Red clover silage: an alternative for mitigating the impact of nitrogen excretion in ovine production systems

ABSTRACT The objective was to quantify the flow of intestinal nutrients and nitrogen excretion and retention in sheep receiving isoproteic diets. Eight Texel x Lacaune wethers (average body weight = 25±2.5 kg) were fitted with duodenal cannula and housed in metabolic cages. Wethers were assigned to the treatments in a crossover design with two periods of 20 days each, and all feces and urine produced by the wethers were collected. The treatments consisted of two isoproteic (160 g kg−1 of crude protein on dry matter basis) diets composed of red clover (RC) or lucerne (LU; Medicago sativa) silages plus corn silage and concentrate feed. The digestible organic matter and metabolizable energy intake did not differ between treatments. The intestinal non-ammonia N (NAN) flow was 5.9 g day−1 (37%) higher in RC wethers than in those of the LU treatment. This result was a consequence of both an increase in the efficiency of microbial protein synthesis (12.7% higher) and a decrease in ruminal degradable protein (RDP) content (20% lower) of the diet. However, the increase in the intestinal NAN flow was accompanied by a reduction in intestinal digestibility of N, resulting in similar daily N retention between treatments. The reduction of RDP content was probably the main reason for reductions in N urinary excretion in RC wethers compared with those in the LU treatment, showing that RC silage may be a tool for mitigating the impact of N excretion in ovine production systems, without changes in N retention.

摘要 本研究旨在量化饲喂等蛋白日粮绵羊的肠道营养物质流量、氮排泄量与氮存留量。选取8只特塞尔×拉科讷杂交去势公绵羊（平均体重25±2.5 kg），为其安装十二指肠套管并饲养于代谢笼中。试验采用两周期交叉设计，每周期20天，收集试验绵羊的全部粪便与尿液。试验处理组包含两种等蛋白日粮（干物质基础粗蛋白含量为160 g·kg⁻¹），分别以红三叶（RC）青贮或紫花苜蓿（lucerne, LU；Medicago sativa）青贮搭配玉米青贮与精补料配制而成。两组处理的可消化有机物摄入量与代谢能摄入量无显著差异。RC组绵羊的肠道非氨氮（non-ammonia N, NAN）流量较LU组高5.9 g·d⁻¹（增幅37%），该结果源于日粮的微生物蛋白质合成效率提升12.7%，以及瘤胃可降解蛋白（ruminal degradable protein, RDP）含量降低20%。但肠道NAN流量的提升伴随了肠道氮消化率的下降，最终两组间的每日氮存留量无显著差异。与LU组相比，RC组绵羊的尿氮排泄量降低，其主要原因可能是日粮RDP含量的下降，这表明红三叶青贮可作为绵羊生产系统中降低氮排泄影响的有效手段，且不会改变氮存留量。