Title: Shrub cover impacts on yak growth performance and herbaceous forage quality on the Qinghai-Tibet Plateau, China
Authors: Chuntao Yang, Tianhai Yan, Yi Sun and Fujiang Hou*
Journal: Rangeland Ecology and Management
Impact factor: IF2019 = 2.095
Abstract: Shrub cover in alpine meadows around the world has experienced significant changes during the past 20 yr. An increase in shrub cover has often been associated with large influences in ecosystem functions. The objectives of the present study were to investigate the impact of shrub cover on herbaceous forage quality and yak grazing efficiency on the Qinghai-Tibetan Plateau, China. Forty-eight yak steers were randomly assigned to four grazing pastures with different shrub cover rates (control, low, middle, and high). The whole grazing period was categorized as vegetative stage (June to July), bloom stage (August to October), and senescent stage (November to December). Herbaceous forage chemical composition and body weight of yaks were measured, and serum and rumen samples were analyzed. Although shrub cover had no effect on herbaceous forage chemical composition and serum biochemical parameters of yaks, total herbaceous forage production in pastures and crude protein intake of yaks decreased with increasing shrub cover. Such changes decreased average daily gain of yaks. As expected, increasing the herbaceous forage maturation significantly decreased crude protein content while increased dry matter, neutral detergent fiber and acid detergent fiber contents, consequently, reduced herbaceous forage crude protein and organic matter intakes and average daily gain of yaks. The rumen of yaks has higher ammonia nitrogen and total volatile fatty acid concentrations and butyrate proportion in the bloom stage of forage compared with those of the senescent stage. The results indicate that shrub cover on the Qinghai-Tibetan Plateau needs a certain level of control for the sustainable grazing yak production, although it has little negative effect on blood health and rumen fermentation. Additionally, it is vital to select the optimum time to market livestock or supplement feed with yaks during the cold season on the Qinghai-Tibetan Plateau.