Late gestation heat stress in Sahiwal cows and its effects on neonatal immunocompetence and early growth

The present study aimed to determine the complex interrelationships between late gestation heat stress (HS), colostrum quality and associated physiological responses in Sahiwal cow progenies. Late gestation Sahiwal cows (N = 24) were exposed to natural heat stress (NHS) or provided cooling treatment in a climate-controlled chamber (CLT). Calves born were categorized into four groups: IUHS (intrauterine HS), IUCL (intrauterine cooled), HSCL (IUHS calves supplied colostrum from CLT cows), and CLHS (IUCL calves supplied colostrum from NHS cows). The environmental variables were recorded and temperature-humidity index (THI) was calculated reflecting thermal stress in NHS group (THI≥84). Colostrum constituents exhibited non-significant variations (P > 0.05), although numerically lower values were observed in NHS group. Additionally, CLT group colostrum had significantly (P < 0.05) higher IgG concentration and lower somatic cell count (SCC) values. Overall mean physiological responses viz. rectal temperature (RT), heart rate (HR), respiration rate (RR) and skin temperature (ST) were significantly (P < 0.05) higher in calves of IUHS and HSCL calves compared to calves born from CLT dams. Mean hematological parameters varied significantly (P < 0.05) among the intrauterine HS and intrauterine CLT calves, with an inconsistent variation observed with colostrum feeding from CLT cows and age. Higher THI around late gestation had a negative relationship with birth weight and average daily gain of neonate calves. In conclusion, late gestation HS abatement exerts variable carryover effects on offspring, suggesting that prenatal thermal stress impairs homeorhetic regulation and subsequent immunocompetence via both epigenetic modifications and compromised colostrum quality critical for neonatal development.