Uddin M E, Wattiaux M A
Department of Dairy Science, University of Wisconsin-Madison, Madison 53706.
JDS Commun. 2020 Dec 11;2(1):16-20. doi: 10.3168/jdsc.2020-0012. eCollection 2021 Jan.
Reducing overall reactive N losses from dairy production systems depends substantially on reducing the atmospheric emission of manure ammonia (NH). The objective of this study was to determine potential NH-N emission of reconstituted manure using an in vitro protocol. Feces and urine were collected from a companion study designed as a Latin square in which 4 Holstein and 4 Jersey cows were fed diets containing 2 levels of forage neutral detergent fiber (NDF) [low-forage NDF (19%) vs. high-forage NDF (24%; dry matter basis)] from either alfalfa silage or corn silage (70:30 vs. 30:70 ratio of alfalfa silage NDF:corn silage NDF) arranged as a 2 × 2 factorial. All diets contained similar levels of crude protein (17%) and starch (23%), and had forage-to-concentrate ratios of 55:45 and 68:32 for low- and high-forage NDF diets, respectively. Measurements of NH-N emission were conducted in a laboratory-scale chamber with 16 g of reconstituted manure (urine plus feces) incubated for 48 h at 15°C with sampling at 1, 3, 6, 12, 24, 36, and 48 h. Hourly NH-N emissions data were analyzed using a repeated-measures mixed model in R (https://www.r-project.org/). The fixed effects were breed, forage NDF level, forage NDF source, time of sampling, and all possible interactions; cow was included as a random term. The cumulative 48-h NH-N emissions and the scaled-up emissions accounting for daily output of manure from each cow were analyzed using the same model but without time of sampling. Level and source of forage in the diet tended to influence the pattern in hourly rate and 48-h cumulative emission, respectively. Accounting for daily manure volume differences, low-forage NDF diets led to lower estimates of daily NH-N emissions than high-forage NDF diets (20% on a cow basis, 15% on a raw manure basis, and 18% on a manure-N basis). Compared with Holsteins, Jerseys emitted 17% lower estimated NH-N on a cow basis, mainly due to lower manure excretion but tended to emit 15% more NH-N expressed on a manure-N basis. Findings of this study suggested that cow breed and dietary forage NDF level should be considered in the prediction of NH-N emission from the dairy industry.
减少奶牛生产系统中总的活性氮损失在很大程度上取决于减少粪肥氨（NH₃）的大气排放。本研究的目的是使用体外试验方案来确定重构粪肥中潜在的氨氮（NH₃-N）排放量。粪便和尿液取自一项设计为拉丁方的配套研究，该研究中4头荷斯坦奶牛和4头泽西奶牛被饲喂含有2种饲草中性洗涤纤维（NDF）水平的日粮[低饲草NDF（19%）与高饲草NDF（24%；干物质基础）]，饲草来源为苜蓿青贮或玉米青贮（苜蓿青贮NDF与玉米青贮NDF的比例为70:30或30:70），采用2×2析因设计。所有日粮的粗蛋白（17%）和淀粉（23%）水平相似，低饲草NDF日粮和高饲草NDF日粮的饲草与精料比例分别为55:45和68:32。氨氮排放的测定在实验室规模的试验箱中进行，将16克重构粪肥（尿液加粪便）在15℃下孵育48小时，在1、3、6、12、24、36和48小时进行采样。使用R语言（https://www.r-project.org/）中的重复测量混合模型分析每小时的氨氮排放数据。固定效应包括品种、饲草NDF水平、饲草NDF来源、采样时间以及所有可能的交互作用；奶牛作为随机项纳入。使用相同模型但不考虑采样时间，分析了48小时的累积氨氮排放量以及按每头奶牛粪便日产量放大后的排放量。日粮中饲草的水平和来源分别倾向于影响每小时排放速率模式和48小时累积排放量。考虑到每日粪便量的差异，低饲草NDF日粮导致的每日氨氮排放量估计值低于高饲草NDF日粮（以每头奶牛计低20%，以原粪计低15%，以粪肥氮计低18%）。与荷斯坦奶牛相比，泽西奶牛以每头奶牛计的氨氮排放量估计值低17%，主要是由于粪便排泄量较低，但以粪肥氮计的氨氮排放量倾向于高15%。本研究结果表明，在预测奶牛养殖业的氨氮排放时应考虑奶牛品种和日粮饲草NDF水平。
