The development of beef calves born of Charolais (CH), Nellore (N), and Charolais × Nellore crossbred cows with Charolais (CHP) and Nellore (NP) predominance, was evaluated from birth to 12 months of age. The cows were grouped into three age classes: primiparous, young and adult. The net energy requirements for maintenance and gain of the calves were also evaluated, as were the production and availability of energy in the milk of the evaluated cows. We used 93 pairs of contemporary cows and calves maintained in natural pasture. From birth to 21 days of age and from 21 to 42 days of age, the calves of adult cows presented the highest average daily weight gain (ADG), while the calves of young and primiparous cows had similar ADG. The highest net energy requirements for maintenance (NEm) and gain (NEg) were for crossbred and Charolais calves, the latter being similar to Nellore calves. The energy available in the milk of the adult cows was 33% higher than that of primiparous cows. The weight gain of calves was influenced by the age of the cow until weaning. The pre-weaning and post-weaning weights of calves were affected by the genetic group, and adult and young cows produced heavier calves in the pre-weaning period than primiparous cows.

The objective of this work was to analyze the effects of immunocastration on the performance and carcass quality of steers in the finishing phase, compared with non-castration and surgical castration. Data from ten studies with records of 1,261 male bovines were analyzed. The studies included in the meta-analysis necessarily contained treatments with immunocastration specifically against the gonadotropin-releasing hormone. Each study was considered as a random effect in the statistical model used. The data were tested for homogeneity of variances and residue normality, and then subjected to the analysis of variance. Means were compared by Student’s t-test. Non-castrated steers showed greater daily weight gain, feed efficiency, slaughter and hot carcass weights, and loin eye area, besides lower fat thickness than surgically-castrated animals and the lowest a* and b* meat coloration values. Overall, immunocastrated steers were inferior to the non-castrated ones, but superior to those surgically-castrated. Immunocastrated steers present performance and carcass traits superior to those of surgically-castrated animals, but similar meat quality.

O objetivo do estudo foi, por meio de uma revisão de literatura, avaliar os efeitos da nutrição de vacas de corte durante a gestação sobre a qualidade e o desempenho da progênie após o nascimento. Nos últimos anos, inúmeras pesquisas foram desenvolvidas para avaliar os efeitos da nutrição materna durante a gestação (programação fetal) sobre a produtividade da progênie. Diante dos resultados apresentados, está claramente elucidado que as condições nutricionais do útero grávido alteram de várias maneiras a saúde, a fisiologia, o metabolismo e, consequentemente, o desempenho pós-parto da progênie. Estas alterações podem variar de acordo com o grau e intensidade do desafio nutricional, momento deste desafio no decorrer da gestação e capacidade adaptativa das vacas gestantes em particionar os nutrientes ao feto. A literatura sugere que os efeitos da programação fetal são mais facilmente constatados nos meses iniciais de vida dos descendentes, desaparecendo com o avançar da idade, porém, a restrição nutricional da vaca durante a gestação também pode levar à formação de um indivíduo com maior capacidade de adaptação e mais preparado para sobreviver em ambientes mais desafiadores na vida pós-natal. Além disso, a formação de um fenótipo “econômico” poderá resultar em um desempenho compensatório durante a vida adulta dos bezerros de vacas que passaram por desafios nutricionais durante a gestação.

Cattle farming becomes more intensive when the productive efficiency of the cows is increased, and nutrition is adjusted to the animal biotype. Eighty purebred Charolais and Nellore cows and their crosses between 3 and 7 years of age, were grouped for body weight at calving into Light (332.6 kg), Moderate (385.3 kg) and Heavy (444.6 kg). Cows and their calves were weighed at calving, at 63 days (early weaning) and at 210 days. The estimated milk production of the cows was evaluated by manual milking at 21, 42 and 63 days postpartum. The difference in the weight of the cows at calving was maintained during lactation and at 210 days postpartum. The body size of the cow did not influence milk production. Heavier cows produce heavier calves up to 365 days of age compared to lighter cows. The reproductive performance of the cows is not affected by their weight. The production of kilograms of calf for every 100 kilograms of cow at calving and weaning is higher in Light cows. The production of kilograms of calf adjusted for the pregnancy rate of the cows is higher in Heavy cows. Production efficiency in kilograms of calf per area is lower in Heavy cows.

The objective was to evaluate factors that influence calving probability in the first and second reproductive years of beef heifers that reached the minimum recommended body weight (BW) in the first breeding season. Two hundred twentyseven 24-month-old Charolais × Nellore heifers that mated between 2003 and 2012 were analyzed. The parameters evaluated were: year effect; individual and maternal heterozygosis; percentage of Charolais genotype; average daily gain (ADG) from weaning to the end of the first breeding season; BW at 18 and 24 months of age, end of breeding season, parturition, and weaning; Julian date of calving; and adjusted calf weight at weaning. These variables were subjected to logistic regression. Calving rates in the first and second reproductive years were 58.1 and 49.5%, respectively. Performance until the end of the first breeding season, BW before the first breeding season, and individual heterozygosis affected the calving probability in the first breeding season. In the second breeding season, BW variation from the first breeding season and calving, Julian date of calving, and BW at the end of the second breeding season influenced calving probability. Until the end of the first breeding season, ADG of beef heifers responded positively to the calving probability, even after reaching the usually recommended BW for the first breeding season. Primiparous cows calving at the beginning of the breeding season and gaining more BW between the first and second breeding season are more likely to give birth in the second breeding season.