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Using a randomized controlled trial design, a randomly allocated intervention group of 15 cows received a slow-release bolus that delivered 100 days of monensin. The negative control group of 15 cows received a placebo bolus that was identical to the monensin bolus, except without the monensin. Two weeks after bolus administration, all cows were challenged with a 2 ml subcutaneous injection of a live tachyzoite suspension. Whole blood and serum samples were collected from each cow every week for the first month post-challenge, and then every 2 weeks for the next 2 months. The extracted DNA from whole blood was tested for the Nc-5 gene fragment of Neospora caninum using a quantitative real time polymerase chain reaction. Serum was tested for antibodies to N. caninum using the IDEXX ELISA. Cows treated with monensin boluses had a significantly lower humoral immune response than cows treated with placebo boluses at one time point post-challenge (week 4 post-challenge). However, when adjusting for repeated measures within cows, the P value for this humoral difference was 0.098. No DNA for N. caninum was detected in either group, likely due to study design features., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The aims of this study were to evaluate the performance and agreement of various commercial and in-house Neospora caninum antibody assays used in dairy cattle in North America, and to investigate reproducibility of two assays performed in different laboratories. From 1998 to 2005, three enzyme linked immunosorbent assays (ELISAs, a competitive ELISA-VMRD Inc., an indirect ELISA-Biovet Inc., and another indirect ELISA-Herdchek IDEXX Corp.), two indirect fluorescent antibody tests (IFATs, VMRD Inc., and in-house USDA) and one N. caninum agglutination test (NAT, in-house USDA) were utilized to test 397 randomly selected dairy cattle serum samples from 34 herds in eastern Canada for antibodies to N. caninum. The manufacturers' recommended cut-off values were used to evaluate test performance and agreement between tests. One IFAT (VMRD Inc.) performed well (sensitivity and specificity: 0.97 and 0.97, respectively) using reference sera (n = 452), therefore, results from this IFAT on the 397 samples could subsequently be used as the reference standard to calculate test characteristics for the other assays. Only 11% of the 397 sera were found to be N. caninum-positive with the IFAT. Prevalence-adjusted bias-adjusted kappa (PABAK) ranged from 0.06 to 0.99. Positive agreement was moderate to very good (P(pos) = 0.25-0.96). Negative agreement was very good for all assays (P(neg) > 0.94) except NAT (P(neg) = 0.66). Sensitivity was > or =0.89 for all assays except the NAT, which had a significantly lower sensitivity (0.66). Specificity was high (>0.94) for all assays except for one indirect ELISA (specificity = 0.52). This indirect ELISA did not perform satisfactorily when used in 1998, but an improved version of the ELISA performed as one of the best assays in 2004. Reproducibility of the competitive ELISA was excellent, but the reproducibility of the indirect ELISA that was improved was low (concordance correlation coefficient = 0.90 and 0.36, respectively). The performance characteristics observed for most assays in this study make them useful for screening antibodies to N. caninum in cattle.

The purpose of this research was to determine the effects of seropositivity for exposure to bovine leukemia virus (BLV), bovine viral diarrhoea virus (BVDV), Mycobacterium avium subspecies paratuberculosis (MAP) and Neospora caninum (NC) on overall and reason-specific culling in Canadian dairy cattle. Serum samples from, approximately, 30 randomly selected cows from 134 herds were tested for antibodies against BLV, MAP and NC using commercially available ELISA test kits, while 5 unvaccinated cattle over 6 months of age were tested for antibodies to bovine viral diarrhoea virus (BVDV). For analyzing the time (in days) to culling of cows after the blood testing, a two-step approach was utilized, non-parametric (Kaplan-Meier survival graphs) visualization and then semi-parametric survival modelling (Cox proportional hazards model), while controlling for confounding variables and adjusting for within herd clustering. For all reasons of culling, MAP-seropositive cows had a 1.38 (1.05-1.81, 95% C.I.) times increased hazard of culling compared to MAP-seronegative cows. Seropositivity for the other pathogens was not associated with an increased risk of overall culling. Among cows that were culled because of either decreased reproductive efficiency or decreased milk production or mastitis, MAP-seropositive cows were associated with 1.55 (1.12-2.15, 95% C.I.) times increased hazard compared to MAP-seronegative cows. Among cows that were culled because of reproductive inefficiency, NC-seropositive cows had a 1.43 (1.15-1.79, 95% C.I.) times greater hazard than NC-seronegative cows. Among cows that were culled because of decreased milk production, cows in BVDV-seropositive herds had a 1.86 (1.28-2.70, 95% C.I.) times increased hazard compared to cows in BVDV-seronegative herds. BLV-seropositive cows did not have an increased risk of reason-specific culling as compared to BLV-seronegative cows. No significant interaction on culling among seropositivity for the pathogens was detected, but only a limited number of cows tested seropositive for multiple pathogens. Results from our research will help in better understanding the economic impacts of these pathogens and justification for their control.

Our purpose was to determine direct production losses (milk loss, premature voluntary culling and reduced slaughter value, mortaliy loss, and abortion and reproductive loss) and treatmetn costs (veterinary services, medication cost, and extra farm labour cost) due to four infectious diseases in the maritime provinces of Canada: bovine viral diarrhoea (BVD), enzootic bovine leukosis (EBL), Johne's Disease (JD), and neosporosis. We used a partial-budget model, and incorporated risk and sensitivity analyses to identify the effects of uncertainty on costs. Total annual costs for an average, infected, 50 cow herd were: JD$ 2472; BVD$ 2421; neosporosis $ 2304; EBL$ 806. The stochastic nature of the proportion of infected herds and prevalence of infection within a herd were used to estimate probability distributions for these ex post costs. For all diseases, these distributions were right skewed. A sensitivity analysis showed the largest effect on costs was due to milk yield effects. For example, changing milk production loss from 0 to 5% for BVD increased the costs for the disease by 266%.

Bovine viral-diarrhoea (BVD), enzootic bovine leukosis (EBL), Johne's disease (JD), and neosporosis lower on-farm productivity, reduce export competitiveness, and increase consumer concerns regarding safety. Our purpose was to examine the relationship between 27 control practices and the estimated true seroprevalences for these four diseases for 2604 cattle in 90 dairy herds in the Maritimes provinces of Canada. Overall, 37.8, 20.4, 3.4, and 19.2% of all sampled cattle were truly exposed to the agents of BVD, EBL, JD, and neosporosis, respectively. The median within-herd true prevalences were 0, 9.3, 0, and 12.3%, respectively. Factor analysis reduced the 27 control practices to two highly correlated factors. Tobit-regression analyses determined that vaccination practices were associated with reduced prevalence of exposure for Bovine viral-diarrhoea and EBL. Also, farms that tended to purchase their dairy animals were associated with higher seroprevalence for Johnes' disease. Neither of these two factors was associated with the seroprevalence of Neospora caninum infection. The few routine biosecurity measures that were investigated in this study were generally not related to the seroprevalences of these farms.

The seroprevalence of Neospora caninum was compared among New Brunswick, Nova Scotia, and Prince Edward Island in 1998, 1989, and 1979. In 1998, the seroprevalence was lowest in Prince Edward Island, where it was the same as in 1989. Neospora caninum was present in 1979, but at a lower prevalence.