Ontogenesis of peptide transport and morphological changes in the ovine gastrointestinal tract
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The purpose of this study was to examine developmental and dietary regulation of the potential for peptide transport via PepT1 and morphological changes in the gastrointestinal tract of lambs. A 2 x 4 factorial arrangement of treatments with four blocks was created based upon gender, birth type (single or twin), birth weight, birth date, and breeding with 32 cross-bred lambs. Lambs were randomly allotted at birth to receive or not to receive a creep diet and all lambs were allowed to nurse. Sampling times of 2, 4, 6, or 8 weeks were randomly allotted to lambs. Samples for RNA extraction and histological evaluation were taken from the dorsal rumen, ventral rumen, omasum, duodenum, jejunum, and ileum. The DMI was similar for ewes nursing lambs that had or did not have access to creep feed (2,630 and 2,574 g h-1 per day, respectively). Lambs with access to creep feed consumed DM at the rate of 2, 22, 129, 219, and 227 g h-1 per day, respectively when they were approximately 12, 13, 20, 38, and 52 days of age. Cumulative weight gain was similar for both groups of lambs and increased linearly (P < 0.001) with age. Villi were about 7% shorter (P < 0.09) in lambs receiving creep feed. Papillary height and width increased linearly (P < 0.01) with age. In the stomach, total and keratinized epithelial cells decreased (P < 0.03 and <0.01, respectively) with age and were fewer (P < 0.01) in lambs receiving creep feed. Even with the modest intakes observed in this study, creep feeding appeared to slightly alter the mucosal structure of the small intestine and was advantageous in that it stimulated papillae growth, thus predisposing the rumen for the introduction of feed into the diet. A 2.8 kb oPepT1 mRNA was present in all tissues studied by 2 weeks and age did not significantly influence the abundance of oPepT1 mRNA in the small intestine or stomach. Abundance of oPepT1 mRNA was greatest in the jejunum (P < 0.01) of the small intestine and in the dorsal rumen (P < 0.01) of the stomach. Lambs not receiving the creep diet had a greater (P < 0.02) abundance of oPepT1 mRNA in the rumen, particularly the dorsal rumen. Because no dry feed and little or no milk entered the rumen when no creep was fed, it is possible that a stimulus for development from the non-luminal direction, possibly blood-borne, may be involved in the ontogenesis of oPepT1. That PepT1 mRNA was present indicates that peptide transport occurs in the young lamb and the rumen and omasum appear to be involved in this process. 2003 Elsevier Science B.V. All rights reserved.
