18 MARCH 2016
Udder health is a complex issue. In order to improve udder health, and to reduce our use of antibiotics, it’s important to focus on prevention of infections as well as their treatment. On most dairy units, the treatment of mastitis accounts for the vast majority of antibiotic use. This includes clinical mastitis cases, and antibiotic dry cow therapy.
The whole point of using antibiotics is to prevent new infections, and to eliminate existing infections. With new infections, we first need to understand how they occur and what the risk factors are. This requires planning, action and some form of evaluation and monitoring. The National Mastitis Council (NMC) in the USA, provide an excellent 10 point plan for the prevention of new infections:
Establishment of goals for udder health
Maintenance of a clean, dry, comfortable environment
Proper milking procedures
Proper maintenance and use of milking equipment
Good record keeping
Appropriate management of clinical mastitis during lactation
Effective dry cow management
Maintenance of biosecurity for contagious pathogens and marketing of chronically infected cows
Regular monitoring of udder health status
Periodic review of mastitis control program
WHY DO COWS GET MASTITIS?
For a cow to get mastitis, two things have to happen. Firstly, there has to be an overwhelming bacteria load at the teat end, plus there has to be a failure in the cows’ immune system.
Reasons for this could be an excessive bacteria loading at the end of the teat, teat end damage, a suppressed immune system (maybe as a result of calving or other disease factors) or possibly a nutritional deficiency, particularly related to mineral nutrition. If there is an excessive bacterial loading at the teat end it is important to consider hygiene, how stock are handled, milking practices and the condition of the skin on the teats. The teat end itself is a physical barrier and the first line of defence against new infections.
With teat end damage such as hyperkeratosis, the teat is more likely to be colonised by bacteria, whereas cracked teats are 1.8 times more likely to acquire a new infection through the dry period.
TYPES OF MASTITIS
Everyone has an opinion on the types of mastitis that they encounter on their own farms, whether the types of pathogen have ever been tested or not. Knowing what bacteria are infecting your cows is important, and you can’t tell just by looking. For instance, in the picture below, all of the samples were caused by E.Coli.
There are also other ways of classifying the type of mastitis you have, away from the exact pathogen responsible.
ACUTE OR CHRONIC? CLINICAL OR SUB-CLINICAL?
An acute infection is the first active stage of an infection, where milk is abnormal and the cow is showing clinical symptoms. This period usually lasts about 6 to 8 days. A chronic infection happens when the bug has made itself at home in the udder for over 2 months. This is usually a sub-clinical case, where milk appears normal but the cow has an elevated SCC. This cow will often then cycle between clinical and sub-clinical until she is treated and cured.
CONTAGIOUS OR ENVIRONMENTAL?
A contagious pathogen is transmitted from cow to cow, either through milking, contaminated equipment or on hands. These pathogens include Staph. Aureus, Strep. Agalactiae and Mycoplasma. An environmental pathogen is transmitted when teats are exposed to bacteria that originated within the environment, through bedding, mud, manure or through poor milking hygiene. This group of pathogens includes E.Coli, Klebsiella, Enterobacter and some environmental Staphs. & Streps. Whilst these bacteria can be classified like this, it is important to note that these bugs don’t always follow the rules; when infection level is high, an environmental pathogen can start to be passed from cow to cow like a contagious bacteria would.
For contagious pathogens, regular screening is crucial. A culture of the bulk milk tank should be undertaken at least quarterly, and preferably monthly. The sample should be a composite of 3-5 days of milk rather than just a single day and should always be taken with a sterile syringe. Try to freeze the samples before shipping, to limit overgrowth of bacteria. Speak to your vet or to the lab that does your analysis for some guidance on what the results mean.
ON FARM CULTURING
The act of collecting milk samples, putting them into growth culture plates, incubating them and then interpreting the results may seem unnecessary, but can be used as a fast and inexpensive way to categorise mastitis bacteria and create treatment decisions.