Diet-dependent and diet-independent metabolic responses underlie growth stasis of pigs at weaning.

The weaning transition in domestic animals involves profound environmental and nutritional changes. Growth stasis is commonly observed in pigs during this period, resulting in significant losses to the swine industry. It has been suggested that the reduced growth rate reflects immune sensitivity to soy antigens in commercial diets; however, few studies have defined metabolic responses in pigs weaned to diets containing soybean meal. The impact of environmental and social changes at weaning on physiological functions, i.e., the metabolic adjustment to new nutritional substrates, has also been overlooked. Accordingly, the aim of this study was to distinguish diet-dependent and diet-independent metabolic responses in pigs weaned to a commercially available corn-soy diet. Focus was on the endocrine pancreas and cytokines associated with stress responses. Three-week-old crossbred pigs were weaned to a corn-soy (cereal) or a milk-based (milk) diet. Blood samples taken 0 (weaning), 1, 2, 5 and 7 d post-weaning demonstrated diet-independent responses including increased (P < 0.05) plasma glucagon concentrations, decreased (P < 0.05) glucose concentrations, increased (P < 0.05) interleukin-1 (IL-1) concentrations during the first 2 d post-weaning, and increased (P < 0.05) fibrinogen concentrations during the latter part of the study. In response to dietary treatment, milk-fed pigs had higher (P < 0.05) plasma insulin and glucose concentrations, reflective of higher food intake during the early post-weaning period. This clear distinction between diet-dependent and diet-independent metabolic responses at weaning suggests consideration of novel strategies to overcome the characteristic weanling growth stasis in pigs.