Herd incidence of bovine mastitis in four Danish dairy. districts II. Evaluation of the effect of the mastitis control scheme.

Bacteriological and cytological examinations have been carried out on samples from 6,808 cows belonging to 339 herds in four Danish dairy districts. After a discussion of differences between the districts as regards intensivity of mastitis control, public health surveillance, etc., definitions are given of certain terms, such as presence of bacteria, infection, pathogenic versus non-pathogenic (less pathogenic) organisms. The rate of infection with pathogenic organisms varies between districts from 23% to32% on a cow basis, and from 8% to 12% on a quarter basis. A comparison, on a cow basis, of the occurrence of pathogens as recorded in 1955/58 in three Danish surveys comprising 11 dairy districts, with the occurrence as recorded in four districts in 1972, showed a decline in incidence of between 7 and 9 percentage units. Together with the decline in incidence a definite change in the composition of the udder flora has taken place during that period. In particular, there was a pronounced fall in the occurrence of Group B, C, G, and L streptococci, and a relative increase in the occurrence of Staphylococcus aureus. A comparison, on a quarter basis, with the occurrence of pathogens in 30 English herds subjected through three years to intensive mastitis control, including systematic treatment of dry cows, teat dipping, and weekly inspection, showed that by such a programme a slightly lower level of infection was reached than in the 399 Danish herds which had been subjected to collective control for 10-15 years. The annual financial loss per cow suffering from mastitis being estimated at D.kr. 600.-, the reduction noted in the occurrence of bacteria in cows' udders implies an annual national saving of D.kr. 42 million on account of the Danish mastitis control. The total annual expenditure on Danish mastitis control is estimated at D.kr. 9million expenses would rise to some 70 million D.kr. if all registered cows were to be treated on drying-off, and if general teat dipping was to be carried out.