Sean Buckley of Australian-based breeding operation Ultra Thoroughbreds, is under investigation for conducting an embryo transfer scheme in Thoroughbred mares, the Racing Post's ANZ Bloodstock reports.

Stewards for Racing Victoria are investigating allegations that the operation has been producing foals through embryo transfer: taking a fertilized egg from a mare in its ranks and placing it into another mare to carry and foal out. One of the mares in question is believed to be Miss Andretti, the 2007 Australian Horse of the Year, who has reportedly had a history of issues conceiving foals.

The allegations list multiple high-profile mares who are accused of using artificial means of conceiving foals during the 2019 Southern Hemisphere breeding season, including Strikeline, the dam of recent Group 1 winner Nature Strip.

The claims allege that Miss Andretti had a filly and Strikeline had a colt during last year's foaling season, both by Buckley-owned stallion Addictive Nature, but mare returns have not been reported for either horse. Both mares were covered by another Buckley-owned stallion, Shamus Award, in December.

The rules of the Australian Stud Book – along with any globally recognized Thoroughbred stud book – state that a registered Thoroughbred can only be conceived through a live cover. Other forms of conception, including embryo transfer, artificial insemination, and cloning, are strictly prohibited within the Thoroughbred breed, through they are more commonplace within the racing spheres of the Standardbred, Quarter Horse, and Arabian breeds.

The investigation was supported on-record by representatives for breed organizations Thoroughbred Breeders Australia and Thoroughbred Breeders Victoria.