ABSTRACT

The climate-relevant enteric methane (CH₄) formation represents a loss of feed energy that is potentially meaningful for energetically undersupplied peripartal dairy cows. Higher concentrate feed proportions (CFP) are known to reduce CH₄ emissions in cows. The same applies to the feed additive 3-nitrooxypropanol (3-NOP), albeit through different mechanisms. It was hypothesised that the hydrogen not utilised for CH₄ formation through the inhibition by 3-NOP would be sequestered by propionate formation triggered by higher CFP so that it could thereby give rise to a synergistically reduced CH₄ emission. In a 2 × 2-factorial design, low (LC) or high (HC) CFP were either tested without supplements (CON_LC, CON_HC) or combined with 3-NOP (NOP_LC, 48.4 mg/kg dry matter (DM); NOP_HC, 51.2 mg 3-NOP/kg DM). These four rations were fed to a total of 55 Holstein cows from d 28 ante partum until d 120 post partum. DM intake (DMI) was not affected by 3-NOP but increased with CFP (CFP; p < 0.001). CH₄/DMI and CH₄/energy-corrected milk (ECM) were mitigated by 3-NOP (23% NOP_LC, 33% NOP_HC) (p < 0.001) and high CFP (12% CON, 22% 3-NOP groups) (CFP × TIME p < 0.001). Under the conditions of the present experiment, the CH₄ emissions of NOP_LC increased to the level of the CON groups from week 8 until the end of trial (3-NOP × CFP × TIME; p < 0.01). CO₂ yield decreased by 3-NOP and high CFP (3-NOP × CFP; p < 0.001). The reduced body weight loss and feed efficiency in HC groups paralleled a more positive energy balance being most obvious in NOP_HC (3-NOP × CFP; p < 0.001). ECM was lower for NOP_HC compared to CON_HC (3-NOP × CFP; p < 0.05), whereas LC groups did not differ. A decreased fat to protein ratio was observed in HC groups and, until week 6 post partum, in NOP_LC. Milk lactose and urea increased by 3-NOP (3-NOP; p < 0.05). 3-NOP and high CFP changed rumen fermentation to a more propionic-metabolic profile (3-NOP; CFP; p < 0.01) but did not affect rumen pH. In conclusion, CH₄ emission was synergistically reduced when high CFP was combined with 3-NOP while the CH₄ mitigating 3-NOP effect decreased with progressing time when the supplement was added to the high-forage ration. The nature of these interactions needs to be clarified.

摘要

与气候相关的肠道甲烷 (CH ₄ ) 的形成代表了饲料能量的损失，这对于能量供应不足的围产期奶牛来说可能是有意义的。众所周知，较高的浓缩饲料比例 (CFP) 可以减少奶牛的CH ₄排放。这同样适用于饲料添加剂 3-硝基氧基丙醇 (3-NOP)，尽管机制不同。假设通过 3-NOP 的抑制未用于 CH ₄形成的氢将被更高 CFP 触发的丙酸盐形成隔离，从而它可以由此产生协同减少的 CH ₄排放。在 2 × 2 因子设计中，低 (LC) 或高 (HC) CFP 在没有补充剂的情况下进行测试 (CON _LC , CON_HC ) 或与 3-NOP 组合（NOP _LC，48.4 mg/kg 干物质 (DM)；NOP _HC，51.2 mg 3-NOP/kg DM）。这四个口粮送入从d 28共有55头荷斯坦母牛产前直到d 120产后。DM 摄入量 (DMI) 不受 3-NOP 的影响，但随 CFP 增加（CFP；p < 0.001）。CH ₄ /DMI 和 CH ₄ /能量校正牛奶 (ECM) 被 3-NOP（23% NOP _LC，33% NOP _HC）（p < 0.001）和高 CFP（12% CON，22% 3-NOP ）缓解组）（CFP × TIME p < 0.001）。在本实验条件下，NOP的 CH ₄排放量从第 8 周到试验结束，_LC增加到 CON 组的水平（3-NOP × CFP × TIME；p < 0.01）。CO ₂产量降低了 3-NOP 和高 CFP（3-NOP × CFP；p < 0.001）。HC 组中体重减轻和饲料效率的降低与 NOP _{HC 中}最明显的更正能量平衡平行（3-NOP × CFP；p < 0.001）。ECM是为NOP下_HC相比CON _HC（3- NOP×CFP; p <0.05），而组LC没有差异。在 HC 组和NOP _LC组观察到脂肪与蛋白质比率降低，直到产后第 6 周. 牛奶乳糖和尿素增加了 3-NOP（3-NOP；p < 0.05）。3-NOP 和高 CFP 将瘤胃发酵改变为更多的丙酸代谢特征（3-NOP；CFP；p < 0.01），但不影响瘤胃 pH 值。总之，当高 CFP 与 3-NOP 结合时，CH ₄排放协同降低，而当将补充剂添加到高饲草日粮中时，CH ₄减轻 3-NOP 效果随着时间的推移而降低。需要澄清这些相互作用的性质。