The Rapid Mastitis Test (RMT), also known as the Californian Mastitis Test is often recommended to farmers as a simple ‘cowside’ test they can do to quickly identify cows with high somatic cell counts that may be contributing to a grading problem.
It is a simple test to do, but many people are unsure or scared of this test and therefore shy away from it or turn to more expensive options such as electronic testers, which may not be as good as we originally thought at picking up genuine high SCC cows.
Inflammation of the udder causes massive numbers of white blood cells to move into the milk to fight the infection. These white blood cells, together with a smaller number of damaged udder cells make up the ‘somatic’ cells of the milk, thus the SCC increases in cows with mastitis.
It is these cells that react with the RMT reagent and cause the formation of a thickened slime or gel. This makes the RMT test very specific to somatic cells and therefore probably more reliable than other cowside tests out there.
So, how do you do it?
Get hold of an RMT paddle and reagent. The newer blue ones are easier to read than the older ones so use them.( If you own an older white paddle, consider painting the inside of the wells black to make interpretation easier) Never make up your own reagent; always use a proper commercially prepared RMT reagent for consistent results. Old washing liquids or shed detergents do not work and will handicap your efforts to find problem cows.
Discard the first few squirts of milk and then squirt 2-5mls of milk from each quarter into a separate well on the RMT tray. (A little bit of cow dung won’t affect your results; a lot might - if this happens start again)
Get out from under the cow before she knocks that paddle out of your hand forcing you to do it again!
Mix each milk sample with an equal amount of reagent
Swirl the mixture vigorously for 10 or 20 seconds then assess the degree of gelling in each sample
Rinse the RMT paddle in clean water and move to the next cow to repeat the test.
The reagent ruptures the somatic cells and causes them to thicken into a gel. The degree of gelling or thickening will give you an indication of how severe the infection is or how high the SCC is in that quarter.
Detection and interpretation is subjective, but with practice you can get pretty good at deciding what is important and what isn’t. Here is a scoring system guide to help you interpret what you see:
Score Gelling approximate SCC appearance
Negative none 100,000 or less normal milk, no thickening
Trace slight 100-300,000 slight thickening then disappears
1 slight to moderate 300-900,000 distinct thickening but no gel forms
2 moderate around 3,000,000 thickens immediately and gel forms
3 heavy around 8,000,000 obvious gel forms with “fried egg”
Remember that this relates to SCC for an individual quarter when deciding what cows need to come out:
A slight gel in one quarter represents a count in that quarter of maybe 300,000. If the other quarters are negative then her total SCC would be say 500,000 ÷ 4, which is 125,000. She is unlikely to be the cow causing you grading problems.
You are generally looking for cows with strong reactions in a single quarter or moderate reactions in multiple quarters that are the ones you need to remove from supply and sample i.e. the 2’s & 3’s.
You will find the first time you sample a large number of cows with the RMT to sort out a SCC problem that you will pull out a lot of cows. Don’t panic. Pull them out and then bring them back in after milking and resample them to sort out the real problems from the others, which for now should be monitored and examined more closely after your next herd test.
Generally there are only a handful of cows causing you to grade and they are ones you need to find and remove.
Time of year is also important:
In spring, colostrum contains very high numbers of somatic cells, which can cause mild gel reactions, whereas milk from an infected quarter will create a very thick, almost solid gel. Look for very definite reactions when testing cows within a few days of calving.
In very late lactation, low milk volumes and the natural drying off process can also increase the cow’s SCC, so once again, only interpret the very definite gel reactions as sub-clinical mastitis.
Where we have helped a client get on top of a SCC problem we generally get them to grant us 3rd party access to their production details in Fencepost.com This enables us to keep an eye on their count through the rest of the season and be ready to respond if a problem appears to be re-surfacing. To get third party access we need your username & password or you can grant it to us from your end using our username “prolapse”. We particularly want access to your 10-day production & quality records, SCC graph, production & quality summary and historical production records because these can help us when investigating trends in grading problems.