Effects Of Feeding Yeast And Bacillus Subtilis On Milk Performance, Immune And Antioxidant Capacity, And Nitrogen Emission In Dairy Cows

This study was conducted to investigate the effects of dietary supplement of yeast and bacillus subtilis on milk performance,immune function and antioxidant capacity,and nitrogen emission in Holstein dairy cows,to provide a reference for scientific application of these two probiotics in dairy industry.The thesis consists of two parts:Part one was a META analysis of response of performance of Holstein cows to dietary active yeast and bacillus subtilis,based on published experiments on PubMed,ScienceDirect,and CNKI reporting “active yeast”,“bacillus subtilis”,“dairy cows”,and “performance” with their data reanalyzed.The results indicated that dietary supplement of active yeast increased dry matter intake,milk yield,and milk fat content,but decreased milk protein content;dietary supplement of bacillus subtilis increased dry matter intake and milk yield,but decreased milk fat content and milk protein content of Holstein cows.In part two,active yeast and bacillus subtilis probiotics were selected as the research objects.36 Chinese Holstein cows in their mid-lactation were selected and divided into 3 groups according to the principle of similar parity,weight,stage of lactation and milk yield,with 12 cows for each group.Treatments included control group,feeding yeast group,and feeding bacillus subtilis group.Cows of control group were fed basal diet without probiotics;cows in yeast group were supplemented with active yeast probiotics in diet(20g/d for each cow);and cows in bacillus subtilis group were supplemented with bacillus subtilis probiotics(10g/d for each cow).Effects of feeding active yeast and bacillus subtilis on milk performance,immune and antioxidant capacity,and nitrogen emission in dairy cows were analyzed.The experiment lasted for 60 days,including 4 periods B1,B2,B3 and B4 with 15 days in each period.Samples were collected at the last two days of each period.Results showed that:(1)Dietary active yeast probiotics and Bacillus subtilis had no significant effect on milk yield of Holstein cows.But numerically,milk yield in yeast group was lower than that of control in each period.Milk protein content in Bacillus subtilis group was higher than the other two groups numerically,and significantly higher than that of control group(P<0.014)and yeast group(P<0.002)at the day of 45.At the 45 d,lactose content in yeast group was lower than that of Bacillus subtilis group;and at the 60 d,lactose content in yeast group was significantly lower than that of control group and Bacillus subtilis group(P<0.032;P<0.039).At the 60 d,the total solid in milk in yeast group was significantly lower than that of Bacillus subtilis group(P<0.012).At the 15 d,the somatic cell count of Bacillus subtilis group was significantly lower than control group(P<0.014).At the 30 d of experiment,the somatic cell count of Bacillus subtilis group was significantly lower than yeast group(P<0.048).At the 60 d,the content of milk urea in yeast group was significantly lower than that in control group(P<0.025).(2)Dietary active yeast and Bacillus subtilis probiotics showed no significant difference in contents of Ig A,IgG,IgM and sCD8.At the day of 45,the levels of sCD4 in control group was significantly higher than that of yeast group(P<0.002)and Bacillus subtilis group(P<0.007);at the day of 60,the levels of sCD4 in yeast group and Bacillus subtilis group were significantly lower than that of control group(P<0.021).The contents of SOD,MDA and GSH-Px in serum were not affected by the addition of active yeast and Bacillus subtilis.(3)The nitrogen concentration in feces was numerically lower in group Bacillus subtilis than the control group in every experimental period,but there was no significant difference between them.At the day of 60,the urine nitrogen was significantly lower in both yeast and Bacillus subtilis groups than the control group(P<0.019).The blood urea nitrogen concentration tended to increase in each group,and besides B4,blood urea nitrogen concentration was higher in group of yeast than the control group numerically but not statistically.At the day of 60,ammonia concentration of blood was significantly lower in group of yeast than control group(P<0.012)and Bacillus subtilis group(P<0.013).In conclusion,the addition of probiotics in diet could reduce urine nitrogen,improve immunity and antioxidant capacity,and tend to improve the milk quality of dairy cows.