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Abstract The change in lactation of Maiwa yak was studied based on the data of locating Maiwa yak in warm seasons during 2003 -2009. The results showed that the milk yield was increasing gradually during days 30 -70 after calving, reached the peak at days 70-110, and decreased gradually to no milking vvhenafter. The milk yield of Maiwa yak was greatly influenced by lactation age rather than the yearly effect.
Key words Maiwa yak; Milk yield; Lactation; Traits
Yak, a specific livestock in alpine pastoral areas of China, mainly distributes in Qinghai - Tibetan Plateau and adjacent regions. It occupies an irreplaceable ecological and economical position in the distribution regions. Currently, there are approximately 14 million yaks worldwide, of which over 90% are in China 11. Yak can supply human being the livestock products like beef, milk , hair, fur and feces121. Having a specific ability to adapt the alpine pastoral areas, yak is a special animals capable of conversing alpine grazes to green foodstuffs like beet and milk, as well as the only bovine species adaptable to alpine pastoral ecology in Qinghai - Tibetan Plateau. The high quality daily products produced by yak in alpine pastoral areas are usually preferred by local people. However, due to the influence of season, climate and genetic factors, the milk yield of female yak is low. Female yak would breast - feed the calf during the feeding process, when the yak milk yield measured would be usually lower. It is of great significance to investigate the change in lactation oí Maiwa yak in warm seasons.
Maiwa yak is a relatively original species with lower intensive selection degree, lower productivity, larger population number and broad distribution range in alpine pastoral areas of Northwest Sichuan Province. It is provided with the excellent traits including strong adaptability, stable inheritance, high quality beef and milk, and high grease content. In the present study, the changes during yearly lactation and milk yield of Maiw'a yak was studied based on the data of locating Longri Breeding Farm of Sichuan province during 2003 - 2009, aiming at providing theoretical basis for the breeding and production of Maiwa yak.
1 Materials and Methods
The experimental yak population was from Longri breeding farm in Hongyuan...