PSX-21 Impact of shade and chromium supplementation on performance and blood metabolites of finishing steers under heat stress conditions.

Abstract Livestock productivity and welfare are significantly impacted by heat stress (HS), which can lead to increased nutrient requirements and insulin resistance in animals. Different management strategies can be applied to mitigate HS across various sectors of the beef industry. Providing shade is one of the simplest strategies to aid in heat dissipation. From the nutritional management perspective, Chromium (Cr) is an essential trace mineral that has been shown to influence protein absorption and metabolism, improve insulin sensitivity, and enhance the performance of feedlot cattle. Nevertheless, there is a lack of comprehensive research on the impact of Cr supplementation on finishing cattle exposed to high temperatures. The objective of this study was to evaluate the effects of high-dose Cr supplementation on dry matter intake (DMI), body weight (BW), and concentrations of cortisol, insulin, glucose, insulin-like growth factor-1 (IGF-1), beta-hydroxybutyrate (BHB), urea, and creatinine in finishing steers exposed to heat stress (HS) conditions with or without access to shade. Twenty-four Bos indicus-influenced steers (1023 ± 40 kg) were randomly assigned to one of three treatments: (1) no shade and no Cr supplementation; (2) shade with no Cr supplementation; and (3) shade with Cr supplementation. Chromium (0.5 mg/kg DMI) was top-dressed onto the basal diet daily. Animals were fed twice daily (60% in the morning and 40% in the afternoon), with orts measured, and DMI calculated daily. Body weight and blood samples were collected on days 0, 14, 28, 42, 56, and 80. Serum samples were analyzed for urea nitrogen, glucose, creatinine, and BHB using a Beckman Coulter AU480 Chemistry Analyzer (Beckman Coulter Inc., Brea, CA), while cortisol, IGF-1, and insulin were measured using chemiluminescent enzyme immunoassays (Immulite 2000; Siemens Medical Solutions Diagnostics, Los Angeles, CA). Data were analyzed using a generalized linear mixed model, with treatment and day as fixed effects. Pen was included as a random effect to evaluate treatment and day effects on DMI, while animal was included as a random effect to assess treatment and day effects on blood metabolites. Treatment, day, and their interaction significantly influenced DMI and BW (P < 0.05). Day had a significant effect on cortisol, IGF-1, insulin, glucose, BHB, urea, and creatinine concentrations (P < 0.05). In conclusion, these findings contribute to a better understanding of the effects of Cr supplementation on finishing steers under HS conditions