Zhao Y G, Gordon A W, O'Connell N E, Yan T
J Anim Sci. 2016 Dec;94(12):5321-5331. doi: 10.2527/jas.2016-0541.
Nitrogen excretion from sheep production systems is an important source of nitrate, ammonia, and nitrous oxide responsible for groundwater pollution and global warming. The present study aimed to identify key parameters influencing N utilization efficiency and develop prediction equations for manure N, feces N, and urine N outputs in sheep. Data used were collected from 82 sheep offered fresh perennial ryegrass () as the sole diet in 6 metabolism experiments (data from non-grass-only diets were not used). Sheep were from breeds of Highlander, Texel, Scottish Blackface, and Swaledale at the age of 5 to 18 mo and weighing from 24.5 to 62.7 kg. Herbage was harvested daily from 6 swards of contrasting harvest dates (May to December), offering wide variation in feed value to cover the range that would be offered in most practical farm situations. Before the commencement of each study, the experimental sward was harvested at a residual height of 4 cm and allowed to grow for 2 to 4 wk to target an average pregrazing sward height in a range of 8 to 15 cm depending on the time of year. Sheep were housed in individual pens for 14 d and then transferred to individual metabolism crates for 4 d with feed intake and feces and urine outputs measured. Data were analyzed using the linear mixed model procedure to develop prediction equations for feces N, urine N, and manure N outputs using N intake, herbage chemical composition, and digestibility with effects of sex, breed, and experimental periods removed. Nitrogen intake was the best single predictor for N output in feces, urine, and manure, and the value for prediction of manure N output was greater than those for feces N and urine N (0.86 vs. 0.70 and 0.77, respectively; < 0.001). Animal BW and herbage DM, ether extract, NDF, ADF, water soluble carbohydrate, and DE concentrations and N digestibility were also used to predict N outputs because N intake may not be available in commercial practice. The prediction equations for N utilization efficiency indicated that increasing feeding level and ME concentration and reducing N concentration could improve N utilization efficiency and shift N excretion into feces rather than urine ( < 0.001). The equations developed in the current study provide an approach for sheep producers to quantify N excretion against production and, consequently, to develop their own mitigation strategies to reduce the environmental impact of sheep production systems.
绵羊生产系统中的氮排泄是硝酸盐、氨和一氧化二氮的重要来源，这些物质会导致地下水污染和全球变暖。本研究旨在确定影响氮利用效率的关键参数，并建立绵羊粪便氮、尿液氮和粪肥氮产量的预测方程。所使用的数据来自6个代谢实验中的82只绵羊，这些绵羊仅以新鲜多年生黑麦草为唯一日粮（未使用非仅以草为日粮的数据）。绵羊品种包括高地羊、特克塞尔羊、苏格兰黑脸羊和斯瓦尔代尔羊，年龄在5至18个月之间，体重在24.5至62.7千克之间。每天从6块收获日期不同的草场上收割牧草（5月至12月），提供饲料价值差异很大的牧草，以涵盖大多数实际农场情况下可能提供的范围。在每项研究开始前，将实验草场的牧草收割至剩余高度4厘米，然后让其生长2至4周，根据一年中的时间，目标是使放牧前的平均草高在8至15厘米范围内。绵羊被单独关在围栏中14天，然后转移到单独的代谢笼中4天，测量其采食量以及粪便和尿液产量。使用线性混合模型程序分析数据，以建立粪便氮、尿液氮和粪肥氮产量的预测方程，该方程使用氮摄入量、牧草化学成分和消化率，去除性别、品种和实验期的影响。氮摄入量是预测粪便、尿液和粪肥中氮产量的最佳单一指标，粪肥氮产量的预测值大于粪便氮和尿液氮的预测值（分别为0.86对0.70和0.77；P<0.001）。动物体重以及牧草干物质、乙醚提取物、中性洗涤纤维、酸性洗涤纤维、水溶性碳水化合物、消化能浓度和氮消化率也用于预测氮产量，因为在商业实践中可能无法获得氮摄入量。氮利用效率的预测方程表明，提高饲养水平和代谢能浓度以及降低氮浓度可以提高氮利用效率，并将氮排泄转移到粪便而非尿液中（P<0.001）。本研究中建立的方程为绵羊生产者提供了一种方法，可根据生产情况量化氮排泄，从而制定自己的减排策略，以减少绵羊生产系统对环境的影响。
