The Effects Of NDF Levels In Diet On Rumen Fermentation And Milk Performance Of Dairy Cows During The Period Of Peak Lactation

This study was conducted to investigate the effects of dietary NDF levels on rumen fermentation characteristics in vitro and feeding activity, rumen fermentation and milk performance of dairy cows during the period of peak lactation by using the technology of gas production in vitro and feeding experiment. The study concluded two experiments, the methods and results were shown below:The first experiment, we used the technology of short-term artificial rumen and dynamic gas production real-time recording to investigate the effects of different NDF levels in diet on the parameters of rumen fermentation and gas production in vitro of dairy cows during the period of peak lactation. The four NDF levels in the diet were 25.05%,28.05%,31.22% and 34.19%, respectively. The results showed that, with increased dietary NDF level in vitro:1) the IVDMD and GP48 decreased linearly (P<0.05); 2) the concentrations of propionate and butyrate decreased linearly (P<0.05), the pH-value and the ratio of acetate and propionate increased linearly (P<0.05), the concentration of ammonia nitrogen tended to decrease linearly (P=0.05), and there was no significant influence on the concentrations of microbial protein and total volatile fatty acid (P>0.05), but there was a trend to decrease.The second experiment, a total of eight Holstein dairy cows averaging 50±15 days in milk, of which four had permanent rumen fistulas, were selected in a double 4×4 Latin square design. We conducted to investigate the effects of NDF levels in diet on on feeding activity, rumen fermentation, blood metabolism, nutrient digestibility, and milk performance of dairy cows during the period of peak lactation. The four NDF level in the diets was 25.05%,28.05%, 31.22%and 34.19%, respectively. The results showed that, with increased NDF level in diet,1) The DMI decreased linearly (P<0.05), the intake of NDF, peNDF8.0,peNDF1.18 and the time of daily feeding, rumination and chewing increased linearly (P<0.05), there was a trend to increase linearly or firstly decrease then increase on the feeding, rumination and chewing time per kg of DM, NDF, peNDF8.0and peNDF1.18 intake (P<0.05); 2) the pH-value, the concentrations of acetate and the ratio of acetate and propionate increased linearly (P<0.05), the concentrations of ammonia nitrogen (NH3-N), microbial protein (MCP), total volatile fatty acid (TVFA), propionate, butyrate and lactate decreased linearly (P<0.05); 3) the activity of four cellulolytic enzymes firstly increased then decreased, among which the 28%NDF group was the highest, there was no significant influence on the activity of cellulase, glucanase and xylanase, but the activity of cellobiase changed quadratically (P<0.05); 4) the quantities of Fibrobacter succinogenes, Ruminococcu flavefaciens and Streptococcus bovis increased linearly (P<0.05); 5) serum glucose (GLU) and insulin (INS) concentrations reduced linearly (P<0.05); the serum non-esterified fatty acids (NEFA), P-hydroxybutyrate (BHBA) and urea nitrogen (BUN) concentrations increased linearly (P<0.05); triglyceride (TG) (P=0.06) and cortisol (COR) (P=0.07) concentrations tended to increase linearly, but did not have significant influence on total cholesterol (TC) concentration (P>0.05); 6) the apparent digestibility of NDF and ADF increased linearly (P<0.05); 7) milk yield, lactose yield, milk protein yield and nitrogen nitrogen efficiency decreased linearly (P<0.05), milk fat percentage and milk urea nitrogen concentrations increased linearly (P<0.05); feed efficiency and milk fat yield tended to increase linearly (P=0.05); milk protein percentage tended to decrease linearly (P=0.08), while 4% FCM yield and lactose percentage were not significantly influenced (P>0.05); 8) the concentrations of C6:0, C8:0, C10:0, C12:0, C14:0, C14:1 and C15:0 in milk decreased linearly (P<0.05), while the concentrations of C 18:0 and C18:ln9c increased linearly (P<0.05);Conclusion:we combined the results of the gas production experiment in vitro with feeding experiment, it is suggested that the requirement level of dietary NDF be 28% of dairy cows milk production about 40 kilogram per day during the period of peak lactation.