State Key Laboratory of Animal Nutrition, Beijing Engineering Technology Research Center of Raw Milk Quality and Safety Control, College of Animal Science and Technology, China Agricultural University, No.2 Yuanmingyuan West Road, Haidian, Beijing, 100193, People's Republic of China.
Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, SK, S7N 5A8, Canada.
BMC Genomics. 2018 Feb 17;19(1):148. doi: 10.1186/s12864-018-4529-9.
Improving the efficiency of animal production is a relentless pursuit of ruminant producers. Energy utilization and partition can be affected by dietary composition and nutrient availability. Furthermore, the liver is the central metabolic intersection in cattle. However, the specific metabolic changes in the liver under conditions of limit-feeding remain unclear and require further study. The present study aimed to elucidate the effects of a wide range of dietary forage:concentrate ratios (F:C) on energy utilization, and identify potential changes in molecular metabolism by analyzing hepatic transcriptional profiles. Twenty-four half-sib Holstein heifers were fed four F:C diets (20:80, 40:60, 60:40, and 80:20 on a dry matter basis), with similar intake levels of metabolizable energy (ME) and crude protein. Liver biopsy samples were obtained and RNA sequencing was conducted to identify the hepatic transcriptomic changes. Moreover, the ruminal fermentation profiles, growth characteristics, and levels of metabolites in the liver and plasma of the heifers were monitored.
The proportion of acetate showed a linear increase (P < 0.01) with increasing dietary forage levels, whereas the proportion of propionate showed a linear decline (P ≤ 0.01). Lower levels of average daily gain and feed efficiency (P < 0.01) were observed in heifers fed high levels of forage, with a significant linear response. Using the Short Time-series Expression Miner software package, the expression trends of significant differentially expressed genes (DEGs) were generally divided into 20 clusters, according to their dynamic expression patterns. Functional classification analysis showed that lipid metabolism (particularly cholesterol and steroid metabolism which were in line with the cholesterol content in the liver and plasma) was significantly increased with increasing dietary forage levels and slightly reduced by the 80% forage diet. Nine DEGs were enriched in the related pathways, namely HMGCS1, HMGCR, MSMO1, MVK, MVD, IDI1, FDPS, LSS, and DHCR7.
The ruminal fermentation and feed efficiency results suggest that different mechanisms of energy utilization might occur in heifers fed different F:C diets with similar levels of ME intake. Increased cholesterol synthesis from acetate might be responsible for the reduced efficiency of energy utilization in heifers fed high-forage diets.
提高动物生产效率是反刍动物生产者不懈的追求。能量的利用和分配会受到日粮组成和营养素供应的影响。此外，肝脏是牛的中央代谢交汇点。然而，限饲条件下肝脏的具体代谢变化尚不清楚，需要进一步研究。本研究旨在阐明广泛的饲粮粗饲料：精料比例（F:C）对能量利用的影响，并通过分析肝转录谱来确定潜在的分子代谢变化。24 头半同胞荷斯坦奶牛饲喂 4 种 F:C 日粮（干物质基础上分别为 20:80、40:60、60:40 和 80:20），具有相似的可代谢能（ME）和粗蛋白摄入量水平。采集肝活检样本并进行 RNA 测序以鉴定肝转录组变化。此外，监测了奶牛的瘤胃发酵谱、生长特性以及肝和血浆中代谢物的水平。
随着饲粮粗饲料水平的增加，乙酸的比例呈线性增加（P < 0.01），丙酸的比例呈线性下降（P ≤ 0.01）。饲喂高粗饲料水平的奶牛平均日增重和饲料效率较低（P < 0.01），具有显著的线性反应。使用 Short Time-series Expression Miner 软件包，根据其动态表达模式，将显著差异表达基因（DEG）的表达趋势大致分为 20 个簇。功能分类分析表明，脂代谢（特别是胆固醇和类固醇代谢，与肝和血浆中的胆固醇含量一致）随着饲粮粗饲料水平的增加而显著增加，而 80%粗饲料日粮则略有减少。9 个 DEG 在相关途径中富集，即 HMGCS1、HMGCR、MSMO1、MVK、MVD、IDI1、FDPS、LSS 和 DHCR7。
瘤胃发酵和饲料效率结果表明，在 ME 摄入量相似的情况下，饲喂不同 F:C 日粮的奶牛可能通过不同的能量利用机制发挥作用。饲喂高粗饲料日粮的奶牛中，乙酸合成胆固醇的增加可能是能量利用效率降低的原因。
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