Endocrine and thermoregulatory responses to acute thermal exposures in 6-month-old pigs reared in different neonatal environments

1. Endocrine and thermoregulatory responses to acute heat (34 degrees C) and cold (10 degrees C) exposures were determined in eight pigs at 6 months of age. Half of the pigs had been reared in a cycling upper thermal environment (27-32 degrees C) for the first 28 days of life, while the others had been reared in a lower thermal environment (21 degrees C). 2. Concentrations of cortisol increased significantly during both acute heat and cold thermal exposures (P = 0.0001) although the response was greater in the heat than in the cold (P = 0.003). A prolactin response occurred during acute heat exposure (P = 0.004). Growth hormone secretion increased during acute cold exposure (P = 0.001). There was a strong tendency for increased epinephrine secretion during both acute heat and cold exposures (P = 0.06). No significant effects of either exposure were found on plasma norepinephrine (P = 0.9), or triiodothyronine (P = 0.11). 3. Neonatal environment did not affect daily core body temperature (T-c) before acute heat or cold exposures, but did alter amplitude of the 24-h T-c cycle. The amplitude was significantly greater in animals reared in the lower thermal environment (P < 0.001). 4. Acute heat exposure resulted in significant increases in T-c (P < 0.001) and heat production (P < 0.01). Neonatal thermal environment had no significant effect on T-c and heat production responses to acute heat and cold thermal exposures. (C) 1997 Elsevier Science Ltd.