It is often suggested that the benefits of supplemental rumen-protected choline (RPC) might be greater in cows predisposed to fatty liver, such as those that are overconditioned; however, limited data support this suggestion. Therefore, the hypothesis of this study was that responses to supplementing RPC to transition dairy cows is not dependent on the degree of fatness prepartum. Objectives were to evaluate the effects of supplementing RPC to transition dairy cows according to body condition score (BCS) prepartum on production and metabolic responses. Data from 2 randomized block experiments that evaluated the effects of RPC supplementation during the transition period were combined. Within each experiment, cows were assigned randomly to receive 0 (CTRL) or 12.9 g/d choline ion in an RPC form (CHOL) daily top-dressed onto the diet from 21 d prepartum to 21 d postpartum. Body condition was evaluated twice prepartum before enrollment and the mean value was used as an explanatory variable for statistical analyses. Data were collected for the last 21 d of gestation and the first 105 d postpartum. The BCS (mean ± standard deviation) prepartum were 3.51 ± 0.29 and 3.51 ± 0.32 for CTRL and CHOL, respectively, and ranged from 2.69 to 4.25. A total of 215 cows were enrolled in the respective experiments and contributed data for the incidence of diseases, whereas 192 cows contributed data for analyses of production responses, plasma metabolites, and liver composition. Irrespective of BCS, supplementing transition diets with CHOL increased yields of milk by 1.8 kg/d, fat by 0.08 kg/d, lactose by 0.08 kg/d, true protein by 0.04 kg/d, energy-corrected milk (ECM) by 1.9 kg/d, and fat-corrected milk by 2.1 kg/d. The improvements in productive performance were not followed by increased dry matter intake or measures of lipomobilization. Therefore, CHOL cows were more efficient in converting dry matter intake into ECM. Feeding CHOL increased concentration of hepatic triacylglycerol (CTRL = 3.23 vs. CHOL = 3.87% wet basis) in the first 21 d postpartum. Overconditioned cows were more prone to having exacerbated lipomobilization and increased prevalence and incidence of fatty liver, but no interactions between treatment and BCS were observed for body weight, BCS, or concentrations of metabolites in plasma or hepatic triacylglycerol. Treatment did not affect incidence of clinical diseases. Opposite to common suggestions, cows with increased hepatic triacylglycerol content also had increased yields of milk and ECM in the first 105 d postpartum. Collectively, these findings indicate that the effects of RPC supplementation during the transition period are independent of the degree of fatness of dairy cows prepartum. The findings also suggest that the effects on productive performance are not necessarily mediated by improvements in markers of metabolic health or reductions in hepatic triacylglycerol.

中文翻译：

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过渡奶牛对瘤胃保护性胆碱的反应不取决于产前身体状况。

经常有人建议，在易患脂肪肝的母牛（如过度适应的母牛）中，补充瘤胃保护胆碱（RPC）的益处可能更大。但是，有限的数据支持该建议。因此，本研究的假设是对补充RPC过渡奶牛的反应不取决于产前脂肪的程度。目的是根据产前身体状况评分（BCS）对产奶和代谢反应评估补充RPC到过渡型奶牛的影响。合并了来自2个随机块实验的数据，这些实验评估了过渡期RPC补充的效果。在每个实验中，将母牛随机分配为接受0（CTRL）或12。从产前21天到产后21天每天以RPC形式（CHOL）每天9 g / d胆碱离子的饮食。产前对身体状况进行两次评估，并将平均值用作统计分析的解释变量。在妊娠的最后21天和产后的最初105天收集数据。对于CTRL和CHOL，产前BCS（平均值±标准偏差）分别为3.51±0.29和3.51±0.32，范围为2.69至4.25。共有215头母牛参加了各自的实验，并为疾病的发病率提供了数据，而192头母牛为生产反应，血浆代谢物和肝脏组成的分析提供了数据。不考虑BCS，向过渡饮食中添加CHOL可以使牛奶的产量提高1.8千克/天，脂肪的产量提高0.08千克/天，乳糖的产量提高0.08千克/天，真正的蛋白质为0.04千克/天，能量校正的牛奶（ECM）为1.9千克/天，脂肪校正的牛奶为2.1千克/天。生产性能的改善并未随之增加干物质摄入量或脂动化措施。因此，CHOL母牛在将干物质摄入量转换为ECM方面更有效。在产后前21天，喂养CHOL会增加肝三酰甘油的浓度（CTRL = 3.23 vs. CHOL = 3.87％湿基）。过度适应的母牛更容易加剧脂代谢和脂肪肝的患病率和发生率，但是在体重和BCS或血浆或肝三酰甘油中代谢物的浓度方面，未观察到治疗与BCS之间的相互作用。治疗不影响临床疾病的发生。与常见建议相反，产后前105 d肝三酰甘油含量增加的奶牛的牛奶和ECM产量也增加。总而言之，这些发现表明，在过渡期补充RPC的效果与产前奶牛的肥胖程度无关。研究结果还表明，对生产性能的影响不一定是通过改善代谢健康标志物或减少肝三酰甘油来介导的。