Effects of sunshade net on environment of fenced feed lot and physiological characteristics of beef cattle in northwest China in summer

In order to study the effects of sunshade net applied in fenced feed lot in northwest China to alleviate heat stress of beef cattle in summer, this paper was conducted to measure environmental parameters, and recorded the physiological characteristics of beef cattle to evaluate the environment of fenced feed lot in different periods. This test was in Zhangye city, Gansu province (38.55 °N, 100.26 °E). The experiment was conducted from June 2018 to July of the same year. The fence feed lot was 198 m long and 100 m wide. There were 4 rows of cattle pens in the feed lot, each row had 11 columns. The length of each pen was 18 m and the width of 18 m. 2 black plastic shading nets were installed along the diagonal of the second row of cattle hurdles, with a light transmittance of about 40%, providing a shading area of 5.4 m2 for each cattle. Each stall was provided with a drinking tank for beef cattle to drink freely, and the feeding method was manual feeding at 8:00 and 17:00. 12 Simmental crossbred beef cattle with red and white coats were kept in each stall. Measurement parameters included temperature, relative humidity, wind speed, solar radiation intensity, skin temperature of beef cattle, respiration rate and behavior of beef cattle. Each environmental index was measured 3 times a day at 7:00, 14:00 and 19:00, and denoted as morning, afternoon and evening respectively. 3 stalls in the second row were selected for the recording of environmental parameters. The results showed that the microclimate environment under the shading net was relatively comfortable, which could provide a suitable feeding environment for beef cattle and improve animal welfare. At noon, the environment in the no shaded area would cause great heat stress to the cattle. The mean values of THIadj（adjusted temperature-humidity index，THIadj）, BGHI（black globe-humidity Index，BGHI） and HLI（heat load index，HLI） were 86.24, 92.98 and 93.89 respectively, all of which exceeded their upper critical values. However, sun shade net could decrease 87% of the solar radiation, decrease the temperature by 3.95 ℃ at the same time, meanwhile decrease black-globe temperature by 19.9%, and also can transfer the environment from severe heat stress into a moderate heat stress state. Through the behavior of beef cattle, it is believed that due to the level of heat stress, the main behaviors of beef cattle were different. The percentage of lying behavior of beef cattle increased from 14.21% to 59.9% (P<0.01), while the percentage of standing behavior decreased from 64.5 % to 29.7% (P<0.01). It was observed that the behavior of lying mostly occurred in the shade area at noon. In addition to the significantly increased proportion of lying behavior, the cattle were more inclined to move in the shelter area. Therefore, we considered that the sunshade net could improve the environment in summer and reduce the degree of heat stress. The outcome of various environmental comprehensive parameters on the physiological characteristics of beef cattle indicated that in this experiment, solar radiation was the main factor affecting the physiological characteristics of beef cattle. Black-globe temperature in no sunshade net area had the highest correlation with beef cattle skin temperature and their respiratory rate, correlation coefficients were 0.53 and 0.20 respectively. According to comparing the environment and the change of the beef cattle physical characteristics, the results indicated that the sunshade net reduced the beef cattle heat stress level mainly by reducing the radiation from the sun, improved the environment condition of the beef cattle. Thus, it could help to maintain the performance of beef cattle, improve the animal welfare at the same time. This study can provide a reference for the application effect of sunshade net in beef cattle industry in China.