A preliminary study on amino acid nutrition requirements of lactating yak grazing in a warm season pasture in alpine meadows

In order to investigate the amino acid (AA) nutrition requirements of lactating yak during grazing, it was determined that the AA content in edible forage and yak blood, hair coat, milk, and feces, and the correlation between them. Three lactating Tianzhu white yaks were selected from a warm season pasture(August) and blood, hair coat, milk, and fecal samples were collected. In addition, the edible forage samples were also collected from the grazing pasture. Three major results were observed. 1) The concentration of total AA (TAA) was 1 257.06, 9 007.87, 8 752.68, 1 318.36 mg·kg^–1, and 499.58 mg·L^–1 in forage, blood, hair coat, feces, and milk, respectively. The ratios of essential AA (EAA) to TAA were close to 40% and EAA/non-essential AA (NEAA)(E/N) was more than 60% in edible forage. 2) The correlation was significant between AA in forage and AA in blood, milk, hair coat, and feces (P < 0.05); it was significantly correlated with the AA content in the forage and in blood, yak milk, and hair coat (P < 0.05); Further, there were negative correlations between some the content of AA in blood and in hair coat (P < 0.05). 3) The yak milk AA, had a relatively lower score of Lys and His (81.96% and 84.52%) in the edible forage; the yak hair coat AA had a lower score of Cys + Met and Arg (37.83% and 46.39%); and the yak blood AA, had a lower score of His, Arg, Leu, and Lys (35.69%, 73.31%, 76.65%, and 77.25%). In summary, the warm season pasture of alpine meadows could provide high-quality forage for lactating yak. Meanwhile, the nutrition management in the area of lactating yak, should be paid more attention to Lys, His, Arg, Cys, and Met deficiencies. If not, it may lead to poor health and inefficient production in yaks.