Effects Of Fat Addition Level And Different Ratios Of Fat Sources On Production Performance And Fatty Acids Profile In Milk Of Dairy Cows

This experiment was conducted to study the effects of fat addition level and different fat source ratio on apparent digestibility,production performance and milk fatty acids in dairy cows.42 early-lactating Holstein cows and 30 mid-lactating Holstein cows were selected.According to parity,milk yield and postpartum days,the early-lactating dairy cows were divided into 7 groups by random unit block method,6 cows in each group,and the mid-lactating dairy cows were divided into 5 groups,6 cows in each group.The basic diet consists of whole plant corn silage,alfalfa hay and concentrate supplement.Early lactation dairy cows were added 4%and 5% levels of fat on the dry material basis of the diet,respectively.Under different levels of fat addition,different proportions of fat sources were added: 70: 30(rumen undegradable unsaturated fat: flaxseed,70 represents the proportion,the same below);55: 45(55);100 % palm fat powder(0).The fat addition level(%)/ ratio was used to represent the seven groups,which were E0/0,E4/70,E4/55,E5/70,E5/55,E4/0 and E5/0,respectively.The trial period of early lactation dairy cows was 67 d,which was divided into 7 d prefeeding period and 60 d sampling period.In mid-lactating dairy cows,4 % and 5 % fat were added to the dry material basis of the diet,respectively.Under different fat levels,different proportions of fat sources were added: 70: 30(70);55:45(55).The fat addition level(%)/ ratio was used to represent five groups,namely,M0/0,M4/70,M4/55,M5/70 and M5/55.The experimental period of mid-lactation dairy cows was 37 d,which was divided into 7 d pre-feeding period and 30 d sampling period.The results showed that: 1)In early lactation cows,the dry matter intake(DMI)of palm fat powder group was significantly higher than that of55:45 fat groups(P<0.01).The feed conversion rate(FCM/DMI)of 70:30 fat group was significantly higher than that of control group(P<0.05).In mid-lactation cows,there was no significant difference in DMI among groups(P<0.05).2)In early lactation cows,the apparent digestibility of 55:45 fat group was significantly higher than that of palm fat powder group(P<0.05),and there was no significant difference in other nutrient digestibility among groups(P<0.05).There was no significant difference in the apparent digestibility of nutrients in each group of mid-lactation dairy cows(P>0.05).3)In early lactation dairy cows,the milk fat corrected milk(FCM)yield and milk fat yield of 70: 30 fat group were significantly higher than those of 55:45 fat group and control group(P<0.05).The milk protein rate in the 5 % fat addition group was significantly higher than that in the 4 % fat addition group(P<0.05).The FCM yield and milk fat yield in the 70: 30 ratio fat group and 55: 45 ratio fat group were significantly higher than those in the control group(P<0.05).4)In mid-lactation cows,the glucagon concentration in the 5 % fat addition group was significantly lower than that in the 4 % fat addition group(P<0.01).5)In early lactation cows,the content of unsaturated fatty acids in milk fatty acids in the 70: 30 fat group was significantly higher than that in the control group and palm fat powder group(P<0.05).The saturated / unsaturated fatty acid ratio of palm fat powder group was significantly higher than that of the 70: 30 fat group(P<0.05),and the long chain fatty acid content of 70: 30 fat group was relatively higher.In mid-lactation cows,the polyunsaturated fatty acid content in the 70: 30 fat group was significantly higher than that in the 55: 45 fat group and the control group(P<0.05).Based on the comprehensive analysis of the above conclusions,the optimal addition amount was 5 % fat and 70: 30 ratio of rumen-pass unsaturated fat to flaxseed oil(flaxseed).