Antimicrobial Susceptibility in Respiratory Pathogens and Farm and Animal Variables in Weaned California Dairy Heifers: Logistic Regression and Bayesian Network Analyses
Brittany L. Morgan Bustamante,
Munashe Chigerwe,
Beatriz Martínez-López,
Sharif S. Aly,
Gary McArthur,
Wagdy R. ElAshmawy,
Heather Fritz,
Deniece R. Williams,
John Wenz,
Sarah Depenbrock
Affiliations
Brittany L. Morgan Bustamante
Public Health Sciences, School of Medicine, University of California, Davis, Davis, CA 95616, USA
Munashe Chigerwe
Department of Veterinary Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA
Beatriz Martínez-López
Center for Animal Disease Modeling and Surveillance, Department of Veterinary Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA
Sharif S. Aly
Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California, Davis, Tulare, CA 93274, USA
Gary McArthur
Swinging Udders Veterinarian Services, Galt, CA 95632, USA
Wagdy R. ElAshmawy
Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California, Davis, Tulare, CA 93274, USA
Heather Fritz
California Animal Health and Food Safety Laboratory System, School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA
Deniece R. Williams
Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California, Davis, Tulare, CA 93274, USA
John Wenz
Field Disease Investigation Unit, College of Veterinary Medicine, Washington State University, Pullman, WA 99163, USA
Sarah Depenbrock
Department of Veterinary Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA
Weaned dairy heifers are a relatively understudied production group. Bovine respiratory disease (BRD) is the most common cause of antimicrobial drug (AMD) use, morbidity, and mortality in this production group. The study of antimicrobial resistance (AMR) is complicated because many variables that may affect AMR are related. This study generates hypotheses regarding the farm- and animal-level variables (e.g., vaccination, lane cleaning, and AMD use practices) that may be associated with AMR in respiratory isolates from weaned dairy heifers. A cross-sectional study was performed using survey data and respiratory isolates (Pasteurella multocida, Mannheimia haemolytica, and Histophilus somni) collected from 341 weaned dairy heifers on six farms in California. Logistic regression and Bayesian network analyses were used to evaluate the associations between farm- and animal-level variables with minimum inhibitory concentration (MIC) classification of respiratory isolates against 11 AMDs. Farm-level variables associated with MIC classification of respiratory isolates included the number of source farms of a calf-rearing facility, whether the farm practiced onsite milking, the use of lagoon water for flush lane cleaning, and respiratory and pinkeye vaccination practices. Animal-level variables associated with a MIC classification included whether the calf was BRD-score-positive and time since the last phenicol treatment.
