Non-invasive assessment of the incidences of pregnancy and pregnancy loss in the feral horses of Sable Island.

This research study assesses the rate of pregnancy and pregnancy loss among the untamed feral horses of Sable Island, Nova Scotia, by monitoring the estrogen levels in fecal samples from the mares. The study supports the assertion that fecal estrogen levels are a valid indicator of pregnancy after around 120 days of gestation.

Methodology

• The study monitored around 400 completely untamed feral horses in Sable Island over a period of four years. The researchers collected and analyzed fecal samples from 154 identified female horses during this time to assess their estrogen levels.

Key Findings

• 92.1% of the mares that were sampled and later gave birth displayed increased fecal estrogen levels between 15 October and 30 March.
• The majority (95%) of births took place from April through July, which aligns with patterns observed in other feral horse populations.
• The rate of foaling – or giving birth – for mares aged 3 years or older was 62.0%, with half of these mares giving birth every three or four years.
• Low foaling rates (4.1%) were observed in mares that had been bred as yearlings. This rate increased with the age of the mares, peaking at 70.8% for those bred as four-year-olds.
• The researchers identified a 26.0% rate of fetal loss after Day 120 of gestation, with significant annual variations (between 9.6% and 37.3%) and changes depending on the age of the mare when bred.
• Among the mares that had been sampled every year of the study, around half of the barren years could be attributed to fetal loss after 120 days of gestation.
• All mares fell pregnant at least twice during the four-year study, which indicates that pregnancy loss, even after Day 120 of gestation, plays as significant a role in barren years as failure to conceive does.

Conclusion

• This study has demonstrated that fecal estrogen levels are a reliable indicator of pregnancy in feral horses, after approximately 120 days of gestation.
• The findings also highlight the extent of pregnancy loss after day 120, and its importance alongside conception failure in causing barren years for these wild horses.