Response to environmental temperatures in Brahman calves during the first compared to the second day after birth.

Brahman calves (n = 28) were used to evaluate the effect of environmental temperature during the 1st or 2nd d after birth. Calves were removed from their dams within 30 min of birth (newborn; D0) before suckling or at 20 h of age and fasted for 4 h before treatment (day-old; D1). Calves were placed in either a warm (W; 25 degrees C) or a cold (C; 5 degrees C) environment for 2 h and either maintained in or transferred to, respectively, W for 22 h. Blood samples were collected via jugular catheters at 15-min intervals beginning at initial placement in W or C through 3 h and at 4, 5, 6, 8, 10, 12, 14, 18, and 24 h. Rectal temperature (Tr) was recorded with each sample. Following the 60-min and 12-h samples, each calf was administered 1 liter of colostrum from its dam. Serum or plasma was analyzed for glucose, lactate, plasma urea nitrogen, triglycerides, nonesterified fatty acids, insulin, cortisol, triiodothyronine (T3), and thyroxine (T4). Rectal temperature of D0C calves was lower (P less than .05) than that of other calves from 75 min through 3 h. Insulin, lactate, T3, and plasma urea nitrogen concentrations were not different among all calves. Higher (P less than .01) cortisol and T4 concentrations were observed in D0 than in D1 calves. Cortisol (P less than .008) and nonesterified fatty acid (P less than .05) levels were greater in C than in W calves. All D0 calves had lower (P less than .0001) glucose concentrations than D1 calves until the 12-h feeding.(ABSTRACT TRUNCATED AT 250 WORDS)