Longevity and reproductive traits in Angus cattle: Genetic parameters, predicted and realized genetic change

Abstract

The objectives of this study were to estimate genetic parameters for longevity and reproductive and to evaluate their likely consequences on selection. We used calving records of 10,517 Aberdeen Angus cows, born between 1975 and 2012, with first calving in spring, from bulls with 5 or more daughters, herds with 25 or more observations, and pertaining to contemporary groups of 5 or more cows. Longevity variables were length of productive life (LPL) and stayability at 5 years (ST5); the reproductive variables were days to first calving (days1), calving success at second parity (CS2), and success of having the first three consecutive calvings (S3). CS2, S3 and ST5 were defined as binary, and days1 and LPL as continuous variables. A multi-trait, threshold-linear model was used, including contemporary group effects (herd-year of birth; days1 also included management group), age at first calving (covariate), and the genetic effect of the animal. Given the parameters, five strategies were explored to predict annual genetic progress: selection of 5% or 25% of progeny tested males, with progeny groups of 5 or 15 daughters (no selection in females), and mass selection of 75% in females (no selection in males). Annual realized genetic trends and correlated responses when selecting for ST5, CS2 or S3 were also calculated. The estimates (mean ± standard deviation a posteriori) of heritability for longevity traits were 0.08±0.03 for LPL and 0.11±0.05 for ST5; for reproductive traits, estimations were 0.08±0.02 for days1, 0.23±0.04 for S3, and 0.24±0.04 for CS2. The genetic correlation between LPL and ST5 was favourable and large (0.79); and were also favourable and large for reproductive characteristics (negative, -0.66 for days1-S3 and -0.73 for days1-CS2, and positive, +0.83 for S3-CS2). Correlations between longevity and reproduction were variable, from not different from zero (days1 with ST5 and LPL) to medium (+0.45 for ST5-S3). Realized annual genetic trends indicated small but significant favourable changes for ST5 and LPL, and unfavorable for days1, CS2 and S3. Correlated responses were, in general, also favourable, although less than the progress achieved by direct selection. There are wide possibilities for genetic improvement in these characteristics.