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Johne’s disease (JD) is a chronic enteric disease in cattle caused by Mycobacterium avian subsp. paratuberculosis (MAP). Eradicating JD is a difficult task due to the long incubation period of MAP, inefficient diagnostic tests, and delayed clinical signs. Effective control strategies can help farmers to reduce prevalence, but those most acceptable to farmers combine specific information about lactation performance and testing results, which existing models do not provide. This paper presents an individual-based model of MAP infection dynamics and assesses the relative performance of the applied alternative control strategies. The base dairy herd model included the daily life events of a dairy cow and reflects several current dairy management processes. We then integrated MAP infection dynamics into the model. The model adopted four different test-based control strategies based on risk-based culling decisions and three hygiene scenarios. The model tracked the source of each infection and quantified the efficacy of each control strategy in reducing the risks of different transmission routes. The results suggest that risk-based culling can reduce prevalence compared with no control, but cannot eliminate the infection. Overall, this work provides not only a valuable tool to investigate MAP transmission dynamics but also offers adaptability to model similar infectious diseases.

Johne’s disease (JD) is a chronic enteric disease in cattle caused by Mycobacterium avian subsp. paratuberculosis (MAP). Eradicating JD is a difficult task due to the long incubation period of MAP, inefficient diagnostic tests, and delayed clinical signs. Effective control strategies can help farmers to reduce prevalence, but those most acceptable to farmers combine specific information about lactation performance and testing results, which existing models do not provide. This paper presents an individual-based model of MAP infection dynamics and assesses the relative performance of the applied alternative control strategies. The base dairy herd model included the daily life events of a dairy cow and reflects several current dairy management processes. We then integrated MAP infection dynamics into the model. The model adopted four different test-based control strategies based on risk-based culling decisions and three hygiene scenarios. The model tracked the source of each infection and quantified the efficacy of each control strategy in reducing the risks of different transmission routes. The results suggest that risk-based culling can reduce prevalence compared with no control, but cannot eliminate the infection. Overall, this work provides not only a valuable tool to investigate MAP transmission dynamics but also offers adaptability to model similar infectious diseases.

Mycobacterium avium ssp. paratuberculosis (MAP), the causative agent of ruminant Johne's disease, presents a particular challenge with regard to infection mitigation on dairy farms. Diagnostic testing strategies to identify and quantify MAP and associated antibodies are imperfect, and certain facets of the relationship between diagnostic tests remain to be explored. Additional repeated-measures data from known infected animals are needed to complement the body of cross-sectional research on Johne's disease-testing methods. Statistical models that accurately account for multiple diagnostic results while adjusting for the effects of individual animals and herds over time can provide a more detailed understanding of the interplay between diagnostic outcomes. Further, test results may be considered as continuous wherever possible so as to avoid the information loss associated with dichotomization. To achieve a broader understanding of the relationship between diagnostic tests, we collected a large number of repeated fecal and milk samples from 14 infected cows, in addition to bulk milk samples, from 2 low-prevalence dairy herds in the northeast United States. Predominately through the use of mixed linear modeling, we identified strong associations between milk ELISA optical density, fecal quantitative PCR, and fecal culture in individual animals while concurrently adjusting for variables that could alter these relationships. Notably, we uncovered subtleties in the predictive abilities of fecal shedding level on milk ELISA results, with animals categorized as disease progressors reaching higher ELISA optical density levels. Moreover, we observed that spikes in fecal shedding could predict subsequent high ELISA values up to 2 mo later. We also investigated the presence of MAP in individual milk samples via PCR and noted an association between poor udder hygiene and MAP positivity in milk, suggesting some level of environmental contamination. The paucity of positive milk samples and the complete absence of detectable MAP in the bulk tank throughout the study period indicate that contamination of milk with MAP may not be of chief concern in low-prevalence herds. An enhanced understanding of the interrelationships between diagnostic tests can only benefit the development of testing strategies and objectives, which in turn may lessen MAP infection prevalence in dairy herds.

Endemic diseases can be counted among the most serious sources of losses for livestock production. In dairy farms in particular, one of the most common diseases is Johne's disease, caused by Mycobacterium avium ssp. paratuberculosis (MAP). Infection with MAP causes direct costs because it affects milk production, but it has also been suspected to increase the risk of clinical mastitis (CM) among infected animals. This might contribute to further costs for farmers. We asked whether MAP infection represents a risk factor for CM and, in particular, whether CM occurrences were more common in MAP-infected animals. Our results, obtained by survival analysis, suggest that MAP-infected cows had an increased probability of experiencing CM during lactation. These results highlight the need to account for the interplay of infectious diseases and other health conditions in economic and epidemiological modeling. In this case, accounting for MAP-infected cows having an increased CM occurrence might have nonnegligible effects on the estimated benefit of MAP control.

The diagnosis of clinical salmonellosis in dairy cattle is usually based on clinical examination of the animal and bacteriological culture of the feces. Bacteriological culture is considered the gold standard for the diagnosis of salmonellosis, but the few studies that have evaluated its performance have indicated that it might suffer from a less than ideal sensitivity., American Association of Bovine Practitioners Proceedings of the Annual Conference, 2008

Infection with Salmonella spp can cause a variety of diseases in the bovine species, from subclinical infections to bacteremia, endotoxemia and death, as well as enteritis, abortion or dry gangrene of the extremities in calves. The aim of our study was to determine which clinical signs were associated with a diagnosis of salmonellosis in dairy cattle., American Association of Bovine Practitioners Proceedings of the Annual Conference, 2008

Salmonellosis in dairy cattle ranges from subclinical infections to serious illness. Many studies have assessed fecal shedding. The objective of our study was to determine the incidence of clinical salmonellosis in dairy animals in the northeastern United States., American Association of Bovine Practitioners Proceedings of the Annual Conference, 2005

Naturally occurring cases of clinical mastitis (CM) were studied among J-5 vaccinates or controls on three commercial dairy farms. Measures of clinical severity, milk production change and survival in the herd were evaluated for differences between the two groups. Particularly the study looked at protection against being culled with mastitis as the primary reason, including time-to-event analysis., American Association of Bovine Practitioners Proceedings of the Annual Conference, 2004

Despite preventing morbidity and mortality in properly immunized cattle, sometimes bovine viral diarrhea virus (BVDV) vaccines have failed to prevent reproductive consequences of BVDV infection, in particular, persistently infected animals. High (SN) titers may provide fetal protection in at-risk breeding heifers. Our objective was to test different types and sequences of administration of killed and modified-live virus (MLV) vaccines to determine which produced the greatest titer response., American Association of Bovine Practitioners Proceedings of the Annual Conference, 2004

Using data for 161 calves from a matched case control study nested in an observational prospective cohort study, the half-life of virus-specific maternal serum antibodies was estimated. Each calf had virus-neutralizing antibody titres measured against bovine viral diarrhoea virus (BVDV), infectious bovine rhinotracheitis, parainfluenza 3, and bovine respiratory syncytial viruses determined postcolostrally, and at one or two time points later in life (but before 100 days of age). In this calf population, few calves were infected with viruses, because only 16 virus isolations from 15 animals were obtained and the population showed declining titres for viruses. The half-life for virus-specific antibodies was estimated as 23 days or less (95% confidence interval [CI], 21 to 26 days). This corresponds to the half-life for IgG found in many other studies with different study designs. If the three calves persistently infected (PI) with BVDV and/or five suspected-BVDV-PI-calves were excluded, the estimated half-life did not change. If samples from calves >30 days of age were excluded from the analysis, the half-life was determined to be 12 days (95% CI, 10 to 17 days)., The Bovine Practitioner, Vol. 35, No. 2 (2001 June)

The potential association between seroconversion to respiratory disease agents and isolation from transtracheal wash fluids (TTW) was investigated in pneumonic dairy calves, The Bovine Practitioner, Vol. 34, No. 2 (2000 May)

Clinical, clinicopathological and surgical data from 458 adult dairy cows with right abomasal displacement or abomasal volvulus were analysed to determine the association between these variables and outcome, classified as productive, salvaged or terminal. Heart rate was higher in the salvaged and terminal cattle, than the productive cattle. Hyponatraemia was increasingly severe in the salvaged and terminal cows. All groups of cows were hypochloraemic and hypokalaemic, with the lowest values in the salvaged group. Cows in the productive and salvaged groups had metabolic alkalosis. As the outcome became less favorable there was evidence of superimposed metabolic acidosis with increased anion gap., The Bovine Practitioner, No. 26 (1991 September)

Data at admission and at surgery were collected on 458 cows with right abomasal displacement or abomasal volvulus to derive multiple logistic regression models for predicting postsurgical outcome (productive, salvaged or terminal). Three admission variables (heart rate, base excess, and plasma chloride concentration), and five surgical variables (heart rate, base excess, diagnosis, method of decompression used, and appearance of abomasal serosa) were used in the final models. Predicted outcomes using the admission and surgical models were closely related with actual outcomes., The Bovine Practitioner, No. 26 (1991 September)