Staphylococcus aureus and Streptococcus dysgalactiae in Norwegian herds after introduction of selective dry cow therapy and teat dipping.

The objective was to promote a reduction in the prevalence of Staphylococcus aureus and Streptococcus dysgalactiae after 2 years of selective dry cow therapies and teat dipping/external teat sealant implementation. Three different dry cow treatments, one long-acting and two short-acting penicillin-based products were tested at herd level together with a negative control teat dipping group, an iodine teat dipping group and DryFlextrade mark, an external teat sealant. The regimes were independently randomly allocated to 178 dairy herds. Yearly bacteriological quarter milk samples were collected from all cows at the beginning of the trial, after 1 year and 2 years. At herd level, a total of 15% of the herds showed no Staphylococcus aureus isolates after 2 years, compared with 5% at the beginning. The distribution of Streptococcus dysgalactiae infected herds remained the same after 2 years. At cow level, there were no significant differences in the reduction of Staph. aureus between the different dry cow therapies and teat dipping regimes. But there was a significant reduction of Str. dysgalactiae in the iodine teat dipping group compared with Dryflextrade mark and the negative control group. The proportional rate of Staph. aureus positive quarters was reduced from 65.9% to 54.9% after 2 years. As for Str. dysgalactiae, an increase was observed from 14.2% to 15.2%.