Optimal use of antibiotics at acute clinical mastitis in dairy cows

Clinical mastitis (visible inflammation of the udder) is a painful disease which mostly is caused by udder infection with bacteria and is the most common cause of antibiotic treatment in Swedish dairy cows. The long-term aim of the project was to improve animal welfare and the economy of the herds by producing new treatment guidelines resulting in reduced and more efficient use of antibiotics, which in turn leads to fewer injections and fewer new cases of mastitis due to reduced risk of spread of udder infections between cows. 

To answer the project aims we needed approximately 900 cases of clinical mastitis (CM) from all over the country. Despite several reminders to veterinarians and farmers it was, however, difficult to get enough cases. We also investigate the possibility to do parts of the project in Denmark  but that was not possible. Therefore, we applied for permission to finish the project prematurely on Feb 18 2022. Although we could not achieve the goals of the project we have tried to extract some knowledge from the information we did collect.

In total, we got data from just over 100 cows with CM from 25 herds during a period of approximately 1.5 years. The reasons for the low number may be lack of time, especially during the pandemic, and strict inclusion criteria. The symptoms of the cows varied. The general condition of the cows was affected (e.g. ppor appetite) in approximately one third of the cows and approximately 20% had fever (>39.5ºC). Just over 80% of the cows had symptoms in the udder (e.g. swelling) and all had changes in milk appearance. These results were largely according to expectations. Moreover, just over 80% of the cows were treated with anti-inflammatory drugs (mainly NSAID).

The proportion of cases (40-50%) that were excluded from the study was higher than expected and many of those could have been avoided (e.g. contaminated milk samples, no/poor follow-up). The results also indicate that the routine to take two milk samples for bacteriological examination at follow-up is a good routine despite the higher cost involved. 

The remaining cows were divided between treatments (T) 1-3 as follows: 38% got T1 (systemic treatment with benzyl penicillin procain (BPP) for 5 d), 26% got T2 (systemic treatment with BPP d 1 and local treatment with BPP d 1-5) and 35% got T3 (both systemic and local treatment with BPP d 1-5). As expected growth of Staphylococcus (S.) aureus, Streptococcus (Str.) dysgalactiae or Str. uberis ​was most common. The results, which must be treated with great care due to the low number of cases, indicated that 46 of 65 fall (68%) was clinically healthy and that the udder infection was cured in 36 of 54 cases (53%) 4 weeks after start of treatment. Clinical cure did not seem to differ between the most common intramammary infections or between treatments. Udder infections with S. aureus did, however, not cure as often as infections with streptococci and the cure tended to be better in T3 than in T 1 and T2, especially for S. aureus ​cases.

Although the material is too small to draw any real conclusions the results still indicate that, at present, there are no reason to change existing recommendations for treatment of CM in cows with antibiotics.