Protein Requirements and Nutritional Metabolic Characteristics of Yak Calves on the Qinghai-Tibetan Plateau.

Abstract

Understanding the nutritional protein requirements of yak calves is the basis of precise feed formulation. Regulating feed protein can reduce environmental impacts, which is particularly crucial for the rearing and management of yak calves. In this study, we used a combination of comparative slaughter, feeding, and digestibility trials to determine the net protein requirements of suckling yak calves. Thirty-five yak male calves with similar weights at 60 d of age were divided into 5 groups: early slaughter (ES), mid-term slaughter (MS), late slaughter (AL), 70% feeding (R70), and 40% feeding (R40). The ES, MS, and AL groups were used for comparative slaughter trials, while the AL, R70, and R40 groups were used for ad libitum feeding experiments. The results indicated that at different feeding levels, low feeding levels were not conducive to calf growth. For yak calves with body weights of approximately 40-90 kg, the nitrogen digestibility ranged from 49.36% to 59.32%, and the nitrogen retention rate ranged from 36.59% to 48.97%. The net protein requirement for yak calf maintenance is 2.90 g/kgW^0.75·d^-1. The equation for the net protein requirement for yak calf growth is NPg(kg) = 0.0543 × EBW^0.0833(kg). Muscle metabolomics results indicated that the protein content in the muscle tissue did not increase with feeding level or body weight. With an increase in the feeding level, the nutritional protein level provided by the diet increases, which regulates changes in steroid hormone biosynthesis, ovarian steroidogenesis, cortisol synthesis and secretion, and carbon metabolism, promoting an increase in hormone-like metabolites in the muscle tissue. These data we obtained provide guidance for the efficient rearing of yak calves and provide basic data for further research on the nutritional requirements.