Suplementação com gordura protegida para vacas de corte desmamadas precocemente mantidas em pastagem natural

Environmental factors on the probability of pregnancy in early or conventionally weaned beef cows

Potential variables for the reproductive success of beef cows were evaluated. Included in the model were the age of the cow at calving; the interval between the Julian calving date and the end of the breeding season; the body weight and conditions at calving, at 75 days post-partum and at the end of the breeding season; and the mean daily variation in weight between these dates. Logistic regression was used in the analysis, with the parameters evaluated using the odds ratio statistic, estimating the chance of pregnancy. The mean rate of pregnancy was 84% and 55% for early and late-weaned cows, respectively. For early weaned cows, the regression variables were the Julian calving date, age of the cow, weight gain from calving to 75 days post-partum, and from 75 days post-partum to the end of the reproductive period. For late-weaned cows, there were only two regression variables, weight at calving and weight gain from calving to the end of the reproductive period. For every year above the average age of the herd, early weaned cows have an 80.9% greater chance of pregnancy, while a reduction of one year reduces the chance of pregnancy by 44.7%. In early weaned cows, every seven days after the mean Julian calving date reduces the chances of pregnancy by 22.6%, whereas every seven days before the mean calving date increases pregnancy by 29.2%. Greater gains in cow body weight, from calving to the end of the reproductive period, determine a greater probability of pregnancy.

Productive performance of beef cows subjected to different nutritional levels in the third trimester of gestation

In general, calf production occurs in less intensive systems. The limitation of nutrients during the gestation phase of beef cows can have negative impacts on the consequent productivity of females. Therefore, this study aimed to evaluate the effects of nutritional levels in the third trimester of pregnancy on the productive performance of beef cows kept in a natural pasture (NP). Eighty-three Charolais × Nelore cows were used, ranging in age from 4 to 12 years, which were divided according to their nutritional levels during the third trimester of pregnancy: NP, cows supplemented with 100% of their energy and protein requirements (SP100) and cows supplemented with 150% of their energy and protein requirements (SP150). The experimental design was completely randomized with three treatments and a varied number of repetitions. The SP100 and SP150 cows presented better body condition at calving (2.92 and 2.99 vs 2.81 points) and at the start of the breeding season (2.90 and 2.95 vs 2.80 points) than did NP cows. The nutritional level of the cows in the third trimester of gestation did not influence the blood metabolite concentrations. The plasma levels of albumin and total proteins were 3.11 and 8.18 g/dl, respectively. Glucose and cholesterol showed values of 74.96 and 166.50 mg/dl. The lowest concentration of blood metabolites was observed in the first postpartum weeks. The SP100 and SP150 cows showed faster follicular growth and, consequently, a higher percentage of females with ovulatory follicles at 21 days postpartum than did NP cows (45.68, 41.11, and 11.00%, respectively). The SP150 cows had a higher pregnancy rate (40.74%), total calf production (295.88 kg/cow), and consequently, offspring sale value. An increased nutritional level in the third trimester of pregnancy improves the postpartum metabolic condition and productive efficiency of beef cows kept on NP.