日粮RDP水平对生长期肉牛蛋白质补偿沉积的作用机制

生长期肉牛的补偿生长主要表现为蛋白质的补偿沉积。尽管补偿生长的优势已经被广泛用于肉牛的养殖生产，但是日粮蛋白质限饲后恢复对生长期肉牛蛋白质补偿沉积的作用机制尚不清楚。日粮中的蛋白质可分为瘤胃可降解蛋白（RDP）和瘤胃非可降解蛋白（RUP）。基于前期对Molly机理模型中瘤胃氮代谢和尿素氮循环的研究基础，本课题旨在研究日粮RDP水平对生长期肉牛在补偿生长阶段瘤胃微生物蛋白合成和骨骼肌蛋白质沉积的作用机制。试验拟通过维持RUP水平而调控日粮RDP来构建肉牛补偿生长的动物模型，利用消化代谢试验测定微生物蛋白合成量、尿液中尿素氮排泄量和体蛋白沉积量，结合高通量测序技术研究瘤胃微生物的菌群结构变化和肌肉组织中功能基因的差异表达，来阐明日粮RDP水平对生长期肉牛蛋白质补偿沉积的作用机制，为提高饲料蛋白质转化效率，改善牛肉品质提供理论依据和实证支持。

The compensatory growth of growing beef cattle is mainly represented by protein allometric accretion. Although the advantage of compensatory growth has been widely applied in the beef industry, the mechanisms regarding protein allometric accretion in growing beef cattle induced by dietary protein restriction and subsequent protein re-alimentation remain to be fully elucidated. Dietary protein can be divided into rumen-degradable protein (RDP) and rumen-undegradable protein (RUP). Based on our previous studies of Molly cow model on ruminal nitrogen metabolism and nitrogen recycling, we aim to investigate the mechanisms of dietary RDP concentration on microbial protein synthesis as well as protein accretion in skeletal muscle during a period of compensatory growth in growing beef. A protein allometric accretion phenomenon will be induced by manipulating dietary RDP restriction and succedent re-alimentation without changing RUP. We will conduct an animal trial to quantify synthesized microbial protein in the rumen, urinary urea excretion, and protein retention in the whole body. Meanwhile, we will use the high-throughput sequencing technology to study the composition of rumen microbiota and the differential expression of functional genes in longissimus dorsi muscle tissue. The results of this study will allow us to better understand mechanisms of protein accretion in growing beef cattle during a period of compensatory growth, which will provide important theoretical basis and empirical support to improve dietary protein conversion rate and meat quality for beef cattle.