Shwartz G, Rhoads M L, VanBaale M J, Rhoads R P, Baumgard L H
Department of Animal Sciences, The University of Arizona, Tucson, AZ 85721, USA.
J Dairy Sci. 2009 Mar;92(3):935-42. doi: 10.3168/jds.2008-1496.
Multiparous, lactating Holstein cows (n = 23; 120 +/- 30 d in milk, 690 +/- 67 kg of body weight) housed in climatic chambers were randomly assigned to 1 of 2 dietary treatments: a diet containing a novel yeast culture formulation (YC) for heat stress (n = 12, 10 g/d) or a control diet (n = 11). The trial length was 28 d and consisted of a 7-d thermal neutral period (TN; 18 degrees C, 20% humidity) followed by 21 d of heat stress (HS; cyclical daily temperatures ranging from 29.4 to 37.8 degrees C and 20% humidity). Cows were individually fed a total mixed ration consisting primarily of alfalfa hay and steam-flaked corn. During TN, the YC feeding had no effect on production variables or most body temperature indices. During HS, all body temperature indices increased and YC had no effect on rump surface temperature, respiration rate, or sweating rates. Cows fed YC had lower rectal temperatures at 1200 and 1800 h (40.29 vs. 40.02 degrees C and 40.35 vs. 40.12 +/- 0.07 degrees C, respectively) compared with control-fed cows. Cows fed both diets lost body weight (42 kg) during HS, but there were no differences between diets. Control-fed cows had increased dry matter intake (DMI) and milk yield (19.1 vs. 17.9 +/- 0.5 kg/d and 32.15 vs. 29.15 +/- 0.02 kg/d, respectively) compared with YC-fed cows, but intake and milk production were similar between diets when evaluated on a body weight basis. Heat stress progressively decreased DMI (29%) and milk yield, with milk production reaching a nadir (33%) in the third week. Heat stress decreased milk protein (7%) and lactose (5%) levels, but did not alter milk fat content. Heat-stressed cows were in calculated negative energy balance (-1.91 +/- 0.70 Mcal/d) and this was unaffected by diet. Independent of diet, HS decreased plasma glucose (11%), but neither diet nor HS altered basal nonesterified fatty acid levels. Heat stress increased plasma urea N concentrations (11.5 vs. 14.8 +/- 0.4 mg/dL). Despite YC-fed cows having slightly reduced body temperatures indices, feeding YC did not prevent the negative effects of HS.
将23头经产泌乳荷斯坦奶牛（产奶120±30天，体重690±67千克）置于气候箱中，随机分为两种日粮处理组之一：一种日粮含有用于热应激的新型酵母培养物制剂（YC，n = 12，10克/天），另一种为对照日粮（n = 11）。试验为期28天，包括7天的热中性期（TN；18℃，20%湿度），随后是21天的热应激期（HS；每日循环温度范围为29.4至37.8℃，湿度20%）。奶牛单独饲喂主要由苜蓿干草和蒸汽压片玉米组成的全混合日粮。在热中性期，YC饲喂对生产变量或大多数体温指标没有影响。在热应激期，所有体温指标均升高，YC对臀部表面温度、呼吸频率或出汗率没有影响。与对照日粮组奶牛相比，饲喂YC的奶牛在1200时和1800时直肠温度较低（分别为40.29℃对40.02℃和40.35℃对40.12±0.07℃）。两种日粮组的奶牛在热应激期体重均下降（42千克），但日粮间无差异。与饲喂YC的奶牛相比，对照日粮组奶牛干物质摄入量（DMI）和产奶量增加（分别为19.1对17.9±0.5千克/天和32.15对29.15±0.02千克/天），但以体重为基础评估时，日粮间摄入量和产奶量相似。热应激使DMI逐渐下降（29%）和产奶量下降，产奶量在第三周降至最低点（33%）。热应激使乳蛋白（7%）和乳糖（5%）水平降低，但未改变乳脂肪含量。热应激奶牛处于计算得出的负能量平衡状态（-1.91±0.70兆卡/天），且不受日粮影响。与日粮无关，热应激使血浆葡萄糖降低（11%），但日粮和热应激均未改变基础非酯化脂肪酸水平。热应激使血浆尿素氮浓度升高（11.5对14.8±0.4毫克/分升）。尽管饲喂YC的奶牛体温指标略有降低，但饲喂YC并不能预防热应激的负面影响。
