Effects of weaning on somatotrophic gene expression and circulating levelsof insulin-like growth factor-1 (IGF-1) and IGF-2 in pigs

The present study evaluated somatotrophic gene expression in liver, muscle and adipose tissue 4 d after weaning, a time point corresponding to greatly reduced serum concentrations of insulin-like growth factor (IGF)-1 and IGF -2 in pigs. Two-week-old barrows were either cross-fostered to a sow (SOW, n = 8) or weaned and fed a phase 1 diet containing either 0 or 7% spray-dri ed plasma (NP, n = 8 and SDP, n = 8; respectively). Piglets were allocated such that two size groups were equivalently represented in each experimenta l group (small, 3.5-4.3 kg and large, 4.6-5.7 kg). Animals were weighed dai ly and sacrificed 4 d after weaning for blood and tissue collection. Daily gains of the SOW piglets were significantly greater than those of the weane d pigs for the first 3 d of the experiment (P < 0.0001). Weight gains in th e SOW and SDP pigs between d 3 and 4 were equivalently elevated relative to the NP pigs (P < 0.0001). Serum IGF-1 and IGF-2 concentrations were decrea sed in both NP and SDP compared to SOW (P < 0.0001). Serum IGF-2 levels wer e significantly lower in small piglets (P = 0.006). A Weaning Group X Size interaction was noted for liver IGF-2 mRNA (P < 0.03), reflecting a higher level of expression in large SOW piglets relative to small SOW piglets. Wea ning did not affect IGF-1, IGF-2, or growth hormone (GH) receptor mRNA leve ls in liver, muscle, or far. (P > 0.05). Liver IGF-binding protein (IGFBP)- 3 and acid-labile subunit (ALS) mRNA levels also were unaffected by weaning . Small pigs had lower levels of liver ALS (P = 0.0003), muscle IGF-2 (P = 0.02), and muscle GH receptor (P = 0.006) mRNAs. In contrast, adipose tissu e IGF-1 and IGF-2 mRNA levels were greatest in the small piglets (P = 0.001 and 0.029, respectively). (C) 2000 Elsevier Science Inc. All rights reserv ed.