Selective dry cow treatment in dairy cows

In the dairy industry, udder health is associated with mastitis management, of which blanket dry cow treatment has been an important part for decades. To prevent the udder from new intramammary infections during the dry period, the use of blanket dry cow treatment has been advocated for more than 50 years as part of the five-point mastitis prevention program. The goal of dry cow treatment is to reduce the prevalence of intramammary infections by eliminating infections already present at drying off and by preventing new infections from occurring during the dry period. Since 2012, preventive use of antimicrobials in veterinary medicine is prohibited in the Netherlands. Therefore blanket dry cow treatment has been replaced by treatment of infected cows only, known as ‘selective dry cow treatment’. Although selection of cows is an important part of selective dry cow treatment and has a great effect on the consequences, not much research had been done in this field. Therefore it was considered valuable to evaluate the effect of various approaches to select cows for dry cow treatment on parameters such as udder health, antimicrobial use, and economics. Understanding and balancing these effects contributes to an optimal strategy in dry cow treatment and to prudent antimicrobial use in the dairy industry. The aims of this thesis were to quantify the effects of selective dry cow treatment on clinical and subclinical mastitis, antimicrobial use and economics. The effect of different somatic cell count threshold-scenarios for selecting cows for dry cow treatment on these parameters were evaluated. The economic consequences of using different numbers of dairy cows with antimicrobials at drying off, were evaluated as was the attitude of the dairy farmer and the veterinarian with respect to selective dry cow treatment and to reduction of antimicrobial use on dairy farms in general. This thesis shows that reduction of antimicrobial use at drying-off leads to an increased risk of mastitis at the individual level. The effect at the herd level was, however, very small. Criteria chosen to select cows for dry cow treatment had a limited effect on udder health, while the effect on the amount of antimicrobials used was large. Economics was found not to be an argument not to reduce the use of dry cow antimicrobials by applying selective dry cow treatment, because in almost all scenarios selective dry cow treatment was economically beneficial over blanket dry cow treatment. Application of selective dry cow treatment appeared to be associated with farmers’ and veterinarians’ attitude. Their mindset towards reduction of antimicrobial use is crucial for successful implementation of a selective dry cow treatment strategy. Over the last years antimicrobial use in the dairy industry in the Netherlands decreased enormously, in which the introduction of selective dry cow treatment played an important role. Although reduction of antimicrobial use at drying-off leads to more mastitis at the individual level, it was successfully implemented in the Netherlands without dramatic effects on udder health. These changes were realized by constructive cooperation between farmers and veterinary practitioners in the field, supported by the main stakeholders