Maternal heat abatement during gestation alters growth, immunity, thermotolerance, and hepatic gene expression in beef offspring during backgrounding

<h4>Introduction</h4>The objective of this study was to evaluate the fetal programming effects of removing maternal heat abatement during late gestation on offspring growth, thermotolerance, physiological responses, and liver gene expression during the backgrounding phase.<h4>Methods</h4>Fifty-six Angus-cross calves [32 steers and 24 heifers, 225 ± 5.3 kg body weight (BW), 9 ± 1.5 months of age] were enrolled at weaning in a 112-day backgrounding study. Calves were born from cows provided (SS, <i>n</i> = 28) or not provided access to shade (NS, <i>n</i> = 28) during gestation. After weaning (d 0), calves were managed as a single group on bermudagrass pastures rotated biweekly. BW and blood samples were collected on d 0, 1, 3, 7, 14, 28, 48, 56, 84, and 112. Intravaginal temperature (IT) was recorded in heifers from d 48 to 56 and d 77 to 84. Liver biopsies were collected on d 56 for transcriptomic analysis. Data were analyzed using the GLIMMIX procedure of SAS, with maternal pasture as the experimental unit. Differential gene expressions (DEGs) were assessed using DESeq2 following read mapping and quality control.<h4>Results</h4>SS calves were heavier at weaning and on d 14, 48, and 112 (<i>p</i> ≤ 0.03), although overall average daily gain did not differ between treatments (<i>p</i> = 0.89). From d 77 to 84, SS heifers exhibited lower IT than NS heifers (<i>p</i> = 0.03). Blood metabolites were not different between treatments (<i>p</i> ≥ 0.19), though SS calves had greater serum urea N on d 0, 3, and 7 (<i>p</i> = 0.04). Nine genes were differentially expressed, with eight downregulated (<i>AOX4, USP25, CFHR5, FGG, MBL2, FGB, GBE1, FGA</i>) and one upregulated (<i>FBLN2</i>) in NS heifers. Gene set enrichment analysis (FDR ≤ 0.05) showed enriched pathways related to heat shock protein binding and depleted of metabolic pathways in NS vs. SS calves. Functional overrepresentation showed enrichment of processes related to vasoconstriction and protein activation cascades in the NS versus SS calves.<h4>Conclusion</h4>Removing maternal heat abatement during late gestation impaired offspring growth and thermoregulation during postweaning, enhanced humoral immunity, and altered liver gene expression.