The enforced transition from blanket dry cow therapy to selective dry cow therapy in the netherlands: an evaluation of the effect on udder health parameters

Introduction

In response to the global increasing interest in the responsible use of antimicrobials and a reduction in the use of antimicrobials, there has been an enforced transition from blanket antimicrobial dry cow therapy (BDCT) to selective antimicrobial dry cow therapy (SDCT) in the Netherlands since January 1st 2014. The somatic cell count (SCC) thresholds to select cows for antimicrobial dry cow therapy were based on a simulation study by Scherpenzeel et al.^{(1, 2)} and were assumed to result in an optimal tradeoff between reduced antimicrobial usage associated with udder health versus increased risk of new intra-mammary infection (IMI). Particularly the potential increase in both clinical mastitis and subclinical mastitis and its negative impact on animal welfare and production raised concerns in the veterinary and dairy industry. Therefore, the aim of this study was to evaluate the effect of the enforced transition from BDCT to SDCT, as a result of the legislative guideline on dry cow therapy in the Netherlands, on udder health at national, practice and cow level.

Material and Methods

Udder Health at National Level A random selection of 3500 dairy herds with ≥ 70 cows in DHI recording was made from data available through CRV (Arnhem, the Netherlands). Data of each DHI recording from 2011 through 2015 was available.

An elevated SCC has been used as an indirect measure for the presence of an IMI. Multiparous animals with a SCC ≥ 250,000 cells/ml and primiparous animals with a SCC ≥ 150,000 cells/ml were classified as infected⁽³⁾ . The SCC of each animal that was sampled for DHI, percentage infected and percentage new infected were routinely reported at each new DHI recording and were converted to a monthly variable per herd. This data was next used to calculate the following parameters in relation to dry cow management: herd level SCC, being the mean of the individual animal SCC in that herd; the percentage of animals with a new infection at the first DHI recording after the dry period (% new IMI); and the percentage of animals that were cured of an IMI during the dry period (% cured IMI). [...]