How do we know if vet medicines work?

Occasionally we receive reports of unexpected outcomes after using products on cows. For example, more calves scouring than expected despite the cows having been vaccinated, or apparently higher recurrence rate of clinical mastitis after treatment of clinical cases, or more clinical mastitis cases over the dry period than expected following use of an internal teat sealant. Such reports are often in the context of “we haven’t done anything differently this year, so something must have changed”. The next sentence is often something along the lines of “the product must have changed”.

How do we know a product works?

In New Zealand, veterinary medicines must be registered with the Animal Compounds and Veterinary Medicines (ACVM) group in the Ministry for Primary Industries. The registration process is robust and costs a substantial amount of money. The registration process includes assessment of the target animal safety (i.e. the manufacturer must demonstrate that the product does no harm), the manufacturer must provide data as to what the withholding periods are (meat and milk), provide evidence that the product can be manufactured consistently within a range of specifications and demonstrate that there is ongoing testing of each batch of product, and finally that the product is fit for purpose based on the label claims. If the manufacturer changes the product they must retest it and provide the results to ACVM before marketing it. Above and beyond the ACVM requirements, Anexa’s product assessment team reviews products in the marketplace on behalf of members with actual product selection heavily weighted towards supporting research data.

What happens if there is a report that there may be a problem with a product?

Anexa takes reports of unexpected consequences after treatment (“adverse events”) seriously. We aim to understand what has happened by collecting information about the circumstances in which the product was used, the background of management on the farm and the groups of animals potentially affected, and how, when and why the product was used. The manufacturer of the product is notified, and they may choose to do further investigations themselves. As part of those investigations the certificate of analysis (documentation of the testing of the batch of product prior to its release to the market) is assessed by the manufacturer, and in some cases additional product testing may be undertaken. Manufacturers are required to retain part of each batch manufactured for additional testing if required.

These investigations take time and are complex. For example, where there are reports of increased mastitis over the dry period on a specific farm, many factors need to be considered. Some examples being; has there been a change in staff? Have new cows been bought in? What changes did we see at the milking shed prior to dry off? Is there a district-wide increase in dry period mastitis due to climate factors? And so the questions go on.

While our first instinct may be to suspect the product, it is important to understand that in New Zealand we are in the fortunate position, relative to many other countries, of having robust drug regulations. Products on the market are of good quality, and there is a system in place that requires follow-up and reporting of apparent adverse events. Given the number of animals and treatments that occur in New Zealand every year, the number of such events is low.
If you do have concerns about a specific product or outcome please talk with your vet in the first instance.


Date Added: Wednesday, 4th September 2019


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