Department of Animal Science, University of Nebraska, Lincoln, NE 68583-0908, USA.
J Anim Sci. 2010 Apr;88(13 Suppl):E172-80. doi: 10.2527/jas.2009-2358. Epub 2010 Jan 15.
Nitrogen losses from open beef feedlots are a concern. Methods that decrease volatilization losses will lead to greater manure N, which is likely to be beneficial in open lot beef operations. Twelve or more pens were dedicated to N research whereby N intake, retention, and excretion were quantified and a mass balance conducted using manure, runoff, soil balance, and loss quantities. The objective was to decrease N volatilization losses or increase manure N or both. Dietary CP affects N excretion and N volatilization losses. Four experiments across 2 yr compared industry average CP (13%) to diets that were phase-fed to not exceed protein requirements (12.1 to 10.9%). Phase-fed cattle excreted 12 to 21% less N (P < 0.01), and N volatilization losses were reduced 15 to 33% (P < 0.01). In 2 other experiments, phase-fed diets were formulated to recycle undegradable intake protein. Steer G:F was similar (P = 0.18) or improved (P = 0.09), whereas N excretion and N volatilization losses tended to be reduced (P < 0.11) and N in manure was not affected (P > 0.35) compared with cattle fed 13% CP. Feeding less protein did not affect manure N, indicating manure N from open lots is related to other factors. A series of experiments evaluated increasing OM on the pen surface to increase N in manure. Feeding less digestible diets using fiber increased manure N (P < 0.01) and decreased (P < 0.10) N volatilization losses in 2 experiments conducted from November to May, but did not affect (P > 0.30) manure N or volatilization losses during 2 summer experiments. Adding bedding (i.e., OM) increased manure N in the winter as well. Another method evaluated was increasing pen cleaning frequency, which decreased N volatilization losses by 19 to 44% and increased manure N by 26 to 41% across 3 experiments. Other methods, such as acidifying manure by manipulating dietary cation anion difference, clinoptilite zeolite clay addition, and feeding different amounts of by-products had variable impacts on N volatilization losses. No treatments markedly affected runoff N, which is <5% of excreted N. Dietary protein affects N volatilization losses but not manure N. Other factors, such as OM on the pen surface, affect manure N. Cleaning manure frequently, which decreases exposure of manure N to air, decreases volatilization losses. Treatments should be evaluated across seasons due to seasonal effects.
露天肉牛养殖场的氮素损失令人担忧。减少挥发损失的方法将导致更多的粪便氮，这可能对露天养殖肉牛作业有益。12 个或更多的围栏专门用于氮研究，通过该研究量化了氮的摄入、保留和排泄，并通过粪便、径流、土壤平衡和损失量进行了质量平衡。目的是减少氮挥发损失或增加粪便氮或两者兼而有之。日粮 CP 会影响氮排泄和氮挥发损失。在 2 年的 4 项试验中，将行业平均 CP（13%）与分阶段喂养至不超过蛋白质需求（12.1 至 10.9%）的日粮进行了比较。分阶段喂养的牛的氮排泄量减少了 12-21%（P<0.01），氮挥发损失减少了 15-33%（P<0.01）。在另外 2 项试验中，分阶段喂养的日粮被设计为回收不可降解的可利用蛋白质。育肥牛的 G:F 相似（P=0.18）或有所改善（P=0.09），而氮排泄和氮挥发损失趋于减少（P<0.11），粪便中的氮不受影响（P>0.35）与饲喂 13%CP 的牛相比。减少蛋白质摄入不会影响粪便氮，表明露天养殖场的粪便氮与其他因素有关。一系列试验评估了增加畜栏表面的有机物来增加粪便中的氮。在 11 月至 5 月进行的 2 项试验中，使用纤维喂养更难消化的日粮会增加粪便氮（P<0.01）和减少（P<0.10）氮挥发损失，但在 2 项夏季试验中不影响（P>0.30）粪便氮或挥发损失。在冬季，添加垫料（即有机物）也会增加粪便氮。评估的另一种方法是增加畜栏清洁频率，这在 3 项试验中使氮挥发损失减少了 19-44%，并使粪便氮增加了 26-41%。通过操纵日粮阳离子阴离子差、添加沸石粘土和饲喂不同量的副产品等酸化粪便的其他方法对氮挥发损失有不同的影响。没有处理方法显著影响径流氮，其仅占排泄氮的<5%。日粮 CP 会影响氮挥发损失，但不会影响粪便氮。其他因素，如畜栏表面的有机物，会影响粪便氮。经常清理粪便可减少粪便氮与空气的接触，从而减少挥发损失。由于季节效应，应在不同季节评估处理方法。
