Efeitos do sombreamento artificial no conforto térmico de bovinos confinados

Abstract

The aim of this study was to evaluate the thermal comfort of cattle submitted to confinement with or without artificial shading. A total of 900 male Nellore cattle was used, divided into three groups housing with access to artificial shading (Tshade) and three without it (Tsun). All animals received the same diet. Wind velocity (VV, m / s), black globe temperature (BGT, ° C), air temperature (AT ° C) and relative air humidity (RAU%) were evaluated and used to calculate two indicators of thermal comfort: Globe and Humidity Temperature Index (GHTI) and Radiant Thermal Load (RTL). Statistical analyzes were performed using the SAS statistical program (SAS Inst. Inc., Cary, NC). The PROC MIXED command was used to evaluate the effects of the treatment and the time of day on the GHTI and RTL climate variables. The averages were adjusted by the Tukey test. To evaluate the effect of the treatment on the body surface temperature of the animals, during the confinement days, the hours of the day of evaluation and the period of the day the PROC GLM command was used with comparisons between means adjusted by Test t. A significant effect of the interaction between treatment (TT) and hours (HR) on GHTI (p = 0.001) was found. The GHTI values were statistically different at all times, with higher means values between 13 and 15 hours, then between 9 and 11 hours, followed by 15 to 17 hours. As for RTL, no significant effect (p = 0.07) of interaction between treatment (TT) and time (HR) was found, but Tsun showed higher RTL when compared with Tshade (RTL = 551.25 and 501.35, respectively; p < 0.0001), while the HRs between 09 and 11:00 AM and between 13 and 15:00 PM showed higher RTL than the other times of day (RTL = 490,09b, 549,17a , 551.72a, 514.24b for HR 7-9h00min, 9- 11h00min, 13-15h00 and 15-17h00min, respectively; p < 0.0001). The mean body surface temperature from Tshade was lower throughout all evaluation days, except for d28, when shade or sun exposed animals did not differ statistically (p < 0.05). It is concluded that the access to artificial shading in feedlot reduces the heat stress improving the cattle welfare.