Department of Animal and Veterinary Sciences, AU Viborg-Research Center Foulum, Aarhus University, DK 8830 Tjele, Denmark.
Department of Animal and Veterinary Sciences, AU Viborg-Research Center Foulum, Aarhus University, DK 8830 Tjele, Denmark.
J Dairy Sci. 2023 Aug;106(8):5433-5451. doi: 10.3168/jds.2022-22906. Epub 2023 Jul 5.
The objective was to investigate the effect of nonprotein nitrogen source, dietary protein supply, and genetic yield index on methane emission, N metabolism, and ruminal fermentation in dairy cows. Forty-eight Danish Holstein dairy cows (24 primiparous cows and 24 multiparous cows) were used in a 6 × 4 incomplete Latin square design with 4 periods of 21-d duration. Cows were fed ad libitum with the following 6 experimental diets: diets with low, medium, or high rumen degradable protein (RDP):rumen undegradable protein (RUP) ratio (manipulated by changing the proportion of corn meal, corn gluten meal, and corn gluten feed) combined with either urea or nitrate (10 g NO/kg of dry matter) as nonprotein nitrogen source. Samples of ruminal fluid and feces were collected from multiparous cows, and total-tract nutrient digestibility was estimated using TiO as flow marker. Milk samples were collected from all 48 cows. Gas emission (CH, CO, and H) was measured by 4 GreenFeed units. We observed no significant interaction between dietary RDP:RUP ratio and nitrate supplementation, and between nitrate supplementation and genetic yield index on CH emission (production, yield, intensity). As dietary RDP:RUP ratio increased, intake of crude protein, RDP, and neutral detergent fiber and total-tract digestibility of crude protein linearly increased, and RUP intake linearly decreased. Yield of milk, energy-corrected milk, and milk protein and lactose linearly decreased, whereas milk fat and milk urea nitrogen concentrations linearly increased as dietary RDP:RUP ratio increased. The increase in dietary RDP:RUP ratio resulted in a linear increase in the excretion of total purine derivatives and N in urine, but a linear decrease in N efficiency (milk N in % of N intake). Nitrate supplementation reduced dry matter intake (DMI) and increased total-tract organic matter digestibility compared with urea supplementation. Nitrate supplementation resulted in a greater reduction in DMI and daily CH production and a greater increase in daily H production in multiparous cows compared with primiparous cows. Nitrate supplementation also showed a greater reduction in milk protein and lactose yield in multiparous cows than in primiparous cows. Milk protein and lactose concentrations were lower for cows receiving nitrate diets compared with cows receiving urea diets. Nitrate supplementation reduced urinary purine derivatives excretion from the rumen, whereas N efficiency tended to increase. Nitrate supplementation reduced proportion of acetate and propionate in ruminal volatile fatty acids. In conclusion, no interaction was observed between dietary RDP:RUP ratio and nitrate supplementation, and no interaction between nitrate supplementation and genetic yield index on CH emission (production, yield, intensity) was noted. Nitrate supplementation resulted in a greater reduction in DMI and CH production, and a greater increase in H production in multiparous cows than in primiparous cows. As the dietary RDP:RUP ratio increased, CH emission was unaffected and RDP intake increased, but RUP intake and milk yield decreased. Genetic yield index did not affect CH production, yield, or intensity.
本研究旨在探讨非蛋白氮源、饲粮蛋白供给和遗传产奶量指数对奶牛甲烷排放、氮代谢和瘤胃发酵的影响。采用 6×4 不完全拉丁方设计，选用 48 头丹麦荷斯坦奶牛（初产奶牛 24 头，经产奶牛 24 头），进行 4 个为期 21d 的试验期。奶牛自由采食 6 种试验饲粮：低、中、高瘤胃可降解蛋白（RDP）：瘤胃不可降解蛋白（RUP）比例（通过改变玉米粉、玉米蛋白粉和玉米青贮的比例来调节），并添加尿素或硝酸盐（10gNO/kg 干物质）作为非蛋白氮源。从经产奶牛中采集瘤胃液和粪便样品，并用 TiO2 作为示踪剂估计全肠道养分消化率。对所有 48 头奶牛采集奶样。通过 4 个 GreenFeed 装置测量气体排放（CH、CO 和 H）。我们没有观察到饲粮 RDP：RUP 比例和硝酸盐补充之间、硝酸盐补充和遗传产奶量指数之间对 CH 排放（产奶量、产奶率、排放强度）有显著的互作效应。随着饲粮 RDP：RUP 比例的增加，奶牛的粗蛋白、RDP 和中性洗涤纤维采食量以及粗蛋白全肠道消化率呈线性增加，RUP 采食量呈线性下降。产奶量、校正乳产量、乳蛋白和乳糖产量呈线性下降，而乳脂和乳尿素氮浓度呈线性上升。饲粮 RDP：RUP 比例的增加导致总嘌呤衍生物和尿氮排泄量呈线性增加，但氮效率（奶氮占氮摄入量的百分比）呈线性下降。与尿素相比，硝酸盐补充降低了干物质采食量（DMI）并增加了全肠道有机物消化率。与初产奶牛相比，硝酸盐补充在经产奶牛中降低 DMI 和每日 CH 产量的效果更大，每日 H 产量的增加效果也更大。硝酸盐补充也使经产奶牛的乳蛋白和乳糖产量比初产奶牛下降更大。与接受尿素饲粮的奶牛相比，接受硝酸盐饲粮的奶牛的乳蛋白和乳糖浓度更低。硝酸盐补充减少了瘤胃中嘌呤衍生物的排泄，而氮效率有增加的趋势。硝酸盐补充降低了瘤胃挥发性脂肪酸中乙酸和丙酸的比例。综上所述，我们没有观察到饲粮 RDP：RUP 比例和硝酸盐补充之间、以及硝酸盐补充和遗传产奶量指数之间对 CH 排放（产奶量、产奶率、排放强度）有显著的互作效应。与初产奶牛相比，硝酸盐补充在经产奶牛中降低 DMI 和 CH 产量的效果更大，增加 H 产量的效果也更大。随着饲粮 RDP：RUP 比例的增加，CH 排放没有变化，RDP 采食量增加，但 RUP 采食量和产奶量下降。遗传产奶量指数对 CH 产量、产奶率或排放强度没有影响。
