ABSTRACT The body weight (BW) of an animal is a vital economic trait that might help in decision-making in the handling of animals. The objective of the present study was to develop equations for the prediction of BW in Pelibuey sheep using scrotal circumference (SC). The BW (23.40 ± 6.96 kg) and SC (20.25 ± 6.19 cm) have been recorded in 405 male Pelibuey at the Southeastern Center for Ovine Integration, Mexico. Linear, logarithmic, quadratic, exponential, cubic, and power regression models were used for data analysis. Pearson correlation (R), Coefficient of determination (R2), Adjusted coefficient of determination (Adj.R2) Root mean square error (RMSE), Akaike information criterion (AIC), and Bayesian information criterion (BIC) were used to select the best model. Power regression model showed the highest R (0.93), R2 (0.86), Adj.R2 (0.86) and lowest RMSE (0.02), AIC (-989.44) and BIC (-981.44). The current study suggests that SC might be used as the only predictor for BW of growing Pelibuey sheep raised under tropical conditions.

RESUMO O peso corporal (PC) do animal é uma característica econômica importante, que pode auxiliar na tomada de decisões no manejo dos animais. O objetivo do presente estudo foi desenvolver equações para a predição do PC em ovinos Pelibuey por meio da circunferência escrotal (CE). O PC (23,40±6,96kg) e a CE (20,25±6,19cm) foram registrados em 405 ovinos machos da raça Pelibuey no Centro de Integração Ovina da Região Sudeste do México. Os modelos lineares, logarítmicos, quadráticos, exponenciais, cúbicos e de regressão de potência foram utilizados para a análise dos dados. A correlação de Pearson (R), o coeficiente de determinação (R2), o coeficiente de determinação ajustado (Adj.R2), o erro do quadrado médio (EQM), o critério de informação de Akaike (AIC) e o critério de informação bayesiano (BIC) foram usados para selecionar o melhor modelo. O modelo de regressão de potência apresentou maiores R (0,93), R2 (0,86), Adj.R2 (0,86) e menores EQM (0,02), AIC (-989,44) e BIC (-981,44). O estudo atual sugere que a CE pode ser usada como um único preditor para o PC de ovinos Pelibuey em crescimento criadas em condições tropicais.

ABSTRACT The objective of the study was to evaluate the effect of restricted suckling and feed supplementation on postpartum follicular development and blood progesterone (P4) and estradiol (E2) concentrations in beef cattle. One hundred and twenty lactating Simbrah cows were distributed into four treatments: T1) Continuous suckling with feed supplementation (CCC, n=30), T2) Restricted suckling without feed supplementation (RSC, n=30), T3) Restricted suckling with feed supplementation (RCC, n=30), and T4) Continuous suckling without feed supplementation (CSC, n = 30). Each cow from T1 and T3 received 4 kg of a commercial feed supplement daily (19 % CP and 73.26 % TDN). Throughout the study, the follicular dynamics and the presence of a corpus luteum were determined through transrectal ultrasonography, and blood concentrations of P4 and E2 were measured. The results were evaluated by univariate repeated measures ANOVA, Chi-square, Kaplan-Meier survival analysis and logistic regression. The number, follicular diameter (mm) and blood concentration of P4 (ng/mL) and E2 (pg/ml) were higher in T3 compared to the other treatments (p<0.05). It can be concluded that restricted suckling, along with feed supplementation, reduced postpartum anestrus in Simbrah cows under tropical conditions, through the increase in the number and diameter of ovarian follicles and in blood concentrations of P4 and E2.

El objetivo del estudio fue evaluar el efecto del amamantamiento restringido y la complementación alimenticia sobre el desarrollo folicular posparto y la concentración sanguínea de progesterona (P4) y estradiol (E2) en bovinos de carne. Se utilizaron 120 vacas Simbrah lactantes, distribuidas en cuatro tratamientos: T1) Amamantamiento continuo con complementación alimenticia (CCC, n=30), T2) Amamantamiento restringido sin complementación alimenticia (RSC, n=30), T3) Amamantamiento restringido con complementación alimenticia (RCC, n=30), y T4) Amamantamiento continuo sin complementación alimenticia (CSC, n=30). Cada vaca de los grupos T1 y T3 recibió diariamente 4 kg de alimento comercial balanceado (19 % CP y 73.26 % TND). A lo largo del estudio, se determinó la dinámica folicular ovárica y la presencia de cuerpo lúteo mediante ultrasonografía transrectal, y se midieron las concentraciones sanguíneas de P4 y E2. Los resultados se evaluaron mediante ANOVA univariado de medidas repetidas, Chi-cuadrada, análisis de sobrevivencia de Kaplan-Meier y regresión logística. El número, diámetro folicular (mm) y la concentración sanguínea de P4 (ng/ml) y E2 (pg/mL) fueron mayores en T3 que en los demás tratamientos (p<0.05). Se puede concluir que el amamantamiento restringido, junto con complementación alimenticia, disminuyó el anestro posparto en vacas Simbrah en el trópico, al incrementar el número y diámetro folicular, así como la concentración sanguínea de P4 y E2.