Calving date as a potential predictor for the probability of approval in the first breeding soundness evaluation of Nellore bulls

• Published in: Reproduction in domestic animals Vol. 58; no. 9; pp. 1225 - 1233
• Main Authors: Diaz-Miranda, Edgar Andres, Penitente-Filho, Jurandy Mauro, Gomez-Leon, Victor Enrique, Lopez, Camilo Jose Ramirez, Villadiego, Faider Alberto Castaño, Okano, Denise Silva, Neto, Tamires Miranda, Guimarães, Simone Facioni, Siqueira, Jeanne Broch, Guimarães, José Domingos
• Format: Journal Article
• Language: English
• Published: Germany Blackwell Publishing Ltd 01.09.2023
• Subjects: Biometrics; Breeding; Breeding seasons; Correlation coefficient; Correlation coefficients; Economics; Profitability; Seasons; Semen; Statistical analysis; Natural service; scrotal circumference; breeding season; bull fertility
• ISSN: 0936-6768; 1439-0531
• DOI: 10.1111/rda.14422

Beef production systems primarily use natural service (NS) for breeding. However, a significant number of bulls used for NS are subfertile, limiting the profitability of the cow-calf operations. Therefore, producers should select bulls based on breeding soundness evolutions (BSE) to ensure higher pregnancy rates. Several factors can affect the bull ability to pass a BSE. We hypothesize that calving date would be a factor that affects the bull probability of approval at the first BSE. For this purpose, a multivariate logistic regression in a dataset of 14,737 BSEs from young Nellore bulls was used. Correlations between calving date, biometrics, and semen traits were evaluated using Pearson`s correlation coefficient. Our results demonstrated that the calving date affected the probability of approval at the first BSE (P < 0.05). Indeed, the variable that added more information to our model was the calving date, far more than the age group of the bulls according to Akaike's information criterion. Hence, bulls born on day 0 of the calving season have 1.26 more chances to be approved at the first BSE than bulls born 21 days later. This result highlights the importance of getting the dams of future bulls pregnant as soon as possible in the breeding season. In addition, the calving season should be no longer of 47 days to achieve 80% BSE approval in 20-22 months old Nellore bulls. The strongest correlation was with SC, which decreased as the calving date increased. Therefore, the calving date may be used as a predictor of the outcome of the first BSE in young bulls. In that way, the calving date can help seedstock producers to maximize efficiency making crucial management decisions during the breeding and calving season including nutrition, reproductive, and culling.