Antimicrobial Metaphylaxis and its Impact on Health, Performance, Antimicrobial Resistance, and Contextual Antimicrobial Use in High-Risk Beef Stocker Calves.

The objective of this blinded, cluster-randomized, complete block trial was to evaluate the impact of metaphylaxis on health, performance, antimicrobial resistance, and contextual antimicrobial use (AMU) in high-risk beef stocker calves. Calves (n = 155) were randomly assigned to receive either saline or tulathromycin at the time of arrival processing. Deep nasopharyngeal swabs were collected from each calf at arrival and 14 d later. Calves were monitored for bovine respiratory disease (BRD) for 42 d. Body weights were obtained at arrival, days 14, 28, and 42. Contextual antimicrobial use (AMU) was calculated using dose and mass-based metrics. Calves given tulathromycin had a greater average daily gain (0.96 ±â€…0.07 kg vs. 0.82 ±â€…0.07 kg; P = 0.034) and lower prevalence of BRD than controls (17% vs. 40%; P = 0.008). Proportions of calves with BRD pathogens identified at arrival were similar between treatment groups [17%; P = 0.94]. Proportions of calves with BRD pathogens identified at day 14 were lower for calves receiving tulathromycin compared to controls (15% vs. 60%, P < 0.001). Overall, 81% of Pastuerella multocida isolates and 47% of Mannheimia haemolytica isolates were pansusceptible. When measured as regimens per head in, AMU in calves receiving tulathromycin was higher than calves receiving saline (P = 0.01). Under the conditions of this study, metaphylaxis had positive impacts on the health and performance of high-risk beef stocker calves, did not contribute to the selection of resistant bacterial isolates in the nasopharynx of treated cattle, and increased AMU.

In this study, we investigated the impact of metaphyactic antimicrobial administration on health, performance, and antimicrobial use in high-risk beef stocker calves. Our findings demonstrated that metaphylaxis improves performance and has positive effects on animal health and well-being but increases total antimicrobial use. Additionally, our study revealed that metaphylaxis alone does not contribute to the selection of antimicrobial-resistant pathogens in the upper airway of treated cattle.

Agreement of antimicrobial susceptibility testing of Pasteurella multocida and Mannheimia haemolytica isolates from preweaned dairy calves with bovine respiratory disease.

OBJECTIVE: Evaluate agreement among the antimicrobial susceptibility profiles of Mannheimia haemolytica or Pasteurella multocida obtained by transtracheal wash, nasal swab, nasopharyngeal swab, and bronchoalveolar lavage. ANIMALS: 100 Holstein and Holstein-cross bull calves with bovine respiratory disease. METHODS: Calves > 30 days old with naturally occurring bovine respiratory disease were sampled sequentially by nasal swab, nasopharyngeal swab, transtracheal wash, and then bronchoalveolar lavage. Samples were cultured, and for each antimicrobial, the MIC of 50% and 90% of isolates was calculated, and isolates were categorized as susceptible or not. Categorical discrepancies were recorded. Percent positive agreement and kappa values were calculated between isolates for each of the sampling methods. RESULTS: Antimicrobial susceptibility varied by pathogen and resistance to enrofloxacin, florfenicol, tilmicosin, and spectinomycin was detected. Minor discrepancies were seen in up to 29% of classifications, with enrofloxacin, penicillin, and florfenicol more frequently represented than other drugs. Very major and major discrepancies were seen when comparing florfenicol (1.9%) and tulathromycin (3.8 to 4.9%) across sampling methods. Some variability was seen in agreement for enrofloxacin for several comparisons (8.3 to 18.4%). CLINICAL RELEVANCE: Susceptibility testing of isolates from 1 location of the respiratory tract can reliably represent susceptibility in other locations. Nevertheless, the potential for imperfect agreement between sampling methods does exist. The level of restraint available, the skill level of the person performing the sampling, the age and size of the animal, disease status, and treatment history all must be factored into which test is most appropriate for a given situation.