Seroprevalence of Neospora caninum in dairy cattle of Terceira Island in association with their reproductive efficiency.

Abstract

Neospora caninum is a widespread protozoan parasite and one of the most important infectious causes of reproductive losses in cattle worldwide. Its impact is particularly relevant in pasture-based dairy systems, where continuous exposure to contaminated environments and definitive hosts may increase the risk of infection. While neosporosis has been widely studied in intensive dairy systems, information remains limited for temperate maritime regions such as the Azores, where year-round grazing predominates and dairy production plays a central economic role. The objective of this study was to determine the seroprevalence of Neospora caninum in cattle on Terceira Island, Azores, and to evaluate its association with reproductive performance, particularly calving activity and interpartum interval, within a pasture-based dairy production context. Data were collected between January 2017 and April 2023. A total of 32,133 serological test records from cattle raised on Terceira Island were obtained from the Azores Regional Veterinary Laboratory. Serological testing for N. caninum antibodies was performed using commercial ELISA kits. These data were linked to reproductive and demographic records from the national bovine identification and registration system, including age, sex, production type, animal activity status, calving history, and interpartum intervals. Seasonal and monthly patterns, as well as climatic variables were also evaluated. Associations between seropositivity and explanatory variables were analysed using logistic and linear regression models. The overall seroprevalence of N. caninum was 14.6%, indicating that the parasite is endemic in Azorean dairy herds at levels comparable to those reported in other pasture-based systems internationally. Higher proportions of seropositive animals were observed during spring and autumn. Seropositivity increased with animal age and was more frequent among inactive or culled cattle, suggesting an association with reduced productive lifespan. Reproductive performance was negatively affected; seropositive animals exhibited longer interpartum intervals compared with seronegative cattle (435.4 days versus 418.5 days). Seasonal temperature patterns were also associated with variation in infection risk and reproductive outcomes. This study provides the first large-scale epidemiological assessment of N. caninum in the Azores and addresses an important regional knowledge gap regarding its impact under pasture-based dairy management. The findings have practical implications for disease surveillance and control, highlighting the importance of targeted monitoring during higher-risk seasons and improved biosecurity measures, particularly limiting canine access to grazing areas. These results contribute valuable baseline data to support future research and inform management strategies aimed at improving fertility and productivity in pasture-based dairy systems in temperate environments.