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Antimicrobial resistance has become a major public health concern, and animal agriculture is often implicated as a source of resistant bacteria. The primary objective of this study was to determine prevalence of antimicrobial resistance in Salmonella and E. coli from healthy animals on dairy farms in Pennsylvania. Confidence intervals (CI) of farm prevalence were calculated for resistance, and the comparisons between different animal groups were adjusted for within-farm clustering. The secondary objective was to identify potential risk factors associated with antimicrobial resistance. In particular, we investigated the correlations between previous antimicrobial use and current resistance in E. coli using multiple logistic regression models. A total of 444 composite manure samples were collected from 80 herds in Pennsylvania. Four age and production groups were included: pre-weaned calves, post-weaned calves, dry cows, and lactating cows. E. coli (n = 2370) and Salmonella (n = 1095), when isolated from the manure composite samples (n = 444), were screened for resistance on antimicrobial supplemented agar. Isolates of interest were further assayed against 14 antimicrobials using a broth microdilution method. Salmonella was isolated from at least one composite manure sample from 51 (67%) farms, with 99% being pan-susceptible, and was detected more frequently in lactating cows and dry cows than pre- and post-weaned calves. The most prevalent Salmonella serogroups were K, C1, and C2. Among the E. coli isolates, resistance was more frequently detected in pre-weaned and post-weaned calves than in dry and lactating cows for all 14 antimicrobials tested (P < 0.05). Multi-drug resistance (resistant to ≥3 antimicrobial classes) in E. coli was detected in 66 farms (83%) and was detected more often in pre-weaned calves (P < 0.05). The blaCTX-M and blaCMY genes were found in cephalosporin-resistant E. coli from 5% and 35% of the farms surveyed, respectively. A number of risk factors, including antimicrobial use, were found to be associated with an increased likelihood of resistance in E. coli, and these associations were not limited to the same antimicrobial classes. The results of this study showed dairy farms, especially pre-weaned calves and their environment, are significant reservoirs for antimicrobial resistance, and antimicrobial use may aggravate the resistance problem. [ABSTRACT FROM AUTHOR]

The objective of this research was to determine the range of colonyforming units (cfu) per gram of Mycobacterium avium paratuberculosis (MAP) in manure from cows previously classified as heavy shedders, and the role of these animals in Johne's Disease (JD) in dairy herds. Cattle are typically classified as light, moderate or heavy shedders based on the number of MAP colonies seen on Herrold's egg yolk media (HEYM). Laboratories routinely report the number of cfu up to 70 per HEYM tube. (Seventy cfu corresponds to an estimated 1,470 MAP cfu per gram of manure.) Counts above 70 are reported as 'too numerous to count' and these cows are classified as heavy shedders. Preliminary investigation found that 1:100 and 1:1,000 dilutions of feces from heavy shedders were appropriate for enumerating the actual concentration of MAP in these samples. Subsequently, more than 200 fecal samples from animals currently identified as heavy shedders were diluted and cultured on HEYM. Supershedders (SS) were defined as animals that had manure with more than 10,000 cfu/gm. Culture results on diluted samples demonstrated that a substantial proportion of heavy shedders were SS, with some animals exceeding 1,000,000 MAP cfu/gm. Whole herd cultures from 4 herds found that 10% to 15% of all culture positives were SS. Not all of these SS cattle demonstrated clinical signs of JD at the time of sampling. It was calculated that SS cattle shedding the highest concentration of MAP were shedding more cfu than 2,000 moderate or 20,000 light shedders. Subsequent culture in one herd after the removal of a SS identified up to 15 animals that were potential false positives on the previous culture. This study has demonstrated the previously undocumented presence of MAP supershedders. The results suggest that SS contribute disproportionately to the herd environmental bioburden and the exposure of uninfected animals to MAP organisms. The data also suggest that the bioburden in herds with a SS present may contribute to herdmates being incorrectly identified as culture positive. Identification and removal of SS animals is likely to be a critical component of a JD control and management program. [ABSTRACT FROM AUTHOR]

Salmonella is a prominent foodborne pathogen in the US and dairy cattle have frequently been identified as reservoirs for this organism. Here we describe a long-term outbreak of Salmonella enterica subsp. enterica Cerro that was detected in a Pennsylvania dairy herd during routine monitoring as part of a longitudinal study of several dairy herds. An initial analysis of individual fecal grab samples from the milking herd indicated a very low prevalence of Salmonella (1/102) and Salmonella was not detected in 10 environmental samples. In a subsequent sampling 6 mo later, Salmonella was isolated from 43.5% (47/108) of the cows and 40% of collected environmental samples (10/25). The Salmonella isolated in the first sampling was serovar Typhimurium var. Copenhagen, however isolates from the second herd sampling were serovars Cerro (91.5%) and Kentucky (8.5%). Sporadic environmental sampling between these initial complete milking herd samplings yielded serotypes Kentucky, Typhimurium var. Copenhagen, and Cerro and clinical salmonellosis was observed in several cows shedding Typhimurium var. Copenhagen. The herd was sampled nine additional times over the next 14 mo and fecal prevalence of Salmonella ranged from 8.4% to 89%. Prevalence remained high (58 to 69%) over the following 8 mo, showed evidence of decline over the next 3 mo, and then increased again to 89%. Cerro was the only serotype isolated during this period. Bulk milk was cultured weekly during this 22-mo period and Salmonella was isolated from 5.3% (5/94) of milk samples. For the last 14 mo of the study, milk filters were also cultured for Salmonella on a weekly basis and 65% (37/57) of the filters tested positive. There were no significant health or production concerns in the herd during this outbreak. Based on these observations we conclude that sub-clinical Salmonella enterica subsp. enterica Cerro infection can be persistent in a milking herd. [ABSTRACT FROM AUTHOR]

Field-based and campus-based dairy extension educators collaborated to develop a program to identify bottlenecks to profitability on Pennsylvania dairies. Self-selected teams worked on key areas like udder health and milk quality, reproduction, and replacement management and milk production, while a larger team developed a comprehensive tool to identify bottlenecks. Working through both face to face and electronic communication, the team created the "Profitability Assessment for Dairy" (PADairy). The PADairy tool was developed to use a consistent method of whole farm evaluation and remove bias associated with individual areas of expertise. Each area in the tool is linked to an economic outcome so that bottlenecks and the associated loss in profitability are identified. Training for using PADairy included an on-farm evaluation with multi-disciplinary teams of extension educators. The training model allowed for experimentation with "old methods" of evaluation compared to the more team-based and comprehensive use of PADairy. Evaluations indicated that nearly 80% of the participants were likely to use the tool in the next year and nearly 75% would use the tool with a team of educators. Seventyfive percent of the participants found the team based and on-farm components to training "very effective" while the remaining 25% found the training methods "moderately effective." Following internal training and on-farm testing, PADairy was presented in educational workshops for both agribusiness consultants and dairy producers. The PADairy project provided a more coordinated and effective method for both educational program development and educator training. [ABSTRACT FROM AUTHOR]

Assessing revenue generation opportunities on dairy farms helps producers identify specific areas to target for in-depth troubleshooting on the farm operation. The Profitability Assessment for Dairy (PA Dairy) Tool was developed for that specific task. Using a combination of financial information and DHIA data, the Excel spreadsheet based program generates twenty-one farm-specific values and assesses these values against a series of industry benchmarks. The tool then provides a broad view of a whole farm's profitability, and initially distinguishes whether profitability is limited by the farm's capital efficiency (i.e. use of capital) or operational efficiency (i.e. ability to generate milk revenue). Within the operational efficiency section, four management areas are further assessed for their potential impact on the dairy herd's productivity and whole-farm revenue generation. These four management areas are Milk yield and components, Reproduction, Udder health and milk quality, and Culling and replacements. Once these management areas are ranked on their potential to limit herd productivity, the tool attaches revenue loss estimates to each. These revenue loss estimates can be adjusted to reflect the industry benchmarks or the farmers own goals. The PA Dairy Tool was tested across Pennsylvania on dairy farms ranging in size from 53 to 1035 cows. Based on using industry benchmarks, the tool identified Reproduction as being the most limiting factor on herd productivity in 78% of the farms with Milk yield and components ranking as the second most limiting factor in 66% of the farms. However, when economic loss estimates were attached to these management areas, Milk yield and components was twice as likely to be the most limiting factor on whole farm revenue compared to Reproduction. These results suggest that using industry benchmarks alone may not always identify the largest potential source of revenue loss on the farm. The results of the tool provide an economically-based starting point for drill down investigations to determine specific causes of revenue loss on farms. [ABSTRACT FROM AUTHOR]

The ability to reduce somatic cell counts (SCC) and improve milk quality depends on the effective and consistent application of established mastitis control practices. The US dairy industry continues to rely more on nonfamily labor to perform critical tasks to maintain milk quality. Thus, it is important to understand dairy producer attitudes and beliefs relative to management practices, as well as employee performance, to advance milk quality within the changing structure of the dairy industry. To assess the adoption rate of mastitis control practices in United States dairy herds, as well as assess social variables, including attitudes toward employees relative to mastitis control, a survey was sent to 1,700 dairy farms in Michigan, Pennsylvania, and Florida in January and February of 2013. The survey included questions related to 7 major areas: sociodemographics and farm characteristics, milking proficiency, milking systems, cow environment, infected cow monitoring and treatment, farm labor, and attitudes toward mastitis and related antimicrobial use. The overall response rate was 41% (21% in Florida, 39% in Michigan, and 45% in Pennsylvania). Herd size ranged from 9 to 5,800 cows. Self-reported 3-mo geometric mean bulk tank SCC (BTSCC) for all states was 194,000 cells/mL. Multivariate analysis determined that proven mastitis control practices such as the use of internal teat sealants and blanket dry cow therapy, and not using water during udder preparation before milking, were associated with lower BTSCC. Additionally, farmer and manager beliefs and attitudes, including the perception of mastitis problems and the threshold of concern if BTSCC is above 300,000 cells/mL, were associated with BTSCC. Ensuring strict compliance with milking protocols, giving employees a financial or other penalty if BTSCC increased, and a perceived importance of reducing labor costs were negatively associated with BTSCC in farms with nonfamily employees. These findings highlight the need for a comprehensive approach to managing mastitis, one that includes the human dimensions of management to maintain the practice of scientifically validated mastitis control practices. [ABSTRACT FROM AUTHOR]

The gastrointestinal tracts of dairy calves and cows are reservoirs of antimicrobial-resistant bacteria (ARB), which are present regardless of previous antimicrobial therapy. Young calves harbor a greater abundance of resistant bacteria than older cows, but the factors driving this high abundance are unknown. Here, we aimed to fully characterize the genomes of multidrug-resistant (MDR) and antimicrobial-susceptible Escherichia coli strains isolated from pre-weaned calves, post-weaned calves, dry cows, and lactating cows and to identify the accessory genes that are associated with the MDR genotype to discover genetic targets that can be exploited to mitigate antimicrobial resistance in dairy farms. Results indicated that both susceptible and resistant E. coli isolates recovered from animals on commercial dairy operations were highly diverse and encoded a large pool of virulence factors. In total, 838 transferrable antimicrobial resistance genes (ARGs) were detected, with genes conferring resistance to aminoglycosides being the most common. Multiple sequence types (STs) associated with mild to severe human gastrointestinal and extraintestinal infections were identified. A Fisher's Exact Test identified 619 genes (ARGs and non-ARGs) that were significantly enriched in MDR isolates and 147 genes that were significantly enriched in susceptible isolates. Significantly enriched genes in MDR isolates included the iron scavenging aerobactin synthesis and receptor genes ( iucABCD - iutA ) and the sitABCD system, as well as the P fimbriae pap genes, myo -inositol catabolism ( iolABCDEG-iatA ), and ascorbate transport genes ( ulaABC ). The results of this study demonstrate a highly diverse population of E. coli in commercial dairy operations, some of which encode virulence genes responsible for severe human infections and resistance to antibiotics of human health significance. Further, the enriched accessory genes in MDR isolates (aerobactin, sit , P fimbriae, and myo -inositol catabolism and ascorbate transport genes) represent potential targets for reducing colonization of antimicrobial-resistant bacteria in the calf gut.

Multiple domestic and wild animal species are susceptible to SARS-CoV-2 infection. Cattle and swine are susceptible to experimental SARS-CoV-2 infection. The unchecked transmission of SARS-CoV-2 in animal hosts could lead to virus adaptation and the emergence of novel variants. In addition, the spillover and subsequent adaptation of SARS-CoV-2 in livestock could significantly impact food security as well as animal and public health. Therefore, it is essential to monitor livestock species for SARS-CoV-2 spillover. We developed and optimized species-specific indirect ELISAs (iELISAs) to detect anti-SARS-CoV-2 antibodies in cattle, swine, and chickens using the spike protein receptor-binding domain (RBD) antigen. Serum samples collected prior to the COVID-19 pandemic were used to determine the cut-off threshold. RBD hyperimmunized sera from cattle ( n = 3), swine ( n = 6), and chicken ( n = 3) were used as the positive controls. The iELISAs were evaluated compared to a live virus neutralization test using cattle ( n = 150), swine ( n = 150), and chicken ( n = 150) serum samples collected during the COVID-19 pandemic. The iELISAs for cattle, swine, and chicken were found to have 100% sensitivity and specificity. These tools facilitate the surveillance that is necessary to quickly identify spillovers into the three most important agricultural species worldwide.

Food animals are known reservoirs of multidrug-resistant (MDR) Escherichia coli, but information regarding the factors influencing colonization by these organisms is lacking. Here we report the genomic analysis of 66 MDR E. coli isolates from non-redundant veal calf fecal samples. Genes conferring resistance to aminoglycosides, β-lactams, sulfonamides, and tetracyclines were the most frequent antimicrobial resistance genes (ARGs) detected and included those that confer resistance to clinically significant antibiotics (blaCMY-2, blaCTX-M, mph(A), erm(B), aac(6')Ib-cr, and qnrS1). Co-occurrence analyses indicated that multiple ARGs significantly co-occurred with each other, and with metal and biocide resistance genes (MRGs and BRGs). Genomic analysis also indicated that the MDR E. coli isolated from veal calves were highly diverse. The most frequently detected genotype was phylogroup A-ST Cplx 10. A high percentage of isolates (50%) were identified as sequence types that are the causative agents of extra-intestinal infections (ExPECs), such as ST69, ST410, ST117, ST88, ST617, ST648, ST10, ST58, and ST167, and an appreciable number of these isolates encoded virulence factors involved in the colonization and infection of the human urinary tract. There was a significant difference in the presence of multiple accessory virulence factors (VFs) between MDR and susceptible strains. VFs associated with enterohemorrhagic infections, such as stx, tir, and eae, were more likely to be harbored by antimicrobial-susceptible strains, while factors associated with extraintestinal infections such as the sit system, aerobactin, and pap fimbriae genes were more likely to be encoded in resistant strains. A comparative analysis of SNPs between strains indicated that several closely related strains were recovered from animals on different farms indicating the potential for resistant strains to circulate among farms. These results indicate that veal calves are a reservoir for a diverse group of MDR E. coli that harbor various resistance genes and virulence factors associated with human infections. Evidence of co-occurrence of ARGs with MRGs, BRGs, and iron-scavenging genes (sit and aerobactin) may lead to management strategies for reducing colonization of resistant bacteria in the calf gut., Competing Interests: The authors have declared that no competing interests exist.

Antimicrobial resistance (AMR) is a major public health concern, and dairy calves, including veal calves, are known reservoirs of resistant bacteria. To investigate AMR in the fecal microbial communities of veal calves, we conducted metagenomic sequencing of feces collected from individual animals on four commercial veal operations in Pennsylvania. Fecal samples from three randomly selected calves on each farm were collected soon after the calves were brought onto the farms ( n = 12), and again, just before the calves from the same cohorts were ready for slaughter ( n = 12). Results indicated that the most frequently identified phyla were Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. Fecal microbial communities in samples collected from the calves at the early and late stages of production were significantly different at the genus level (analysis of similarities [ANOSIM] on Bray-Curtis distances, R = 0.37, p < 0.05), but not at the phylum level. Variances among microbial communities in the feces of the younger calves were significantly higher than those from the feces of calves at the late stage of production (betadisper F = 8.25, p < 0.05). Additionally, our analyses identified a diverse set of mobile antimicrobial resistance genes (ARGs) in the veal calf feces. The fecal resistomes mostly consisted of ARGs that confer resistance to aminoglycosides, tetracyclines, and macrolide-lincosamide-streptogramin B (MLS), and these ARGs represented more than 70% of the fecal resistomes. Factors that are responsible for selection and persistence of resistant bacteria in the veal calf gut need to be identified to implement novel control points and interrupt detrimental AMR occurrence and shedding., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Salaheen, Kim, Hovingh, Van Kessel and Haley.)

Preweaned dairy calves and lactating dairy cows are known reservoirs of antibiotic-resistant bacteria. To further understand the differences in the resistomes and microbial communities between the two, we sequenced the metagenomes of fecal composite samples from preweaned dairy calves and lactating dairy cows on 17 commercial dairy farms ( n  = 34 samples). Results indicated significant differences in the structures of the microbial communities (analysis of similarities [ANOSIM] R  = 0.81, p  = 0.001) and resistomes (ANOSIM R  = 0.93 to 0.96, p  = 0.001) between the two age groups. Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria were the predominant members of the communities, but when the groups were compared, Bacteroidetes and Verrumicrobia were significantly more abundant in calf fecal composite samples, whereas Firmicutes, Spirochaetes, Deinococcus-Thermus, Lentisphaerae, Planctomycetes, Chlorofexi, and Saccharibacteria-(TM7) were more abundant in lactating cow samples. Diverse suites of antibiotic resistance genes (ARGs) were identified in all samples, with the most frequently detected being assigned to tetracycline and aminoglycoside resistance. When the two groups were compared, ARGs were significantly more abundant in composite fecal samples from calves than those from lactating cows (calf median ARG abundance = 1.8 × 10 0 ARG/16S ribosomal RNA [rRNA], cow median ARG abundance = 1.7 × 10 -1 ARG/16S rRNA) and at the antibiotic resistance class level, the relative abundance of tetracycline, trimethoprim, aminoglycoside, macrolide-lincosamide-streptogramin B, β-lactam, and phenicol resistance genes was significantly higher in calf samples than in cow samples. Results of this study indicate that composite feces from preweaned calves harbor different bacterial communities and resistomes than composite feces from lactating cows, with a greater abundance of resistance genes detected in preweaned calf feces.

The global incidence of human infections associated with extended-spectrum β-lactamase (ESBL)-producing Escherichia coli is increasing. Dairy animals are reservoirs of ESBL-producing E. coli , especially, third-generation cephalosporin (3GC)-resistant strains. To further understand the diversity of 3GC-resistant E. coli across animals of different age groups (e.g., pre- and postweaned calves, lactating cows, and dry cows) and farms, we used pulsed-field gel electrophoresis (PFGE) to characterize 70 fecal isolates from 14 dairy farms located in nine Pennsylvania counties. Results of this analysis indicated that 3GC-resistant E. coli were highly diverse and grouped into 27 PFGE clades (80% similarity cutoff) and 24 unique antimicrobial resistance patterns were observed among the isolates. For eight farms, clonal E. coli with the same resistance patterns were isolated from two or more age groups, indicating that strains were carried in both the calves and adult cows within the same herd. However, there were also several isolates with the same resistance pattern that were distributed to different clades, including isolates from different animal age groups on the same farm, suggesting different strains of E. coli within a farm harbored the same resistance-conferring elements. Results of this analysis indicated that 3GC-resistant E. coli were highly diverse, associated with multidrug resistance, and circulated through different (noncommingled) animal groups on individual farms.

Antimicrobial resistance has become a major global public health concern, and agricultural operations are often implicated as a source of resistant bacteria. This study characterized the prevalence of antimicrobial-resistant Salmonella enterica and Escherichia coli from a total of 443 manure composite samples from preweaned calves, postweaned calves, dry cows, and lactating cows from 80 dairy operations in Pennsylvania. A total of 1095 S. enterica and 2370 E. coli isolates were screened and tested for resistance to 14 antimicrobials on the National Antimicrobial Resistance Monitoring System Gram-negative (NARMS GN) panel. Salmonellae were isolated from 67% of dairy operations, and 99% of the isolates were pan-susceptible. Salmonella were isolated more frequently from lactating and dry cow samples than from pre- and postweaned calf samples. Overall, the most prevalent serotypes were Cerro, Montevideo, Kentucky, and Newport. E. coli were isolated from all the manure composite samples, and isolates were commonly resistant to tetracyclines, sulfonamides, and aminoglycosides. Resistance was detected more frequently in the E. coli isolates from pre- and postweaned calf samples than in isolates from dry and lactating cow samples (p < 0.05). Multidrug-resistant E. coli (i.e., resistant to >3 antimicrobial classes) were isolated from 66 farms (83%) with significantly greater prevalence in preweaned calves (p < 0.05) than in the older age groups. The bla CTX-M and bla CMY genes were detected in the cephalosporin-resistant E. coli from 4% and 35% of the farms, respectively. These findings indicate that dairy animals, especially the calf population, serve as significant reservoirs for antimicrobial-resistant bacteria. Additional research on the colonization and persistence of resistant E. coli in calves is warranted to identify potential avenues for mitigation.

Antimicrobial resistance (AR) is a pressing public health concern, and agricultural operations such as dairy and beef cattle production have been implicated as potential sources of resistant bacteria or genetic elements. This study aimed to determine the prevalence of antimicrobial-resistant Escherichia coli from calf pens in 6 auction houses (56 manure composite samples) and 12 veal calf operations (240 fecal samples in 2 visits: after the calves arrived at the farm and shortly before the animals were sent to slaughter) in the Commonwealth of Pennsylvania. A total of 1567 generic E. coli were isolated and screened for resistance phenotypes. Resistant E. coli were isolated from all auction houses and farms sampled. Based on nonparametric Kruskal-Wallis tests, incremental prevalence of E. coli resistant to ampicillin, azithromycin, cefoxitin, ceftiofur, ceftriaxone, chloramphenicol, streptomycin, sulfisoxazole, trimethoprim-sulfamethoxazole, and tetracycline in the samples from auction houses and the first and second farm visits was observed (χ 2 6.98-15.91, p < 0.05). Multidrug-resistant E. coli (resistant to more than three antimicrobial classes) were identified in 76.8%, 90.8%, and 100% of samples collected from the auction houses, first farm visits, and second farm visits, respectively. The presence of bla CTX-M -E. coli in 11 of the 12 farms presents the possibility of veal production environments being a reservoir for resistant genetic materials that may pose a risk to human health if they are transferred to human pathogens. Additional research on the impact of various management strategies in veal calf rearing is needed for a complete scenario of AR in these production environments.

[This corrects the article DOI: 10.1128/genomeA.00467-18.].

We report four full-genome sequences of bovine coronavirus (BCoV) isolates from dairy calves in Pennsylvania obtained in 2016 and 2017. BCoV is a pathogen of great importance to cattle health, and this is the first report of full-genome sequences of BCoV from PA cattle., (Copyright © 2018 Byukusenge et al.)

Vaccination for Johne's disease with killed inactivated vaccine in cattle herds has shown variable success. The vaccine delays the onset of disease but does not afford complete protection. Johne's disease vaccination has also been reported to interfere with measurements of cell-mediated immune responses for the detection of bovine tuberculosis. Temporal antibody responses and fecal shedding of Mycobacterium avium subsp. paratuberculosis, the causative agent of Johne's disease, were measured in 2 dairy cattle herds using Johne's disease vaccine (Mycopar) over a period of 7 years. Vaccination against Johne's disease resulted in positive serum M. avium subsp. paratuberculosis antibody responses in both herds, and the responses persisted in vaccinated cattle up to 7 years of age. Some vaccinated animals (29.4% in herd A and 36.2% in herd B) showed no serological reactivity to M. avium subsp. paratuberculosis. M. avium subsp. paratuberculosis-specific antibody responses were also detected in milk from Johne's disease-vaccinated animals, but fewer animals (39.3% in herd A and 49.4% in herd B) had positive results with milk than with serum samples. With vaccination against M. avium subsp. paratuberculosis, fecal shedding in both dairy herds was reduced significantly (P < 0.001). In addition, when selected Johne's disease-vaccinated and -infected animals were investigated for serological cross-reactivity to Mycobacterium bovis, no cross-reactivity was observed.

Salmonella is a major cause of bacterial foodborne disease. Human salmonellosis results in significant public health concerns and a considerable economic burden. Dairy cattle are recognized as a key source of several Salmonella serovars that are a threat to human health. To lower the risk of Salmonella infection, reduction of Salmonella prevalence in dairy cattle is important. Vaccination as a control measure has been applied for reduction of preharvest Salmonella prevalence on dairy farms. Salmonella vaccines are usually imperfect (i.e., vaccines may provide a partial protection for susceptible animals, reduce the infectiousness and shedding level, shorten the infectious period of infected animals, and/or curb the number of clinical cases), and evaluation of the potential impacts of imperfect Salmonella vaccines at the farm level is valuable to design effective intervention strategies. The objective of this study was to investigate the impact of imperfect Salmonella vaccines on the stochastic transmission dynamics in an adult dairy herd. To this end, we developed a semi-stochastic and individual-based continuous time Markov chain (CTMC) vaccination model with both direct and indirect transmission, and applied the CTMC vaccination model to Salmonella Cerro transmission in an adult dairy herd. Our results show that vaccines shortening the infectious period are most effective in reducing prevalence, and vaccines decreasing host susceptibility are most effective in reducing the outbreak size. Vaccines with multiple moderate efficacies may have the same effectiveness as vaccines with a single high efficacy in reducing prevalence, time to extinction, and outbreak size. Although the environment component has negligible contributions to the prevalence, time to extinction, and outbreak size for Salmonella Cerro in the herd, the relative importance of environment component was not assessed. This study indicates that an effective vaccination program against Salmonella Cerro spread in the herd can be designed with (1) vaccines with a single high efficacy in reducing either the infectious period or susceptibility of the host, or (2) if such single high efficacy vaccines are not available, vaccines with multiple moderate efficacies may be considered instead. These findings are also of general value for designing vaccination program for Salmonella serotypes in livestock.

The goal of this study was to determine the persistence of Mycobacterium avium subsp. paratuberculosis (MAP) in soil, crops, and ensiled feeds following manure spreading. This bacterium was often found in soil samples, but less frequently in harvested feeds and silage. Spreading of manure on fields used for crop harvest is preferred to spreading on grazing pastures.