Data de parto, desempenho pós-parto e período de lactação sobre a probabilidade de prenhez em vacas de corte

Abstract

Beef cattle is an important productivity sector for the country, but its indicators can be improved, thus increasing the efficiency of this sector. Low production rates are often caused by lack of planning for the use of nutritional resources. Nutrition influences fertility by providing specific nutrients necessary for the processes of follicle development, ovulation, oocyte maturation, fertilization, embryonic survival and the establishment and maintenance of pregnancy. Reproductive potential is influenced by short-term and long-term nutritional effects on estrus and during different physiological states. The body weight gain of cows after parturition and during the reproductive period is essential to improve reproductive performance, exerts a great influence on the reproductive activity of females, intermediate body conditions at parturition, and can guarantee better reproductive performance of females. The lactation phase is the most critical period for cows with higher nutritional requirements. For this reason, it is important that cows at calving have a good body condition to meet the needs required for their maintenance. Due to all the previously mentioned factors, the objective of this study was to evaluate and quantify how much each probable influencing factor in pregnancy can affect with its increase or decrease. The experiment was carried out at Granja Itú, in the municipality of Itaqui - RS. Reproductive performance was evaluated for three years, using 284 lactations of Braford cows, with ages ranging from 3 to 5 years. For the elaboration of the models and statistical analysis, the statistical package SAS (Statistical Analysis System, version 9.2. For analysis of the variables, logistic regression was used, through the LOGISTIC procedure. The variables in the regression equation were submitted to a multicollinearity test and the parameters were evaluated using the odds ratio statistics (odds ratio), in which the change in the chances of pregnancy was estimated from the function of increases or decreases in the units of the regression variables. The one-year increase in age represented a 30% increase in pregnancy, while the one-year decrease decreased the chances of pregnancy by 23%. In the lactation period, seven days more of lactation reduced the chances of pregnancy by 12% and the anticipation of weaning every seven days increased the chances of pregnancy by 14% of the cows. An increase of 0.1 kg in the average daily gain represented increments of 17 and 15% in the cows' chance of pregnancy in the first 60 days postpartum and 60 days to the end of the reproductive period, respectively. On the contrary, the loss of 0.1 kg in the average daily gain promoted a reduction of 14 and 13% in the cows' chances of pregnancy. Factors such as age, precocity of calving in the calving season, reduction of the calf to the cow's foot, improvement in performance between calving and at the end of the mating, are strategies that increase the chances of pregnancy in beef cows.