T. Dorji
Extension Station for Animal husbandry in Naqu Prefecture, Tibetan Autonomous Region, P.R. China
Naqu is located in northern Tibet with topography of high hills averaging 4500 metres above sea level (masl), characterised by sub-cold and arid highland climate with no summer season at all. The annual frostless period is about 120 days. Yak production has been the main income source supporting the Tibetan nomads living in the region. The yak population in Naqu was estimated at 1,455,800 head in 1999, the reproductive females constituting about 45% and the reproductive and survival rate was 56.94%. Due to the non-conception of over 30% of the reproductive females, the yak reproduction and productivity has deteriorated over the years. For example, the live weight of yak in the area was in the range 500–700 kg in 1950's but dropped to 200–300 kg in 1999. To improve the yak reproduction and introduce new yak genes into the region, artificial insemination (AI) has been used on trial base on the high alpine pasture.
The frozen semen was taken from the Daxun Yak Frozen Semen Station. The reproductive females were assembled in the Naqu Farm where the yak were in normal body condition, small body size, black colour, and aged from 5 to 13 years. The bulls were separated from the females during breeding season from August to September to allow the exclusive use of AI. Thawed frozen semen with a live sperm rate of 0.4–0.5 was used. A total of 18 females were involved in the trial. Only 17 of them conceived, representing a conception rate of over 94%. This is almost same with the conception rate by AI in the lower altitude areas (4200 masl). From this preliminary experiment, the live sperm rate of thawed semen, temperature in the breeding season and age of the females are thought to be the key factors affecting the conception rate. A large-scale trial is recommended to verify these results for use by the extension service.
