Compensatory Reproduction in Feral Horses

Abstract

We estimated fetal loss rate in 2 separate herds of feral horses (Equus caballus) with significantly different foaling rates that inhabited the same barrier island. We estimated pregnancy rates for 40 feral mares from Assateague Island National Seashore (NS), where the foaling rate was 32.5% and for 48 mares from Chincoteague National Wildlife Refuge (NWR) where the foaling rate was 62.5%. Fetal loss rates were estimated by comparing fall pregnancy rates with foaling rated during the following spring and summer. The estimated fetal loss for mares from Assateague Island NS and Chincoteague NWR was 7.1 and 6.2%, respectively. Ten of the 40 mares from Assateague Island NS (25%) were lactating and only 2 produced foals, whereas 2 of the 48 mares from Chincoteague NWR (4.1%) were lactating and neither produced foals