Animal Health

On-farm milk culturing a growing

By Dairy News

MOST MASTITIS is caused by a bacterial infection.

However, visual inspection of the milk is not a reliable method for determining which pathogen you might be dealing with.

Traditionally, milk samples from infected quarters or a composite sample from an individual animal needed to be sent to a microbiology laboratory for testing to identify the pathogen and its antibiotic sensitivity profile; with turnaround times of multiple days — and pity the farmer that finds a case of mastitis on the weekend!

Recent trends in technology and antimicrobial awareness have seen an increase in popularity of on-farm or in-clinic culturing systems, using a small incubator, a special culture plate, a sterile smear loop and a sample.

Affected quarters are cleaned and collected, and samples can be plated up as soon as milking is finished.

Using a sterile loop, the sample is smeared in a zig-zag pattern across the quad- or tri- plate (depending on your supplier), placed in the incubator at 37°C for 24 hours, and voila! You have an answer.

Easy-to-use interpretation guides are readily available for purchase or can be found online to assist with bacterial identification depending on colour changes and the location of the growth on the plate.

The plates are divided into sections containing different growth media to encourage colonisation of different bacterial species.

Once the pathogen has been identified, informed treatment decisions can then be made in consultation with your regular vet or using your established treatment protocols. Not all infections require antibiotic treatment, and some may even resolve with the assistance of an anti-inflammatory alone.

This can mean more milk in the vat and less money spent on unnecessary antibiotic usage on your farm.

Others may be better off culled, in which case if you have withheld treatment in anticipation of culture results, this option may still be feasible if the cow is free of any withholding periods. Limitations or challenges with on-farm milk culturing systems can arise where the mastitis-causing pathogen is unusual or difficult to culture (such as Mycoplasma species and some Streptococcus agalactiae cases), samples are contaminated during the collection process and results are uninterpretable, or no growth is detected at all.

Discussing results with your field officer and veterinarian is always a good idea.

Should you decide an on-farm culturing system is not for you, samples should still be collected and frozen prior to treating a cow. It is not possible to get a reliable culture result once milk has been exposed to an antibiotic.

Samples can be dropped off for individual culture through your regular vet, or you may choose to store them in case of treatment failure or an outbreak of clinical cases at a later date.

Record keeping

Good record keeping is also essential for managing mastitis in your herd. Recording treatments can help you identify repeat offenders, discover potential issues around treatment efficacy and make informed management decisions.

It is very difficult for your farm advisery team to help you make good choices when it comes to selecting lactating and dry cow treatments without first understanding your herd’s individual clinical picture.

Your farm’s treatment history, herd test information, a Dairy Antibiogram (Bayer Animal Health), and your personal experiences are all important factors to consider when developing a treatment plan.

On the ground, on-farm culturing means rapid identification of mastitis causing bacteria in your herd, so you can direct your time, money and effort towards the most appropriate management strategies depending on the nature of the bacteria.

Get in touch with your regular vet to have a chat about how this might work for you.

- Lucy Collins, APIAM Animal Health

For more information, visit www.dairyaustralia.com.au/farm/animal-management/mastitis/countdown-resources

The author has no affiliations (financial or otherwise) with Bayer Animal Health.