A health program for commercial dairy herds. 4. Changes in mastitis prevalence.

A study of mastitis prevalence in 10 herds which participated in a herd health program is reported for varying periods, up to a maximum of 10 years. The program was based on teat dipping with idophor or sodium hypochlorite teat dip, regular maintenance of the milking machine, and selective dry period treatment of quarters which were classified as infected on the basis of California Mastitis Test score and bacteriological examination of milk samples taken before drying off. The procedures reduced mastitis prevalence (measured in cows being dried off), incidence of clinical mastitis, and disposal of cows due to mastitis. Results obtained were similar to those found in short-term studies of control programs based on teat dipping and dry period therapy. The only significant difficulty which arose in maintaining the control program over 10 years was loss of enthusiasm by farmers for teat dipping. This was usually induced by teat irritation problems apparently caused by teat dipping. The use of a monitoring procedure for mastitis prevalence was important in persuading farmers to return to the use of teat dip.