Abstract: Indoor feeding of yaks at low altitude is an important means to overcome the winter forage supply problem for the large numbers of livestock in the Tibetan region, and it can also facilitate the growth and development of yak during the cold season and the improve the quality of yak meat. The purpose of our study is to explore the effects of indoor feeding in low-altitude areas on yak growth and development, slaughter performance, muscle quality, and serum indicators, and to provide preliminary data on factors that may influence yak muscle quality when indoor-feeding at low-altitude. Ten healthy 36-month-old male yaks of similar body weight and physical condition at 36 months of age were randomly divided into an indoor-feeding group and a grazing group. The indoor-feeding group were housed for fattening at Guanghan agricultural area (altitude: 600 m), and the grazing group were naturally grazed following traditional yak farming practice at 3500 m altitude in Hongyuan County. The experiment duration was 150 days. It was found that the weight gain of yaks fed indoors was significantly higher than that of the grazing group (P<0.01), and the yak carcass weight, pure meat weight, dressing-out percentage which means ratio of carcass weight to live weight and pure meat percentage were all significantly higher than that of the grazing group (P<0.01). The dietary quality of the longissimus muscle in the indoor-feeding group was significantly improved: The brightness (L^*) was significantly higher than that in the grazing group (P<0.05), the cooking percentage which is also known as cooking loss and intramuscular fat content were significantly higher than those in the grazing group (P<0.05), and the shear force was significantly lower than the grazing group (P<0.05). The nutritional quality of the longissimus dorsi muscle in the indoor-feeding group was also significantly improved: The ether extract content was significantly higher than that in the grazing group (P<0.01). The contents of palmitic acid (C16:0) and stearic acid (C18:0) in the indoor-feeding group were extremely high compared to the grazing group (P<0.01), and the contents of saturated fatty acids, polyunsaturated fatty acids, and trans fatty acids were significantly higher than those in the grazing group (P<0.05). The flavor-forming free amino acid levels were significantly higher in the indoor-feeding group than in the grazing group (P<0.05). For serum indicators, the blood glucose concentration in the indoor-feeding group was significantly higher than that in the grazing group (P<0.05), while increase in triglyceride and total cholesterol levels, compared to the grazing group were highly significant (P<0.01). The concentration of β-hydroxybutyric acid was significantly lower than the grazing group (P<0.01); the acetyl CoA carboxylase enzyme activity was higher than the grazing group (P<0.01); the fatty acid synthetase enzyme activity was significantly higher than the grazing group (P<0.05); and the hormone-sensitive lipase (HSL) enzyme activity was significantly lower than the grazing group (P<0.05). The test results show that yak weight gain and fattening can be achieved by indoor feeding at low altitude in the cold season. Through activation of serum enzyme activity related to lipid deposition in yak, indoor-feeding can facilitate the synthesis and deposition of fat in muscle and improve the dietary quality and nutritional quality of yak meat.

Key words: low-altitude house-feeding, yak, muscle quality, serum index, lipid deposition-associated enzymes