Objetivou-se nesta revisão descrever os principais fatores que influenciam na produção de vacas leiteiras submetidas a pasto e a importância da avaliação do nitrogênio ureico do leite e do plasma para o desempenho animal. As pastagens apresentam fundamental importância na pecuária brasileira, garantindo baixos custos de produção, por ser a forma mais econômica e prática de produzir e oferecer alimentos para o rebanho. No entanto, apesar da grande diversidade de gramíneas com potencial forrageiro de alta qualidade, diversas regiões no Brasil apresentam baixa produtividade. Nos últimos anos, devido aos avanços no melhoramento genético em vacas leiteiras, o consumo de fontes proteicas tornou-se um fator limitante para a produção de leite, principalmente quando criadas em pastejo. A concentração de nitrogênio no leite (NUL) e no plasma (NUP) pode ser usada para monitorar a ingestão de proteína bruta, que deve ser o mais próximo possível das exigências requeridas do nutriente por parte do animal. Quando os valores de NUL são altos (>18 mg/dL) podem indicar excesso de proteína bruta (PB) na dieta, tanto da fração PDR (proteína degradável no rúmen) como da fração PNDR (proteína não-degradável no rúmen), baixa taxa de fermentação ruminal da fração carboidratos não-fibrosos (CNF), ou ainda, relação proteína:energia aumentada. Já valores baixos de NUL (<11 mg/dL) podem indicar deficiência de PB na dieta, limitadas quantidades de PDR e PNDR, ou ainda, alta taxa de fermentação de CNF no rúmen. Destaca-se, a necessidade de buscar estratégias nutricionais adequando-se o teor de NUL e NUP de acordo com o que se recomenda na literatura, que possam maximizar a produção, suprindo as limitações nutricionais impostas aos animais, principalmente daqueles mantidos em pastos tropicais, reduzir custos de produção e ainda diminuir o impacto ambiental causado pelo excesso de nitrogênio excretado.Palavras chave: eficiência do nitrogênio, forragem, produção de leite, suplementação proteica Milk urea nitrogen and plasma urea nitrogen of dairy cows grazing: Review
SUMMARY This study analyzed the effect of including copaiba oil as an additive for cattle supplemented on pasture, during the dry season. Four crossbred steers, castrated, with 245 ± 25 kg, aged about 18 months, fitted with permanent rumen cannula; were randomly assigned to a 4×4 Latin square. All animals were housed in individual paddocks (0.3 ha), uniformly covered with Brachiaria brizantha cv Marandu, with through and drinking fountain; and were given a concentrate at 500g/100 kg BW containing 380 g/kg crude protein (%DM). The copaiba oil was added to the supplement as a spray, in the proportions of 0, 0.5; 1.0 and 1.5 g/kg DM intake. Spraying supplementation was performed daily at the time of supply of the supplement. Data of intake and digestibility of nutrients, ruminal pH; ruminal ammonia nitrogen, and microbial protein synthesis were tested by analysis of variance and polynomial regression, adopting a significance level of 5%. The inclusion of copaiba oil quadratically affected total dry matter intake (P=0.030) and CP digestibility (P=0.043), without altering ruminal metabolism (P>0.05) and microbial protein synthesis (P>0.05) of the animals kept on pasture.
The purpose of this study was to evaluate the behavior of dairy calves bred in tropical climate. Six calves of the Girolando breed at 3 months old in average were used. For the elaboration of the ethogram, the focal animal sampling method was used for five days. The Analysis of Variance was run and treatment means were compared by Tukey’s test at 5% probability. Findings show that calves spent more time in the concentrate intake and foraging, the rumination occurred more frequently during the night, and no significant differences were found between the water intake and the leisure activity. The thermoregulation behavior regarding the shadow demand did not differ statistically when compared to the sun rays demand. However, animals remained in the standing position for longer in the afternoon, and spent more time walking in the morning. Statistical differences were found between the playing interaction 1 and the playing interaction 2, and there were no statistical differences between the stereotypy and vocalization. Therefore, the behavioral states were found to be indicators of the good welfare degree for calves kept in a tropical breeding system.
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