2023 CRWAD

2023 Conference of Research Workers in Animal Diseases (CRWAD)


Exploring the associations between perceived self-efficacy, subjective norms, and the intention to use antibiotics

C. Brooks, T. Cheng, D. Wilson, J. Pempek, K. George, D. Renaud, G. Habing

Human values and attitudes on antibiotic resistance are important when seeking to understand antibiotic use among U.S. dairy farmers. Using Schwartz’s theory of basic human values and Ajzen’s planned behavior theory, we hypothesized that different human values, and attitudes towards perceived ease or difficulty of administering antibiotics influence the use of antibiotics, and the relationship is mediated by what others think of their use. Methods For this study, 269 non-organic dairy farmers were selected from a 2021 survey consisting of 45 questions completed by 315 farmers from FL, MI, OH, VT, and WI. SPSS was used for descriptive, exploratory, and confirmatory analysis. Structural Equation Modeling was used for model fit, mediation, and differences between human values. The construct of perceived selfefficacy included items addressing effort needed to measure and improve how antibiotics are used, availability and use of protocols, and situations meriting the administration of antibiotics in the herd. Intended use was measured by two vignettes of a metritis case warranting antibiotics and whether intramammary antibiotics are used at dry-off. Subjective norms included referencing product labels and the degree of value placed on veterinarian and peer recommendations. The Portrait Values Questionnaire was used to examine differing human values. Results Model fit was appropriate (p ≤ .001; CFI = .96) indicating those with greater self-efficacy for administering antibiotics are more likely to consider advice regarding antibiotic use when necessary. Likewise, the human values model fit was appropriate (p = .04; CFI = .97) indicating those who value stimulation, self-direction, and hedonism perceived themselves as capable of appropriate antibiotic use, would consider advice, and use antibiotics when necessary. Conclusions Results indicate human values can influence the administration of antibiotics as those who value obedience, tradition, benevolence, egalitarianism, security, and stability are less likely to reference product labels and consult veterinarians and peers prior to using antibiotics.

Prevalence and relatedness of Salmonella recovered from Ohio and Wisconsin livestock markets

S.R. Locke, D. Reese, R. Meyer, J. Pempek, D. Sockett, N. Aulik, G. Habing

Livestock markets are critical infrastructure used for animal sales and movement that influence pathogen dissemination on a regional and national scale. Indeed, a 2016 Salmonella serovar Heidelberg outbreak, linked to surplus dairy calves at livestock markets, sickened 63 people across 17 states. This repeated cross-sectional study aimed to assess the prevalence of multidrugresistant Salmonella ser. Heidelberg and other serovars of public health relevance in Ohio and Wisconsin livestock markets. Twenty-four livestock markets (14 from WI and 10 from OH) that frequently sold surplus calves were enrolled. Market environments were sampled twice three months apart. State inspectors used boot swabs to sample the following areas: loading dock, main livestock thruway, and two pens used to hold surplus calves. Swabs were shipped to the Wisconsin Veterinary Diagnostic Laboratory for Salmonella culture, serotyping, and antimicrobial susceptibility testing. Whole genome sequencing was conducted at the Ohio Department of Agriculture and the Applied Microbiology Services Laboratory at The Ohio State University. Sample-level Salmonella prevalence was 99.1% (111/112) in Wisconsin markets and 94.9% (75/79) in Ohio markets. Negative samples from Ohio were from the same market across both sampling dates. Serogroups B, C2, and D1 isolates were selected for susceptibility testing and whole genome sequencing. Multidrug resistance (resistant to 3 or more classes) was exhibited by 41% (12/29) of tested isolates. Salmonella ser. Heidelberg was not recovered from any samples; however, other serovars of public health relevance were identified, including Newport and Agona. Sequencing data revealed related strains across markets. For instance, a closely related Salmonella ser. Panama group was recovered from three Wisconsin markets. These isolates clustered closely with isolates derived from retail meat, other livestock species, and clinical human cases. Results suggest livestock markets play an important and under-recognized role in pathogen dissemination between livestock populations.

Impact of sublethal biocide exposure on antibiotic resistance gene transfer in Salmonella

P. Vinayamohan, S.R. Locke, G. Habing

Salmonella enterica is an economically significant pathogen in livestock and human health, known for resistance to medically important antibiotics and capacity for environmental dissemination. Biocides are used in large volumes for cleaning and disinfection of farm buildings and food processing facilities leading to their accumulation in low concentrations throughout the farm environment. When present at sublethal concentrations, biocides alter bacterial characteristics causing selective survival of resistant bacteria. However, little is known about the impact of biocide application on promoting antibiotic resistance in Salmonella. We hypothesized that sublethal exposure to disinfectants would promote horizontal gene transfer in Salmonella. Salmonella Agona (containing blaTEM, ampicillin-resistant), a livestock environment-derived multidrug-resistant pathogen, and a susceptible strain of E. coli (made nalidixic acid resistant) was used as the donor and recipient strains respectively. Sublethal concentrations (SC) of two widely used biocides, bleach (chlorine) and Tek-trol (phenolic disinfectant) were determined by agar plating methods in which biocides were added in increments in broth until no inhibition in growth of donor and recipient bacteria was observed. Conjugation experiments were conducted by mixing equal concentrations of donor and recipient (1:1) along with the SC of disinfectants and incubating for 24 hours at 37oC. Donor, recipient, and transconjugant colonies were enumerated separately on tryptic soy agar containing ampicillin, nalidixic acid, and ampicillin-nalidixic acid respectively. The results were analyzed using a Mann-Whitney test which demonstrated that biocides, namely bleach at 50 – 100 ppm concentrations, and tek-trol at 4 – 6 mg/ml significantly increased conjugation frequency when compared to the controls. This study provides insights to the potential contribution of biocides on the spread of antibiotic resistance in the environment. However, additional research is needed to better understand the impact of biocides on antibiotic resistance.

Prevalence and sources of Salmonella lymph node infection in special-fed veal calves

J. Pempek, S.R. Locke, R. Meyer, R. Portillo-Gonzalez, D. Sockett, N. Aulik, G. Habing

Peripheral lymph nodes (LNs) have been implicated as potential contaminants of ground beef, yet the source and timing of Salmonella LN infection in cattle is still unclear, limiting targeted intervention. The aim of this study was to leverage the vertical integration of special-fed veal production to identify preharvest environmental exposures, specifically in livestock trailers and harvest facility holding pens where calves spend 30 min to 4 h, that result in Salmonella LN infection. Ten cohorts of 80 to 82 veal calves were followed through the harvest process, and environmental samples were collected in barns, trailers, and holding pens. Mesenteric LNs from 35 calves were collected at harvest, and 25 prefemoral LNs per cohort were pooled. Within the same cohort, for 12 samples for which the serovar of the environmental and calf LN Salmonella isolates matched, the isolates were submitted for whole genome sequencing to determine whether environmental exposure resulted in LN infection. Cohort-level Salmonella mesenteric LN prevalence ranged from 0% (0 of 35 samples) to 80% (28 of 35 samples), and pooled prefemoral LNs were positive for Salmonella in 3 of the 10 cohorts. Salmonella prevalence in samples from barns, livestock trailers, and harvest facility holding pens was 22% (13 of 60 samples), 74% (59 of 80 samples), and 93% (74 of 80 samples), respectively. Some environmental and LN isolates were multidrug resistant. Four instances of Salmonella transmission from trailers and/or holding pens to calf LNs were supported by sequence data. Salmonella serovars Agona, Give, and Muenster were identified in transmission events. One instance of transmission from the livestock trailer, two instances from holding pens, and one instance from either trailer or holding pens were observed. Further research is needed to evaluate the extent of environmental Salmonella transmission in cattle and to determine whether targeted interventions in trailers or holding pens could reduce novel Salmonella LN infection in veal calves before harvest.

Prevalence and characterization of Salmonella in mesenteric lymph nodes of bob veal calves

P. Vinayamohan, S.R. Locke, T. MacLeod, M. Piela, G. Habing

Multi-drug resistant (MDR) Salmonella continues to emerge in food-producing animals. The marketing dynamics of surplus calves that involves transportation from the dairy farms to the auction or livestock markets where they commingle with calves and animals from other farms provide an optimal environment for Salmonella spread. Bob veal calves, or surplus dairy calves marketed at less than three weeks of age, have a higher prevalence of Salmonella than formula-fed veal samples. However, fecal sampling is less sensitive in identifying Salmonella and Salmonella are known to have predilection for lymphoid tissues. Therefore, estimating Salmonella prevalence in lymph nodes in bob veal can be used as a surveillance tool to reveal the earlylife exposures of surplus dairy calf population. The objectives of this study were to estimate the prevalence, strain types, and antimicrobial resistance of Salmonella present in mesenteric lymph nodes of bob veal calves. Ten cohorts of calves were enrolled and mesenteric lymph nodes were collected from randomly selected 30-32 calves per cohort. A Salmonella isolation protocol was applied and all the recovered isolates were characterized by serogrouping. Antimicrobial susceptibility to a panel of 14 antimicrobials was tested by disc diffusion method. Five randomly selected isolates per cohort were whole genome sequenced using Illumina NextSeq platform. Additionally, source information of the calves was collected. Results showed that the number of different sources for calves per cohort ranged between 1 and 19 and cohort-level Salmonella prevalence ranged from 16.7 and 84.8%. A majority of the recovered Salmonella belonged to either B (26.7%), or E/G (26%) serogroups. Eleven percent of the isolates were MDR, which was much lower than the estimates from special-fed veal calves. Overall, the results indicated that the prevalence of Salmonella in bob veal was higher when compared to special-fed veal calves. Hence, identifying Salmonella in bob veal can be used as a proxy for estimating Salmonella prevalence in surplus calf production.

Antimicrobial quantification on dairy farms before and after the implementation of farmworker stewardship training

R. Portillo-Gonzalez, A. Garzon-Audor, R. Pereira, G. Habing

Antimicrobials are critical to preserve animal health. However, the development of antimicrobial resistance represents a public health threat. Veterinarians prescribe antimicrobials, but farmworkers are responsible for making on-farm treatment decisions and their training is vital to promote responsible antimicrobial use (AMU). The objectives of this study were to evaluate the impact of farmworker antimicrobial stewardship (AMS) training and describe AMU on dairy farms across OH and CA. We hypothesized that farms, where AMS training was administered, would have significantly lower AMU compared to farms where training was not administered. We designed a quasi-experimental study with eighteen conventional dairy farms enrolled in Ohio and California. Twelve farms received AMS training and six farms did not. AMS training included a 12-weeks training program focused on increasing accurate diagnosis of cows requiring antimicrobial treatment. We quantified on-farm AMU by measuring the number of used antimicrobial bottles. Treatment incidence using animal daily-doses (ADD) and Poisson regression model were used to analyze AMU data. The highest mean ADD by antimicrobial classes was for cephalosporins at 5.8, followed by penicillins at 5.3 ADD/1000 cowdays. Mean ADD from the training group was at 10.7 and numerically lower when compared to the control group at 13.6 ADD/1000 cow-days. Therefore, AMS training farms had a rate ratio of 0.79 ADD/1000 cow-days lower when compared to farms in the control group. A decreased mean ADD was exhibited for farms in the AMS training group from 11.0 preintervention to 10.2 ADD/1000 cow-days post-intervention. However, Poisson regression mixed model showed that the reduction in the mean ADD post-intervention was not statistically significant (p= 0.916). Cephalosporins followed by Penicillins were the most used antimicrobial classes for the enrolled dairy farms. Intramammary was the primary route of antimicrobial administration used by farm workers. Trained farms did not show a significant reduction in on-farm AMU compared to control farms.