不同能量水平低氮饲粮对藏羊表观消化率、氮代谢和生长性能的影响

试验旨在研究不同能量水平低氮饲粮对藏羊表观消化率、氮代谢和生长性能的影响,为高寒地区反刍家畜冷季补饲提供参考。选取1.5周岁、体重(48.5±1.89) kg和体况相近的健康去势藏羊24只,随机分为低能(LE)、中低能(MLE)、中高能(MHE)和高能(HE)4个处理组,每组6个重复。试验饲粮的粗蛋白质(CP)含量相近(6.97±0.05)%]而能量不同,其消化能(DE)水平分别为8.21、9.33、10.45和11.57 MJ·kg^-1。经过49 d的饲养和全收粪尿法,结果表明:1)藏羊的干物质(DM)、粗蛋白质(CP)、总能(GE)采食量在各处理组间基本相同(P>0.05),其中DM、GE表观消化率都随着能量水平的提高而线性增加(P<0.05);2)当饲粮能量水平升高时,藏羊血清尿素氮(BUN)浓度线性增加(P<0.05),而游离脂肪酸(FFA)浓度却线性降低(P<0.05);3)随着饲粮能量水平升高,藏羊尿氮排出量线性降低(P<0.05),氮平衡和氮沉积率均线性升高(P<0.05),并且氮沉积率(NDR,%)与饲粮能量水平(DE, MJ·kg^-1)呈显著线性正相关,其关系式为NDR=5.2143DE-39.006(R²=0.9616,n=24);4)藏羊的平均日增重(ADG)随着饲粮能量水平的提高而线性增加(P<0.05),除LE组外,其余ADG都为正值。上述研究结果表明,藏羊的蛋白和能量维持需要量较低,低氮条件下提高能量水平可改善藏羊的饲料营养消化率、氮代谢以及生长性能。

Effects of different dietary energy levels on apparent digestibility,nitrogen metabolism and growth performance of Tibetan sheep under low nitrogen conditions

The objective of this study was to investigate the effects of different dietary energy levels on the apparent digestibility, nitrogen metabolism and growth performance of Tibetan sheep under low nitrogen conditions, and thus to provide useful references for the supplementary feeding of alpine ruminants during the cold season. Twenty-four healthy, 1.5-year-old castrated Tibetan sheep with similar body weights (48.5±1.89 kg)were selected and then divided into four treatment groups: LE (low energy), MLE (medium low energy), MHE (medium high energy) and HE (high energy). Each group included 6 replicates. Diets were formulated to have similar crude protein (CP) content (6.97%±0.05%) but four different digestible energy levels: 8.23, 9.31, 10.45 and 11.57 MJ·kg^-1 respectively. The animals were fed these diets for 49 days, with total collection of feces and urine for analysis. The results obtained were as follows: 1) Dry matter (DM), CP and gross energy (GE) intakes were similar among the four groups, whereas DM and GE apparent digestibilities all increased linearly with rising dietary energy levels (P<0.05). 2) Serum free fatty acid (FFA) concentration decreased linearly as dietary energy increased (P<0.05) while urea nitrogen (BUN) increased (P<0.05). 3) As dietary energy levels increased, urinary nitrogen excretion decreased linearly (P<0.05); however, the nitrogen balance and nitrogen deposition rates both increased (P<0.05). There was a strong linear regression between nitrogen deposition rates (NDR, %) and dietary energy levels (DE, MJ·kg^-1): NDR=5.2143DE-39.006 (R²=0.9616,n=24). 4) With the exception of the low energy group, all the average daily gain (ADG) values were positive and increased linearly with dietary energy (P<0.05).These results indicate that while the energy and protein requirements of Tibetan sheep are relatively low their apparent digestibility, nitrogen metabolism and growth performance could be improved with supplements of dietary energy.