Mastitis is a very significant disease of dairy cattle and occurs in all dairy herds. It is an inflammation of the udder usually caused by a bacterial infection, although stress can predispose to this disease. Mastitis may occur in clinical form, where changes in milk are obvious, or subclinical form, where there are no visible changes. It can also be acute, where the cow is seriously ill, or chronic, where the cow may show no outward sign of ill health.
In general, mastitis pathogens belong to one of two categories: contagious or environmental. Bacteria causing contagious mastitis are spread from infected quarters to other healthy quarters of the same or other cows. The spread of this type may be caused by the milker, the milking machine or dirty bedding. Mastitis caused by environmental bacteria is generally associated with dirty, wet bedding and frequently occurs in poorly ventilated housing areas. The bacteria can also be transmitted during the process of milking. Environmental mastitis often affects cows around the time of calving when protection provided by antibiotic dry cow therapy has waned and immunity may be reduced.
The cost of mastitis to the UK Dairy Industry is currently estimated at £93 million per year (British Mastitis Conference, 1997). These costs arise from antibiotic treatment, discarded milk, financial penalties, reduced lactation yield following an infection and increased milking times. The disease results in discomfort, pain and premature culling.
The incidence of both clinical and sub-clinical mastitis has fallen over recent decades. Somatic cell counts (SCC) provide a broad indication of the general level of udder health within the herd and have fallen from almost 600,000 cells/ml in 1971 to about 170,000 in 1997. Papers presented at the British Mastitis Conference in 1997 indicate that clinical cases per 100 cows have fallen from 135 in the early 1960s and are considered to be between 35-40 at the present time.
The decrease in both clinical and sub-clinical mastitis is largely attributed to the introduction of the National Institute for Research in Dairying (NIRD)/Central Veterinary Laboratory Five Point Plan. A reduction in cell counts has been hastened by relating milk payments to cell counts and EC Directive 92/46, which effectively prohibits milk with a high count from being sold off-farm for liquid milk consumption. Latterly, milk buyers have imposed more stringent financial penalties on milk with high SCC and some pay bonuses for very low counts. Experience has shown that where there is a problem with mastitis in herds, part or all of the Five Point Plan is usually improperly implemented. However, where environmental mastitis is a problem, additional attention needs to be paid to the hygiene of the lying area, particularly in calving areas.
The visual identification of clinical cases is primarily subjective and tends to underestimate the number of quarters with a bacterial infection. Although clinical cure rates following antibiotic administration may be high, the elimination of bacteria may not have occurred following such treatment. Experimental evidence has identified that early detection of mastitis and early treatment allow for a greater bacteriological cure. The presence of bacteria in the udder leads to a reduction in the conductivity of infected milk and may prove a useful marker in identifying early cases of mastitis.
A third type of mastitis, referred to as summer mastitis, is an acute illness of dry cows and heifers which causes extensive and painful damage to the udder. The infected quarter is permanently damaged and results in early culling of the cow. Infections are more likely to occur when cows are in an environment where teats can be damaged and fly populations are high. In the UK, summer mastitis affects around 20,000 cattle each year. The disease is transmitted by flies and peak incidence occurs when these are most frequently around cattle. Clinical signs of summer mastitis are a hot, hard and swollen quarter in association with a thick secretion, characterised by a foul smell. In severe cases, cows may develop swollen hocks and become lame. Summer mastitis can also lead to abortion and death in extreme cases.
All dairy producers should follow the Five Point Plan:-
- Hygienic teat management – combined with sound housing management
- Prompt treatment of clinical mastitis
- Dry cow therapy
- Culling chronically affected cows
- Correct maintenance of the milking machine
In addition, it is a requirement of the Dairy Products (Hygiene) Regulations 1995 that the foremilk is examined and discarded. Foremilking is considered the best means of detecting the early signs of mastitis and allows for the stimulus for milk let down.
Environmental mastitis is more likely to occur when cows are housed when there is greater exposure to faecal contamination. Pre-milking dipping with an approved disinfectant may be beneficial.
Poor environmental conditions predispose to mastitis and there is evidence that loose housing in straw yards results in a higher incidence of mastitis than housing in cubicle yards. However, there are good and bad examples of both types of housing: much depends on stockmanship and management. Whatever system is used, cleanliness is a most important factor and plays a significant part in controlling mastitis.
Since de-regulation of the milk market in November 1994, SCC data are no longer collected centrally. This is regrettable and needs addressing to allow proper measurement of trends and to allow the data to be used in breeding programmes. On-farm records of clinical mastitis need to be collated to provide a national picture of clinical mastitis and to aid breeding and research programmes.
More funding of mastitis research is required to identify further the causes and therefore aid prevention and treatment of this costly disease. With antibiotic resistance becoming a concern, research is urgently needed to look for effective alternatives.
- All dairy producers should adhere to the NIRD/CVL Five Point Plan which, together with good stockmanship, will help control mastitis infection.
- Mastitis control should be part of herd health monitoring with targets set for incidence.
- Monitoring and recording of antibiotic tube usage should be an integral part of herd monitoring and should include tubes used per herd and per individual cow.
- Mastitis monitoring and control should be a part of routine veterinary visits. Milk samples should be taken in order to identify the causal agent and antibiotic sensitivity testing carried out to allow better targeting with antibiotics or other efficacious treatments.
- The development of systems to aid the early detection of mastitis should be encouraged by the Government and the industry.
- Controls for summer mastitis should include control of flies (particularly from July to September), use of eartags impregnated with insecticide, sprays or pour-on preparations and avoidance of high risk pastures.
- If summer mastitis occurs as a significant herd problem, veterinary advice should be sought and a suitable control programme implemented.
- Further research should be undertaken to develop vaccines, and other treatments, for the prevention and control of mastitis and to avoid routine usage of antibiotics.
- Consideration should be given by the industry to the central collection of SCC data, and records of cases of clinical mastitis, to aid monitoring of mastitis health in the national herd.