Increased IGF-1 serum levels and discordant protein and mRNA IGF-1 receptor expression in the small intestine of formula-fed piglets

The present investigation addresses the question whether feeding piglets on formulated milk alters the insulin-like growth factor-1 (IGF-1) system differently in normal versus low birth weight piglets. In this study, both types of piglets were either sow-fed until 28 days of age or until 3 days of age and subsequently formula-fed until day 28. Formula-fed piglets had higher serum IGF-1 levels compared to suckled piglets, whereas low birth weight piglets had lower IGF-1 levels in comparison with normal birth weight piglets. In contrast, the mRNA expression of IGF-1 receptor (IGF-1R) showed lower expression in formula-fed piglets versus suckled piglets. However, the opposite effect was observed for IGF-1R protein abundance. Moreover, birth weight did not markedly affect IGF-1R mRNA or protein abundance. In conclusion, formula-fed piglets have higher IGF-1 serum levels and altered gene and protein expression of IGF-1R in the small intestine, irrespective of their birth weight.