and hematological parameters from
                         steers with low, medium, and high residual feed intake (RFI) a
                                  Low                Medium            High
Parametersb                       RFI                 RFI              RFI            SE      P-value

Number of steers                  54                  64               51             ----       ----
Cortisol Parameters:
    Pre-Cortisol, ng/mL           21.30              25.51            22.12           1.94        .11
    Post-Cortisol, ng/mL          35.84              37.51            36.85           1.94        .74
    Post-Cortisol:Pre-Cortisol     2.47               2.00             3.24           1.40        .73
    Day 0 Cortisol, ng/mL         36.60              32.78            33.21           1.78        .12
Day 0 Hematological Parameters:
    RBC, 106 cells/L            9.92                 9.81             9.79          0.14         .68
    HB, g/dL                    13.38                13.14            13.13          0.20         .43
    HCT, %                      38.03                37.43            37.41          0.62         .60
    MCH, pg                     13.55                13.44            13.43          0.17         .80
    WBC, cells/L             7763                 7574             7194           481            .59
    NEUT, %                     28.85                26.16            26.68          1.69         .33
    LYMPH, %                    65.16                65.84            66.68          2.09         .83
    MONO, %                      3.05                 4.69             4.00          0.50         .02
Day 70 Hematological Parameters:
    RBC, 106 cells/L             9.21                9.20             9.19          0.17         .99
    HB, g/dL                     13.36               13.52            13.67          0.25         .57
    HCT, %                       37.95               38.53            38.72          0.75         .67
    MCH, pg                      14.53               14.72            14.91          0.16         .12
    WBC, cells/L             7518                 7586             8300           393            .17
    NEUT, %                      32.45               31.46            32.36          1.65         .84
    LYMPH, %                     61.63               63.14            61.42          1.74         .62
    MONO, %                       4.10                4.78             2.96          0.49         .005
 a
   Low, medium and high RFI steers were < 0.5 SD,  0.5 SD, and > 0.5 SD from the mean RFI of 0.0 ± .82
kg/d (mean ± SD), respectively.
 a
   RBC = red blood cell; HB = hemoglobin; HCT = hematocrit; MCH = mean corpuscular hemoglobin
(HB*10/RBC); WBC = white blood cell; NEUT = neutrophils; LYMPH = lymphocytes; MONO =
monocytes.

								
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