Yak is one of the unique domestic animals living on the Qinghai- Tibetan plateau. It is dominance in this area is attributed anoxia condition and feed shortage in cold seasons. It provides important products for the herders who live in the area. Due to cyclic nutrient deficiency or unbalanced nutrient supply within short growing seasons for herbage growth, the annual cycle of weight loss is a cold season and weight gain or compensatory growth in warm seasons in Yak is a common phenomenon.
We knew that endocrine activity regulates animals nutritional balance and growth. Many reports have demonstrated that nutritional status profoundly affects the circulating concentration of growth hormone. Insulin is known to be responsible for catabolic processes such as fat mobilisation and reduced protein accretion.Thyromin and tri-iodothyronine, hormones of the thyroid gland, are major regulators of metabolic rate, growth and development animals.
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Ref: http://agtr.ilri.cgiar.org/documents/Library/docs/yakpro/SessionE2.htm