Incidence Law Of Mastitis In Holstein Cows And Its Effect On Reproductive Performances In A Large Dairy Farm In Jiangsu Province

Mastitis has been affecting the development of dairy farming,resulting in issues such as lower milk production,reduced milk quality and shorter service life of cows.Therefore,in this paper,we studied and analyzed the incidence of clinical mastitis and the main pathogenic bacteria in a dairy farm in Jiangsu Province from 2015-2021 to understand the incidence regularity of clinical mastitis and the prevalence of the main pathogenic bacteria in the region.A total of 143 cows with 1st and 2nd parities calving in October 2020 were selected,including 74 cows with 1st parity and 69 cows with 2nd parity.According to the health status of cows from calving to the first AI period,they were divided into healthy group,subclinical mastitis group and clinical mastitis group.The tail vein blood of cows was collected for the first artificial insemination（AI）,and the levels of Tumour necrosis factor-α（TNF-α）,Interleukin-1β（IL-1β）,Malondialdehyde（MDA）,Superoxide dismutase（SOD）,Catalase（CAT）,Gonadotropin-releasing hormone（GnRH）,Luteinizing hormone（LH）,Estradiol（E2）,Prostaglandin（PG）,Anti-Miillerian hormone（AMH）in plasma were measured by ELISA.To collect data on first AI pregnancy rate,number of AI,difficulty of calving,the days of first AI,the days open,the gestation period and calf birth weight.The chi-square independence test and multivariate analysis of variance were used to investigate the effects of subclinical mastitis and clinical mastitis in cows from calving to the first AI period on the physical condition and reproductive performance of dairy cows at the time of first AI.The results are as follows:1.The average incidence of clinical mastitis in this dairy farm is 5.46%.Clinical mastitis incidence varied significantly（P<0.01）across years,seasons,months,parities and udder quarters was extremely,with the lowest incidence in 2015（3.37%）and the highest incidence in 2016（6.98%）.The incidence of clinical mastitis is high in summer,particularly in August,with 6.94%and 10.44%respectively.The incidence of clinical mastitis in 1st parity to 4th parity cows increased with the parities.The incidence of single-udder quarters was the highest（94.56%）in clinical mastitis cases,and the incidence of single-udder quarters in each year was over 90%,the right udder quarters is a high incidence of clinical mastitis cows（27.11%）,the left udder quarters has the lowest incidence（19.81%）.The incidence of clinical mastitis caused by different pathogenic bacteria and different years of infection with Escherichia coli（E.coli）,Staphylococcus aureus（S.aureus）,Klebsiella peneumoniae（K.peneumoniae）and mixed infections was extremely significant（P<0.01）,the most common pathogenic bacteria were E.coli（41.29%）and S.aureus（28.22%）,followed by K.peneumoniae（13.96%）,and the Bacillus was the least one（4.80%）.The proportion of clinical mastitis caused by E.coli infection increased then decreasedbetween years,with the highest proportion in 2018,while,the proportion of clinical mastitis caused by S.aureus infections showed a trend of decreasing and then increasing,with the lowest proportion in 2018.Better control of clinical mastitis caused by mixed infection.2.The plasma levels of TNF-α and IL-1β were lower in clinical mastitis cows.Both subclinical and clinical mastitis cows had higher plasma levels of MDA;subclinical mastitis cows had higher plasma SOD and CAT levels than clinical mastitis cows.However,between calving and the first AI,the effects of subclinical and clinical mastitis on plasma TNF-α,IL-1β,MDA,SOD and CAT levels in cows did not reach statistically significant levels（P>0.05）.3.The plasma levels of GnRH,LH and E2 were higher in subclinical mastitis cows,while LH and E2 levels were lower in clinical mastitis cows.Healthy cows,subclinical mastitis and clinical mastitis cows showed a sequential decrease in plasma PG levels.Cows with clinical mastitis have higher plasma AMH levels.Healthy cows,subclinical mastitis cows and clinical mastitis cows showed had a lower pregnancy rate at first AI（41.30%、33.33%、19.05%）and a higher proportion of calving that required artificial assistance（4.55%、9.52%、21.43%）.The number of AI required for successful pregnancy in subclinical mastitis and clinical mastitis cows increased by 0.53 and 0.37 times,respectively,compared with healthy cows.Subclinical mastitis cows have 14.76 increase inopen days compared with healthy cows,while the gestation period is shorter,and calf birth weight is lower.The results showed that during the period from calving to the first AI,the effects of subclinical and clinical mastitis on plasma GnRH,LH,E2,PG and AMH levels in dairy cows at the time of the first AI,the first AI pregnancy rate,number of AI,difficulty of calving,days of first AI,days open,gestation period and calf birth weight did not reach a significant level（P>0.05）.In conclusion,the incidence of clinical mastitis in varied significantly（P<0.01）acorss years,seasons,months,parities and udder quarters of the dairy farm was extremely the main pathogenic bacteria in the dairy farm were E.coli and S.aureus.Subclinical mastitis and clinical in cows from calving to the first AI influenced plasma immune factors,oxidative stress factors and reproductive hormone levels at the time of first AI,as well as reproductive performance indicators,but none of them reached significant levels（P>0.05）.The reasons for this need to be investigated in further research.