Genetic correlations between scrotal circumference, heifer fertility and stayability in Charolais-Charbray cattle

Records from Charolais, Charbray and Charolais-Zebu crosses provided by Charolais-Charbray Herd Book de Mexico, were used to estimate heritabilities and genetic correlations between scrotal circumference (SC, n = 18,972), heifer fertility (HF, n = 91,250), and stayability (STAY, n = 17,696). Measurements of SC were adjusted to 365 days limiting the age range from 320 to 410 days of age. The trait HF was coded as 1 if the heifer calved before 1,281 d of age and 0 otherwise. The trait STAY was defined as the probability of whether or not a cow calved a second calf before the six years of age given that, at least, the cow had calved a calf at three years of age or before. A three trait animal model and a Bayesian linear-threshold-threshold analysis were used to estimate (co)variance components. Heritability estimates were 0.18 +/- 0.02, 0.11 +/- 0.01, and 0.26 +/- 0.03 for SC, HF and STAY, respectively. Strong genetic correlations were detected between SC and STAY (0.76 +/- 0.04), and between HF and STAY (0.57 +/- 0.07), suggesting that selection of sires based on SC, and HF could lead to an improvement of STAY of cows in the Charolais-Charbray population of Mexico. A weak genetic correlation was found between SC and HF ( - 0.08 +/- 0.10). Overall, the heritabilities and genetic correlations estimated for the three traits evaluated in this study support the feasibility of improving by selection the reproductive performance of the Charolais-Charbray population of Mexico.