Moore C E, Kay J K, Collier R J, Vanbaale M J, Baumgard L H
Department of Animal Sciences, The University of Arizona, Tucson 85721, USA.
J Dairy Sci. 2005 May;88(5):1732-40. doi: 10.3168/jds.S0022-0302(05)72846-0.
Heat-stressed dairy cattle are bioenergetically similar to early-lactation cows in that dietary energy may be inadequate to support maximum milk and milk component synthesis. Study objectives were to evaluate whether conjugated linoleic acids- (CLA-) induced milk fat depression (MFD) during heat stress would allow for increased milk and milk component synthesis. In addition, CLA effects on production variables and its ability to induce MFD were compared between Holstein and Brown Swiss cows. Multiparous cows (n = 8, Holstein; n = 5, Brown Swiss) averaging 97 +/- 17 d in milk were used in a crossover design during the summer (mean temperature-humidity index = 75.7). Treatment periods were 21 d with a 7-d adaptation period before and between periods. During adaptation periods, all cows received a supplement of palm fatty acid distillate (242 g/d). Dietary treatment consisted of 250 g/d of CLA supplement (78.9 g/d of CLA) or 242 g/d of palm fatty acid distillate to provide equal amounts of fatty acids. The CLA supplement contained a variety of CLA isomers (3.0% trans-8, cis-10; 3.4% cis-9, trans-11; 4.5% trans-10, cis-12; and 4.8% cis-11, trans-13 CLA). Treatments were applied 2 x/d with half of the supplement top-dressed at 0600 h and the remainder top-dressed at 1800 h. There was no overall treatment effect on dry matter intake (23.9 kg/d), milk yield (40.0 kg/d), somatic cell count (305,000), protein (2.86%), or lactose content (4.51%) or yields of these milk components. Supplementation with CLA decreased overall milk fat content and yield by 26 and 30%, irrespective of breed. The reduction of milk fat content and yield was greatest on d 21 (28 and 37%, respectively). Energy availability predicted by energy balance was improved with CLA supplementation compared with controls (3.7 vs. 7.1 Mcal/d, respectively). Respiration rate (78 breaths/min) and skin temperature (35.4 degrees C) during maximum heat load were not affected by treatment. The group receiving CLA had higher total milk fat CLA concentration (9.3 vs. 4.9 mg/g). Supplementation with CLA induced MFD and altered milk fat composition similarly between breeds and improved calculated energy balance during heat stress, but had no effect on production measures under these conditions.
热应激奶牛在生物能量方面与早期泌乳奶牛相似，即日粮能量可能不足以支持最大量的牛奶和乳成分合成。研究目的是评估在热应激期间共轭亚油酸（CLA）诱导的乳脂降低（MFD）是否能增加牛奶和乳成分的合成。此外，比较了荷斯坦奶牛和瑞士褐牛之间CLA对生产变量的影响及其诱导MFD的能力。在夏季（平均温度 - 湿度指数 = 75.7），采用交叉设计使用平均产奶97±17天的经产奶牛（n = 8头荷斯坦奶牛；n = 5头瑞士褐牛）。处理期为21天，每期前后各有7天的适应期。在适应期内，所有奶牛都补充棕榈脂肪酸馏出物（242克/天）。日粮处理包括每天补充250克CLA（78.9克/天CLA）或242克棕榈脂肪酸馏出物，以提供等量的脂肪酸。CLA补充剂含有多种CLA异构体（反式 - 8，顺式 - 10为3.0%；顺式 - 9，反式 - 11为3.4%；反式 - 10，顺式 - 12为4.5%；顺式 - 11，反式 - 13 CLA为4.8%）。处理每天施用2次，一半补充剂在0600时进行表层施肥，其余在1800时进行表层施肥。在干物质摄入量（23.9千克/天）、产奶量（40.0千克/天）、体细胞计数（305,000）、蛋白质（2.86%）、乳糖含量（4.51%）或这些乳成分的产量方面没有总体处理效应。补充CLA使总体乳脂含量和产量分别降低了26%和30%，与品种无关。乳脂含量和产量的降低在第21天时最大（分别为28%和37%）。与对照组相比，补充CLA后能量平衡预测的能量可用性得到改善（分别为3.7与7.1兆卡/天）。在最大热负荷期间的呼吸频率（78次/分钟）和皮肤温度（35.4摄氏度）不受处理影响。接受CLA的组总乳脂CLA浓度更高（9.3与4.9毫克/克）。补充CLA在不同品种间诱导MFD并改变乳脂组成相似，且在热应激期间改善了计算出的能量平衡，但在这些条件下对生产指标没有影响。
