SERUM HORMONES AND INSULIN-LIKE GROWTH-FACTOR-I IN MALE AND FEMALE CALVES AND THEIR POSSIBLE RELATION TO GROWTH

Precolostral and preprandial concentrations of insulin, cortisol, trii odothyronine (T3) and insulin-like growth factor-I (IGF-I) were determ ined in the blood serum of male and female Holstein calves at 0 and 4. 5 months, of age. The values obtained were similar for both sexes exce pt for slightly but statistically significantly higher mean neonatal c ortisol, higher IGF-I at 4.5 months and lower T3 at 4.5 months in the male (n = 21) than in the female group (n = 22). Insulin, cortisol and T3 concentrations fell and IGF-I increased with age. Moreover, statis tically significant correlation coefficients were found between neonat al T3 and cortisol levels and between final IGF-I concentrations and b oth daily gain and final body weight in each group. Multiple regressio n analysis indicated that only two of the nine parameters examined (ne onatal T3 and IGF-I concentrations at 4.5 months) were associated inde pendently with rate of gain of the female calves (R(2) = 0.495). Howev er, seven of the nine variables together accounted for 83% of the vari ance associated with daily gain in the male calves (R(2) = 0.831). Nev ertheless, the contribution of measurements obtained at birth alone wa s not sufficiently large to allow prediction of subsequent growth beca use, even in the male calves, they only described 60% of the variance associated with daily gain in the period examined.