不同年龄段放牧牦牛生长发育及肌内脂肪沉积规律研究

Study on Growth and Development and Deposition Rule of Intramuscular Fat of Grazing Yaks at Different Ages

本试验旨在研究不同年龄段放牧牦牛生长发育、激素分泌、肌肉品质及肌内脂肪(IMF)沉积规律。于同一牧场内选取不同年龄段(0.5、1.5、2.5、3.5、4.5岁)健康麦洼公牦牛各6头,采集晨牧前颈静脉血液,统一屠宰采集牦牛背最长肌肌肉样本。结果显示:随着年龄的增长,牦牛体重显著增加(P<0.05)。血清尿素氮(UN)含量在2.5、3.5和4.5岁显著高于0.5岁(P<0.05),血清胆固醇(CHO)含量呈现类似趋势。4.5岁牦牛血清胰岛素(INS)水平显著高于0.5、1.5和2.5岁牦牛(P<0.05);2.5、3.5和4.5岁牦牛血清瘦素素(LEP)水平显著高于0.5岁牦牛(P<0.05);3.5和4.5岁牦牛血清胰高血糖素(GLN)和抵抗素(RETN)水平显著低于1.5岁牦牛(P<0.05);2.5、3.5和4.5岁牦牛血清胰岛素样生长因子-Ⅰ(IGF-Ⅰ)水平显著低于0.5和1.5岁牦牛(P<0.05)。牦牛肌肉剪切力随年龄的增长逐渐增大,0.5和1.5岁牦牛显著低于4.5岁牦牛(P<0.05)。牦牛肌肉IMF含量随着年龄的增长逐渐增加,4.5岁牦牛显著高于0.5、1.5和2.5岁牦牛(P<0.05)。肌肉脂肪合成代谢关键酶中,1.5、2.5、3.5和4.5岁牦牛乙酰辅酶A羧化酶(ACC)活性显著高于0.5岁牦牛(P <0.05),3.5和4.5岁牦牛甘油三酯合成酶-1(DGAT-1)活性显著高于0.5和1.5岁牦牛(P<0.05),4.5岁牦牛脂蛋白脂酶(LPL)显著高于0.5、1.5岁牦牛(P<0.05),脂肪酸合成酶(FAS)与硬脂酰辅酶A去饱和酶(SCD)活性在各年龄段牦牛之间无显著差异(P>0.05);在肌肉脂肪分解代谢关键酶中,随着牦牛年龄的增长,激素敏感脂肪酶(HSL)活性总体呈现降低趋势,1.5岁牦牛显著高于3.5岁牦牛(P<0.05),脂酰辅酶A氧化酶(ACOX)、肉碱脂酰转移酶-Ⅰ(CPT-Ⅰ)活性无显著变化(P>0.05)。综上所述,随着年龄的增长,牦牛在生长发育的同时机体通过能量代谢相关激素和脂肪代谢关键酶的调控,促进脂肪合成,抑制脂肪分解,从而沉积IMF,至3.5~4.5岁时达到IMF沉积旺盛期。

The purpose of this experiment was to study the growth and development,hormone secretion,muscle quality and intramuscular fat(IMF)deposition rule of grazing yaks at different ages.In the experiment,six healthy Maiwa male yaks at different ages(0.5,1.5,2.5,3.5 and 4.5 years old)were selected in the same pasture.Jugular vein blood was collected before morning grazing,and samples of longissimus dorsi muscle were collected after slaughter.The results showed that the body weight of yak increased significantly with age(P<0.05).Serum urea nitrogen(UN)content of yaks at 2.5,3.5 and 4.5 years old was significantly higher than that of yaks at 0.5 years old(P<0.05),and serum cholesterol(CHO)content showed a similar trend.Serum insulin(INS)level of yaks at 4.5 years old was significantly higher than that of yaks at 0.5,1.5 and2.5 years old(P<0.05);serum leptin(LEP)level of yaks at 2.5,3.5 and 4.5 years old was significantly higher than that of yaks at 0.5 years old(P<0.05);serum glucagon(GLN)and resistin(RETN)levels of yaks at 3.5 and 4.5 years old were significantly lower than those of yaks at 1.5 years old(P<0.05);serum insulin-like growth factor-Ⅰ(IGF-Ⅰ)level of yaks at 2.5,3.5 and 4.5 years old was significantly lower than that of yaks at 0.5 and 1.5 years old(P<0.05).The muscle shear force of yaks increased gradually with age,and yaks at 0.5 and 1.5 years old was significantly lower than yaks at 4.5 years old(P<0.05).The content of IMF increased gradually with age,and the IMF content of yaks at 4.5 years old was significantly higher than yaks at 0.5,1.5 and 2.5 years old(P<0.05).Among the key enzymes of muscle fat anabolism,the acetylCoA carboxylase(ACC)activity of yaks at 1.5,2.5,3.5 and 4.5 years old was significantly higher than yaks at 0.5 years old(P<0.05);the diacylglycerol-O-acyltransferases-1(DGAT-1)activity of yaks at 3.5 and 4.5years old was significantly higher than that of yaks at 0.5 and 1.5 years old(P<0.05);the lipoprotein lipase(LPL)activity of yaks at 4.5 years old was significantly higher than that of yaks at 0.5 and 1.5 years old(P<0.05);there were no significant differences in the activities of fatty acid synthetase(FAS)and stearoyl-CoA desaturase(SCD)among yaks at different ages(P>0.05).Among the key enzymes of muscle fat catabolism,the hormone-sensitive lipase(HSL)activity was decreased with age,and yaks at 1.5 years old was significantly higher than yaks at 3.5 years old(P<0.05),while there were no significant changes in the activities of acylCoA oxidase(ACOX)and carnitine palmitoyl transferase-Ⅰ(CPT-Ⅰ)(P>0.05).To sum up,along with the growth of yaks,the promoted fat synthesis and suppressed lipolysis,which consequently result in IMF deposition,may be through the regulation of energy metabolism-related hormones and key enzymes of lipid metabolism.The vigorous period of IMF deposition in yaks is at the age of 3.5 to 4.5 years old.