Effect of shade and limit feeding in growing beef heifers during periods of heat stress.

Experiments were conducted during the summers of 2021 and 2022 to evaluate the effects of feeding strategy and shade on growth performance, animal comfort, water usage, apparent diet digestibility, and ruminal fermentation characteristics of growing heifers during periods of heat stress. In Exp. 1, 852 heifers (initial body weight [BW] = 251 ± 13 kg) were assigned to one of 4 treatments: high-energy diet limit-fed at 2.2% of BW (dry matter [DM] basis; LIM) or high-roughage diet fed for ad libitum intake (ADLIB) with shade (SH) or without shade (NSH). Pen BWs were measured on day 0, weekly from days 14 to 84, day 90, and day 97. Pen weights were used to adjust weekly intakes of LIM. Refusals for ADLIB were targeted at 5% of feed consumed the previous day. Following the 90-d feeding period, a gut-fill equilibration diet was fed to all cattle at 2.5% of BW (DM basis) for 7 d to balance differences in gut-fill between dietary treatments. Dry matter intake was lesser (P < 0.01) for LIM compared with ADLIB. Average daily gain (ADG) and gain:feed (G:F) were greater (P < 0.01) for LIM compared with ADLIB. In addition, ADG and G:F were greater (P < 0.01) for SH compared with NSH. Water usage was less (P < 0.01) for SH heifers compared with NSH and was also less (P < 0.01) for LIM compared with ADLIB. Mean panting scores were lower (P < 0.01) for SH compared with NSH and LIM compared with ADLIB. In Exp. 2, 16 heifers (initial BW = 254 ± 22 kg) were arranged in 4 replicated 4 × 4 Latin squares to evaluate treatments from Exp. 1. Apparent total tract digestibility of DM and organic matter was greater (P < 0.01) for LIM compared with ADLIB. Ruminal pH was more acidic (P = 0.02) for LIM compared with ADLIB. Shade did not affect (P ≥ 0.68) apparent diet digestibility; however, ruminal pH was greater (P < 0.01) for SH compared with NSH. In conclusion, LIM improved feed efficiency, reduced mean panting score, and reduced water usage compared with ADLIB. In addition, SH improved growth performance, reduced water usage, and improved animal comfort during periods of heat stress.