| Erhualian (Er) and Large White (LW) pigs differ significantly in growth performance. Previous studies of our laboratory found that this phenotypic divergence is largely reflected in differences of expression patterns of growth axis genes. The fast-growing Large White pigs expressed significantly higher GH receptor in liver and muscle compared with the slow-growing Erhualian pigs. Small intestine is one of the most important organs responsible for digestion and absorption of nutrients required for growth and development, and is most likely one of the target organs for GH action. Therefore, Erhualian and Large White pigs were taken as animal models in the present experiment to study the developmental patterns of growth axis gene (GHR, IGF-1, IGF-1R) expression in duodenum with semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). Meanwhile the morphological changes of duodenum of two porcine breeds at different stages of postnatal growth were investigated by histological method. The relationship between duodenum morphological development and expression of investigated gene was also analyzed in order to reveal the role of somatotropic axis on intestinal growth and development. The results are shown as follows:1. The morphological changes of duodenum in Erhualian and Large White pigsHistological method was employed to compare the morphological changes of duodenum in Er and LW pigs at 0 (at birth, DO), 3, 20, 30(LW)/45(Er), 90 and 120 days of age. The result showed that villus height of Er pig increased significantly from D1 to D3 (P<0.05) when a peak of 147.49 m was reached. In LW pigs however, the peak villus height of 162.90 urn was achieved at D20. This result indicates that although Er pigs mature earlier in terms of the date of peak villus height, the peak value of villus height is significantly smaller than LW pigs. From D20 onwards, the LW pigs exhibited longer duodenal villus than Er pigs at the same age. The villus of duodenum became shorter with the age, while their width and the thickness of intestine wall increased progressively withmore and more developed plica in duodenum. These results demonstrated that the striking difference of growth rate between Er and LW pigs owes to, at least in part, the difference of intestinal development. The development of intestine tract is one of the important factors affecting animal growth.II. Development patterns of duodenal GHR mRNA expression in Erhualian and Large White pigsFrom birth to 120 days of age, the duodenal expression of GHR mRNA in Er pigs kept stable in general, with no obvious sex difference. In LW pigs however, the duodenal expression of GHR mRNA up-regulated significantly at D20 (PO.05) and maintained at relatively higher level thereafter. At birth and on D3, Er pigs expressed slightly higher duodenal GHR mRNA than LW pigs, while a turning point appeared at D20 when LW boars expressed significantly higher level of GHR mRNA in duodenum than Erhualian boars (P<0.05). From D20 onwards, LW pigs exhibited higher GHR mRNA expression in duodenum than Er pigs at the same age. The differences of duodenal expression of GHR mRNA were found to be in accordance with the differences of morphological changes, suggesting the role of GH on duodenum development via its locally expressed receptors.ill. Development patterns of duodenal IGF-1/IGF-1R mRNA expression in Large White and Erhualian pigsFrom birth to D120, no significant variation of IGF-1 mRNA expression was found in Erhualian pigs, although a tendency of step-wise increase was observed. The IGF-1 mRNA expression levels at D180 were slighter higher than that at D45, D90 and D120, and the latter were slightly higher than that at DO, D3 and D20, so as a result, the level at D180 was significantly higher (P<0.05) than neonatal stages at DO, D3 and D20 in both sexes of Er pigs. Compared with Er boars, LW boars expressed higher level of duodenal IGF-1 mRNA than Erhualian boars throughout the period of experiment, with the differences between breeds being significant at birth, D20, D...
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