Effects of high altitude and season on fasting heat production in the yak Bos grunniens or Poephagus grunniens

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Abstract
Thirty growing yaks Bos grunniens or Poephagus grunniens, 1·0–3·5 years and 50–230kg, from their native altitudes (3000–4000m), were used to study the basal metabolism in this species and to evaluate the effects of high altitude and season on the energy metabolism. Fasting heat production (FHP) was measured at altitudes of 2260, 3250 and 4270m on the Tibetan plateau in both the summer and the winter, after a 90d adaptation period at each experimental site. Gas exchanges of the whole animals were determined continuously for 3d (4–5 times per d, 10–12 min each time) after a 96 h starvation period, using closed-circuit respiratory masks. Increasing altitude at similar ambient temperature (Ta) did not affect (P>0·10) FHP in the summer, but decreased (PPPPP0·52 at Ta 8–14°C and on 704 kJ/kg body weight0·52 at Ta -15°C respectively. We conclude that in the yak high altitude has no effect on the energy metabolism, whereas the cold ambient temperature has a significant depressing effect. The results confirm that the yak has an excellent adaptation to both high altitude and extremely cold environments.

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