Pen-Shade and Morning Versus Afternoon Feeding on Feedlot-Performance and Respiratory Rate of Growing Calves Under Hot Weather

Sixty four Brahman cross calves (223 ± 18.67 kg) were used to evaluate the effect of pen-shade and morning versus afternoon feeding on feedlot-performance and respiratory rate of growing calves under hot weather. Calves were individually weighed and using initial weight as blocking criteria, in a completely randomized block design, in groups of four calves were assigned to treatments as follows: 1) Placed in ground pen (6 x 12 m) without shade and morning feeding (0700 and 0900); 2) Ground pen without shade and afternoon feeding (1700); 3) Ground pen fitted with central roof (4 m² of shade/calf) and morning feeding (0700 and 0900); and 4) Ground pen fitted with central roof and afternoon feeding (1700). Calves were fed ad libitum with a diet (15% CP and 1.34 Mcal NE_m/kg DM) formulated with corn silage, steam flaked corn, soybean meal and mineral premix. Calves were weighed in days 1 and 28. Data was analyzed by ANOVA for a completely randomized block design with a 2 x 2 factorial arrangement. Mean air temperature from 0800 to 1800 was lower (P < 0.01) in pen-shade 33.8 vs. 36.7 °C; relative humidity was higher (P < 0.01) 62.1 vs. 58.2%; and THI values were lower 85.1 vs. 88.1 (P < 0.01). Pen-shade and afternoon feeding increased (P < 0.01) average daily gain. An interaction (P = 0.02) in ADG was observed, where morning fed calves (shaded and unshaded pens) exhibits similar ADG, but calves allotted in shaded pens fed afternoon have highest gain than calves fed afternoon but placed in unshaded pens (1.56 vs. 1.19 kg). Pen-shade increased DMI (P = 0.02). Gain/feed ratio was increased both for Pen-shade (P = 0.05) as by feeding time (P < 0.01). A tendency for interaction (P = 0.09) was observed where the lower values were found in calves fed during morning (shaded and Unshaded pens), but inner afternoon fed calves those were provided with pen-shade had higher response (P = 0.02) than placed in unshaded pens (0.255 vs. 0.220 kg/kg). Serum cortisol values were lower (P < 0.01) in shaded pens calves (1.02 vs. 3.10 µg/dL). At 0800 h respiratory rate was similar across treatments (P > 0.15), but from 1000 to 1800 respiratory rate was lower (P < 0.01) in shaded pens calves (56.4 vs. 84.9 breaths/minute). Results suggest providing pen-shade and afternoon feeding contributes to increase feedlot performance of calves under hot weather.