Summary of Major Findings AgriFutures Case Control Study
Joan Carrick, Victoria Brookes, Cara Wilson
During 2022-2023 we completed a case controlled study investigating the risk factors associated with pregnancy loss in the 2021 foaling season. The following article details the important findings. Some of the results indicate that certain changes could help to reduce pregnancy losses, so we would like to get more data to confirm the findings and further expand our knowledge. We have funding from AgriFutures to investigate the risk factors associated with pregnancy losses again during the 2025 season.
Farm Pregnancy Losses
In 2022-23 we collected information about mares that aborted on 7 stud farms in the Hunter Valley, NSW during the 2021 foaling season. There were a total of 1680 mares on these farms of which 962 (57%) were resident the whole year. We were able to collect data on 810 of these resident mares. There was an average pregnancy loss of 5.4% but high variability between farms with a range of 4% to 18%.
Mare Characteristics
AGE
The age of the mares that lost their pregnancies or delivered a foal that died shortly after birth was 10.7 years which is similar to the age of the mares that successfully delivered a live foal which was 9.7 years.
NUMBER OF COVERS
Mares that lost their pregnancies took a similar average number of covers to get pregnant (1.47 covers) as mares that delivered a live foal (1.39 covers).
PREVIOUS PREGNANCY LOSSES
The average number of previous pregnancies lost by both groups of mares was similar, with mares that lost pregnancies in 2021 having lost an average of 0.4 previous pregnancies and mares that successfully completed their pregnancies having lost an average of 0.3 previous pregnancies.
These findings reflect some differences with previous studies and with many experienced breeder’s opinion. Another extensive study will help us better understand these findings.
Mare Management Strategies to Prevent Pregnancy Losses
Caslick Vulvoplasty
The mare that lost pregnancies were just as likely to have a Caslick vulvoplasty (51%) as mares that foaled successfully (42%).
Hormone (altrenogest/regumate) treatment
The mares that lost pregnancies were just as likely to be treated with hormones (39%) as the mares that delivered a live foal (37%).
Pregnancy Monitoring
Mares that lost pregnancies were more likely to be monitored during pregnancy (37%) than mares that delivered a live foal (18%). The reason for monitoring was not recorded and needs further investigation.
Antibiotic Treatment
Pregnancy loss mares (19%) are slightly more likely to be treated with antibiotics than mares that delivered a live foal (8.3%).
Anti-inflammatory drug treatment
Mares that lost their pregnancy (15%) were slightly more likely to be treated with anti-inflammatory drugs than mare that delivered a live foal (6.7%)
The reason for antibiotic and anti-inflammatory drug treatment was not recorded; the mares that lost their pregnancies may have presented with premature lactation or vulval discharge. This also needs further investigation.
Vaccination
Salmonella vaccination
Only 56% of the mares that lost their pregnancies were vaccinated for Salmonella which is lower than the 88% of mares that foaled which were vaccinated for Salmonella. This is an unexpected finding and needs further investigation.
Timing of Pregnancy Losses
Most observed pregnancy losses occur after 270 days of gestation.
The foaling period is when the highest number of losses/day is occurring – one quarter of all losses occur in this period.
Pregnancy losses that occur after 270 days are less likely to be investigated.
Unobserved losses account for one quarter of all losses.
Most unobserved losses are likely to occur earlier in pregnancy and more research into the timing and causes of these losses would improve the number of live foals delivered.
Investigation of the causes of loss in the foaling unit could identify management strategies to reduce this significant cost to the industry.
Environmental Factors
Mares that successfully delivered a live foal were more likely to be in paddocks that
- were next to a main road (sealed road)
- had fenced trees (native and non-native)
- had non-native tree lines
- were next to bushland
These interesting findings need more investigation.
If you are interested in participating in our study this year please contact Dr Joan Carrick:
Mobile : 0417768618
Email : joan@equinespecialistconsulting.com
