James McDonald's bid to have his punishment for betting on his own horse downgraded has failed after a split decision by the Racing NSW Appeal Panel.

In a disappointing judgment for the 25-year-old former Godolphin jockey, all three panel members agreed the Australian Racing rule should make a distinction between betting on your own mount compared to a rival horse.

But only principal member Richard Beasley thought the 18-month disqualification imposed last December, after McDonald admitted to placing a bet on debutant Astern at Randwick in December 2015, should be reduced.

Beasley argued a 15-month suspension would be more appropriate but fellow panel members John Fletcher and Kevin Langby said the original punishment, which included a six-month discount because McDonald pleaded guilty and co-operated with Racing NSW stewards, should stand.

Had Beasley been been supported McDonald would have been able to resume limited involvement with the industry and return to racing on February 15 next year.

But Fletcher and Langby said the 18-month disqualification was the "appropriate penalty" although they agreed with Beasley the rule that stipulates betting is illegal for jockeys should be revised.

"There should be a separate Rule dealing with the circumstances where a jockey places a bet on a horse that he or she is riding in a race, and where a jockey places a bet on another horse," the judgment said.

"Both courses of conduct should be subject to a penalty, but the latter is far more serious conduct."

The mandatory two-year penalty for betting offences was introduced in March 2013 in response to champion Melbourne jockey Damien Oliver receiving a 10-month ban by Racing Victoria officials after he placed a $10,000 bet on a rival horse in 2012.

McDonald, who is Sydney's reigning premier jockey, laid his bet through professional punter Anthony Gardiner and collected $4000 when Astern won.

In a 13-page summary released on Thursday, Beasley described the mandatory two-year disqualification as "severe" in McDonald's case.

"Penalising a jockey who places a moderate bet, on one occasion, on a horse they are riding in a race by means of a mandatory two-year disqualification is a penalty out of all proportion to the conduct, and potential harm of the conduct," he said.

"I accept there may be a number of reasons why such conduct (a jockey betting) should properly be prohibited by the Rules, and punished if such conduct occurs.

"It nevertheless is a long way short of the kind of cheating and corruption type offences (often involving the use of prohibited drugs) that are otherwise in the main listed in AR 196(5) and that attract mandatory minimum disqualifications.

"I cannot see any logical basis for including an offence of a jockey betting on his or her own mount in a list of cheating type offences that are by many factors more objectively serious."

McDonald's disqualification expires on May 15, 2018.