|Randel, R - TEXAS AG. EXP. STATION|
|Olson, T - UNIVERSITY OF FLORIDA|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: December 7, 2007
Publication Date: September 8, 2008
Citation: Chase, C.C., Randel, R.D., Riley, D.G., Coleman, S.W., Olson, T.A. Genetic Effects on Circulating Concentrations of Cortisol At and After Weaning in Breed-types Adapted to the Subtropics[abstract]. Journal of Animal Science Supplement. Southern Association of Agricultural Scientists. Journal of Animal Science Supplement. Vol. 86, E-Suppl.3. Paper No. 5. Technical Abstract: The objective of this study was to evaluate circulating concentrations of cortisol in calves (heifers and steers) at weaning (day 0) and on d 1 and 3 post-weaning. Calves (n = 938) were produced from a three breed diallel mating design and included calf crops from 2002 to 2004. Breed-types of calves were purebred Angus (AA), Brahman (BB), and Romosinuano (RR) and all F1 crossbred combinations (AB, BA, AR, RA, BR, RB). At weaning (day 0) and on d 1 and 3 post-weaning, a blood sample was collected via jugular venipuncture from each calf. Plasma was frozen and stored until analysis of cortisol concentrations using RIA. Fixed effects included sire and dam breed (n = 3 each) and their interaction, calf sex, year (n = 3), location (n = 3), day of sampling (n = 3), and cow age. Order through the chute, calf age, and calf weaning weight were used as covariates. Random effects were calf and sire. Heifers had higher (P < 0.001) plasma concentration of cortisol than steers (37.1 ± 0.78 vs. 32.9 ± 0.79 ng/mL, respectively). For purebred calves, cortisol concentration was lowest (P < 0.05) for AA (29.3 ± 1.60 ng/mL) and did not differ (P > 0.10) between BB (33.7 ± 1.56 ng/mL) and RR (35.2 ± 1.21 ng/mL). Estimates of heterosis (P < 0.04) were 5.1 ± 1.20 ng/mL (16.2%) for AB, 2.8 ± 1.03 ng/mL (8.7%) for AR, and 2.2 ± 1.05 ng/mL (6.5%) for BR. Heterosis for BA was greater (P = 0.03) than that for BR. Direct breed effects for Romosinuano were 6.5 ± 2.58 and for Angus were –8.8 ± 2.88 ng/mL. Maternal breed effects for Angus were 3.7 ± 1.60 ng/mL. Direct and maternal breed effects not mentioned were not significant. Day 1 cortisol concentration (36.5 ± 0.80 ng/mL) was greater (P < 0.02) than cortisol concentration on day 0 (33.6 ± 0.82 ng/mL) or day 3 (35.0 ± 0.80 ng/mL). The difference between day 0 and 3 approached significance (P = 0.053) and would suggest that cortisol concentrations were slightly elevated 3 d after weaning. To our knowledge these are some of the first results that evaluate circulating cortisol in diverse genotypes adapted to the subtropics.