Abstract: The aim of the study was to investigate that subclinical mastitis of dairy cow causes the decline of milk yield and the change of milk composition. Detect milk fatty acids of 57 Holstein cows (32 of them suffer from subclinical mastitis)with gas chromatography,and compare fatty acid composition of normal milk with subclinical mastitis milk. The results showed that 21 fatty acids which were from C4 to C22 could be found out, the content of palmitoleic(C16∶1) in subclinical mastitis milk was higher than that in normal milk,but other 20 kinds of fatty acids were lower, 9 fatty acids in subclinical mastitis milk were significantly lower than that in nomal milk(P<0.05), and 2 fatty acids in subclinical mastitis milk were great significantly lower than that in nomal milk(P<0.01). Subclinical mastitis reduced the total content of milk fatty acids and the content of saturated fatty acid, monounsaturated fatty acid and polyunsaturated fatty acid. Saturated fatty acid percentage and monounsaturated fatty acid percentage of subclinical mastitis milk were higher than that in normal milk,but polyunsaturated fatty acid percentage of subclinical mastitis milk was lower than that in normal milk. Consequently, subclinical mastitis affects the synthetic process of cow fatty acids and changes the composition of fatty acids.

Key words: Holstein cows, subclinical mastitis, the composition of fatty acids