Abstract: The objective of this study was to investigate the effects of different amylose to amylopectin ratio in starter feed on the development of the ruminal epithelium in pre-weaned lambs. Twenty-four 10-day-old lambs were divided into three groups, and were fed on iso-starch diets containing cassava starch (CS, n=8), maize starch (MS, n=8), and pea starch (PS, n=8). The lambs were separated from their mothers from 4:00-19:00 every day and placed in individual pens. The lambs received starter feed with different amylose-to-amylopectin ratios (CS, MS, and PS) ad libitum. Lambs were fed with their mothers’ milk for 1 h at fixed times (6:30, 10:30, and 15:30) during this period. All lambs received oat hay and water ad libitum. The lambs were slaughtered at 56 days old. Part of the ruminal tissue sample was used for morphological observations. Another part of the ruminal tissue sample was used to extract RNA to quantify the mRNA levels of various genes. Compared with the MS and PS diets, the CS diet significantly (P<0.001) increased the length and surface of rumen papillae in lambs. The rumen papillae of lambs were significantly wider (P=0.001) in CS and MS group than in the PS group. The thickness of different strata of the rumen epithelium in lambs was measured. The stratum corneum was significantly thicker in the CS and PS groups (P<0.001) than in the MS group. The stratum granulosum was significantly thicker in the CS and MS groups (P<0.001) than in the PS group. The total strata, stratum spinosum, and basale of the rumen epithelium were significantly thicker in the CS group (P<0.001) than in the MS and PS groups. The qRT-PCR results showed that different amylose to amylopectin ratios in the starter feed significantly affected the transcript levels of CDK2 and CDK6 (CS>MS>PS, P<0.001); the transcript levels of cyclin A and CDK4 were significantly higher in the CS group (P<0.05) than in the PS group. The transcript level of cyclin D1 was significantly lower in the CS group (P=0.012) than in the PS group. The transcript level of IGF-1 was significantly higher in the CS group (P<0.001) than in the MS and PS groups. The transcript levels of IGF-1R were significantly higher in the CS and MS groups (P=0.001) than in the PS group. These results indicated that a high amylopectin ratio in starch in starter feed promoted ruminal epithelial growth, which was associated with up-regulated expressions of IGF-1 and cell cycle protein in pre-weaned lambs. The results of this study have important significance for formulating appropriate nutritional strategies for lambs.

Key words: starch, ruminal epithelia, cell proliferation, insulin-like growth factor-1, lamb