New study on concurrent use of cattle vet medicines

AgriHealth recently completed new research investigating the impact of the concurrent use of veterinary medicines on antibiotic concentration in milk.  Technical Manager Dr Laura Young says the reason for the study was a change in the Ministry for Primary Industries (MPI) milk supply regulations.  Subsequently, some dairy farm auditors checked whether written milk with-holding advice was provided by veterinarians when two or more vet medicines were concurrently used to treat cows.  Affected farmers approached veterinarians for this written authorisation last year, and veterinarians subsequently asked key vet medicine suppliers for assistance.

It is relatively common-place, and often best practice, to use multiple medicines to treat a single disease.  Examples include use of an intramammary antibiotic alongside an injectable antibiotic, or the use of an anti-inflammatory and antibiotic concurrently, when treating mastitis.  Additionally, when vets are called to see a sick cow, or perform surgery such as a caesarean, often several medicines are used to improve the cow’s chance of recovery. 

Laura believed that milk clearance of antibiotics was unlikely to be affected by using more than one treatment, and felt further validation with commonly used vet medicine examples would provide extremely useful data for local vets and farmers.  Consequently, AgriHealth funded an extensive study quantitatively measuring the concentration of antibiotics in milk following treatment with vet medicines. 

Twenty pairs of veterinary medicine concurrent treatment regimes were included in the Study. Milk was proportionally sampled from five cows per treatment group, once the longest milk with-holding period for either vet medicine in the product pair was met.  Milk samples were then tested, with results compared to the NZ Maximum Residue Level (MRL) for that antibiotic vet medicine. 

Only two individual cows of the total 100 cows in the Study tested slightly above the MRL at the milking after the longest withholding period was met. The two outlier cows tested below MRL 24 hours (two milkings) later.  It is important to note that all four quarters were treated with intramammary antibiotics.

AgriHealth believes this data provides reasonable confidence for vets to provide farmers with written milk with-holding period recommendations for concurrent use of veterinary medicines, and should reduce the volume of milk discarded unnecessarily. 

AgriHealth Managing Director Ed Catherwood received numerous accolades from NZ veterinarians for funding this study.   In particular, the large number of commonly used vet medicine product pairs tested (including use of numerous products outside the AgriHealth portfolio) was praised. 

See the Technical Bulletin A6, titled 'Concurrent use of registered veterinary medicines in lactating dairy cows in New Zealand' here.