Abstract: Fatty acids compositions in milk of four kinds of crossbred yaks,such as Simmental × Tibetan cattle × yak,Holstein cows × Tibetan cattle × yak,Holstein cows ×yak,Juanshan cattle × yak were analyzed. After being extracted from milk samples,methyl esterification of fatty acids was carried out,and then their compositions were analyzed using GC-MS. Results demonstrated that 18 varieties fatty acids show significant difference with different yak varieties except hendecanoic acid lauric acid(p<0.05). There is great difference among contents of unsaturated fatty acids in milk of different varieties yaks,ranging from 42.20% to 50.22%. The content of unsaturated fatty acid in milk of Simmental × Tibetan cattle × yak(50.22%) is obviously higher than that of unsaturated fatty acid in milk of Juanshan cattle × yak(42.20%). Significant difference among contents of polyunsaturated fatty acids exists with different yak varieties,and the highest is in milk of Holstein cows ×yak(30.53%) with ratio of MUFA/PUFA 0.61:1. The results indicated that milk of Holstein cows × yak has high nutritional value,which has the important meaning to dairy products development of yak and breeding of cattle.

Key words: crossbred cattle, milk, fatty acid, GC-MS