PREPRANDIAL AND POSTPRANDIAL CONCENTRATIONS OF SOME METABOLIC HORMONES AND PERFORMANCE IN WEANED PIGLETS FED DIFFERENT DIETS

Serum concentrations of insulin, cortisol, insulin-like growth factor-1 (IGF-1), thyroxine (T4) and triiodothyronine (T3) were determined before and after feeding weaned piglets fed different diets in two experiments carried out in the winter and summer. In experiment 1 the standard diet (CP - 20.2%) was replaced with an isocaloric ration containing slightly less crude protein (17.5%; diet 2). Diet 3 (CP - 19.6%) was isonitrogenous with diet 1 but more concentrated. Except for very low preprandial insulin concentrations in most piglets, serum hormone concentrations were within the ranges given by other authors. The slightly better performance of the piglets fed diet 3 was significantly correlated with increased concentrations of T3 and T4. IGF-1 was lower in the piglets fed less protein. Postprandial insulin concentrations were negatively correlated with postprandial cortisol concentrations probably due to differences in the reaction of individual piglets to the overnight fast. In experiment 2 the fishmeal supplement in the standard diet was replaced by yeast meal. Although the piglets fed the experimental ration performed better, the very low concentrations of thyroid hormones indicated an inadvertent iodine deficiency. Cortisol and insulin concentrations were similar to those found in experiment 1 but IGF-1 values were lower. It was concluded that the diet and season probably combined to allow a lower basal metabolic rate in the piglets in experiment 2 especially those fed diet 2 They were therefore more resistant to the overnight fast, ate more slowly but grew faster than the piglets in experiment 1 because fewer nutrients were used for maintenance requirements.