Shorter Grazing Time and Supplementation Are Beneficial for Gastrointestinal Tract Development and Carcass Traits of Growing Lambs

SIMPLE SUMMARY: A shorter grazing time and supplementation have been demonstrated to increase the grazing efficiency and growth performance of lambs. However, the effects of a shorter grazing time on the gastrointestinal development and carcass quality of growing lambs are poorly understood. In the present study, lambs were offered 2, 4, 8 or 12 h of grazing and separately fed supplementation when off pasture. The results showed that, in comparison to longer grazing times, shorter grazing times—especially 4 h of grazing per day with supplementation—best improved gastrointestinal tract and carcass quality. Therefore, restricting the grazing of lambs to 4 h per day instead of grazing for more extended periods is a better grazing management approach in Inner Mongolia. ABSTRACT: The effects of restricted grazing durations on the gastrointestinal development and carcass quality of growing lambs are poorly understood. In this study, 32 lambs were randomly assigned to four groups (n = 8, body weight = 21.86 kg) corresponding to 2, 4, 8 and 12 h of grazing per day. When off-pasture, all lambs were housed and fed concentrate and hay. When the grazing time decreased from 12 h to 2 h, the abomasum weight and large intestine length decreased (p = 0.019; p = 0.069). Compared to lambs grazed for 12 h, animals grazed for 2–4 h had a greater villus height and villus-to-crypt ratio in the duodenum, jejunum and ileum segments (p < 0.05); the 2 h lambs had superior carcass quality and a smaller diameter and area of the gluteus medium muscle fibers (p < 0.05), with no significant change after 4 h of grazing. The results indicated that shorter grazing times and supplementation were beneficial for the gastrointestinal tract development and carcass quality of growing lambs. Therefore, a better grazing management approach in Inner Mongolia could be to restrict the grazing of lambs to 4 h per day instead of grazing for more extended periods.