Institute of Agricultural Sciences in the Tropics, Animal Nutrition and Rangeland Management in the Tropics and Subtropics, University of Hohenheim, 70593 Stuttgart, Germany.
Institute of Agricultural Sciences in the Tropics, Animal Nutrition and Rangeland Management in the Tropics and Subtropics, University of Hohenheim, 70593 Stuttgart, Germany.
J Dairy Sci. 2021 Apr;104(4):4223-4235. doi: 10.3168/jds.2019-18005. Epub 2021 Jan 21.
The aim was to study the effects of rumen N balance (RNB), dietary protein source, and their interaction on feed intake, N partitioning, and rumen microbial crude protein (MCP) synthesis in lactating dairy cows. Twenty-four lactating Holstein cows were included in a replicated 4 × 4 Latin square experimental design comprising four 20-d periods, each with 12 d of adaptation to the experimental diets and 8 d of sampling. The dietary treatments followed a 2 × 2 factorial arrangement (i.e., 4 treatments) with 2 main protein sources [faba bean grain (FB) and SoyPass (SP; Beweka Kraftfutterwerk GmbH, Heilbronn, Germany)] offered at 2 dietary RNB levels each [0 g/kg of dry matter, DM (RNB0) and -3.2 g/kg of DM (RNB-)]. The RNB was calculated as the difference between dietary crude protein (CP) intake and the rumen outflow of undegraded feed CP and MCP and divided by 6.25. Composition of concentrate mixtures was adjusted to create diets with desired RNB levels. Each of these protein sources supplied ≥35% of total dietary CP. Both diets for each protein source were isoenergetic but differed in CP concentrations. The DM intake (kg/d) was lower for RNB- than for RNB0 in diets containing FB, whereas no differences were seen between the RNB levels for SP diets. The RNB- decreased N intake and urinary N excretion but increased milk N use efficiency in both FB and SP diets, with greater differences between the RNB levels for FB diets than for SP diets. Similarly, duodenal MCP synthesis (g/kg of digestible organic matter intake) estimated from purine derivatives in the urine was lower for RNB- than for RNB0 in FB diets but similar between the RNB levels in diets containing SP. Low RNB of approximately -65 g/d (approximately -3.2 g/kg of DM) in diets reduced feed intake, N balance, and performance in high-yielding dairy cows with possibly more pronounced effects in diets containing rapidly degradable protein sources.
本研究旨在探讨瘤胃氮平衡（RNB）、日粮蛋白来源及其互作对泌乳奶牛采食量、氮分配和瘤胃微生物粗蛋白（MCP）合成的影响。24 头泌乳荷斯坦奶牛采用 4×4 拉丁方试验设计，包含 4 个 20 天的试验期，每个试验期包括 12 天适应期和 8 天采样期。试验日粮采用 2×2 因子设计（即 4 种处理），2 种主要蛋白源[豌豆籽粒（FB）和 SoyPass（SP；Beweka Kraftfutterwerk GmbH，Heilbronn，德国）]，每种蛋白源提供 2 种 RNB 水平[0 g/kg 干物质（RNB0）和-3.2 g/kg 干物质（RNB-）]。RNB 为饲粮粗蛋白（CP）摄入量与瘤胃未降解饲粮 CP 和 MCP 流出量之差，再除以 6.25。调整浓缩料混合物组成以创建所需 RNB 水平的日粮。这 2 种蛋白源提供的 CP 均≥35%的总饲粮 CP。对于 FB 日粮，RNB-组的干物质采食量（kg/d）低于 RNB0 组，但 SP 日粮的 RNB 水平之间没有差异。RNB-降低了 FB 和 SP 日粮的氮摄入量和尿氮排泄量，但提高了这 2 种日粮的乳氮利用率，对于 FB 日粮，RNB 水平间的差异大于 SP 日粮。同样，基于尿中嘌呤衍生物估测的十二指肠 MCP 合成量（g/kg 可消化有机物采食量）在 FB 日粮中 RNB-组低于 RNB0 组，但在 SP 日粮中 RNB 水平间没有差异。RNB 约为-65 g/d（约-3.2 g/kg 干物质）的低水平降低了高产奶牛的采食量、氮平衡和生产性能，对于含有快速降解蛋白源的日粮，其影响可能更明显。
