ENDOCRINE RESPONSES TO WEANING AND CHANGES IN POST-WEANING DIET IN THE YOUNG-PIG

The effects of weaning and changing post-weaning diet composition on g rowth patterns and growth-related hormonal profiles were evaluated in neonatal pigs. Forty-eight crossbred piglets were assigned to two grou ps (n = 24/group) based on weaning at 2 or 3 wk of age (2W and 3W grou ps, respectively). At weaning, piglets were removed from the sow and p laced on a commercial starter ration for the first 11 d post-weaning ( Phase I diet), At Day 12 post-weaning, pigs were placed on a growing r ation for the remainder of the study (Phase II diet). Body weights and blood samples were collected twice weekly from birth until 42 d of ag e. Serum insulin-like growth factor (IGF)-1 IGF-2, and average daily g ain (ADG) were reduced (P < 0.05) in both groups asa result of weaning , whereas serum growth hormone (GH) was elevated (P < 0.05). Earlier w eaning resulted in a greater reduction in growth rate and serum IGF-2 values (P < 0.05). Mild reductions in ADG occurred after the Phase I t o II dietary change in both weaning groups (P < 0.05), but serum IGF-1 decreased only in the 2W group (P < 0.05). Growth hormone concentrati ons tended to increase after the change in post-weaning diets (P = 0.0 7 and 0.16 in 2W and 3W, respectively). Serum thyroxine (T-4) and trii odothyronine (T-3) levels were unaltered by weaning but declined in bo th groups after the change in starter diets (P < 0.05). Changes in cor tisol concentrations were not associated with weaning or the change in post-weaning diets. With the exception of serum IGF-I concentrations, which were elevated in the 2W group, growth and endocrine endpoints w ere equivalent between experimental groups at the end of the study (42 d of age). These results indicate that earlier weaning and changing s olid diets can more severely affect patterns of early growth and relat ed hormone secretion, but effective compensatory mechanisms restore no rmal physiological and physical development. (C) Elsevier Science Inc. 1998.