Effects of infusing milk precursors into the artery on rumen fermentation in lactating cows

This experiment was conducted to investigate the effects of infusing milk precursors into the external pudic artery on rumen fermentation in lactating dairy cows. Eight multiparous Holstein cows were randomly assigned to Group A(experimental group) and Group B(control group) with 4 cows each. A2×4 complex factor crossover design was used. Cows in Group A were fed corn straw as the only roughage, and cows in Group B were fed mixed roughage. The experiment was divided into two periods.In the first period, cows in Group A, received treatments: 1) a basal infusate as a control(CSC); 2) a milk fat precursor infusion including C16:0, C18:0, C18:1 c9, C18:2 c6, C18:3 n3, acetic acid(CSF); 3) a milk protein precursor infusion including 16 amino acids(CSA); 4) the mixed infusion of milk fat and protein precursors(CSFA). And meanwhile, cows in Group B were infused the basal infusate as a control group. In the second period, the cows in both Groups A and B were crossed over, which cows in Group A were named as Group B and the cows originally in Group B were in Group A. The experimental results showed that cows in experimental group had higher ruminal pH compared with the control, and ruminal pH in CSC, CSF, CSA were significantly higher than those in their respective control group(P < 0.05). The concentration of ammonia nitrogen(NH_3-N) was significantly higher in CSA and CSFA compared with Group B(P < 0.05). We also observed that the infusion of mixed amino acids significantly increased the bacterial protein(BCP) content in rumen(P < 0.05) and influenced the rumen acetic acid concentration as well as the acetic to propionic ratio(P < 0.05). Milk fat precursors infusion significantly affected butyric acid concentration(P < 0.05). In addition, the content of lipopolysaccharide(LPS) in CSA was significantly higher than that in the control group(P < 0.05). It is concluded that the milk precursors infused into external pudic artery caused feedback effects on ruminal fermentation under the corn straw roughage conditions. The milk protein precursor increased the ruminal pH, the contents of BCP and acetic acid, which adjust rumen fermentation and improve milk performance.

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.