|
189. 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.
190. 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.
191. 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.
192. 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.
193. 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 (see paragraph 198). 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.
194. 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.
195. 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.