Department of Animal and Avian Sciences, University of Maryland, College Park 20742.
Department of Animal and Avian Sciences, University of Maryland, College Park 20742.
J Dairy Sci. 2020 Jul;103(7):6070-6086. doi: 10.3168/jds.2019-17591. Epub 2020 Apr 29.
The objective of this experiment was to examine production performance responses to feeding rumen-protected choline (RPC) or methionine (RPM), or both, during the periparturient period. Fifty-four Holstein cows (25 primiparous, 29 multiparous) were used in a randomized block design experiment with a 2 × 2 factorial treatment structure. Cows were blocked by expected calving date and parity and assigned to 1 of 4 treatments: CON (no RPC or RPM); RPC (13.0 g/d of choline ion); RPM (9 g/d of dl-methionine prepartum; 13.5 g/d of dl-methionine postpartum); or RPC + RPM. Treatments were applied once daily as a top-dress from 3 wk before through 5 wk after calving. Dry matter intake and milk production were recorded daily, and milk samples were obtained once weekly. Data were analyzed for primi- and multiparous cows separately, using a repeated-measures mixed model that included random effects of cow and block and fixed effects of RPC, RPM, week, and their interactions; week served as the repeated effect. Initial BW and previous lactation milk yield were included as covariates in the statistical model for multiparous cows. Feeding RPC without RPM increased milk yield for multiparous cows by 8.7 kg/d, but this increase was not observed when RPC was fed with RPM. In multiparous cows, feeding RPM increased milk fat concentration and tended to increase milk fat yield. Because of this, RPM increased fat-corrected milk (FCM) by 2.8 kg/d at wk 2 postpartum, and this increase was sustained through wk 5 postpartum. In contrast, RPM did not affect overall milk fat yield and concentration for primiparous cows. Feeding RPC increased milk yield for primiparous cows by 3.5 kg/d irrespective of RPM inclusion, which is contrary to observations in multiparous cows, where RPC increased milk yield only in the absence of RPM. These results indicate that responses to RPC during the periparturient period may be dependent upon supply of methionine. Our observations also demonstrate that primi- and multiparous cows respond differently to RPC and RPM supplemented individually or simultaneously during the periparturient period. This variation in response could have been mediated by putative differences in choline and methionine requirements of primiparous versus multiparous cows, or by differences in the levels of milk production between the 2 groups (36 vs. 25 kg of FCM/d). However, cows in this study did not experience severe negative energy balance (mean nadirs of -6.6 and -5.0 Mcal/d for multiparous and primiparous cows, respectively), which likely affected their responses to RPC and RPM.
本试验旨在研究围产期添加瘤胃保护性胆碱（RPC）或蛋氨酸（RPM）或同时添加两者对奶牛生产性能的影响。选用 54 头荷斯坦奶牛（初产 25 头，经产 29 头），采用 2×2 因子设计的随机分组试验，根据预计产犊日期和胎次将奶牛分为 4 个处理组：CON（不添加 RPC 或 RPM）；RPC（每天 13.0 g 胆碱离子）；RPM（产前每天 9 g 蛋氨酸，产后每天 13.5 g 蛋氨酸）；或 RPC+RPM。从产前 3 周开始至产后 5 周，每天以顶部撒料的方式添加一次处理。每天记录干物质采食量和产奶量，每周采集一次奶样。对初产和经产奶牛分别进行分析，采用重复测量混合模型，包括奶牛和分组的随机效应和 RPC、RPM、周和它们的交互作用的固定效应；周作为重复效应。在统计模型中，初产奶牛还包括初始 BW 和上一个泌乳期产奶量作为协变量。单独添加 RPC 提高了经产奶牛的产奶量 8.7 kg/d，但与添加 RPM 时的效果不同。在经产奶牛中，添加 RPM 增加了乳脂浓度，并倾向于增加乳脂产量。因此，在产后第 2 周，RPM 增加了 2.8 kg/d 的校正乳脂肪（FCM），这种增加一直持续到产后第 5 周。相比之下，RPM 对初产奶牛的总乳脂产量和浓度没有影响。添加 RPC 提高了初产奶牛的产奶量 3.5 kg/d，与添加 RPM 无关，这与经产奶牛的观察结果相反，在经产奶牛中，只有在不添加 RPM 的情况下，RPC 才会增加产奶量。这些结果表明，围产期 RPC 的反应可能取决于蛋氨酸的供应。我们的观察还表明，初产和经产奶牛对围产期单独或同时添加 RPC 和 RPM 的反应不同。这种反应的差异可能是由于初产和经产奶牛对胆碱和蛋氨酸的需求不同，或者由于两组奶牛的产奶量水平不同（36 与 25 kg FCM/d）。然而，本研究中的奶牛没有经历严重的负能平衡（经产和初产奶牛的负能平衡最小值分别为-6.6 和-5.0 Mcal/d），这可能影响了它们对 RPC 和 RPM 的反应。
