Analysis of plasma IGF-I hormone level and its correlation with live weight and age in Holstein-Friesian heifers

Abstract. The aim of this study was to evaluate the changes and relation of live weight and IGF-I plasma concentration during the rearing period in HF heifers. Number of animals was 85 kept in similar housing and feeding conditions. Blood samples were collected monthly at the same hour of the day and weight of the calves were scaled simultaneously up to the 14th month of age. Plasma IGF-I concentration was measured by RIA procedure. Data were analysed by STATISTICA, SPSS 10.0 version and POST HOC TEST programs. Results of this work allow to conclude that change of plasma IGF-I c.c. and live weight show similar trend. Rearing phase of calves shows three peaks: 1st at birth; 2nd closed to sexual maturity; 3rd closed to first service. IGF-I-profile can be taken as similar for all individual and animals can be categorised into groups with low or high hormone concentrations. There is only negative correlation (r = −0.24) between IGF-I levels at birth and at 4 months of age. Bulls have special effect on IGF-I c.c. at birth, at 5th, 13th and 14th months of age (P < 0.1). On contrary to previous findings IGF-I level and weight of calves correlated negatively (r = −0.31, P < 0.05) in the whole population, while within progeny groups positive and negative correlation may occur, too. Negative correlation prove the compensation ability of animals in growth rate. In comparison with the overall mean of IGF-I c.c., the subpopulation below average has lower live weight, too and with high IGF-I level a higher live weight is bound.