New Zealand Thoroughbred Racing will ban the use of anabolic steroids for horses both in and out of competition.

New Zealand's current rules of racing prohibit anabolic steroids in horses only on race day.

The new ban will apply to all thoroughbreds from the age of six months, with this period of permitted steroid use allowed only in the interests of animal welfare.

NZTR chief executive Greg Purcell says while the use of steroids hasn't been a major problem in New Zealand, the zero-tolerance approach makes it clear there is no place for performance-enhancing drugs in racing.

"It's important we take a clear and definitive position in the interests of integrity and public perceptions of thoroughbred racing in New Zealand," he said.

The new ban requires an amendment to the rules, which is expected to be implemented by December 1 this year.

The ban will be effective from May 1 next year.

The prohibition will apply to any horse that comes within the legal jurisdiction of the New Zealand regulatory authorities to conduct out-of-competition testing.

The Australian Racing Board last month announced a ban on the use of anabolic steroids both in and out of competition.

In line with New Zealand's move, the Australian ban will apply to all thoroughbreds from the age of six months with that period allowed in the interests of animal welfare.

Purcell said that in considering the ban, NZTR took into account that some countries ban anabolic steroids from birth to retirement.

NZTR also consulted its veterinary advisor, the Equine Veterinary Association, Trainers' Association, Breeders' Association, New Zealand Bloodstock, Harness Racing Trainers' and Drivers, and Standardbred Breeders.