The Epidemiology of Mid to Late-Term Pregnancy Loss in Australian Mares

The thesis aimed to investigate the impact of equine pregnancy loss on the Australian horse breeding industry and to gain a deeper epidemiological understanding of the issue. Equine pregnancy loss is defined as the abortion, death or absorption of the equine embryo or foetus at any stage during the pregnancy from fertilization to term, which can be caused by infectious or non-infectious factors. A PRISMA-guided scoping review of the literature was undertaken to ascertain the current state of knowledge about mid to late-term equine pregnancy loss regarding potential causes and global distribution. The scoping review results guided the formation of a survey questionnaire distributed to Australian horse breeders to collect data on a cross-sectional study investigating pregnancy loss in mares. The survey aimed to analyse the spatiotemporal distribution, prevalence, and risk factors associated with pregnancy loss in mares in Australia and to explore the current state of knowledge, practices, and personal protective equipment (PPE) used by Australian horse breeders in managing equine pregnancy loss.
The survey collected 713 responses, and horse breeders reported that 10.8% of their mares experienced pregnancy loss at some stage during gestation. The spatiotemporal distribution of pregnancy loss was explored through a spatial analysis, which identified a cluster of pregnancy loss cases located in Southeast Queensland. The study used a Bayesian network (BN) model to investigate the probability of pregnancy loss occurring at an on-farm level and found that with increased monitoring and experience, breeders increased their reporting of pregnancy loss. The BN model also identified other potential risk factors that have not been explored, such as maternal stress from events such as transportation or moving mares outside of their established social groups.
Finally, the study explored breeders' knowledge relating to equine pregnancy loss management, zoonotic diseases, and the PPE and personal hygiene procedures used when foaling or working with pregnant mares. A qualitative analysis and a multiple correspondence analysis were conducted on the survey responses. The analysis revealed that some breeders had poor knowledge and practices related to equine pregnancy loss management, including difficulty recognizing the signs of placentitis, which can lead to pregnancy loss. This thesis highlights the need for increased awareness, education, and training in equine pregnancy loss management and zoonotic disease prevention in the Australian horse breeding industry.