Seasonal and nutrients intake regulation of lipoprotein lipase (LPL) activity in grazing yak (Bos grunniens) in the Alpine Regions around Qinghai Lake

Lipoprotein lipase (LPL) is considered as a key enzyme in the lipid deposition and metabolism in tissues. To better understand fat cycling in grazing yak to adapt to the harsh environment on the Qinghai-Tibetan Plateau, and we have therefore explored seasonal and nutritional regulation of LPL in adipose tissue, liver and skeletal muscle. Sixty 3 year old growing yaks (BW. 120.3 ± 15.28 kg) were subdivided into six groups, each used to determine effects on chemical body composition and LPL activity in different tissues. The alpine pastures had the highest Crude protein (CP, 11.06%) contents and the gross energy (GE, 11.49 MJ/kg) in summer. Growth rates and body fat content were responsive to CP and GE intake regimen. Late spring up-regulation of LPL activity in the subcutaneous adipose tissue was consistent with a pronounced increase of body weight (BW) and whole body fat content. The highest LPL activity in the skeletal muscle was found in September (774 ± 64.1 mU/g tissue), which may serve to cover the increased energy demands for compensatory growth and maintenance of adiposity in the coming cold season. Furthermore, the seasonal regulation of LPL involves some factors in addition to insulin and triglycerides (TG). These results suggest that yaks could rely, in part, on LPL activity to adapt to the harsh forage environment. During the growing season, an enhanced synthesis of LPL production in the adipose tissues along with mechanisms for the recycling of fat contributes toward the rapid recovery of body weight.