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.

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.

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.

The objective of this study was to, through a meta-analysis of published data, evaluate the effects of dietary supplementation on the performance of beef cattle grazed on Brachiaria pastures during the rearing and finishing phases of growth. Data from 15 Brazilian studies were analyzed, totaling 462 animals given different types and levels of supplementation. Animals were divided into two categories: 319 in the rearing phase, and 143 in the finishing phase. The reviewed studies evaluated the effects of protein, energy, and protein/energy supplementation on animal performance parameters. Daily weight gain and final live weight were analyzed using forest plots. Daily weight gain during the rearing phase was similar across all supplement types used. Animals given supplementation gained an average of 119 g more per day compared to those who received no supplementation. Specifically, protein supplementation resulted in an increase of 28.22 kg. Animals given supplementation of any kind, represented by the subgroups shown in the plots, gained an average of 24.47 kg more compared to the control group.

The objective was to evaluate the influence of calving and postpartum characteristics, measured in different genetic predominance, on the postpartum rebreeding. Were evaluated 437 partum from cows that received feeding management consisting of a forage base of the native field and the mating season consisted of 90 days. The measurements were used from the data base (age of cow, genetic predominance, body weight, body condition score and date of calving) of the cows in the partum and postpartum period. The variables were submitted to analysis of multiple variances, multiple regression, correlation and cluster. Already the groups formed by cluster analysis were submitted to analysis of variance and F test and the means, compared by Student's t-test, α=0.05 probability. The increase in the mean at 0.14 points in the body condition score at calving and the occurrence of calving 9 days earlier at the calving season gives the Charolais genetically predominant cows repeat calves. The Nellore genetic predominance when they calved with similar body condition score (2.32 points) and showed a negative body weight gain at weaning (-3.0 kg and -2.1 kg) showed different behaviors, where they did not repeat the offspring, when they calved and weaned with smaller body weight.

The objective of this meta-analysis was to evaluate the effects of weight loss or weight gain of beef cows during the second and/or third trimester of gestation on the postnatal performance of the progeny. The variation in cow weight during the gestational period was calculated to standardize the treatments, being them: severe loss (SL = cows that lost more than 10% of weight); moderate loss (ML = cows that lost from 0 to 10% of weight) and weight gain (WG = cows that gained weight). The intensity of the cow weight variation effect was calculated as the mean difference (MD) with a 95% confidence interval and heterogeneity determined using the Q test and the I2 statistic. A meta-analysis of random effects was conducted for each indicator separately with the means of the control and experimental groups. Calves from WG cows were higher for birth weight (P = 0.0094); weight adjusted to 205 days (P = 0.0127) and average daily gain during pre-weaning (P < 0.0001) in relation to calves from ML cows. The W205 of calves from SL cows was 11.6 kg lower than the progeny from ML cows. The post-weaning performance of the progeny tended (P = 0.0868) to be higher in the progeny of WG cows than ML ones. The weight gain of beef cows during gestation improves the pre- and post-weaning performance of the progeny, with more evident effects in the early months of life of the offspring.

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.

Espécies de pastagem anual de verão são utilizadas no Brasil para fornecer forragem em épocas desfavoráveis e/ou atender categorias mais exigentes. Objetivou-se avaliar os parâmetros produtivos da forragem e o desenvolvimento de novilhos (195,0±13,40 kg; 14±0,19 meses) em pastagens de milheto ou sorgo forrageiro. Os tratamentos consistiram em: Pastagem de sorgo (Sorghum bicolor L. Moench) e Pastagem de milheto (Pennisetum americanum Leeke). O delineamento experimental foi de blocos ao acaso. O período experimental foi de 84 dias, subdivido em três períodos de avaliação. A pastagem de milheto proporcionou maior oferta de lâminas foliares (3,64 vs. 1,98 kg MS/100 kg de peso corporal), porém as demais características não diferiram entre as espécies forrageiras (P>0,05). A evolução de peso e estrutura corporal dos novilhos foi semelhante entre as forrageiras, assim como, a produtividade animal por unidade de área (P>0,05). Os períodos de avaliação influenciaram significativamente a produção vegetal e animal (P<0,05). O avanço no ciclo de utilização das pastagens resultou em piora na estrutura da forragem, com menor oferta de lâminas foliares, surgimento acentuado de espécies espontâneas e redução na produtividade da forragem. Houve evolução de peso e escore corporal com o avanço dos períodos de pastejo, com diferença significativa a cada 28 dias (P<0,05). Sorgo forrageiro e milheto apresentam parâmetros produtivos similares, mostrando-se como boas opções alimentares para novilhos em crescimento. O avanço no ciclo produtivo acarreta modificações na estrutura da pastagem, reduzindo a produtividade por área.