Fike J H, Staples C R, Sollenberger L E, Moore J E, Head H H
Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
J Dairy Sci. 2002 Apr;85(4):866-78. doi: 10.3168/jds.S0022-0302(02)74145-3.
This experiment tested performance and physiological responses to evaporative cooling, bovine somatotropin (bST), and supplemental silage of lactating cows grazing bermudagrass (Tifton 85; Cynodon dactylon x C. nlemfuensis cv.) pastures. Multiparous (n = 32) cows (196 d in milk) were assigned one of five treatments arranged in two replicates. Treatments were 1) cows maintained continuously on pasture with access to shade, 2) treatment 1 + bST, 3) night housing on pasture, then free-stall housing with fans and misters from 0730 to 1630 h, 4) treatment 3 + bST, and 5) treatment 4 + corn silage fed at 0.5% of body weight (dry matter basis) in the barn. A grain supplement was fed at a rate of 0.5 kg/kg of milk produced. Time spent grazing ranged from 4 to 7.2 h/d, with cows fed corn silage spending the least amount of time. Cows given bST grazed 45 min/d longer than controls, but intake of bermudagrass was unchanged. Intake of bermudagrass ranged from 7.4 to 9.5 kg/d of organic matter, with the lowest intake by cows fed corn silage. With the exception of cows fed corn silage, cows kept in a cooling barn during the day ate equivalent amounts of pasture as those given unlimited access to pasture. Production of 4% fat-corrected milk was greater by cows injected with bST (17.7 vs. 15.8 kg/d) compared with controls and tended to be greater for cows given daytime cooling compared with cows on pasture continuously (17.2 vs. 16.3 kg/d). Cows provided evaporative cooling did not lose weight compared with continually pastured cows (6.3 vs. -10.9 kg/24 d). Cows injected with bST compared with controls maintained their body weight better (2.5 vs. -7.1 kg/24 d). Cows given bST had increased concentration of plasma insulin-like growth factor-I (142 vs. 89 ng/ml), insulin (0.60 vs. 0.56 ng/ml), and nonesterified fatty acids (318 vs. 239 mEq/L). Cows given bST and those continually on pasture had greater diurnal body temperatures. Use of barn cooling systems and bST treatments as management tools provided limited improvement in performance of midlactation cows managed in pasture-based systems.
本试验研究了泌乳奶牛在放牧百慕大草（蒂夫顿85；狗牙根×牛鞭草杂交种）牧场时，对蒸发冷却、牛生长激素（bST）和补充青贮饲料的性能及生理反应。将32头经产奶牛（产奶196天）分为五个处理组，每组两个重复。处理组分别为：1）持续在牧场放牧且有遮荫处的奶牛；2）处理组1 + bST；3）夜间在牧场圈养，然后从0730至1630时在自由栏舍中饲养，配有风扇和喷雾器；4）处理组3 + bST；5）处理组4 + 在牛舍中按体重0.5%（干物质基础）饲喂玉米青贮饲料。以每产1千克牛奶饲喂0.5千克谷物补充料。放牧时间为每天4至7.2小时，饲喂玉米青贮饲料的奶牛放牧时间最短。注射bST的奶牛每天放牧时间比对照组多45分钟，但百慕大草采食量未变。百慕大草的采食量为每天7.4至9.5千克有机物，饲喂玉米青贮饲料的奶牛采食量最低。除饲喂玉米青贮饲料的奶牛外，白天在凉爽牛舍饲养的奶牛与可自由放牧的奶牛采食的牧草量相当。注射bST的奶牛4%乳脂校正乳产量高于对照组（17.7对15.8千克/天），白天进行冷却处理的奶牛的4%乳脂校正乳产量也高于持续放牧的奶牛（17.2对16.3千克/天）。与持续放牧的奶牛相比，进行蒸发冷却处理的奶牛体重未减轻（6.3对 - 10.9千克/24天）。与对照组相比，注射bST的奶牛体重维持得更好（2.5对 - 7.1千克/24天）。注射bST的奶牛血浆胰岛素样生长因子 - I（142对89纳克/毫升）、胰岛素（0.60对0.56纳克/毫升）和非酯化脂肪酸（318对239毫当量/升）浓度升高。注射bST的奶牛和持续在牧场放牧的奶牛昼夜体温更高。在基于牧场的系统中，将牛舍冷却系统和bST处理作为管理工具，对泌乳中期奶牛性能的改善有限。
