Heat stress mitigation during prepartum and postpartum altered the plasma metabolome in <i>Bos indicus</i>-influenced cow-calf pairs

This study evaluated the impacts of access to artificial shade during prepartum and postpartum periods on the plasma metabolome of heat-stressed cow-calf pairs. On day 0, 64 pregnant Brangus crossbred beef heifers (<25% Bos indicus; 20 to 22 mo of age) were stratified by body weight (BW) (454 ± 37 kg) and body condition score (6.3 ± 0.28) and allocated to 1 of the 16 bahiagrass pastures (1 ha and 4 heifers per pasture). Treatments were randomly assigned to pastures (8 pastures per treatment) and consisted of heifers provided (SH) or not provided (NSH) access to artificial shade from day 0 to 133 (83 ± 4 days prepartum until 50 ± 4 d postpartum). Calves were weaned on day 203 (120 d of age) and limit-fed the same concentrate at 3.25% of BW until day 268. Calves were vaccinated against pathogens associated with bovine respiratory disease on day 222. Blood samples were collected from all heifers 30 d before calving (day 55) and from calves on days 222 and 223 to determine the plasma metabolome using liquid chromatography. Principal component and partial least squares-discriminant analyses were conducted daily to distinguish treatment groups. Metabolite concentrations were compared between SH and NSH groups using SAS MIXED, and differentially expressed metabolites were analyzed for canonical pathways via Ingenuity Pathway Analysis. A clear separation was observed on day 55 for SH and NSH heifers. Effects of treatment (P ≤ 0.05) were detected for 16 metabolites and tended to be detected (P ≤ 0.10) for 9 metabolites from the top 100 variable importance in projection. Nine pathways related to glutamate, alanine, and aspartate metabolism were upregulated (P ≤ 0.03), whereas glutamate degradation I was downregulated (P = 0.02) in SH versus NSH heifers. Clear separations were observed for calf metabolome on days 222 and 223. Plasma concentrations of 12 and 5 metabolites associated with amino acid and lipid metabolism increased (P ≤ 0.05) in SH versus NSH offspring on days 222 and 223, respectively. Shade access upregulated (P ≤ 0.01) 9 calf metabolic pathways related to amino acid and antioxidant metabolism on day 222 but did not impact (P > 0.10) calf metabolic pathways on day 223. Thus, access to shade for pregnant heifers altered their glutamate metabolism and appeared to decrease lipolysis compared with no access to shade. Access to shade programmed the calf metabolism to increase primarily glutamate utilization and reduce oxidative stress markers.