The BLM has stated that the 25-30 late-term, spontaneous abortions that have occurred in the Fallon holding facilty where 1861 Calico mustangs linger, are due to the poor health of the mares. This has been disputed by veterinarians.
“Nutritional deficiencies have not been associated with abortion in mares. In general, if mares are in good condition (body condition of greater than 2 on a scale of 0 to 5, where 5 is very fat), they will carry a foal. Mares that are too thin, however, will not cycle or conceive.” from http://www.omafra.gov.on.ca/english/livestock/horses/facts/05-061.htm
Also, from an equine vet: “20-25 abortions in captivity are not likely due to range conditions. Infections, vaccination reaction, but most likely stress is the cause. In fact, that many abortions are cause for concern, anywhere.”
+ Pace of Wild Horse Deaths Accelerates Examiner.com
+ Officials Critical of BLM’s Secrecy Billings Gazette Article