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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 adrenocorticosteroidogenesis in vitro. Dom. Anim. adrenal function to growth rate in Bos Indicus and Bos Endo. 13(4):339-349. Taurus cattle. S. Afr. J. Anim. Sci. 3:25-27 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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