Effects of late gestation heat stress in Buffalo heifers on postnatal growth, thermoregulatory, and suckling behavior responses of their newborn calves under subtropical environment.

This study aimed to evaluate various growth, physiological, and suckling behavioral parameters of calves born to nulliparous buffalo heifers exposed to summer heat stress (HT, provided only shade, n = 12) or winter coldness (CL, n = 12) during the final 60 days of gestation. Calves were individually housed and were monitored from birth until 6 days of age. Rectal temperature, pulse rate, and respiratory rate were measured, and heat tolerance and adaptability indices were calculated. Suckling responses, suckling durations, and milk drinking speeds were also recorded. HT calves had lighter birth weights, with approximately 1.26 kg and 1.06 kg differences for male and female calves, respectively. They gained less weight from birth to 6 days, with a difference of 0.12 kg/d for males and 0.11 kg/d for females and weighed about 1.9 kg less at 6 days old. HT calves exhibited elevated rectal temperatures, respiration rates, and pulse rates, with increases of approximately 0.7 °C, 27 breaths/min, and 20.3 beats/min, respectively, compared to CL calves. Female calves were more susceptible to heat stress than males and exhibited lower heat tolerance and adaptability. HT calves exhibited a shorter total suckling duration immediately after birth compared to CL calves by about 55.3% and demonstrated faster milk drinking speeds by about 44%. Only HT female calves exhibited slower milk drinking speeds compared to HT males, with a reduction of about 18.7%. In-utero heat stress during late gestation had negative immediate and prolonged effects on postnatal performance and suckling behavior in buffalo calves, particularly in female calves.