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Dry-cow therapy is used to both cure existing intra-mammary infections (IMI) at drying off and to prevent new IMI from occurring during the dry period (Halasa et al., 2009). The early and late dry period represents the time at which dairy cows are most at-risk for IMI (Halasa et al., 2009). IMI also increases the risk of clinical mastitis in the subsequent lactation, most commonly during the first 30 to 60 days in milk (Pantoja et al., 2009). The use of antibiotic dry-cow therapy, environmental pathogen load, and a cow’s immune system contribute to risk of developing a new IMI during the dry period (Green et al., 2007). Therefore, dry-off antibiotic use is common during this period to decrease the effect of IMI or clinical mastitis on milk quality and quantity. In the Netherlands, approximately 61% of dairy cattle that were dried off received antibiotic dry-cow therapy in 2013 (Santman-Berends et al., 2016), which can be provided as selective dry-cow treatment (SDCT – treatment is based on presence of infection at the quarter- or cow-level) or blanket dry-cow treatment (BDCT – all quarters are treated regardless of IMI status) (Halasa et al., 2009). A survey of dairy farmers from Germany concluded approximately 79% of farms performed blanket dry-cow treatment, and only 31% of farms performed bacteriologic examination of milk at dry-off (Bertulat et al., 2015). The National Dairy Study (2015) in Canada found similar results in which 84% of herds used BDCT and 11% used SDCT (Kelton, 2015 [unpublished]). Recently selective dry-cow therapy has gained popularity for its role in proper antimicrobial stewardship and as a means to reduce antibiotic use in the dairy sector (Lam et al., 2017).

Because the prudent use of antibiotics is an imperative in agriculture, it is important to examine the relative efficacies of all antibiotics used to cure existing IMI at dry-off. A systematic review of randomized controlled trials generates the highest level of evidence for the efficacy of a treatment under field conditions (Sargeant and O’Connor, 2014). The addition of a network meta-analysis creates the opportunity to assess antibiotic products used beyond a pair-wise analysis by using a network meta-analysis approach to estimate the relative efficacy of multiple antibiotic options. This review and network meta-analysis will add to existing knowledge by providing up-to-date comparisons of currently licensed antibiotics used for dry-cow therapy. Conducting a systematic review and meta-analysis in this area of research ensures producers and veterinarians are able to make decisions on the basis of efficacy, and if products are equivalent in efficacy, they can use other factors such as level of importance for human health to improve the effective use of antibiotics.

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