How do you know when a cow is cured or not?

This is not straightforward to answer when considering whether the treatment has cured the bacterial infection in a cow. The best answer to the question is obtained by milk sampling a cow before treatment and again 2 to 3 weeks later and comparing the results of bacterial culture. While useful in a research setting, this is not so useful on farm.

What we usually mean by this question is “When should I stop treating a cow?” and “When is it okay to return a cow to the vat?”  

Stop treating a clinical case once you have completed the prescribed course of treatment for that cow, the udder feels normal, and the milk appears clean visually.  Milk at this stage will still test high on a rapid mastitis test (RMT). Leave the cow out of the vat until the withholding period has been completed and then the cow can go back in the vat under normal circumstances. Where the herd has a high BMSCC, check the milk with an RMT.  Strong reactors should be held out for an extra 24 to 48hrs and monitored before going back into the vat.  

Cows that should continue with treatment at the end of the prescribed course are those whose milk and udder can be detected as abnormal by touch and visual appraisal. Cows that should be kept out of the vat are those whose milk is visually abnormal, i.e., contains clots, flecks, or is discoloured.  In most cases, a repeat treatment will “cure” the infection and the cow can be managed as in the above paragraph. Where this is not the case, talk to your vet to discuss the most appropriate course of action.

Dr David Hawkins BVSc - Farm Vet & Consultant