ASSOCIATIONS BETWEEN PLASMA CONCENTRATIONS OF IGF-1 IN YOUNG HOLSTEIN-FRIESIAN HEIFERS AND PRODUCTIVE AND REPRODUCTIVE PARAMETERS IN THEIR FIRST LACTATIONS

摘要

Thirty Holstein-Friesian animals were monitored for a period of 19 months from 13 months of age through until the end of their first lactations. Blood samples were taken as well as recording milk yield and measurements of reproductive performance. Variation in plasma concentrations of IGF-1 was seen throughout this period but each animal was ranked relatively consistently within the group throughout the transition from a non-lactating growing heifer to a lactating cow, but decreasing slightly with time. Plasma IGF-1 concentrations were correlated positively to reproductive performance and negatively to milk yield, although these relationships were not statistically significant. Measuring plasma IGF-1 at a young age could be a useful physiological indicator for dairy cows in a pasture-based production system and assist in management and breeding decisions.