Selective dry-cow therapy (SDCT) could be used to reduce antibiotic use on commercial dairy farms in the United States but is not yet widely adopted, possibly due to concerns about the potential for negative effects on cow health. The objective of this study was to compare culture- and algorithm-guided SDCT programs with blanket dry-cow therapy (BDCT) in a multi-site, randomized, natural exposure, non-inferiority trial for the following quarter-level outcomes: antibiotic use at dry-off, dry period intramammary infection (IMI) cure risk, dry period new IMI risk, and IMI risk at 1 to 13 d in milk (DIM). Two days before planned dry-off, cows in each of 7 herds were randomly allocated to BDCT, culture-guided SDCT (cult-SDCT), or algorithm-guided SDCT (alg-SDCT). At dry-off, BDCT cows received an intramammary antibiotic (500 mg of ceftiofur hydrochloride) in all 4 quarters. Antibiotic treatments were selectively allocated to quarters of cult-SDCT cows by treating only quarters from which aseptically collected milk samples tested positive on the Minnesota Easy 4Cast plate (University of Minnesota, St. Paul, MN) after 30 to 40 h of incubation. For alg-SDCT cows, antibiotic treatments were selectively allocated at the cow level, with all quarters receiving antibiotic treatment if the cow had either a Dairy Herd Improvement Association test somatic cell count >200,000 cells/mL during the current lactation or 2 or more clinical mastitis cases during the current lactation. All quarters of all cows were treated with an internal teat sealant. Intramammary infection status at enrollment and at 1 to 13 DIM was determined using standard bacteriological methods. The effect of treatment group on dry period IMI cure, dry period new IMI, and IMI risk at 1 to 13 DIM was determined using generalized linear mixed models (logistic), with marginal standardization to derive risk difference (RD) estimates. Quarter-level antibiotic use at dry-off for each group was BDCT (100%), cult-SDCT (45%), and alg-SDCT (45%). The crude dry period IMI cure risk for all quarters was 87.5% (818/935), the crude dry period new IMI risk was 20.1% (764/3,794), and the prevalence of IMI at 1 to 13 DIM was 23% (961/4,173). Non-inferiority analysis indicated that culture- and algorithm-guided SDCT approaches performed at least as well as BDCT for dry period IMI cure risk. In addition, the final models indicated that the risks for each of the 3 IMI measures were similar between all 3 treatment groups (i.e., RD estimates and 95% confidence intervals all close to 0). These findings indicate that under the conditions of this trial, culture- and algorithm-guided SDCT can substantially reduce antibiotic use at dry-off without negatively affecting IMI dynamics.
Bibliographical noteFunding Information:
We are very grateful for the participation and tremendous cooperation by owners and staff at the 7 participating dairies. We also thank the technicians that assisted at each study site: California (Maria Amaral, Gema Camacho, Pablo Duque, Pallavi Nahata, Kruthika Patel, Maria Jose Perez, Cinthya Tovar, and Juanita Zaragoza; DairyExperts, Tulare, CA), Iowa (Jordan Stratman, Courtney Behrens, Emily Schwake, and Austin Ashbacher; Iowa State University, Ames), Minnesota (Kelli Bowman, Joshua Brown, Pedro Paulo Cecillio Ferro, Chandra Dahike, Kaylan Risacher, and Victor Moro Taveira; University of Minnesota, St. Paul), and New York (Lauren Pitman and Michaela Thomas; Cornell University, Ithaca, NY). We also thank Richard Maclehose and Darin Erickson (both at University of Minnesota) for their input on statistical methods. S. M. Rowe was involved in local and multi-site coordination, fieldwork, laboratory work, data management, statistical analysis, and manuscript preparation. S. M. Godden was involved in study conceptualization, herd recruitment in Minnesota and Wisconsin, and supervision of fieldwork and manuscript editing. P. Gorden and A. Lago were involved in study conceptualization, local site coordination, fieldwork, and manuscript editing. D. V. Nydam was involved in study conceptualization, New York herd recruitment, local site coordination, and manuscript editing. A. K. Vasquez was involved in fieldwork, local site coordination, and manuscript editing. E. Royster was involved in study conceptualization and manuscript editing. J. Timmerman was involved in laboratory work and manuscript editing. M. J. Thomas was involved in local site coordination, fieldwork, and manuscript editing. This study was funded by the United States Department of Agriculture National Institute for Food and Agriculture (NIFA, Washington, DC; Award # 2018-67015-28298) and was supported by an in-kind donation of product (Spectramast DC, Orbeseal) from Zoetis (Parsippany, NJ). The Minnesota Easy 4Cast plate is manufactured by the University of Minnesota (St. Paul, MN). However, the study investigators have no financial interest in the sale of this plate. The authors have not stated any other conflicts of interest.
- antibiotic stewardship
- dry-cow therapy
- intramammary infection
- on-farm culture
- selective dry-cow therapy
PubMed: MeSH publication types
- Journal Article
- Randomized Controlled Trial, Veterinary