Productive and Physiological Response of Grazing Steers Supplemented with Energy–Protein Supplements During Summer in a Subtropical Humid Region

In the context of climate change and increased frequency of droughts, summer supplementation of grazing cattle may improve productivity and resilience of pastoral systems. However, the provision of supplements may increase the risk of heat stress in cattle. This study aimed to evaluate the productive and physiological response of grazing steers supplemented during summer. Three independent studies were conducted over three summers (2020–2023). In each experiment, steers grazing native grasslands with access to shade were allotted to one of two treatments: control (CONT) and supplementation (SUPPL), in a completely randomized block design. SUPPL steers were group-fed in the morning three days per week with an energy–protein ration at a level of 1.98% body weight (BW) on days of feeding. Pasture attributes, animal performance, respiration rate (RR), and body temperature (BT) were analyzed using a mixed model. According to the temperature–humidity index, cattle were exposed to heat stress 32% of the time. Summer supplementation increased average daily gain and final body weight of steers. Although supplementation temporarily increased BT (morning) and RR (afternoon), daily average RR and BT were similar for both treatments. These findings show that summer supplementation improves animal performance of grazing steers without increased risk of severe heat stress. These results are aligned with the concept of sustainable livestock intensification, which aims to enhance animal source foods to feed a growing population without causing collateral animal welfare issues.