Prototheca. Chances are you haven't heard of it before — but it's worth knowing about this nasty little bug and the damage it can do to your herd.

Prototheca causes mastitis in cows (often subclinical), and damages the udder tissue which causes a high somatic cell count and eventually causes the infected quarter to dry up.

Prototheca mastitis cannot be cured by using antibiotics as it is caused by an algae, and the treatment of choice is to cull the cow from the herd.

It can occur as one-off sporadic infection in a single cow — however, there are an increasing number of herds both globally and within New Zealand that are experiencing widespread outbreaks with as much as 30 per cent of the herd infected.


One of the major sources of infection for Prototheca is not drying cows off hygienically.
This might look like not cleaning the end of the teat end correctly, or warming tubes of product in water.

Prototheca cannot be cured by antibiotic treatment, so if tubes of dry cow treatment are contaminated when you administer them you can cause cows to become infected.

Other risk areas are areas of stagnant water on the farm that cows walk through, herd-housing situations or contaminated water sources.

Cows can pick an infection up either from the environment, or through cow-to-cow transmission in the milking shed.

Keep a look at for the warning signs of Prototheca infection in your herd, and make sure you get a culture on any cows that show the following signs: A high SCC with quarters that are going light, non-responsiveness to treatment, or on a herd level a bulk milk somatic cell count that keeps rising and/or a history of having to repeat treatments on mastitis cows.

There is very little known about the risk factors and prevalence of Prototheca specifically in New Zealand, however we do know that the impact an outbreak can have on a farmer and their herd is devastating.

So keep a close eye on your herd, do regular herd tests and milk sampling through your vet, and keep this nasty little bug in the back of your mind when dealing with unusual and difficult to treat cases of mastitis.