This study aimed to evaluate the effects of adding slow release urea to replace conventional urea in diets for feedlot sheep on nitrogen metabolism and microbial protein synthesis. The substitution levels used as treatments were 0, 20, 40, 60 and 80%. We used 25 Santa Ines x SRD sheep distributed in the treatments in a completely randomized design. The animals were given 50% Tifton-85 hay and 50% concentrate, comprising diets with approximately 12% crude protein. The ingestion, digestion and excretion of nitrogen were not affected by the addition of slow release urea to the diet, in which the digested nitrogen accounted for 72.98% of the ingested. The concentration of plasma urea-N showed a quadratic variation, with the maximum at the level of 72.18% substitution. The microbial protein production and conversion efficiency of the protein into total digestible nutrients were not affected by the addition of slow-release urea in the diets. The replacement of conventional urea with slow release urea in the diet changes the concentrations of urea-N in plasma, however, does not affect the nitrogen balance, nor microbial synthesis and efficiency.Metabolismo do nitrogênio e síntese microbiana em ovinos alimentados com dietas contendo ureia de liberação lenta em substituição à ureia convencional RESUMO. Objetivou-se avaliar os efeitos da inclusão de ureia de liberação lenta em substituição à ureia convencional em dietas para ovinos confinados sobre o metabolismo de nitrogênio e síntese microbiana. Os níveis de substituição utilizados como tratamentos foram 0; 20; 40; 60 e 80%. Foram utilizados 25 ovinos Santa Inês x SRD, distribuídos nos tratamentos na forma de delineamento inteiramente casualizado. Os animais foram alimentados com 50% de feno de capim tifton-85 e 50% de concentrado, compondo dietas de aproximadamente 12% de proteína bruta. A ingestão, excreção e digestão de nitrogênio não foram influenciadas pela inclusão de ureia de liberação lenta na dieta, em que o nitrogênio digerido representou 72,98% do ingerido. A concentração de N-ureico no plasma variou de forma quadrática, com ponto máximo no nível de 72,18% de substituição. A produção de proteína microbiana e a eficiência de conversão da proteína em nutrientes digestíveis totais não foi afetada pela inclusão de ureia de liberação lenta nas dietas. A substituição da ureia convencional pela de ureia de liberação lenta na dieta provoca variação nas concentrações de N-ureico no plasma, entretanto, não afeta o balanço de nitrogênio nem a síntese e a eficiência de síntese microbiana.Palavras-chave: balanço de nitrogênio, eficiência microbiana, nitrogênio não proteico. 56Alves et al.

The objective of this study was to assess the effect of substituting corn with soybean hulls on the ingestive behavior and nitrogen balance of Santa Ines lambs. A total of 25 lambs with an initial body weight of 20±2 kg at approximately six months of age, sheltered individually in stalls (1.10 m×1.0 m), considering an entirely casual experimental delineation. Soybean hulls were substituted for corn at 0, 250, 500, 750, and 1,000 g/kg of dry matter (DM). The time spent feeding, ruminating, masticating, and resting was not affected by the substitution of corn with soybean hulls. In fact, the feeding efficiency in g DM/h and the rumination efficiency in g DM/bolus increased linearly with soybean hull substitution in the feed. Although the nitrogen balance was not altered by the use of soybean hulls as a substitute for corn in the diets of Santa Ines lambs, the N ingested and N digested expressed in g/d, N retained as a percentage of that ingested, and N retained as a percentage of that digested displayed quadratic behavior. In conclusion, corn can be substituted with soybean hulls up to 1,000 g/kg of dry matter in the concentrate, without changing the ingestive behavior and nitrogen balance.

ABSTRACT. This study aimed to evaluate the ingestive behavior of sheep fed increasing levels of mesquite pod meal (0, 15, 30 and 45% in total dry matter diet), replacing grass silage elephant. Eight noncastrated Santa Inês sheep with average weight of 32 kg were divided into two 4 x 4 Latin squares, each lasting 15 days. The sheep were submitted to visual observation every ten minutes, for 24 hours, in the 13 th day of each experimental period. There was no significant regression (p > 0.05) relative to the time spent on feeding, rumination and resting, depending on the levels of substitution of mesquite pod meal. The average time spent on feeding, rumination and resting was 5.64, 10.88 and 8.8h day -1 , respectively. There was a positive linear effect (p < 0.05) regarding the levels of replacement of elephant grass silage by mesquite pod meal on dry matter intake (DMI), neutral detergent fiber intake (NDFI), feeding efficiency of DM, rumination efficiency of DM, rumination efficiency of NDF. The use of observation intervals of up to 30 minutes does not alter the assessment of time spent on feeding, rumination and resting.

ABSTRACT. Eight Santa Ines sheep were assigned to two 4 x 4 Latin squares, to evaluate the effects of replacing elephant grass silage with different levels of mesquite pod meal (MDM) (15, 30 and 45% DM) on intake, apparent digestibility of dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE), acid detergent fiber (ADF), neutral detergent fiber (NDF), total carbohydrates (TC) and non-fiber carbohydrates (NFC) and the nitrogen balance. There was a linear increase (p < 0.05) in the intake of DM, OM, CP, ADF, NDF, NFC and TC according to the addition of MPM to the diet. The digestibility of DM, OM and CP increased (p < 0.05) with the addition of MDM. We observed a positive linear effect (p < 0.05) for the nitrogen intake. The addition of mesquite pod meal up to 45% increased the intake of DM, NDF, ADF, CP, OM, NFC and TC but reduced the digestibility of EE and NDF. MPM at 30 and 45% propitiated a positive nitrogen balance.Keywords: forage conservation, Prosopis juliflora, silage.Farelo de vagem de algaroba em dietas de ovinos: consumo, digestibilidade aparente dos nutrientes e balanço de nitrogênio RESUMO. Foram utilizados oito ovinos da raça Santa Inês, distribuídos em dois quadrados latinos 4 x 4, com o objetivo é avaliar os efeitos da adição do farelo de vagem de algaroba -FVA (15, 30 e 45% da MS) em substituição à silagem de capim elefante sobre o consumo, digestibilidade aparente da matéria seca (MS), matéria orgânica (MO), proteína bruta (PB), extrato etéreo (EE), fibra de detergente ácido (FDA), fibra em detergente neutro (FDN), carboidratos totais (CT) e carboidratos não fibrosos (CNF) e balanço de nitrogênio. Foi observado efeito linear crescente (p < 0,05) dos níveis de FVA sobre os consumos de MS, MO, PB, FDA, FDN, CNF e CT. Os coeficientes de digestibilidade da MS, MO e PB aumentaram (p < 0,05) com a adição de FVA. Observou-se efeito linear positivo (p < 0,05) para a ingestão, excreção fecal e retenção de nitrogênio, enquanto que a excreção de N na urina não variou (p > 0,05) em função dos níveis de substituição. A adição de FVA em até 45% proporcionou o aumento do consumo de MS, FDN, FDA, PB, MO, CNF e CT, mas, reduziu o coeficiente de digestibilidade do EE e de FDN. Os níveis 30 e 45% de FVA proporcionaram balanço de nitrogênio positivo.Palavras-chave: conservação de forragem, Prosopis juliflora, silagem.

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