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

Abstract

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 DryFlex™, 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 Dryflex™ 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%.