Intake, digestibility and nitrogen balance in sheep fed diets containing detoxified castor cake

ABSTRACT The effect of substituting soybean meal (SM) with four levels (0, 33, 67 and 100%) of detoxified castor cake (DCC) on intake, nutrient digestibility and nitrogen balance was evaluated in uncastrated, male, crossbred sheep in a randomised complete block design with four treatments and five replications. There was a decreasing linear effect from the levels of substitution on dry matter (DM), organic matter (OM) and crude protein (CP) intake, total carbohydrates (TC), non-fibrous carbohydrates (NFC) and total digestible nutrients (TDN), and on DM, OM and TC digestibility, for reductions of 2.04, 1.70, 0.35, 1.56, 1.89 and 1.67 g dia-1 and 0.34, 0.53 and 0.51 g kg-1 DM respectively, for each 1% SM substituted with DCC. DMI and NDFap expressed, in %BW and g kg-0.75, showed a quadratic response, with a maximum value of 3.85 and 1.73%BW, and 95.15 and 42.47 g kg-0.75, for 25.00, 65.00, 20.75 and 61.50% SM substituted with DCC respectively. There was a linear increase in the intake of acid detergent fibre and in ether extract digestibility. The nitrogen balance was not affected by the substitution of SM with DCC. Substituting soybean meal with castor cake detoxified by autoclaving in lamb diets alters nutrient intake and digestibility without affecting the nitrogen balance.摘要 本试验采用随机完全区组设计，设置4个处理组、5次重复，评估了以4个梯度（0、33%、67%和100%）脱毒蓖麻粕（detoxified castor cake，DCC）替代豆粕（soybean meal，SM）对未阉割雄性杂交绵羊采食量、养分消化率及氮平衡的影响。随脱毒蓖麻粕替代豆粕的比例升高，干物质（dry matter，DM）、有机物（organic matter，OM）、粗蛋白（crude protein，CP）采食量，总碳水化合物（total carbohydrates，TC）、非纤维碳水化合物（non-fibrous carbohydrates，NFC）及总可消化养分（total digestible nutrients，TDN）摄入量，以及DM、OM、TC消化率均呈线性下降趋势；每1%豆粕被替代时，对应降幅分别为2.04、1.70、0.35 g·d⁻¹，1.56、1.89、1.67 g·d⁻¹，以及0.34、0.53、0.51 g·kg⁻¹ DM。以占体重百分比（%BW）及每千克代谢体重（g·kg^-0.75）表示的干物质采食量（DMI）与NDFap均呈二次响应趋势，当分别以25.00%、65.00%、20.75%和61.50%的豆粕用脱毒蓖麻粕替代时，其峰值分别为3.85%BW、1.73%BW，以及95.15 g·kg^-0.75、42.47 g·kg^-0.75。酸性洗涤纤维（acid detergent fibre，ADF）采食量及乙醚提取物消化率则呈线性升高趋势。脱毒蓖麻粕替代豆粕对氮平衡无显著影响。在羔羊日粮中使用经高压灭菌脱毒的蓖麻粕替代豆粕，可改变养分采食量与消化率，但不会对氮平衡产生影响。