|Van Vleck, Lloyd|
Submitted to: Tecnia Pecuaria En Mexico
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2004
Publication Date: 8/1/2004
Citation: Martinez-Velazquez, G., Gregory, K.E., Bennett, G.L., Van Vleck, L.D. 2004. Genetic parameters for scrotal circumference, age at puberty in heifers and weaning rate in several breeds of beef cattle. Tecnia Pecuaria En Mexico.42(2):159-170. Interpretive Summary: Records for yearling scrotal circumference (SC, 7,580), age at puberty in heifers (AP, 5,292), and weaning status following first breeding season (WR1, 7,003) from 12 Bos taurus breeds collected at the Meat Animal Research Center (USDA) between 1978-1991 were used. Estimates of heritability for yearling scrotal circumference indicate that this trait should respond readily to direct selection. Estimates of heritability for age at puberty in heifers suggest a better response to direct selection for age at puberty for breeds with lower levels of milk production than for breeds with intermediate and higher levels of milk production. Estimates of heritability for weaning rate of heifers suggest that genetic response could be achieved through direct selection, especially in breeds with large mature size and low milk production. Little variation in scrotal circumference, age at puberty and weaning rate of heifers is due to maternal genetic effects. Estimates of direct-maternal genetic correlations for weaning weight were consistently large and unfavorable across all groups. Direct genetic correlations between scrotal circumference and age at puberty or weaning rate, and between age at puberty and weaning rate were, on average, small. Those estimates suggest that, in these populations, genetic response in age at puberty and weaning rate by selecting sires on yearling scrotal circumference may be less effective than previously reported in the literature.
Technical Abstract: Records for yearling scrotal circumference (7,580), age at puberty in heifers (5,292), and weaning status following first breeding season (7,003) from 12 Bos taurus breeds collected at the Meat Animal Research Center (USDA) between 1978-1991 were used. Groups were: Charolais (C), Limousin (L), and MARC I composite (Group 1); Simmental (S), Gelbvieh (G), Braunvieh (B), and MARC II composite (Group 2); Hereford (H), Angus (A), Pinzgauer (P), Red Poll (R), and MARC III composite (Group 3); C, L, S, G, B, H, A, P, R (Group 4), and MARC I, MARC II, and MARC III composites (Group 5). Random effects in all models were direct genetic, maternal genetic, maternal permanent environmental, and residual. A derivative-free REML algorithm was used to estimate the variance components. Direct genetic correlations between SC and AP and between SC and WR1 were -0.41 and 0.22 (Group 1), -0.09 and -0.03 (Group 2), 0.19 and 0.04 (Group 3), 0.03 and -0.02 (Group 4), and -0.28 and 0.20 (Group 5). Direct genetic correlations between AP and WR1 were -0.08, 0.02, 0.42, 0.30, and -0.22 for Groups 1, 2, 3, 4, and 5, respectively. Direct genetic correlations between SC and AP (WR1) were, on average, small. Genetic response in AP or WR1 by selecting sires on yearling SC is not expected to be effective.