Animal Nutrition & Physiology Team, AgResearch Limited, Palmerston North, New Zealand.
School of Veterinary Sciences, Massey University, Palmerston North, New Zealand.
J Anim Sci. 2019 Jul 30;97(8):3498-3510. doi: 10.1093/jas/skz148.
This study examined the impact of weaning age (4 vs. 6 wk) on rumen morphological and metabolic development in artificially reared lambs. Thirty-two mixed-sex lambs (2 to 5 d old) were randomly allocated to 1 of 2 weaning groups: early weaning (EW; 4 wk) and control (Ctrl; 6 wk). Lambs were individually penned and fed milk replacer (MR; 24% CP and 25% fat, DM basis) at 20% of their corresponding initial BW. Weaning was achieved by gradual reduction of MR allowance over a period of 3 wk using a step-down procedure. Concentrate and meadow hay were offered ad libitum from 1 d of the study until 6 wk, when lambs were transferred to a mixed sward pasture. At week 4, individual DMI were recorded and blood samples collected to measure β-hydroxybutyrate (BHBA) and NEFA. Eight animals per group were euthanized at week 4 and 16 to evaluate short chain fatty acids (SCFA) and histomorphometry of the rumen walls: dorsal (DS), ventral (VS), dorsal blind (DBS), and ventral blind (VBS) sacs. Linear mixed models were used to analyze the effect of weaning treatments at week 4 and 16, and to compare between timepoints and between rumen sites. Dry matter intake and rumen SCFA profiles were similar between groups (P > 0.10) at week 4 and 16. Plasma concentrations of BHBA were greater (P = 0.03) in EW than in Ctrl lambs, while NEFA did not differ (P > 0.10) between groups at week 4. No effect of weaning age on rumen empty weight, and papillae density, length, width, surface area ratio, and muscle layer thickness at any of the 4 rumen sites was found (P > 0.10) at either week 4 or week 16, except for greater (P = 0.02) papillae epithelium thickness in the DBS at week 4 in EW than Ctrl lambs. Papillae morphology and muscular thickness differed across rumen sites at week 4 and week 16 (P < 0.05), except for papillae density and surface area ratio at 4 week (P > 0.10). Rumen papillae length, width, and muscle layer thickness increased while papillae density and surface area ratio decreased (P < 0.05) between 4 and 16 wk. The results of this study indicate that morphological and physiological development of the rumen can be accelerated to support weaning of artificially reared lambs at 4 wk, using a step-down weaning system. Morphological differences between rumen sacs denote that future studies in lambs evaluating the impact of different diets should involve representative sampling across the rumen rather than a single site to more accurately study rumen development and ontogenic changes.
本研究旨在探讨断奶日龄（4 周对比 6 周）对人工饲养羔羊瘤胃形态和代谢发育的影响。将 32 只雌雄混合的羔羊（2-5 日龄）随机分配到 2 个断奶组中的 1 个：早期断奶（EW；4 周）和对照组（Ctrl；6 周）。羔羊单独围栏饲养，以 20%的初始体重（BW）接受代乳粉（MR；24%CP 和 25%脂肪，DM 基础）。通过逐步减少 MR 供应，在 3 周内断奶。从研究的第 1 天开始，自由采食浓缩饲料和草地干草，持续到 6 周，此时羔羊被转移到混合草地牧场。在第 4 周，记录个体干物质采食量（DMI），并采集血液样本以测量 β-羟丁酸（BHBA）和非酯化脂肪酸（NEFA）。每组 8 只动物在第 4 周和第 16 周被安乐死，以评估瘤胃壁的短链脂肪酸（SCFA）和组织形态学：背侧（DS）、腹侧（VS）、背侧盲囊（DBS）和腹侧盲囊（VBS）。线性混合模型用于分析断奶处理在第 4 周和第 16 周的影响，并比较时间点和瘤胃部位之间的差异。第 4 周和第 16 周时，干物质采食量和瘤胃 SCFA 谱在组间无差异（P>0.10）。与对照组相比，早期断奶组羔羊的 BHBA 血浆浓度更高（P=0.03），而第 4 周时 NEFA 无差异（P>0.10）。在第 4 周和第 16 周，除了在第 4 周时 EW 组的 DBS 中的乳头上皮厚度更大（P=0.02）外，断奶日龄对任何 4 个瘤胃部位的瘤胃空重、乳头密度、长度、宽度、表面积比和肌层厚度均无影响（P>0.10）。在第 4 周和第 16 周，乳头形态和肌层厚度在不同瘤胃部位存在差异（P<0.05），但在第 4 周时乳头密度和表面积比无差异（P>0.10）。在第 4 周到第 16 周之间，乳头长度、宽度和肌层厚度增加，而乳头密度和表面积比降低（P<0.05）。本研究结果表明，通过逐步断奶系统，人工饲养羔羊的瘤胃形态和生理发育可以加速，在 4 周时断奶。瘤胃囊之间的形态差异表明，未来在羔羊中评估不同饮食影响的研究应涉及整个瘤胃的代表性采样，而不是单个部位，以更准确地研究瘤胃发育和发育变化。
