Mastitis

Introduction

Mastitis is one of the three most significant health problems of the UK dairy herds, together with lameness and fertility problems. The effect of mastitis on milk quality has recently gained added importance with the introduction of an EU-wide upper legal limit for somatic cell counts in milk destined for liquid market at 400 000 cells/ml. Public interest in the welfare of production animals and the recognition of mastitis as a major source of pain for affected cows give added focus to mastitis concerns.

TREATMENT

LACTATING COW TREATMENT

Mild clinical mastitis is usually diagnosed and treated by the farmer using intramammary tubes. On the basis of probably efficacy penicillin/aminoglycoside combinations have as successful a "cure" rate as any other antibiotic; they have short withdrawal times and are cheap.

Acute and per-acute cases are best treated by systemic injection. Intramammary treatment with the same antibiotic is appropriate but this would probably be only in the uninfected quarters since frequent stripping out and inflammation makes intramammary treatment of the infected quarter worthless.

The immediate main aim of the antibiotic is to halt the septicaemia and hopefully also to kill the bacteria in the udder. Since the problem is so acute, since isolation of the causative organism is too slow, and since differentiation of the two main bacteria responsible is not always possible on clinical grounds, the aim is to use an antibiotic reasonably effective against these two organisms. Antibiotic therapy in acute mastitic cases is probably secondary to fluid therapy in terms of altering the prognosis. Large volumes of fluid given intravenously can be life-saving.

DRY COW TREATMENT

All quarters in all cows be treated with a "dry-cow" intramammary tube at drying-off. Treatment in the ‘dry* period is

To prevent new infections (60% of all new infections arrive in the dry period, and 90% of these via the teat canal in the first 3 weeks of the dry period).
To remove "chronic" subclinical infection i.e. those leading to persistent high cell counts.
They prevent "summer mastitis" - but this is rarely a reason for their use.
A second infusion after 4 weeks of the dry-period may be valuable if there is a high incidence of infection.

TEST DIPS

In reducing high cell counts, teat dips and hygiene are extremely important. The teat dips should be iodophors, or glutaraldehyde, or hypochlorites in high concentration. Others such as chlorhexidine and quaternary ammonium compounds give poorer efficacy.

Mastitis – causative factors

Our understanding of mastitis has developed in several stages over the past 100 years. An association between mastitis and pathogenic micro-organisms was established in 1887. Most major pathogens were identified by the 1940s. When antimicrobial therapy became available for production animals in 1945 it proved effective in the control of some, but not all, mastitis pathogens. This prompted further research into potential husbandry related causes of mastitis. In the 1960s, the multifactorial aetiology of bovine mastitis was commonly recognized .

Today, mastitis is considered to be a multifactorial disease, closely related to the production system and environment that the cows are kept in. Mastitis risk factors or disease determinants can be classified into three groups: host, pathogen and environmental determinants.

Mastitis and somatic cell counts (SCC)

Somatic cell counts (SCC) have long been used as a way of measuring milk quality. Most dairy companies base their milk pricing policy, among other things, on SCC values of the milk. The SCC levels in the national dairy herd in the UK have declined steadily since the 1970s and are now well below 200 000 cells/ml, both in bulk tank milk and in average individual cow milk in milk-recorded herds. The maximum legal limit for saleable milk is 400 000 cells/ml.

The somatic cells consist mainly of immune cells that enter the milk compartment of the udder. Only a minority of these cells are dead cells from the udder tissue. There are always small quantities of immune cells in the cow’s milk, and their function is to protect the udder against infection by bacteria. The older the animal gets, the more somatic cells it tends to have in its milk. Similarly, the SCC levels are higher immediately after calving and towards the end of each lactation.

When bacteria do enter the udder, the number of immune cells increases rapidly, as the immune system attempts to overcome the infection. Once the infection has been cleared, the SCC levels gradually drop to normal. This can sometimes take weeks, however. In cases of chronic infection, where the bacteria persist in the udder, the SCC levels can remain high throughout the lactation.

High SCC levels in the milk cause deterioration of the milk quality. It has been shown that levels above 500 000 cells/ml decrease cheese yield and affect yoghurt making. The shelf life of milk is also affected, but at a higher level of SCC.

Consistently high SCC levels in a herd are usually a sign of high levels of subclinical mastitis. Most cases of subclinical mastitis are caused by contagious mastitis bacteria (S. aureus or Str. agalactiae), even though Str. uberis is increasingly considered to cause chronic mastitis as well.

Masititis in the UK

In the UK, no national survey data on clinical mastitis has been produced since 1986. Annual incidence in England and Wales was reported at 54.6 cases per 100 cows in 1980 and 41.2 in 1982. A recent survey of DAISY (Dairy Information System) recorded herds in England and Wales reported the following parameters for clinical mastitis: 39.9 cases per 100 cows; 25.9% of cows affected and a recurrence rate of 18.3. Another survey of English and Welsh dairy herds participating in an udder health programme found an average clinical incidence rate of 34 cases per 100 cows. Whilst these surveys offer no data on the prevalence of different mastitis pathogens, sporadic evidence from small field surveys and summaries of VI-centre isolations of mastitis pathogens suggest that E. coli has become the most important mastitis pathogen in the UK, with Str. uberis as the second most important pathogen . This anecdotal evidence also suggests that staphylococcal mastitis has significantly declined in significance in the past 30 years. It is, however, suggested that there are great regional variations in the prevalence of different mastitis pathogens, and that S. aureus still remains an important mastitis pathogen in the north of England and Scotland.

Organic dairy farmers have identified mastitis as a major concern in the UK, mainly due to non-use of antibiotic dry cow therapy and the need to maintain low somatic cell counts in the milk. Animal welfare aspects of controlling and treating mastitis are also important on organic farms, where the maintenance of high welfare standards is important.