Agroscope, Ruminant Nutrition and Emissions Research Group, 8356 Ettenhausen, Switzerland.
Empa, Laboratory for Air Pollution / Environmental Technology, 8600 Dübendorf, Switzerland.
Sci Total Environ. 2023 Oct 20;896:165027. doi: 10.1016/j.scitotenv.2023.165027. Epub 2023 Jun 23.
Less crude protein (CP) in the diet can reduce nitrogen excretion of dairy cattle and lower their ammonia (NH) and nitrous oxide (NO) formation potential. The diet composition might also affect emissions of methane (CH) and carbon dioxide (CO). However, previous studies did not investigate the effect of diets with different CP levels that are customary practice in Switzerland on NH and greenhouse gas emissions on a practical scale. In a case-control approach, we quantified the emissions (NH, NO, CH, CO) in two separate but identical compartments of a naturally ventilated cubicle housing for lactating dairy cows over six days by using a tracer ratio method. Cows in one compartment received a diet with 116 g CP per kilogram dry matter (DM), in the other compartment with 166 g CP kg DM. Subsequently, diets were switched for a second 6-day measurement phase. The results showed that the diet, aside from outside temperature and wind speed in the housing, was driving NH and NO emissions. NH and NO emission reduction per livestock unit (LU) was on average 46 % and almost 20 %, respectively, for the diet with low CP level compared to the higher CP level. In addition, strong relationships were observed between the CP content of the diet, N excretion in the urine and the milk urea content. An increased temperature or wind speed led to a clear increase in NH emissions. Differences in CH and CO emissions per LU indicated a significant influence of the diet, which cannot be attributed to the CP content. Our herd-level study demonstrated that a significant reduction in NH and NO emissions related to LU, energy-corrected milk as well as DM intake can be achieved by lowering the CP content in the diet.
饮食中较少的粗蛋白（CP）可以减少奶牛的氮排泄，降低其氨（NH）和一氧化二氮（NO）的形成潜力。饮食成分也可能影响甲烷（CH）和二氧化碳（CO）的排放。然而，以前的研究并没有调查瑞士常规的不同 CP 水平的饮食对 NH 和温室气体排放的实际规模的影响。在病例对照研究中，我们通过示踪剂比法在一个自然通风牛舍的两个独立但相同的隔间中，在六天内定量测量了泌乳奶牛的排放物（NH、NO、CH、CO）。一个隔间中的奶牛接受了每千克干物质含有 116 克 CP 的饮食，另一个隔间则接受了每千克干物质含有 166 克 CP 的饮食。随后，饮食在第二个 6 天的测量阶段进行了切换。结果表明，除了牛舍内的外部温度和风速外，饮食是 NH 和 NO 排放的驱动因素。与高 CP 水平相比，低 CP 水平的饮食使 NH 和 NO 的减排量分别平均减少了 46%和近 20%。此外，还观察到饮食中 CP 含量、尿液中的氮排泄量和乳尿素含量之间存在很强的关系。温度或风速升高会导致 NH 排放明显增加。CH 和 CO 排放的 LU 差异表明，饮食对其有显著影响，这不能归因于 CP 含量。我们的畜群水平研究表明，通过降低饮食中的 CP 含量，可以显著减少与 LU、能量校正奶和 DM 摄入量相关的 NH 和 NO 排放。
