Genetic relationships between male and female reproductive traits in Retinta beef cattle

Abstract

Scrotal circumference (SC) is an indirect measure used to predict the reproductive fitness of beef cattle raised in an extensive regime with limited seasonal breeding. It stands out for having a moderate to high heritability and favorable correlations, with seminal and reproductive quality traits in both the bull and its daughters. In the present study, we analyzed 2634 SC records of young bulls evaluated in testing stations for future bulls of the Retinta cattle Breed. The data was collected from 828 young bulls which produced 3,616 daughters. Monthly measurements of live weight, average daily gain, feed consumption, and SC were also performed in the bulls during testing. In addition, reproductive controls were performed in the daughters to estimate age at first calving (AFC) and reproductive efficiency (RE). We also estimated genetic parameters for the traits using a classical REML repeatability animal model. Average SC was 34.04 ± 2.43 cm. at 12 months, showing a heritability of 0.282 ± 0.052. Phenotypic (−0.05, 0.11, 0.42) and genetic (0.12, 0.15, −0.09) correlations were obtained between AFC and Reproductive Efficiency (RE) at 3, 6, and last calving and SC. These results suggest a strong environmental influence on the reproductive variables of daughters, probably motivated by the breeding model and the farmer's decision on the date of reproduction of the heifers. However, it can be seen that the AFC, RE3 and RE6 are more favorable for individuals with SC >37 cm, and more unfavorable for SC ≤32 in relation to SC >32 and ≤37. Finally, 85 of the bulls underwent sperm analysis using computer-assisted sperm analysis (C.A.S.A.) technology, using frozen semen samples belonging to the Retinta Breeding Program. Residual phenotypes for SC showed positive correlations with progressivity (0.11 in STR and LIN) and longevity (0.2 in L40 and 0.1 in L50). The highest r² was obtained using a canonical correlation, suggesting that a higher SC may improve sperm quality in bulls. It can therefore be confirmed that the use of this selection criterion (SC) in the breeding program of this breed will determine a response to positive selection, both for the fertility of the bull and its daughters.