Characteristics and spatio-temporal distribution of fetal loss in thoroughbred mares in New South Wales, Australia

Introduction

Despite emerging disease syndromes in Australian Thoroughbred horses in recent years, there is no formal surveillance for fetal loss in the industry. This study aimed to characterise the distribution of equine pregnancy loss > 45 days of gestation in a major Thoroughbred breeding region to provide insights into causes, prevention, and surveillance feasibility.

Methods

Data were collected from 574 fetal loss submissions to veterinary pathology services between February 2015 and November 2021. Variables included date of fetal loss, gestational age, diagnosis, foal weight, and mare age. Diagnoses were grouped into 14 categories, including infectious and non-infectious causes. Time-series analysis was conducted to identify trends and seasonality, while spatial analysis used Kulldorf’s space-time permutation scan statistic to detect spatio-temporal clusters of fetal loss cases.

Results

Of the 574 cases analysed, 467 had a confirmed cause, with infectious agents responsible for 54 % and non-infectious causes for 46 %. The most common diagnoses were cord occlusion (19.5 %) and unknown causes (18.6 %). Time-series analysis revealed seasonal trends in fetal loss, with a peak in 2016 due to a Chlamydia psittaci placentitis outbreak. This was also the only cause for which spatial clusters were identified.

Conclusion

The findings indicate that, while cases of twinning and EHV-1 still exist, conditions such as placentitis due to C. psittaci are emerging. Despite these changes, the overall predictable temporal distribution of pregnancy loss indicates the potential for early outbreak detection within a surveillance system for Thoroughbred pregnancy loss in this region.