断奶前补饲不同直/支链淀粉比开食料对羔羊瘤胃上皮发育的影响

Effects of different amylose to amylopectin ratios in starter feed on the development of ruminal epithelium in pre-weaned lambs

为了研究断奶前补饲不同直/支链淀粉比开食料对羔羊瘤胃上皮发育的影响,选取24只体况良好、胎次一致、体重相近的10日龄羔羊(湖羊),将其随机分为3组,在饲喂相同母乳的基础上,分别补饲以纯木薯(CS)、玉米(MS)和豌豆淀粉(PS)(直/支链淀粉比分别约为0.11,0.27和0.44)为唯一淀粉来源的开食料。试验期间,每天4:00-19:00将羔羊抱入补饲栏补饲不同直/支链淀粉比的开食料,并且在6:30,10:30和15:30将羔羊抱回母羊舍哺乳1h。羔羊自由饮水,单栏饲喂,自由采食燕麦干草。56日龄时屠宰采样,采集瘤胃组织样品制作石蜡切片进行瘤胃乳头形态测定,采集瘤胃上皮样品提取RNA测定相关基因表达。结果表明:CS组羔羊瘤胃乳头长度和表面积显著(P<0.001)高于MS和PS组,CS和MS组羔羊瘤胃乳头宽度显著(P=0.001)高于PS组。对瘤胃上皮各层厚度统计显示,CS和PS组羔羊瘤胃上皮角质层厚度显著(P=0.001)高于MS组;CS和MS组羔羊瘤胃上皮颗粒层厚度显著高于(P<0.001)PS组;CS组羔羊瘤胃上皮棘基层厚度和总厚度显著(P<0.001)高于MS和PS组。qRT-PCR结果显示:不同直/支链淀粉比开食料显著影响羔羊瘤胃上皮CDK2和CDK6的mRNA表达量(CS>MS>PS,P<0.001);CS组羔羊瘤胃上皮细胞cyclin A和CDK4的mRNA表达量显著(P<0.05)高于PS组,但与MS组无显著差异;CS组羔羊瘤胃上皮cyclin D1的mRNA表达量显著(P=0.012)低于PS组,但与MS组无显著差异。CS组羔羊瘤胃上皮类胰岛素生长因子-1(insulin like growth factor,IGF-1)的mRNA表达量显著(P<0.001)高于MS和PS组,CS和MS组羔羊瘤胃上皮IGF-1R的mRNA表达量显著(P=0.001)高于PS组。上述结果表明:较高支链淀粉比开食料与较高直链淀粉比开食料相比,在瘤胃中较易降解生成挥发性脂肪酸,促进瘤胃上皮IGF-1及细胞周期蛋白mRNA的表达,进而有利于断奶前羔羊瘤胃上皮的发育。研究结果对制订羔羊营养方案具有重要指导意义。

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 CDK 2 and CDK 6 （CS〉MS〉PS, P 〈0.001）; the transcript levels of cyclin A and CDK 4 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.