Mastitis can cause a significant headache and cost to farmers throughout the year and, without collecting a milk sample, it is impossible to tell which bacteria are responsible for infections.
Cows are currently at their peak milk production and a setback through mastitis or even a spike in somatic cell count can be very costly on the business, so knowing what bacteria is causing the problem is essential for proper treatment and rapid recovery.
A milk sample can be processed in a microbiology lab to identify the bacteria present. However, the problem is that all bacteria will be identified whether they come from the cow’s udder, your hands, or the cow’s dirty tail.
This is known as milk culturing, where a lab grows the bacteria in the samples you have submitted and assesses the colonies that form to identify the causative agents.
The causatives agents are generally staph, aureus, strep, uberis, or agalactiae, along with others that can cause issues on farm level.
It is essential to know which bacteria you are dealing with, as treating cows with the wrong antibiotics may result in the infection persisting. It will also be costly as it means sending more milk into a dump bucket rather than the bulk tank.
Milk sample
A sensitivity analysis then examines the resistance or susceptibility of the cultured bacteria to a list of antibiotics to see the effectiveness.
This is the final step to help identify the appropriate treatment for your cows that require an antibiotic treatment.
The success of milk culturing and sensitivity analysis is completely determined by the cleanliness of the sampling technique as bacteria from the environment, such as your hands or dirt from the cow’s udder or teat, can contaminate the sample.
If the sample gets contaminated, then it is useless and collecting it a waste of time, so a strategy to successfully harvest the milk sample should be implemented.
The following steps have been set out by Animal Health Ireland (AHI) to take a sterile milk sample:
- Clean the teats with running water and disinfectant/cleaning solution;
- Dry the teat or teats with a paper towel;
- If you are sampling more than one teat, disinfect (for a minimum of 10 seconds) the farthest teats first;
- Check the cotton ball or wipe. If it is dirty, repeat and scrub using a clean cotton ball until no more dirt is seen;
- Remove the cap of the sample bottle – avoiding touching the inside surface of the cap or bottle;
- Squeeze the first couple of squirts of milk onto the ground. This also helps to remove any contaminants that might be just inside the opening of the teat;
- Hold the bottle at an angle (to avoid anything falling into it) at least 3-4cm from the end of the teat;
- Squirt 2-4ml of milk into the bottle.
A culture and sensitivity test takes 48 hours and it is then tested, which takes a further 12 hours. In total, test results will take three days.
The test should give you a better picture of the bacteria causing mastitis/cell count issues on your farm and you can then (after consulting your vet), select the antibiotics that will work best in your herd.
Not every cow needs to be tested, but more than one cow should have a sample taken in order to ensure accuracy.
Ideally, the sample should be kept cool and arrive at the lab within 24 hours. If this is not possible, most mastitis bacteria survive freezing, so they can be stored in a freezer before delivery.
