Variability Of The Milk Fatty Acids In Southern Chinese Holstein And Impacts From Mastitis

With the rapid development of Chinese economy, great concern is focused on the diet nutrition. Fatty acids are closely related to human health, milk is rich in a variety of nutrients containing all the fatty acids the body needs, however, season, mastitis and other factors would exert great impact on the content of fatty acids in milk. In this research,61lactating cows in a dairy farm from Yangzhou, Jiangsu, were used as research subjects to determine the content of raw milk fatty acids in milk by Gas Chromatography (GC), aiming to explore variability of fatty acids in a complete lactation period. The impacts from month of sampling, month of lactation, feed ingredients, milk composition and mastitis on milk fatty acids and its proportion were analyzed. Three healthy Chinese Holstein cows with similar age and calving number were infected artificially by Staphylococcus aureus to induce bovine mastitis models, and to expose the variation in milk fatty acids and its proportion before and after the infection. The study included the following:1.The study explored the milk fatty acid variability of Southern Holstein in a complete lactation period.446normal milk samples were screened based on the negative results of mastitis detection, and used Gas Chromatography for the determination of fatty acids in raw milk. The results showed that:1)34kinds of fatty acids in total including C4-C24were found in raw milk. The ratio among SFA, MUFA and PUFA was about68:27:5by saturation. The ratio among sc-FA, mc-FA and lc-FA was about3:21:76by the length of carbon chain.2) In addition to C15:0, C18:2t, C20:0and PUFA, the month of determination affected fatty acids in milk samples significantly (P＜0.05); Lactation month had a significant effect on the content of total SFA and total MUFA (P<0.05), but the impact on the content of total PUFA was not significant; Lactation month had an extremely significant effect on the content of mc-FA and lc-FA levels (P＜0.01), while the impact on the sc-FA content was not significant.3) The saturation of raw milk fatty acid were affected not only by gry matter and crude fiber in feed, but also by milk component indexes, such as daily milk yield, milk fat content and acidity. The relative proportion of different carbon chain length fatty acids were affected not only by dry matter, digestible protein, crude fat, milk net energy and crude fiber in feed, but also by milk component indexes, such as daily milk yield, milk fat rate and acidity.2. The study explored the effect of different mastitis degrees on milk fatty acid composition and its proportion. Mastitis detection and classification were carried out for485dairy cows, and determined their milk fatty acid composition and its proportion. The results showed that:the content of saturated fatty acids C4:0, C6:0, C8:0, C10:0, C12:0, C13:0, C14:0, C18:0, C22:0and C24:0among each grade of mastitis showed significant difference (P＜0.05) or highly significant (P＜0.01). The content of total MUFA among each level of mastitis showed significant difference (P<0.05), while the grade of mastitis has no significant effect on the content of total PUFA. The grade of mastitis affected the content of sc-FA, mc-FA and lc-FA levels reaching an extremely significant level (P＜0.01).3. The effect of S. aureus-induced mastitis on milk fatty acid composition and its proportion was also explored in this study. According to the udder structure, bacterial suspension of Staphylococcus aureus was injected into the udder through the teat canal using a milk needle, and established Staphylococcus aureus-induced mastitis model. Fatty acids in raw milk were determined by Gas Chromatography. The results showed that:invasion of Staphylococcus aureus had significant impact on the saturation of raw milk fatty acids in experimental group. The content of total SFA after infection showed a decreasing trend after the first increase, but the content of total SFA showed no significant difference before and after the infection; The content of total MUFA decreased significantly after infection, while the content of total PUFA significantly increased after infection. Because of systemic reactions, control group had similar symptoms later in the infection, but it recovered gradually with time. The restore ability of experimental group is very weak, and even lactation ability lost.