Abstract: The purpose of this study was to evaluate the variation in gastrointestina1 structure and function of Hu lambs pre and post-early weaning lambs so as to provide theoretical basis for early breeding of lambs.22 male lambs with similar birth weight(3.81 kg士0.55 kg) were selected.Lambs were fed breast milk from 1 to 7 days old, separated from ewes at 8-day-old, and began to be fed milk replacer (MR) (at 2% of BW measured on day 8, three equal amounts) and starter feeds (ad libitum).MR feeding was stopped at 35 days of age.Six lambs were slaughtered at 8, 21 and 42 days of age, respectively, the weight of rumen, reticulum, omasum and abomasum, and the length and weight of duodenum, jejunum, ileum, cecum, colon and rectum were measured.The rumen and small intestine tissues were collected, sliced and stained with eosin and hematoxylin.The rumen nipple length, width, circular muscle thickness, villus height, width and recess depth of small intestine were detected, and the villus to recess ratio (villus height/recess depth) was calculated.The contents of rumen, duodenum and jejunum were collected to detect the activities of amylase, cellulase, lactase, trypsin and lipase and the concentrations of ammonia nitrogen (NH₃-N) and volatile fatty acids (VFA).The results showed that the weight of rumen, reticulum, omasum and the proportion of rumen to total stomach weight increased significantly with the increase of day age (P<0.05), and the proportion of abomasum weight to total stomach weight decreased with the increase of day age (P<0.05).The length and weight of duodenum, jejunum, ileum, cecum, colon and rectum increased with age (P<0.05), the ratio of duodenum and ileum at 42 days old was significantly higher than that at 8 and 21 days old (P<0.05), the height, width and thickness of rumen papilla increased significantly with age (P<0.05), the villus height, villus width and recess depth of duodenum and jejunum decreased with the increase of age.The activities of duodenal amylase, trypsin, lipase, jejunal amylase and trypsin increased significantly with age (P<0.05), The activity of amylase and the concentrations of acetic acid, propionic acid and butyric acid in rumen of 42-day-old lambs were significantly higher than those of 21 day old lambs (P<0.05).The above results showed that compared with before weaning (21-day-old), the rumen development of weaned lambs was enhanced, the tissue morphology of abomasum and small intestine became smaller, and the activities of main digestive enzymes in rumen and small intestine were enhanced.

Key words: lambs; early weaning; gastrointestinal development; enzyme activity; fermentation parameters