Avaliou-se a utilização das equações do Cornell Net Carbohydrate and Protein System (CNCPS) e Nacional Research Council (NRC) nível 1 para predição de consumo de matéria seca e ganho em peso médio diário em condições tropicais de confinamento. Utilizou-se 23 bovinos mestiços Holandês/Zebu confinados em baias individuais com idade média de 20 meses e 260 kg de peso vivo no início do experimento. As dietas experimentais eram isonitrogenadas compostas por dois níveis de ingestão de energia com 50 ou 80% de inclusão de concentrado na base da matéria seca para os tratamentos médio (TM) e alto (TA), respectivamente. Observou-se respostas variáveis dos valores observados e preditos de consumo de matéria seca e ganho em peso em função dos níveis alimentares sendo que as melhores predições de consumo foram para o tratamento de médio nível de concentrado em que as equações de regressão apresentaram R2= 0,61 e 0,63 para o CNCPS e NRC, respectivamente. Os modelos foram ineficientes para predição do consumo de matéria seca no tratamento de alta inclusão de concentrado e não apresentaram predição acurada de ganho em peso médio diário em nenhuma das condições experimentais analisadas.
Context Tannins are polyphenolic compounds found in legumes, trees and forage shrubs, such as Mimosa tenuiflora, and form hydrogen bonds with proteins. Aims The objective of the present study was to determine the optimal dietary concentration of natural tannins from M. tenuiflora for enhancing intake, digestibility, nitrogen (N) and tannin physiological balance, performance, carcass traits and commercial cuts of lambs. Methods Forty-eight uncastrated Santa Ines lambs were distributed between two experiments, each with four diets containing natural tannins (1.21 (control), 9.29, 17.4 and 25.4 g/kg dry matter (DM) total) from M. tenuiflora hay. Key results With increasing level of inclusion of natural tannins from M. tenuiflora hay in the diet, there were quadratic increases (P ≤ 0.05; up to 17.4 g/kg DM inclusion) in the daily nutrient intake, N faecal excretion, N urinary excretion, performance, carcass traits and rib and loin commercial cut weights of lambs. However, intake, faecal excretion, physiological balance of tannins and carcass leg circumference increased (P ≤ 0.05) linearly with an increasing inclusion of tannins from M. tenuiflora hay. Furthermore, there were linear decreases (P ≤ 0.05) in the digestibility of DM, crude protein, neutral detergent fibre corrected for ash and protein, acid detergent fibre, non-fibrous carbohydrate and total digestible nutrients and decreases in faecal excretion of total phenolic compounds and feeding efficiency in lambs with increasing dietary concentration of tannins. Conclusions It is recommended that M. tenuiflora hay replace Brachiaria decumbens hay at 250 g/kg of dietary roughage, corresponding to 17.4 g/kg DM of tannins, in the diet of Santa Ines finishing lambs because the resulting increased bioavailability of tannins improves nutrient intake, N retention, average daily gain, carcass weight and the weights of the most profitable cuts (leg, loin and rib). Implications The use of M. tenuiflora legume (which is common in the Caatinga biome) as hay roughage in the lamb diet increases tannin bioavailability and the efficiency of protein use, consequently improving performance and contributing to the economic viability of sheep production in the region.
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