1 July 2014

7 minute read

The recommended 5 point plan has historically helped to keep mastitis under control, writes Eric Hillerton, chief scientist for DairyNZ Ltd, New Zealand.

The plan is based on the following practices; disinfecting teats after milking, treating mastitis cases promptly, dry cow treatment of all cows, culling chronic cows and keeping the milking system in good condition.

Mr Hillerton writes that, of these, post-milking teat disinfection is probably the most cost efficient measure to prevent mastitis. The biggest challenge in mastitis management right now is the need for a careful use of antibiotics.

The recommended 5 point plan has helped reduce cases of clinical mastitis by up to 80 per cent (from about 150 to 40 cases/100 cows/year) since it was introduced around 40 years ago. The plan is based on the following practices:

1) Disinfect all teats after every milking

A huge number of studies show that properly applied teat disinfectants significantly reduce the rate of new intramammary infections. Post-Milking Teat Disinfection is probably the most cost efficient measure to prevent mastitis. It is imperative that the disinfectant acts to promote healing of teat skin lesions. Prior to the development of teat disinfection, 80 per cent of teats were contaminated with Staphylococcus aureus and 60 per cent of teats had sores. Modern disinfectants contain sophisticated teat-conditioning constituents to counter the adverse effects of all forms of environmental and mechanical stresses to teat skin.

2) Treat all cases of mastitis promptly and record data

The development of penicillins and later antibiotics allowed effective treatment, especially of new cases of clinical mastitis with significant rates of bacteriological cure being achieved. It is economically justifiable to treat non-chronic clinical mastitis caused by Gram-positive bacteria with antibiotics but for Gram-negatives it is more questionable.

3) Use dry cow antibiotic treatment (DCT) on all cows that will remain in the herd after the next calving

Some 60 per cent of all new infections have been shown to occur in the dry period, either in the first 21 days after the end of lactation or in the few days around calving. Dry cow treatment cures both many of the infected udders at drying off and the rate of new infection. DCT is an effective procedure in reducing the prevalence of infection.

4) Cull all persistently infected animals

Antibiotics are available to treat all mastitic infections caused by bacteria. However, even when sensitive to the product used, a proportion fails to cure, largely for pathological reasons. When three or more attempts at treatment in a lactation or dry cow treatment have failed, the only sensible advice is to remove the cow from the production herd, a culling. Culling obviously reduces the prevalence of infection by limiting the duration of infection. It also has an effect on the rate of new infection by reducing exposure of the rest of the herd, particularly to highly infectious bacteria such as staphylococci. Culling is obviously a limitation to longevity but this must be balanced by the potential for reduction in mastitis and enhancing the rate of genetic gain, including resistance to mastitis.

5) Carry out at least annual inspection and servicing of the milking machine, and regular maintenance and replacement to manufacturers’ specifications

A key part of hygienic milk production is to reduce exposure to infectious bacteria. Whilst teat disinfection is highly effective after milking, a number of mechanisms may occur during the milking procedure that lead to contamination from infected teats to uninfected teats within the udder and to uninfected cows milked subsequently. These are very much related to the design and operation of the machine milking process. The milking machine has to be configured and operating properly at all times so that the most effective milking vacuum, pulsation characteristics and optimal components are applied.

Economic Impacts

Mastitis costs consist mainly of money from lost production and costs of response e.g. labour and drugs. The costs are rarely understood by farmers. These can all be modeled and calculated but vary with severity of the disease. Prevention also costs and this is more obvious in terms of chemical and equipment purchases, along with labour. For many farmers none of this is real until it affects actual income including milk quality penalties. Certainly the longer-term impacts of failure to recover replacement costs and loss of genetic potential from culling are even less appreciated. Time rather than money is usually the motivation to manage mastitis better.

Challenges

A range of new challenges face today’s dairy farmers. These challenges vary widely between farming systems and regulatory jurisdictions.

Resistance to antibiotics - The easily available antibiotics led to highly significant improvements in removal of infection. Two main methods of treatment are possible:

Lactation treatment - Treating clinical mastitis as rapidly as possible with effective antibiotic products increases the likelihood of a successful cure. Only antibiotic treatment has been proven to aid cure. Treating subclinical mastitis, if the farmer can diagnose it, may help eliminate bacteria but has no proven economic benefit. However, treatment during lactation is also very costly to farmers due to the milk loss and chronic cases should not be treated.

Dry period treatment - A more successful form of treatment is the use of long-acting antimicrobial intramammary infusion immediately after the last milking of the lactation. This achieves a bacterial cure rate of up to 80 per cent compared with 20-60 per cent (varying by pathogen) for lactation treatment. There is no substitute for cure but prevention by an internal teat sealant has offered huge new opportunities for controlling mastitis. This also poses risks if not used properly. As dry cow treatment is the main target of the aim to reduce antibiotic use in dairy cows, at least one useful alternative tool is available.

Technology changes - Technology will continue to substitute for labour in milking cows. This will require a growing area of sensors and information systems. After 20 years, robotic milking systems are an indelible part of dairy farm systems. Now, even more refined robotic technologies are being adopted.

Milk quality - Good average cell counts are the norm in many countries, although all still have a tail of poorly conforming suppliers. Increasing market demand will force those suppliers to comply or force them from the market, eventually.

Vaccines or Genetics?

For forty years vaccines to aid in control of mastitis have been promised; some have reached the market with very limited success. Of greater potential is to understand how some cows of long life never suffer from an intramammary infection – the extent and mechanisms of genetic-based resistance. The ultimate tool in mastitis prevention may yet be selecting for physical defense mechanisms.

Do Better With What is Already Known

Good producers achieve superb milk quality, minimal udder health issues and, therefore, have little need to intervene and treat. This is because:

• They prevent mastitis by diligent application of good technologies.
• They are proactive in management because they are trained and apply good risk assessment.
• They have incentives to do well and are motivated. Various countries have run milk quality competitions for many years. The longest running may be in the US where, out of 50,000 dairy farms, the finalists regularly include the same farms.
• They obviously know what to do and how to do it. It is clear that they exploit all the help available to them from the support and supply industry.
• Their equipment works properly, their products (chemicals etc) are right for the job and the advice available, from veterinarians and others, is pertinent and used properly.

For successful mastitis control, the issue is not necessarily to invent something better but to do better with what is already known.

Key Messages

• Basic control plan was developed 40 years ago. It is still essential but can be customised
• Do not underestimate the value mastitis control, 80 per cent reduction in clinical cases and more than 50 per cent reduction in level of infection
• No new problems have arisen; residual problems need fresh, additional initiatives
• On any individual farm, failures are usually in application of control
• Further advances will come from improved detection and animal genetics
• Biggest challenge is use of antibiotics