Shade effect on behaviour, physiology, performance, and carcass weight of heat-stressed feedlot steers in humid subtropical area

Context Environmental conditions during hot weather decrease feed intake and cattle growth. Aims This study conducted over three consecutive years, during the summer, evaluated access to shade as a strategy to mitigate heat stress of finishing cattle in Uruguay. Methods Each year, 32 Bos taurus and/or Bos taurus crossbred steers (initially weighing 461 +/- 28 kg) were blocked by initial liveweight and assigned to one of eight pens, where one of two treatments were applied, namely, no shade access or shade access (mean shaded area 4.5 m(2)/animal). Finishing diet was offered three times per day and cattle had ad libitum access to water. Twenty-four pens were considered in a randomised complete-block design. Average daily gain (ADG), dry matter intake (DMI) and feed efficiency were measured, and hot carcass weight was collected at slaughter. Ruminal pH and temperature were obtained using ruminal boluses. Feeding, drinking, rumination, inactive behaviours, respiration rate and painting score were observed. Key results Mean days on feed were 70.6 +/- 5.5. The average THI ranged from 70 to 72. Steers with access to shade had greater DMI (P = 0.003), ADG (P = 0.004), and feed:gain ratio (P = 0.05) than did not shaded steers. Ruminal pH was higher (P < 0.0001) in shaded than in not shaded animals. The slaughter weight of shaded steers was 10 kg greater (P = 0.02) than that of not shaded steers. A trend (P = 0.06) to higher hot carcass weight after dressing was obtained by shaded steers. The average respiration rate and panting score was consistently lower (P < 0.0001) for shaded than for not shaded steers, except in the early morning. Access to shade increased the time spent by animals feeding (P = 0.008) and ruminating (P = 0.001), decreasing inactive time (P < 0.0001). Conclusions Shade could improve performance and welfare of feedlot cattle during summertime, even in regions with an average THI from 70 to 72. Implications Access to shade allowed fattening cattle to dissipate heat stored during the day at night and to alleviate the effect of heat load during summer in subtropical region.