Serum concentrations of insulin-like growth factors and thyroid hormones in healthy and ketotic dairy cows during the puerperium

The purpose of this investigation was to compare peripheral circulating con centrations of the insulin-like growth factors (IGF) and thyroid hormones ( T3 and T4) during the periparturient period in dairy cows in different situ ations, in Study 1 from an average of about 4 days prepartum to 4 days post partum the decreases in serum T3, T4 and IGF-I were more marked in a group of cows (n = 24) with mean body condition score (BCS) 4.2 than in a group ( n = 24) with mean BCS 3.2. Serum IGF-II increased, thereby maintaining a re latively constant molar sum for the two growth factors. In a second study d aily samples taken in March from twelve healthy cows over the same interval showed similar alterations with a statistically significant minimum for se rum IGF-II on the day of calving. Opposite time-related trends were observe d for T3, T4 and IGF-I in this group in comparison with a later group of he althy cows (n = 12) which received an equivalent diet containing fresh gree n lucerne instead of ensiled lucerne hay. Levels postpartum of all four hor mones were low in cows (n = 12) exhibiting ketonuria, While the closest cor relations were found between serum T3 and T4 levels, there were significant independent relationships between the levels of one or other thyroid hormo ne and serum IGF-I concentration. The characteristic interrelationships bet ween the four hormones were maintained in both studies indicating that mech anisms controlling their synthesis and degradation are interdependent and p reserved under some conditions of nutritional excess and deficiency.