| Yak is mainly distributed in the Qinghai-Tibetan Plateau, where the cold season last seven months every year, and the yaks chronically suffer from hungry. This is the primary cause responsible for yak off-weight and death. The experiments were conducted to study the effect on body weight, body size and body composition, to study the effect on biochemical indices, enzymes and hormones, to study the pathway of starvation in regulating protein synthesis of yaks skeletal muscle, to study the effect on underlying mechanisms regulating protein metabolism, and to provide experimental data for yak nutrition research and disaster resistance and livestock protection in cold season.We carried out our experiments including three parts. In part one, the tested 8 ale yaks, weighed 110.3 ± 5.85 kg, were divided into two experiment groups. Once attained to test site, yaks in the control group were slaughtered, while yaks in the treatment group were deprived of feed (without to water) for 8 d. The body weight and body size of the yaks tested forth daily throughout the experiment. Body composition was tested, skeletal muscle and liver sample were collected for the anises of nutrition contents. The blood serum sample of the yaks tested twice daily throughout the experiment at 8:00 in the morning, centrifuged and stored at -20 ℃。 Our results showed as following:(1) There were significant effect on body weight, heart girth, carcass weight, gastrointestinal tract were observed (P<0.05). The absolutely weight of heart, liver, spleen, kidneys were significantly decreased with deprived time increased (P<0.05), while the relatively weight of them were not affected by deprivation (P>0.05). The significantly decreased of the protein content of tenderloin, outside flat, shank, thick flank and liver were observed (P<0.05). While the content of essential amino acids and total amino acids of liver were significantly increased, and significantly decreased in tenderloin by deprivation (P<0.05).(2) The significant effect on biochemical indexes was observed. The concentration of blood glucose, albumin and triglyceride dropped significantly after derived of food for 8 days (P<0.05). And the concentration of blood urea nitrogen, purine trione, creatinine, globulin, cholestenone raised significantly after deprived of food for 8 day (P<0.05).(3) At the same time, the activity of glutamic oxalacetic transaminase and. glutamic-pyruvic transaminase were significantly decreased with starvation time increased in blood (P<0.05). The concentration of insulin were significantly decreased (P<0.05), but it raised up to initial value following the prolonging of the starvation. The concentration of glucagon and glucocorticoid increased in 2d and 4d (P<0.05), decreased in 6d and maintained this level (P<0.05).(4) The activity of glutamic oxalacetic transaminase and glutamic-pyruvic transaminase in liver, the concentration of insulin and insulin-like growth factor in liver were significantly decreased by starvation (P<0.05). However, the concentration of glucocorticoid in liver was significantly increased by starvation, while the concentration of glucagon in liver increased, but it was not significant compared with the control groups.(5) The activity of glutamic oxalacetic transaminase and the concentration of insulin in tenderloin were significantly decreased by starvation (P<0.05). The concentration of insulin-like growth factor and glucocorticoid in tenderloin increased by starvation (P< 0.05). The concentration of glucagon in tenderloin was the same with that in liver. The activity of glutamic oxalacetic transaminase and glutamic-pyruvic transaminase in eyeround and the concentration of insulin-like growth factor, glucagon and glucocorticoid increased by 8 d starvation, and the concentration of insulin-like growth factor was significant compared with the control groups (P<0.05), but the concentration of insulin in eyeround decreased by 8 d starvation (P<0.05).(6) The starvation affected on the mRNA expression of the skeletal muscle of tenderloin and eyeround about protein synthesis and decomposition. The result suggested that indexes such as the mRNA expression of Myf5, MyoD1 and MSTN had difference compared with control group (P<0.05). The mRNA expression of genes about protein synthesis in tenderloin was significantly decreased (P<0.05), and the mRNA expression of genes about protein degradation in tenderloin were significantly increased compared with control group (P<0.05). The mRNA expression genes of both protein synthesis and degradation in eyeround were significantly increased compared with control group (P<0.05).It can be concluded that yaks survived under starvation, through nutrition control by themselves to affect the yak serum metabolites, hormone secretion such as INS, GN, IGF-1, GCs of muscle and liver, the activity of key enzymes such as AST, ALT, and regulation of protein metabolism genes expression, such mTOR signaling pathways mediating protein synthesis and AMPK signaling pathways mediating protein synthesis and decomposition. So as to reducing muscle protein content, accelerating the decomposition of muscle protein, enhancing organism on the protein intermediate metabolites in urea nitrogen, uric acid and creatinine using ability, maintaining the yak glucose oxidation stability and power, which leads to the body weight, chest circumference, carcass weight and the nutrient of the muscle changed, to sustain the life of the yak. The protein decomposition rate of psoas major is more than that of half tendons, showing that different parts of the skeletal muscle protein decomposition have different space distribution characteristics under starvation. |
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