Epidemiological impact of Neospora caninum in Victorian dairy farms: Modelling effective control strategies

Neospora caninum is a major cause of abortion in cattle worldwide, causing significant economic losses. Despite Victoria's critical role in Australian dairy production, little is known about the local epidemiology of N. caninum and the effectiveness of control measures. This study aimed to evaluate infection dynamics and management strategies in Victorian dairy farms. Field data were collected from five dairy farms in Gippsland, including 1029 cow and calf samples. Vertical, horizontal and colostral transmission were assessed through longitudinal monitoring. Diagnostic performance of PCR and enzyme-linked immunosorbent assay (ELISA) was compared. Deterministic and stochastic epidemiological models were developed and calibrated using local data to simulate infection dynamics and the impact of management strategies, including 'Test and Cull' and testing of replacement animals under varying biosecurity conditions. Prevalence of N. caninum was 36.7% in cows, 25.7% in calves and 32.3% overall. Vertical transmission occurred in 43% of calves from infected cows, while horizontal and colostral transmission contributed to 16% of infections in calves from uninfected cows. Longitudinal monitoring revealed 8.3% of previously negative dams seroconverted during gestation. PCR and ELISA showed poor concordance, highlighting their complementary role in surveillance. Model projections indicated rising prevalence under baseline conditions, particularly in closed herds. The 'Test and Cull' strategy consistently reduced prevalence, achieving <15% herd prevalence within 10 years, with further reductions under enhanced biosecurity. Testing replacement animals was effective only in herds sourcing their stock externally.