The relationship between plasma insulin-like growth factor-I (IGF-I) level and body weight in the horse

The relationship between plasma insulin-like growth factor-I (IGF-I) level and body weight was studied in six breeds of horse. The correlation coefficients between plasma IGF-I and body weight in males and females of 1 year old heavy horses (Percheron and Breton breeds) were 0.62 and 0.12 respectively. The mean plasma IGF-I of males was higher than that of females (p < 0.01). However, the plasma IGF-I levels of heavy horses did not exceed those of light horses (Thoroughbred) or ponies (Shetland and Falabella). These data suggest that IGF-I is at least related to the difference of body weights between sexes in heavy horses.