Plasma concentrations of insulin-like growth factor-I and insulin in the infant calf: ontogeny and influence of altered nutrition

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Abstract
The developmental pattern of plasma insulin-like growth factor-I (IGF-I) and insulin in calves subject to different patterns of weaning was investigated from birth until the age of 6 months. Fifteen male Friesian calves were fed on whole milk (10% of body weight per day) for the first 8 weeks after birth, then allocated into three balanced groups. Group 1 was weaned at 8 weeks; group 2 was weaned at 8 weeks, returned to milk-feeding at 13 weeks to be weaned again at the age of 16 weeks; group 3 was weaned at 12 weeks. After weaning the calves were fed on concentrates and lucerne hay. At birth, circulating concentrations of IGF-I correlated with birth weight (r = 0·78, P< 0·001). There was a significant (PPPP125I-labelled bovine GH to hepatic membranes of neonatal calves was low at birth (specific binding; 1·56 ±0·29% n=3). Somatotrophic binding was apparent at 6 weeks (6·43 ±0·42%, n = 3) and increased (9·2± 1·1%, n=3) at the age of 12 weeks. Thus the early postnatal changes in plasma IGF-I may reflect the transition from GH-independent to GH-dependent IGF-I secretion. Plasma concentrations of insulin at birth correlated with IGF-I (r = 0·54, PPJ. Endocr. (1988) 119, 43–50