Mader T L, Dahlquist J M, Hahn G L, Gaughan J B
Department of Animal Science, University of Nebraska, Northeast Research and Extension Center, Concord 68728, USA.
J Anim Sci. 1999 Aug;77(8):2065-72. doi: 10.2527/1999.7782065x.
In each of three summertime trials conducted over consecutive years, approximately 110 predominantly black and black-white-face steers were blocked by weight and randomly allotted to one of 16 pens in a 2x2 factorial arrangement of treatments. Factors consisted of cattle being fed in facilities with or without wind barriers and with or without shade. Steers were fed dry-rolled corn-based diets (1.43 Mcal/ kg, NEg). Mean starting date and days on feed were June 26 and 79, respectively. In unshaded areas, temperature and humidity averaged 21.6 degrees C and 77.9%, and the blackglobe-humidity index (BGHI) at 1500 averaged between 84.0 and 89.1. Each of four 6.1-x6.1-m structures (mean height = 3.4 m) with white steel roofs provided shade (2.65 m2/steer) for two pens. In facilities with wind barriers provided, airflow was reduced from the north and northwest by a 25-m-wide shelterbelt containing six rows of trees. For cattle fed in pens with wind barriers, shade increased (P<.05) gain from 0 to 56 d and decreased (P<.05) DMI/ADG from 0 to 28 d. Differences (P<.05) in performance were not found between shaded and unshaded cattle in any portion of the feeding period for cattle fed in the pens without wind barriers and over the entire feeding period in either type of facility. The shade response in pens with wind barriers seemed to be greater the 1st yr than in subsequent years. Differences in weather patterns among years, especially air temperature, humidity, and solar radiation, may partially explain this interaction. Also, in yr 1, cattle tended to have greater fat thickness at finish than in yr 2 and 3. Correlations between BGHI and DMI tended to be greater during the early portion of the trial (0 to 28 d) than over the entire trial. Correlations between the difference in BGHI under shade vs no shade and percentage of shade use had the greatest magnitude and were significant only in the first 28 d vs over the entire feeding period. Although no heat-related cattle deaths occurred in this study, results suggest that shade improves cattle performance in the summer when they are fed in facilities with winter wind protection available and have not become acclimated to hot conditions. Once cattle are acclimated or hot conditions subside, compensation by unshaded cattle offsets much of the initial benefits of providing shade.
在连续三年进行的三项夏季试验中，每年约有110头主要为黑色和黑白花色的阉牛按体重进行分组，并以2×2析因试验设计随机分配到16个畜栏中的一个。试验因素包括在有或没有防风屏障以及有或没有遮荫设施的畜栏中饲养牛。阉牛饲喂以干碾压玉米为主的日粮（1.43兆卡/千克，净能）。平均开始日期和采食天数分别为6月26日和79天。在无遮荫区域，温度和湿度平均分别为21.6℃和77.9%，15:00时的黑球湿度指数（BGHI）平均在84.0至89.1之间。四个6.1米×6.1米的白色钢顶结构（平均高度 = 3.4米）为两个畜栏提供遮荫（每头阉牛2.65平方米）。在设有防风屏障的设施中，气流被一条宽25米、有六排树的防护林带从北方和西北方向减弱。对于在有防风屏障的畜栏中饲养的牛，遮荫使0至56天的增重增加（P<0.05），并使0至28天的干物质采食量/平均日增重降低（P<0.05）。对于在没有防风屏障的畜栏中饲养的牛，在采食期的任何阶段以及在任何一种设施中的整个采食期，有遮荫和无遮荫牛之间均未发现性能差异（P<0.05）。有防风屏障的畜栏中遮荫的效果在第一年似乎比随后几年更大。年份间天气模式的差异，尤其是气温、湿度和太阳辐射，可能部分解释了这种相互作用。此外，在第一年，牛在育肥结束时的脂肪厚度往往比第二年和第三年更大。BGHI与干物质采食量之间的相关性在试验早期（0至28天）往往比整个试验期更大。遮荫与无遮荫条件下BGHI的差值与遮荫使用百分比之间的相关性最大，且仅在试验的前28天与整个采食期相比具有显著性。尽管本研究中未发生与热相关的牛死亡，但结果表明，当牛在有冬季防风设施且尚未适应炎热条件的设施中饲养时，遮荫可改善夏季牛的性能。一旦牛适应了炎热条件或炎热天气消退，无遮荫牛的补偿作用抵消了提供遮荫的许多初始益处。
