It's taken them a long time to make the decision. A mare can be scanned in foal within 2 weeks of covering so they'll have known there was an issue since March. A shame but there's always a chance they can fix it given time. Cacique had serious issues with only a handful of mares in foal from his first two seasons, they then "retired" him for a year or so before giving hoping another try. Sometimes maturity helps.