What Are You Missing?

Warrnambool Veterinary and more recently Count Down Down Under have recommended taking samples from cows with mastitis and getting cultures done.

We admit sometimes the results are frustrating and sometimes you get the same results. But not always. Recently we have had some different results. Without regular cultures the farms involved could have had a major problem. Two farms found a bug called Pseudomonas aeroginosa in some cows with clinical mastitis. As outlined below, pseudomonas can be lethal – luckily we found the source on both farms before a major problem occurred.

Pseudomonas bacteria:

  • is a bug which loves water. On one farm the bug was in the rubber hose used to wash the dairy. On the other farm it was in the tank storing water for dairy washing.
  • is rarely a cause of mastitis, but when it does it can make cows VERY sick VERY quickly and they can die rapidly.
  • gets into the cow when water droplets are floating around when cows are milked. The worst case I have seen happened when pseudomonas was in the water supply at the dairy. The bug got into the cow at dry off time, but did not cause illness until the stress ofcalving. Once calved, these cows died quickly.
  • is resistant to all the antibiotics we can use in cows!
  • on both these farms, could have caused a serious mastitis problem.

We have had other farms with a bug called Mycoplasma which cannot be treated with antibiotics!

Culture Results

Unfortunately, often culture results come back as either:

No growths – this means there was not much of the bug in the sample despite the mastitis OR the bug died getting to the lab. It is usual to get about 25% no growths


Contaminated – This means some bugs from the teat OR your hands have got in the sample jar at collection. Contamination usually results from poor milk collection technique and because the lab grows several bugs, we do not know which bug is causing the mastitis.

So to get the best out your milk samples and get the best bang for your buck, here’s a reminder on good collection techniques.

When to culture

Clean cow udderWarrnambool Veterinary recommend taking a sample from every case of clinical mastitis before the first treatment. Antibiotic in the sample – even if the wrong antibiotic - will make is very difficult to grow a bug. Put the sample in the fridge or freezer - ensure sample labeled with date of collection and cow number. If you only end up having a couple of cases and they respond to treatment, you don’t need to send the samples for culture, but if you do wish to investigate further, you’ve got some to start with.

Milk cultures are especially recommended whenever a herd problem emerges, either more clinical cases than acceptable, rising cell counts, or failure to recover after treatment. They are used to indicate which bacteria are present within the herd, so samples from a number of cows are required to give a representative picture. Ideally a minimum of 10 samples are needed.

Cows with high cell counts

To investigate a herd cell count problem, it is sensible to sample some of the individual cows with high cells counts. Here the sample is often a composite one (some milk from all four quarters). In some cases the infection can be missed because the bacteria from one infected quarters is diluted by milk from the others. In this case 10 samples is a minimum, as there are likely to be some “no growths”. Submitting more than 10 samples can be useful. As a general rule, it is not economic to treat high cell count cows without clinical mastitis. In some circumstances, however, it may be done after long discussion with your vet. Knowing which bugs are involved is the first step.

Collecting Milk Samples

Sterile collection is the most important step for successful culturing of milk samples. Poor technique will give misleading results and re-sampling will be required. Good technique requires some planning and patience. It is a good idea to set yourself up a “kit” with the necessary equipment in a clean box in a prominent location in the dairy.

Have the following ready in the dairy:

  • Sterile sample bottles – available from the clinic. Do NOT use an old jar.
  • Marker pen to label the bottle
  • Disposable gloves
  • Paper towels
  • Cotton balls
  • A mixture of 70% alcohol (7 parts methylated spirits to 3 parts (clean) water!) or teat wipes.

How to collect milk samples

1. Collect a milk sample from ALL cases of mastitis before treating.

2. Label the bottle.
> Unlabelled samples are useless – it’s important to identify the sample.
> Do this before collection as it can be difficult to write on a label with milk sprayed on it.
> Label with the date, cow ID and quarter sampled.

3. Restrain the cow so she can’t move around too much.

4. Put on disposable gloves.
> Remember, your hands carry bugs AND you could carry this mastitis bug to the next cow.

5. Wash and dry the teats
> You might skip this step if the teats look clean.
> Wash teats with running water.
> Avoid getting too much water on the udder, the udder is hard to dry, and drops of  contaminated water can easily fall into the sample.
> Dry teats with paper towel.

6. Disinfect the end of the teats to be sampled – this step is critical!
If you are sampling more than one teat, disinfect the ones furthest away first.
This reduced the risk of unintentionally contaminating an already disinfected teat.
Disinfect vigorously scrubbing the teat opening with a cotton ball and alcohol (or teat wipes) for a minimum of 10 seconds.
Check the cotton ball. If there is any dirty color, repeat the scrub using a clean cotton ball until there is no more dirt seen.

7. Get the sterile bottle ready
Remove the cap and place upside down in a position not likely to be contaminated.
Do not touch the inside surface of the cap or bottle.

8. Establish the direction of flow from the teat.
Squeeze the first couple of squirts of milk onto the ground.
This also helps remove any contaminants that might be just inside the opening of the teat.

9. Collect the sample in the bottle.
Hold the bottle at the angle of about 45 degrees (to avoid anything falling onto it) at least 3-4cm from the end of the teat. Squirt 2-4ml of milk into the bottle.
Only a small amount of milk is required for culture.
Trying to get a large sample increases the chance of contamination.
If you are collecting a combined sample from all quarters, move the bottle away from the first teat, and repeat the initial squirts of the next teat before moving the bottle back.
Take the first samples from the teats closest to you.
Try to get the same amount from each teat.
A combined sample from all quarters may be less likely to grow bacteria because milk from one infected quarter is diluted by milk from the clean quarters.

10. Replace the cap and secure it tightly.
Place sample in fridge straight away.

11. Wash your hands
Use running water and dry on paper towel
Wash your hands after each cow, including the last cow.

12. Deliver sample to vet that day or freeze until delivery is arranged.