A rule designed to improve horse welfare is having the opposite effect according to the NSW Trainers Association.

From August 1, the Australian Racing Board extended the length of time for the pre-race administration of corticosteroids, widely used to ease joint pain which is exacerbated by hard tracks.

Instead of giving the therapeutic substance five to seven days before a horse races, the new rule states the stand down period is 10 days, or eight clear days, from administration to raceday.

Trainer Anthony Cummings says the rule is not in the best interests of horses and will shorten their preparations leading to smaller fields.

"What they decided to do was to fall in line with some overseas places without giving proper regard to the fact that our racing conditions are different on harder tracks," Cummings said.

"The treatments done in a safe and timely fashion deal with that.

"With that now gone you get the situation where in Melbourne (during the spring) nearly every second horse, the jockey came back and said it felt the track.

"At the Cranbourne meeting on Friday three horses were scratched when the track was upgraded.

"Those things will become more commonplace and field sizes will diminish.

"One of the claims when we went to a meeting at the time was that the horses would be treated less often.

"The reality is they are being treated further away from the race and whereas a lot of horses would get two runs out of a treatment now they only ever get one so they are being treated for every start rather than every second.

"The protection that used to be there for racing on firm surfaces has dissolved for the sake of a bureaucratic vision of what horse racing is in other places and shows no real understanding of what the horses deal with in Australia.

"Our concern is the welfare of the horses."

The NSWTA is pushing the ARB for a review of the rule.