Transcriptome analysis reveals the molecular regulatory network of dietary supplementation with succinate on muscle fiber characteristics and meat quality in Tan sheep. Transcriptome analysis reveals the molecular regulatory network of dietary supplementation with succinate on muscle fiber characteristics and meat quality in Tan sheep

To investigate the impact of adding succinate to the diet on the production performance, meat quality, muscle fiber characteristics, and transcriptome of the longissimus dorsi muscle in Tan sheep, 36 Tan sheep were selected and fed with different levels of succinate (0%, 0.5%, 1.0%, 2.0%) for a 60-day trial period. Overall, compared to the control group, the addition of succinate to the diet improved the production performance, slaughter performance, and meat quality of Tan sheep. It significantly increased dry matter intake, carcass weight, eye muscle area, and the GR value while significantly reducing the shear force and cooking loss of the longissimus dorsi muscle (p<0.05). Furthermore, the addition of succinate to the diet altered the muscle fiber characteristics of the longissimus dorsi muscle in Tan sheep, significantly increasing the fiber diameter and cross-sectional area of type I and type IIa muscle fibers (p<0.05). The addition of 1.0% succinate to the diet altered the transcriptome of the longissimus dorsi muscle in Tan sheep, with 741 differentially expressed genes identified compared to the control group. These differentially expressed genes were involved in various pathways related to lipid metabolism, energy metabolism, and muscle development, such as insulin secretion, insulin resistance, cAMP signaling pathway, PI3K-Akt signaling pathway, and FoxO signaling, among others. In summary, succinate plays a crucial role in regulating energy metabolism, protein deposition, and glucose and lipid metabolism homeostasis in Tan sheep through insulin signaling pathways and the interaction of muscle cell factors. By modulating the expression of relevant genes, succinate improves the muscle fiber characteristics of Tan sheep, thereby enhancing production performance and meat quality. Overall design: Thirty-six 5-month-old Tan sheep with similar health statuses and weights were selected and randomly divided into four groups, with 9 sheep in each group, and reared in individual pens (4 m × 4 m). The four groups were as follows: control group (basal diet), SUC1 group (basal diet + 0.5% succinate), SUC2 group (basal diet + 1% succinate) and SUC3 group (basal diet + 2% succinate). The diets of each group were formulated according to the "Nutritional Requirements of Sheep" (Ministry of Agriculture of China, 2021) and the actual production of Tan sheep. The pretrial period was 10 days and the formal trial period was 60 days. During the experiment, all experimental sheep had free access to water and were fed twice a day (at 06:30 and 17:30).

为探究日粮中添加琥珀酸（succinate）对滩羊生产性能、肉品质、肌纤维特性及背最长肌（longissimus dorsi muscle）转录组（transcriptome）的影响，本试验选取36只滩羊，饲喂不同梯度琥珀酸添加量（0%、0.5%、1.0%、2.0%）的日粮，试验周期为60天。
总体而言，与对照组相比，日粮添加琥珀酸可改善滩羊的生产性能、屠宰性能及肉品质：显著提高干物质采食量（dry matter intake）、胴体重（carcass weight）、眼肌面积（eye muscle area）及GR值（p<0.05），同时显著降低背最长肌的剪切力（shear force）与蒸煮损失（cooking loss）（p<0.05）。
进一步研究发现，日粮添加琥珀酸可改变滩羊背最长肌的肌纤维特性，显著增加I型与IIa型肌纤维的直径及横截面积（p<0.05）。当日粮添加1.0%琥珀酸时，可改变滩羊背最长肌的转录组，与对照组相比共鉴定出741个差异表达基因（differentially expressed genes）。这些差异表达基因富集于脂代谢、能量代谢及肌肉发育相关的多条通路，包括胰岛素分泌、胰岛素抵抗、cAMP信号通路（cAMP signaling pathway）、PI3K-Akt信号通路（PI3K-Akt signaling pathway）及FoxO信号通路（FoxO signaling pathway）等。
综上，琥珀酸可通过胰岛素信号通路及肌细胞因子互作，调控滩羊的能量代谢、蛋白质沉积及糖脂代谢稳态；通过调控相关基因的表达，改善滩羊肌纤维特性，进而提升其生产性能与肉品质。
试验设计：选取36只健康状况良好、体重相近的5月龄滩羊，随机分为4组，每组9只，单栏饲养（individual pens）（4 m × 4 m）。四组分别为：对照组（基础日粮）、SUC1组（基础日粮+0.5%琥珀酸）、SUC2组（基础日粮+1.0%琥珀酸）、SUC3组（基础日粮+2.0%琥珀酸）。各组日粮均参照《羊营养需要量》（中华人民共和国农业农村部，2021）及滩羊实际生产情况配制。预试期（pretrial period）为10天，正式试验期（formal trial period）为60天。试验期间，所有试验羊可自由饮水，每日饲喂2次（分别于06:30与17:30进行）。