How to take a sterile milk sample for bacteriological culture

Identifying high-risk mastitis pathogens on your farm will play a key role in formulating a control plan.

And understanding which bacteria are causing problems will allow you and your vet to target specific areas in order to reduce the threat of mastitis.

Vet Bridget Taylor from Wright & Morten Veterinary Surgeons explains how to take a sterile milk sample for bacteriological culture.

See also: Mastitis plan cuts cases and saves money

Bacteriological culture of a milk sample from an affected quarter should be the most reliable method of identifying which pathogen is causing mastitis, whether clinical or subclinical.

However, it is vital that the milk sample cultured is not contaminated by stray bacteria on the outside of the teat/udder or from the teat canal, otherwise the culture results will be confusing or misleading.

In the case of clinical mastitis, the sample should be taken when the problem is detected, preferably before the cow is milked.

With subclinical mastitis – where the cow has a high cell count but no obvious clots – the affected quarter should be identified using a California Mastitis Kit and sampled before milking.

Teat preparation

If the teats look clean, go straight to stage two. If the teats are dirty, clean off dirt from the teats only (not the udder) with clean running water from the in line hose, then dry with paper towels.

Pre-dip the teats with rapid acting pre-dip (Fig 1) then dry wipe or use individual proprietary pre-dip impregnated cloth (Fig 2).

Wearing a clean pair of gloves, strip out foremilk from affected teat with 3-4 draws.

The whole teat surface should then be disinfected using a surgical spirit-soaked swab/cotton wool (Fig 3).

Then, with a new spirit soaked swab, scrub the teat end gently.

Taking the sample

Remove the lid from a sterile pot (as supplied by your veterinary surgeon) and hold the pot in one hand at a 45-degree incline to the teat end (Fig 4), then milk out the sample from the teat with the other hand.

Only a few ml are required (Fig 5), not a whole pot full.

Avoid touching the inside of the pot and the lid with the teat or your hand and replace the lid as soon as possible.

Label the pot with the cow’s number and the ID of the affected quarter.

What to do with the samples

Take the sample to your veterinary practice for submission to their own lab or referral elsewhere.

Samples taken from clinical cases of mastitis can be frozen in the farm freezer and submitted as a batch when convenient without significant loss of viable mastitis bacteria from the milk. 

If you intend to take samples from a group of high cell count cows with no clinical signs, then consult your veterinary surgeon prior to sampling.

These samples, taken from identified high cell count quarters, should not be frozen so are best taken at the start of the week to allow immediate postage (if necessary), receipt and processing at the lab on a weekday.