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This study aimed to evaluate urea excretion, nitrogen balance and microbial protein synthesis in lactating goats fed with diets containing different protein sources in the concentrate (soybean meal, cottonseed meal, aerial part of cassava hay and leucaena hay). Four Alpine goats whose mean body weight was 42.6±6.1 kg at the beginning of the experiment, a mean lactation period of 94.0±9.0 days and a production of 1.7±0.4 kg of milk were distributed in a 4×4 Latin square with four periods of 15 days. Diets were formulated to be isonitrogenous, containing 103.0 g/kg of CP, 400 g/kg of Tifton 85 hay and 600 g/kg of concentrate. Diet containing cottonseed meal provided (p<0.05) increased excretion of urea and urea nitrogen in the urine (g/d and mg/kg of BW) when compared with leucaena hay. The diets affected the concentrations of urea nitrogen in plasma (p<0.05) and excretion of urea nitrogen in milk, being that soybean meal and cottonseed meal showed (p<0.05) higher than the average aerial part of the cassava hay. The use of diets with cottonseed meal as protein source in the concentrate in feeding of lactating goats provides greater nitrogen excretion in urine and negative nitrogen balance, while the concentrate with leucaena hay as a source of protein, provides greater ruminal microbial protein synthesis.

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The cottonseed cake is a co-product obtained after extraction of oil cottonseed, and because of their bromatological characteristics has potential use in ruminant feed, can increase the economy efficiency of animal production systems. The objective of this study was to evaluate diets with cottonseed cake in substitution of soybean meal through nitrogen balance, microbial protein synthesis and the ingestive behavior of lambs. Forty crossbred Santa Inês × Dorper non-castrated rams with average initial weight of 20.9 ± 2.5 kg were distributed into a completely randomized design with four treatments and ten replicates, and fed diets containing cottonseed cake in substitution of 0, 33, 66 and 100% of soybean meal. The diets were composed of corn, soybean meal, cottonseed meal and hay, with forage:concentrate reason of 50:50, isonitrogenous, with 14% crude protein. The animals were confined individually in pens with slatted floor, the evaluations of ingestive behavior, which included observations of the feeding, rumination and idle times were performed in a period of 24 hours, in 5-minute intervals. At 82 days of experiment, a spot urine sample was collected from all animals to quantify the concentrations of nitrogen, creatinine, allantoin, uric acid, xanthine and hypoxanthine in the urine. The data were subjected to variance analysis and regression, adopting α= 0.05. There was no significant difference between treatments for nitrogen balance, the synthesis of nitrogen compounds, and microbial efficiency. In addition, there was no effect of replacing soybean meal by cottonseed meal on feeding behavior of animals. Cottonseed cake can replace soybean meal up to 100% in diets for lambs. ResumoA torta de algodão é um coproduto obtido após a extração do oléo do caroço de algodão, e devido às suas características bromatológicas apresenta potencial de uso na alimentação de ruminantes, podendo aumentar a economicidade dos sistemas de produção animal. O objetivo com este estudo foi avaliar dietas com torta de algodão em substituição ao farelo de soja sobre o balanço de nitrogênio, a síntese de proteína microbiana e o comportamento ingestivo de cordeiros. Foram utilizados quarenta cordeiros mestiços Santa Inês x Dorper não castrados, com peso médio inicial de 20,9±2,5 kg, distribuídos em um delineamento experimental inteiramente casualizado, com quatro tratamentos e dez repetições, alimentados com dietas contendo torta de algodão em substituição à 0, 33, 66 e 100% do farelo de soja. As dietas foram compostas de milho, farelo de soja, torta de algodão e feno, com razão volumoso:concentrado de 50:50, isonitrogenadas, com aproximadamente14% de proteína bruta. Os animais foram confinados em baias individuais com piso ripado, as avaliações do comportamento ingestivo, que incluíram observações dos tempos de alimentação, ruminação e ócio foram realizadas em um período de 24 horas, em intervalos de 5 minutos. No 82º dia do período experimental, foram coletadas amostras de urina de todos os animais para quantificar as concentra...