Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2000
Publication Date: N/A
Interpretive Summary: Neonatal growth in the pig is positively related with growth and efficiency beyond weaning as the pig matures toward market weight. Weaning causes a well-documented growth lag that has long-lasting detrimental effects on growth performance. A better understanding of the effects of piglet weaning on growth-regulating factors is needed to develop improved strategies for maintaining early postweaning performance. The present study examined the status of hormonal regulation of growth 4 d after weaning in piglets divided into large and small size groups. Serum levels of growth-promoting hormones (Insulin-like growth factors; IGFs) were severely suppressed by weaning. Interestingly, no evidence was found for concurrent changes in IGF production within important hormone source tissues. Novel differences were observed, however, between small and large piglets with regard to the production of components of the growth-regulating endocrine system. Specifically, higher levels of growth-regulating factors in muscle tissues were observed which are consistent with greater lean growth characteristics. The results of this study increase our understanding of biological responses to piglet weaning and reveal size-related differences in growth-related endocrine function that may reflect long-term growth potential. The information is primarily of interest to the scientific community performing research on growth regulation.
Technical Abstract: The present study evaluated somatotrophic gene expression in liver, muscle and adipose tissue four days 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-dried plasma (NP, n = 8 and SDP, n =8; respectively). Piglets were allocated such that two size groups were equivalently represented in each experimental group (small, 3.5-4.3 kg and large, 4.6-5.7 kg). Animals were weighed daily and sacrificed 4 days after weaning for blood and tissue collection. Daily gains of the SOW piglets were significantly greater than those of the weaned pigs for the first 3 days of the experiment (P < .0001). Weight gains in the SOW and SDP pigs between d 3 and 4 were equivalently elevated relative to the NP pigs (P < .0001). Serum IGF-1 and dIGF-2 concentrations were decreased in both NP and SDP compared to SOW (P < .0001). Serum IGF-2 levels were significantly lower in small piglets (P = .006). A Weaning Group X Size interaction was noted for liver IGF-2 mRNA (P < .03), reflecting a higher level of expression in large SOW piglets relative to small SOW piglets. Weaning did not affect IGF-1, IGF-2, or growth hormone (GH) receptor mRNA levels in liver, muscle or fat (P > .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 = .0003), muscle IGF-2 (P = .02) and muscle GH receptor (P = .006) mRNAs. In contrast, adipose tissue IGF-1 and IGF-2 mRNA levels were greatest in the small piglets (P = .001 and .029, respectively).