Milk fatty acids profiles and milk production from dairy cows fed different forage quality diets

Thirty lactating Holstein cows were used to investigate the effects of different forages quality on milk fatty acids(FA) profiles and production. The cows were assigned to 3 dietary treatments(n = 10 per treatment) in a randomized block design with 3 repeated measures. They were fed the experimental diets for 90 d with 3 days of collection of samples for analysis at about 27 d intervals(samples were collected on days 28,29,30, 58, 59, 60.88, 89 and 90). The treatments were(DM basis): 1) mixed forages diet(MF) consisting of 3.7% Chinese wild rye, 26.7% corn silage and 23.4% alfalfa hay; 2) corn stalk diet 1(CS1) where corn stalk was used to formulate a similar chemical nutrient level to MF; 3) corn stalk diet 2(CS2) which used corn stalk to formulate a similar forage level to MF for the diet. Dry matter intake and BW were similar between treatments, but daily milk yield, milk fat and protein yield decreased(P < 0.05)in CS1 and CS2 compared with MF, with CS2 being the lowest(P < 0.05). In total FA of milk, the compositions of C18:1 c9, C18:3 and unsaturated FA increased(P < 0.05) in CS1 and CS2 compared with MF,and C18:0 and trans-C18:1 were trended to increase(P < 0.10), but C4:0-C16:0 were decreased(P < 0.05).Compared with cows fed CS2, cows receiving CS1 increased the compositions of C4:0 to C12:0 and C18:2(P < 0.05). The results suggests feeding corn stalk could produce a greater proportion of unsaturated fatty acid(UFA) in milk fat without resulting in milk fat depression(MFD) in mid lactation cows, but simply increasing the ratio of concentrate in low forages diets is not an effective way to increase milk fat synthesis and milk production.