Department of Animal Sciences, University of Florida, Gainesville 32611.
Department of Chemistry, University of Tennessee, Knoxville 37996.
J Dairy Sci. 2018 Jul;101(7):5902-5923. doi: 10.3168/jds.2017-13973. Epub 2018 Apr 19.
The objectives were to determine the optimal feeding amount of choline in a ruminally protected form to reduce the triacylglycerol (TAG) concentration in liver and to increase TAG in blood plasma of dairy cows. Pregnant, nonlactating multiparous Holstein cows (n = 77) were blocked by body condition score (3.59 ± 0.33) and assigned to treatment at 64 ± 10 d before calculated calving date. Dietary treatments were top-dressing of 0, 30, 60, 90, or 120 g/d of ruminally protected choline (RPC; Balchem Corp., New Hampton, NY) ions to supply the equivalent of 0, 6.5, 12.9, 19.4, and 25.8 g/d of choline ions. Diets were formulated to exceed nutrient requirements for maintenance and pregnancy and fed in ad libitum amounts for the first 5 d. From d 6 to 15, cows were restricted to consume approximately 31% of their net energy requirements to simulate early lactating cows in negative energy balance. Methionine intake was maintained throughout each 15-d period. Liver was biopsied at 5 and 14 d and analyzed for TAG and glycogen. Blood was sampled on d 5 and 14 and plasma analyzed for glucose, insulin, cholesterol, β-hydroxybutyrate, long-chain fatty acids, and haptoglobin. On d 14, a mixture of saturated long-chain fatty acids, ground corn, and dried molasses (50:37:13) was offered (908 g, as-is basis) 10 h after the single daily feeding. Blood samples were collected for 19 h and plasma analyzed for TAG and cholesterol to assess apparent absorption of dietary fat. Mean dry matter intake and energy balance decreased from means of 9.5 to 3.3 kg/d and from 0.6 to -9.2 Mcal of net energy for lactation/d during the ad libitum and restricted feeding periods, respectively. Plasma concentrations of the lipid-soluble choline biomolecules, namely total phosphatidylcholines, total lysophosphatidylcholines, and sphingomyelin, increased with choline supplementation. Feed restriction increased plasma concentrations of β-hydroxybutyrate and free long-chain fatty acids, whereas those of glucose, insulin, and total cholesterol decreased. During feed restriction, concentration of hepatic TAG and plasma haptoglobin decreased linearly, whereas concentration of hepatic glycogen tended to increase quadratically with increasing intake of RPC. After fat supplementation, mean plasma concentration of TAG increased by an average of 21% with intake of RPC ions, peaking at intakes of ≥6.5 g/d of RPC ion. In summary, feeding RPC ions to cows in negative energy balance had increasing lipotropic effects on the liver when consumed up to 25.8 g/d, whereas feeding only 6.5 g/d increased concentrations of hepatic glycogen and TAG in the blood.
目的在于确定反刍保护形式下胆碱的最佳喂养量，以降低奶牛肝脏中的三酰甘油（TAG）浓度，并增加血浆中的 TAG。将怀孕、非泌乳的经产荷斯坦奶牛（n = 77）按体况评分（3.59 ± 0.33）分组，并在预计产犊日期前 64 ± 10 d 进行处理分配。日粮处理为每天顶部添加 0、30、60、90 或 120 g/d 的反刍保护胆碱（RPC；Balchem Corp.，New Hampton，NY）离子，以供应相当于 0、6.5、12.9、19.4 和 25.8 g/d 的胆碱离子。日粮配方以满足维持和妊娠的营养需求为基础，并在最初 5 d 内自由采食。从第 6 天到第 15 天，奶牛被限制进食约 31%的净能需求，以模拟处于负能平衡的早期泌乳奶牛。在每个 15 d 期间，都维持蛋氨酸的摄入量。在第 5 天和第 14 天对肝脏进行活检，并分析 TAG 和糖原。在第 5 天和第 14 天采集血液，并分析血浆中的葡萄糖、胰岛素、胆固醇、β-羟丁酸、长链脂肪酸和触珠蛋白。在第 14 天，在每日单次饲喂后 10 h 提供一种饱和长链脂肪酸、粉碎玉米和干燥糖蜜（50:37:13）的混合物（908 g，原样基础）。采集 19 h 的血液样本，并分析血浆中的 TAG 和胆固醇，以评估膳食脂肪的表观吸收率。在自由采食和限制采食期间，奶牛的平均干物质采食量和能量平衡分别从 9.5 至 3.3 kg/d 和 0.6 至 -9.2 Mcal/d 下降。随着胆碱补充，脂溶性胆碱生物分子的血浆浓度，即总磷脂酰胆碱、总溶血磷脂酰胆碱和神经鞘磷脂，均有所增加。限制采食量增加了血浆中 β-羟丁酸和游离长链脂肪酸的浓度，而葡萄糖、胰岛素和总胆固醇的浓度则降低。在限制采食量期间，肝脏 TAG 浓度和血浆触珠蛋白浓度呈线性下降，而随着 RPC 摄入量的增加，肝糖原浓度呈二次方趋势增加。在脂肪补充后，RPC 离子摄入量平均增加 21%，血浆 TAG 浓度平均增加 21%，峰值出现在 RPC 离子摄入量为 6.5 g/d 以上时。总之，在处于负能平衡的奶牛中，反刍保护形式的胆碱的摄入量最高可达 25.8 g/d，具有增加肝脏脂肪代谢作用，而仅摄入 6.5 g/d 可增加血液中肝糖原和 TAG 的浓度。
