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

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 less than 0.001). There was a significant (P less than 0.001) fall in plasma IGF-I from birth (40.3 +/- 2.5 micrograms/l) until 5 weeks (23.8 +/- 1.3 micrograms/l), and then a gradual (P less than 0.01) rise until week 8 (35.0 +/- 2.2 micrograms/l). Weaning (groups 1 and 2 after week 8) caused a significant (P less than 0.01) decrease in plasma IGF-I (20.5 +/- 1.9 micrograms/l); thereafter plasma levels of IGF-I rose gradually (P less than 0.01) in animals fed on concentrates. The milk-fed calves (group 3) showed a progressive increase in plasma IGF-I with age until they were weaned at 12 weeks (51.0 +/- 3.4 micrograms/l); IGF-I levels then decreased to be similar to group 1 (32.5 +/- 2.1 micrograms/l).(ABSTRACT TRUNCATED AT 250 WORDS)