Abstract: The aim of this study was to investigate the effect of early mashed and pelleted concentrate starter supplementation on animal performance and development of the gastrointestinal tract in pre-weaned lambs. The findings may provide a basis for the use of pellets in ruminant husbandry. In the present study, 18 newborn Hu lambs with similar birth weights were selected and separated from the ewes at 12 days of age and fed with goat milk powder (goat milk powder:water=1:10). After a three-day acclimation period, they were randomly divided into a control group (n=9, Con) and a treatment group (n=9, TG). The Con lambs received mashed concentrate ad libitum while the TG lambs received pelleted concentrate ad libitum. The two groups of lambs were given the same daily ration of milk powder (600 mL·d^-1). All lambs had free access to clean drinking water throughout the experimental period. During the experimental period, the feed intake of the lambs was recorded daily, and the lambs were weighed weekly to determine their weight gain. At the end of the feeding trial (42 days), all lambs were slaughtered, skinned and each part of the gastrointestinal tract was weighed. Tissue samples from various parts of the gastrointestinal tract were collected and sections were taken for epithelial morphometry. The results obtained revealed that pellet supplementation significantly (P=0.047) increased average daily feed intake of lambs at the age of 6 weeks compared to the control group. Pellet supplementation also significantly increased the average daily gain of lambs aged 4 weeks (P=0.030) and 5 weeks (P=0.019). Pellet supplementation significantly increased body weight of lambs aged 4 weeks (P=0.048), 5 weeks (P<0.001), and 6 weeks (P<0.001). There was no significant (P>0.05) difference between the two groups of lambs in the weight or length of the gastrointestinal tract. However, the length (P<0.001) and width (P<0.001) of the rumen papillae, and absorptive area of ruminal epithelium (P=0.038) were significantly increased by pellet supplementation. The gastrointestinal epithelial structure was observed using hematoxylin eosin staining and it was found that, compared with mashed concentrate, pellet supplementation significantly increased the thickness of the stratum granulosum of the rumen epithelium (P=0.027). The treatment group was observed to have significantly higher duodenal villus height (P<0.001) and ratio of villus height to crypt depth (P<0.001) but had a significantly lower duodenal crypt depth (P=0.010) compared to the control group. The pellet supplementation also significantly reduced jejunal crypt depth (P=0.010) and increased the ratio of jejunal villus height to crypt depth (P=0.087), but did not affect the jejunum villus height (P=0.258). The pellet supplementation significantly increased ileal villus height (P<0.001) and ratio of villus height to crypt depth (P=0.002), but the ileal crypt depths of lambs in both groups were similar (P=0.761). There was no significant difference in the thickness of the cecal epithelium (P=0.266) and colonic epithelium (P=0.526) between the two groups of lambs. These results show that pellet supplementation significantly promoted the development of the rumen epithelium and intestinal epithelium of the lambs, but did not affect the development of the hindgut epithelium.

Key words: pellets, performance, gastrointestinal development, lamb