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

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 < .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 than 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 in making crucial management decisions during the breeding and calving season including nutrition, reproductive, and culling.

Use of nonlinear mixed models for describing testicular volume growth curve in Nellore bulls.

This study aimed to describe longitudinal testicular volume (TV) data of Nellore bulls by using nonlinear mixed models. Dataset consisted of 2,294 TV measurements from 505 bulls with ages ranging from 563 to 4,307 days. Nine nonlinear models were evaluated: Brody, Gompertz, Hill, Logistic I and II, Meloun, Michaelis-Menten, Mitscherlich and von Bertalanffy. Goodness of fit was evaluated by Akaike's information criterion (AIC), Bayesian information criterion (BIC), adjusted R2, percentage of convergence, error sum of squares (ESS), mean absolute deviation (MAD), and average prediction error (APE). These criteria were used to select the best model, then the absolute growth rate (AGR) for TV was estimated by the first derivate of the adjusted model related to time (∂Y/∂t). The values of adjusted R2, ESS, MAD and APE were similar among models. Percentage of convergence was higher for the Logistic I (76.8%), Logistic II (75.5%) and Mitscherlich (78.6%) models, but Logistic I and II showed the lowest values of AIC and BIC, indicating a better fit, so the Logistic I model was chosen for subsequent analyses. The TV growth occurred at a high rate until the inflection point, which was estimated at approximately 22 months of age; it stabilized and reached a plateau at approximately 2,500 days of age. This may suggest that TV is more related to sexual maturity than precocity. Additionally, the Logistic I model was used to estimate the growth curve and the AGR of the testicular length and width. As a result, testicular length increased at a higher rate than testicular width until approximately 1,600 days of age, indicating that the testes become longer with increasing age.

Relationship of testicular biometry with semen variables in breeding soundness evaluation of Nellore bulls.

This study aimed to evaluate the correlation between testicular biometry and semen variables, as well as, to relate testicular variables to the probability of selecting Nellore bulls with desirable sperm morphology when conducting breeding soundness evaluations (BSE). A total of 2055 BSEs from 506 bulls comprised the dataset. Biometric variables evaluated were: scrotal circumference, testicular volume, width, length, ratio and eccentricity; and semen variables were sperm motility, major sperm defects, minor sperm defects and normal sperm. Data of testicular biometry were correlated with data for semen variables using the Pearson's correlation assessment. Effects of testicular variables in selecting for sperm morphology of bulls in the BSE were evaluated by logistic regression. Scrotal circumference, testicular volume, length and width were positively correlated to sperm motility (0.18 to 0.19) and normal sperm (0.24 to 0.27) and negatively correlated with values for major defects (-0.24 to -0.27), but for testicular ratio and eccentricity there were coefficients near zero for all semen traits. Testicular ratio and eccentricity were not suitable for predicting the probability of selecting a bull based on semen variables using the BSE, but scrotal circumference, testicular volume, length and width were highly significant (P < 0.0001) with moderate values of area under ROC (Receiver Operating Characteristics) curve (0.608 to 0.620).

Can scrotal circumference-based selection discard bulls with good productive and reproductive potential?

Nonlinear mixed models were used to describe longitudinal scrotal circumference (SC) measurements of Nellore bulls. Models comparisons were based on Akaike's information criterion, Bayesian information criterion, error sum of squares, adjusted R2 and percentage of convergence. Sequentially, the best model was used to compare the SC growth curve in bulls divergently classified according to SC at 18-21 months of age. For this, bulls were classified into five groups: SC < 28cm; 28cm ≤ SC < 30cm, 30cm ≤ SC < 32cm, 32cm ≤ SC < 34cm and SC ≥ 34cm. Michaelis-Menten model showed the best fit according to the mentioned criteria. In this model, ß1 is the asymptotic SC value and ß2 represents the time to half-final growth and may be related to sexual precocity. Parameters of the individual estimated growth curves were used to create a new dataset to evaluate the effect of the classification, farms, and year of birth on ß1 and ß2 parameters. Bulls of the largest SC group presented a larger predicted SC along all analyzed periods; nevertheless, smaller SC group showed predicted SC similar to intermediate SC groups (28cm ≤ SC < 32cm), around 1200 days of age. In this context, bulls classified as improper for reproduction at 18-21 months old can reach a similar condition to those considered as good condition. In terms of classification at 18-21 months, asymptotic SC was similar among groups, farms and years; however, ß2 differed among groups indicating that differences in growth curves are related to sexual precocity. In summary, it seems that selection based on SC at too early ages may lead to discard bulls with suitable reproductive potential.

Crescimento ponderal de bezerras suplementadas com monensina sódica / Weight gain of heifers supplemented with monensin

O estudo teve como objetivo avaliar o efeito da inclusão de monensina sódica no concentrado inicial de bezerras lactantes, sobre o ganho de peso, perímetro torácico, altura de cernelha, altura de garupa e comprimento corporal. Foram utilizadas 12 bezerras divididas em dois grupos experimentais de acordo com a data de nascimento. Foram avaliados os tratamentos controle (sem suplementação com monensina) e suplementação diária com 0,4 mg de monensina/kg de peso corporal, a dosagem de monensina iniciou em 0,2 mg/kg peso vivo, para adaptação dos animais, sendo os animais acompanhados a partir dos 30 dias até os 86 dias de idade. Os parâmetros avaliados semanalmente foram peso corporal, perímetro torácico, altura de cernelha, altura da garupa e comprimento corporal. Tais parâmetros não apresentaram variação em função da suplementação com monensina, o menor rendimento observado para o grupo suplementado pode ter sido decorrente da diminuição do consumo. A suplementação de monensina não apresentou efeito sobre desempenho ponderal de bezerras leiteiras em sistema de desaleitamento precoce.

The objective of the present study was to evaluate the effects of the inclusion of sodium monensin on the starter concentrate of lactating heifers on weight gain, chest girth, withers height, hip height and body length. Twelve heifers were divided into two experimental groups according to date of birth: a control group without supplementation and a daily supplemented group with 0.4 mg of sodium monensin per kg of body weight. The animals were observed from thirty days of age until 86 days of age. Production parameters as body weight, chest girth, withers height, hip height and body length were weekly evaluated. These parameters did not show variation depending on supplementation with monensin, the lowest yield observed in the supplemented group may have been due to lower consumption. The supplementation of monensin had no effect on weight gain of dairy calves in early weaning system.