122 Changes in blood metabolic profile of beef cows with and without access to shade or chromium supplementation during gestation under heat stress conditions.

Abstract The objective of this study is to evaluate the changes in blood metabolic profile of cows with or without access to shade and chromium (Cr) supplementation during mid and late gestation. Seventy-two fall-calving Angus-cross fall-calving black-hided Angus-cross cows were stratified by body weight (BW; 566 ± 5.38 kg) and body condition score (BCS; 6.3 ± 0.5) and allocated into 1 to 12 bermudagrass pastures (3 to 5 ha pastures). Treatments were randomly assigned to pastures in a 2 × 2 factorial arrangement: cows with or without access to artificial shade and Cr supplementation [shade and Cr (SC), no shade and Cr (NSC), shade and no Cr (SNC), and no shade and no Cr (NSNC)], from day 0 to 150 ± 20 d prepartum. Shade structures provided on average approximately 4.2 m2 of shade per animal/pasture. All pasture areas had no natural shade. The Cr was added to a loose-mineral mix in an organic form (Cr propionate) to provide a target intake of 0.5 mg of Cr/kg of total diet. Cow blood samples were collected on d 0, 30, 60, 90, 120, and 210 via jugular vein using commercial tubes containing no additive for serum harvest. Blood samples were centrifuged at 2,500 × g for 30 min at 4°C for serum. Serum samples were analyzed for albumin, total protein, globulin, urea N, glucose, creatinine, non-esterified fatty acids (NEFA) concentrations, and alanine aminotransferase (ALT), aspartate aminotransferase (AST) and gamma-glutamyl transpeptidase (GGT) activities using a Beckman Coulter AU480 Chemistry Analyzer. Statistical analyses were performed using the mixed procedure of SAS. Differences were determined at P < 0.05. No effects of shade, Cr, or possible interactions between treatments and day were found for albumin and GGT concentrations (P >0.05). Effect of shade and day of the study was found for glucose and NEFA concentrations (P< 0.01). Glucose concentrations were greater for no-shaded cows on d 30, 90 and 120 (P<.0001), whereas NEFA concentrations were reduced for no shaded cows on d 90 and 120 (P< 0.01). ALT concentrations were greater for shaded cows (P=0.03). Effect of Cr and day was found for total protein, globulins, creatinine, and AST. Cows supplemented with Cr showed reduced total protein and globulins on d 60, 90 and 120, reduced creatinine on d 90 and 120, and increased concentrations of ALT on d 90 (P<.0001). Effect of Shade × Cr × day was found for SUN, where NSNC cows had lowest concentration, followed by SNC and similar concentrations between SC and NSC (P< 0.001). Overall, removing shade affected cows’ energy-related metabolites, indicating mobilization of body reserves. Cr supplementation does not seem to attenuate changes on energy-related metabolites but altered indicator of the protein status.