Effects Of BLV Load On Mammary Gland Infection And Milk Quality In Dairy Cows

Bovine leukemia virus(BLV)is an immunodeficiency virus that infects cows and is widely prevalent in China.BLV affected the innate immune function of cows,reduces disease resistance and increases the incidence of inflammatory diseases.Cow mastitis had always been one of the most important diseases that restrict the development of global dairy industry.The pathogenic bacterias of mastitis can be divided into "Infectious pathogenic " and " environmental pathogenic".The economic loss caused by cow mastitis is up to 2 billion US dollars every year in the world.In China,the annual loss caused by cow mastitis is more than 300 million yuan.BLV infection can lead to immunosuppression in dairy cows.but the relationship between BLV load and mastitis and the change of milk quality is still unclear.Therefore,exploring the relationship between the two has important practical value for scientific prevention and control of mastitis and improvement of milk quality.In this study,107 lactating cows in a large-scale pasture in Daqing City were selected to collect blood samples.Quantitative detection of BLV previrus DNA by fluorescent quantitative PCR,Calculate the number of virus copies.BLV antibody was detected by ELISA,and 23 BLV positive cattle were selected by combining the results of the two methods,They were divided into 5 high viral load cows and 18 low viral load cow.Through consultation with veterinarians in the pasture,Milk samples from18 of the 107 cows with mastitis were collected.Based on the screening results of high and low viral load,they were divided into high viral load mastitis group,low viral load mastitis group and BLV negative mastitis group.The milk samples were collect from72 undder quarter of 18 cow in 3 groups were isolated and identified for Escherichia coli,Staphylococcus aureus and Streptococcus,Then a mixed milk sample was collected and sent to Animal Breeding Center of Daqing,and the milk composition was analyzed by whole milk analyzer.To analyze the effects of BLV load on mastitis infection and milk quality.The effects of BLV loading on mammary gland infection and milk quality of dairy cows were analyzed.The results:(1)The incidence rate of mastitis in dairy cows with high viral load was the highest,80%(4/5).The incidence rate of mastitis in dairy cows with low viral load was 27.78%(5/18).The incidence rate of mastitis in BLV negative dairy cows was the lowest,10.71%(9/84).(2)The infection rate of Escherichia coli,Staphylococcus aureus and Streptococcus in the undder quarter was the highest in the high viral load group,but there was no significant difference compared with other groups(P > 0.05).(3)There was no significant difference in the types of bacterial infection(single infection/mixed infection)in different undder quarter of mastitis(P > 0.05).(4)The total number of viable bacteria in high and low viral load mastitis group was higher than that in BLV negative mastitis group,but the difference was not significant(P >0.05).(5)The somatic cells number of cows in high BLV load mastitis group was significantly higher than that in low viral load mastitis group(P < 0.05),the somatic cells number of cows in high viral load mastitis group was extremely significantly higher than that in BLV negative mastitis group(P < 0.01),and the viral load was positively correlated with the somatic cells number(6)Milk yield in High viral load mastitis group was significantly lower than that in BLV negative mastitis group(P <0.05),and there was a negative correlation between viral load and milk yield.(7)Milk fat percentage in high viral load mastitis group was significantly lower than that in low viral load mastitis group(P < 0.05),and there was a wireless relationship between viral load and milk fat percentage.(8)Milk protein percentage in High viral load mastitis group was significantly lower than that in BLV negative mastitis group(P < 0.05),and there was a negative correlation between viral load and milk protein percentage.In conclusion,The viral load load has an effect on the main pathogenic bacteria infection types and quantity of mastitis,but there is no significant difference.The viral load was significantly correlated with the incidence rate of mastitis and milk quality.The viral load was negatively correlated with milk yield and milk protein rate,positively correlated with somatic cell number,but not linearly correlated with milk fat rate.