Within herd comparison of teat dipping and dry cow therapy with only selective dry cow therapy in six herds.

A within herd comparison of teat dipping and dry cow therapy (full treatment) with only selective dry cow therapy (partial treatment) was carried out in six commercial dairy herds for a two year period. In four herds, the incidence of clinical mastitis was 2 to 12 per cent higher in the partial treatment group. In another herd, in which the pattern of clinical mastitis isolates was unusual in that minor pathogens were isolated from 30 per cent of mastitis cases, the incidence was 43 per cent higher in the partial treatment group. In the remaining herd the incidence was 10 percent higher in the full treatment group. Streptococcus uberis mastitis was more common in the partial treatment groups of five herds; coliform mastitis was more common in the full treatment groups of two herds and similar in both groups in the other herds. High rates of coliform mastitis were associated with poor herd environmental conditions but this was not true for Strep uberis mastitis. Rates of staphylococcus aureus and Strep dysgalactiae mastitis were low in all herds. The level of major pathogen infection in cows completing the trial in all herds increased in the partial treatment group from 5 per cent of quarters at the start to 12 per cent at the finish of the trial. In the full treatment group, however, there was only a small increase in this level. In contrast, levels of Corynebacterium bovis infection increased by 17 per cent in both treatment groups. Continued use of teat dipping and dry cow therapy was associated with a higher rate of coliform mastitis in two of the three herds where there were poor standards of hygiene and husbandry.