THE CONTROL OF MASTITIS

When penicillin was introduced in the 1940s it was assumed that with such an effective treatment, mastitis would soon be eliminated. This proved not to be the case. In fact mastitis is an interesting condition because many of the control methods which we can apply to other diseases are simply not relevant.

• Eradication will never be possible because there are so many different sources of infection, many being normal bacteria in the environment.

• Vaccination does not work well because there is a wide range of bacterial serotypes involved and because immune systems in the udder are relatively poor.

• Antibiotic treatment cannot be relied upon to eliminate infection because chronic foci exist which antibiotics are unable to penetrate.

• The breeding of resistant cows has achieved some success, but is a very slow process.

The basis of mastitis control is therefore herd management, specifically aimed at reducing the level of bacterial challenge at the teat end and thereby reducing the rate of new infections. Mastitis can never be eradicated. However, if milking routines and hygiene techniques are improved so that the spread of infection is reduced, the number of new cases will decrease. This must be done within economic constraints: it is undoubtedly more cost-effective to accept a low level of infection within a herd than to spend large sums of money trying to eliminate the last few cases.

For mastitis therefore, all control measures are aimed at prevention, and as with any other infectious disease, the preventive measures can be subdivided into a number of different stages. For mastitis these are:

1. Control the source of infection. Sources of mastitis bacteria are:

• from other cows, either within the udder or on the teats. These are known as contagious mastitis organisms and are spread from cow to cow during the milking process

• from the environment, for example straw, sawdust, bedding or faeces.

• from flies. This applies specifically to summer mastitis, which is discussed in a separate section on page 216

2. Control the vectors which transmit infection from the source to the teat end.

• for contagious mastitis, vectors are anything - hands, gloves, cloths, machine liners - which repeatedly touches the cows’ teats during the milking process

• environmental mastitis vectors are less precise, but they include anything which can splash infection onto the cows’ teats and any milking machine factor (for example, teat end impacts) which can force environmental bacteria up through the teat canal

3. Maximise the natural defence mechanisms of the teat and udder, for example maintaining teats and especially teat ends in good condition and ensuring that nutritional status (including vitamin E/selenium) is good and stress is minimised. (Chapter 1 explains how stress reduces the immune response.)

These three major preventive measures summarise all the important points in the control of mastitis. The remainder of the chapter will be spent in examining the different aspects of mastitis control and how the above factors can be applied on a practical basis.

As stated above, there are three major types of mastitis infection. The organisms involved in each group are:

Contagious mastitis organisms

These are infections contracted from other cows and transmitted during the milking process. The common examples are:

• Staph. aureus (sometimes referred to as coagulase positive staphylococci). Found within the udder and on teat skin, especially if the skin is dry, cracked or chapped

• Strep. agalactiae, found only in the udder

• Strep. dysgalactiae, especially common on damaged teat skin; it is also involved in the summer mastitis complex

• some strains of Strep. uberis

• mycoplasma

Environmental mastitis organisms

These infections are present in the bedding and general environment and are transferred onto the teats between milkings. These include:

• coliforms, including E. coli, Pseudomonas, Klebsiella, Pasteurella, Enterobacter and Citrobacter

• Strep. uberis (most strains)

• bacillus species

• yeasts and fungi

Summer mastitis

This is a fly-transmitted infection of dry cows caused by a range of bacteria; see page 216.

With such a variety of causes of mastitis, and such a wide variation in the epidemiology of the organisms involved, there can clearly be no one single mastitis control programme applicable to every farm. The various control measures available are discussed under the following headings:

• the milking routine

• the milking machine

• milking the mastitic cow

• post milking teat disinfection

• dry cow therapy

• the environment and mastitis