Enhancing bovine abortion surveillance: A learning experience

Abortions and perinatal mortalities (APM) substantially affect cattle industry efficiency. Various infectious and noninfectious factors have been associated with bovine APM worldwide. Infections are often considered pivotal due to their abortifacient potential, leading laboratories to primarily investigate relevant infectious agents for APM cases. Some infectious causes, such as Brucella abortus, have also a zoonotic impact, necessitating monitoring for both animal and human health. However, underreporting of bovine APM is a global issue, affecting early detection of infectious and zoonotic causes. Previous studies identified factors influencing case submission, but regional characteristics may affect results. In Belgium, farmers are obliged to report cases of APM within the context of a national brucellosis monitoring program. The inclusion criteria for this monitoring program cover abortions (gestation length of 42-260 d) and perinatal mortalities of (pre)mature calves following a gestation length of more than 260 d, which were stillborn or died within 48 h after birth. The objective of the present study was to describe the evolution in submission of APM cases within a mandatory abortion monitoring program in relation to subsidized initiatives in the northern part of Belgium. Based on the proportion of APM submissions versus the proportion of bovine reproductive females, an APM proportion (APM_PR) was calculated, and factors at both animal and herd level that may influence this APM_PR were explored by using linear models. This evaluation revealed that the APM_PR increased with the introduction of an extensive analytical panel of abortifacient agents and a free on-farm sample collection from 0.44% to 0.94%. Additionally, an increase of the APM_PR was associated with an outbreak of an emerging abortifacient pathogen (Schmallenberg virus; 1.23%), and the introduction of a mandatory eradication program for bovine viral diarrhea virus (BVDv; 1.20%). The APM_PR was higher in beef compared with dairy cattle, and it was higher in winter compared with fall, spring, and summer. Smaller herds categorized in the first quartile had a higher APM_PR compared with larger herds. Herds that submitted an APM in the previous year had a higher APM_PR in the next year compared with herds without an APM submission. Finally, herds for which there was evidence of the presence of BVDv had a higher APM_PR compared with herds without evidence of the presence of BVDv. In conclusion, the number of APM submissions increased after the introduction of a free on-farm sample collection and an extensive pathogen screening panel. Production type (beef), season (winter), smaller herd size, previous APM, and presence of BVDv seemed to have a positive effect on APM_PR. However, even under mandatory circumstances, APM still seems to be underreported, since the APM_PR was lower than the expected minimal rate of 2%. Therefore, further research is necessary to identify the drivers that convince farmers to submit APM cases to improve submission rates and ensure an efficient monitoring program for APM and eventually associated zoonotic pathogens.