HORSE RACING: Brian O'Connorsays there is more than just the glory of Classic success riding on Moonstone and his five stable-mates in tomorrow's Irish Oaks

QUITE A lot is riding on Moonstone and the five other Aidan O'Brien-trained runners in tomorrow's Darley Irish Oaks. There is the not insubstantial kudos of a Classic victory for one thing. But there is also an opportunity to maintain the champion trainer's momentum towards a first clean sweep of the five Irish classics in 83 years.

And as if that isn't evidence enough of O'Brien's renewed dominance of the racing scene there is also the chance of one more top-flight prize on the road to re-claiming a rather special world-record.

With a dozen Group One races already in the bag this season there is certainly no denying O'Brien's position as Europe's leading trainer right now.

Backed by the might of John Magnier's breeding empire, the 38-year-old has already delivered on his part of the multi-million euro bargain to produce future stallions to the lucrative Coolmore Stud operation just down the road from his Ballydoyle training base.

Henrythenavigator, Duke Of Marmalade, Soldier Of Fortune and Frozen Fire are guaranteed stallion careers. More may be ready for the same onerous task before the season ends.

In that light, success for fillies is a comparative sideline to the main Ballydoyle business but the statistical resonance of victory for one of the six O'Brien runners tomorrow guarantees more of a focus than usual.

It will certainly mean that O'Brien will be long odds-on to complete an Irish Classic clean sweep in September's St Leger. He already holds a "Tiger Slam" since he has won the last six home Classics. But as Tiger Woods and Roger Ferderer will testify there is a special feel to doing it in a calendar year.

No one has felt like it since JT Rogers won all five in 1935. He won the slam with just two horses, Smokeless in the two fillies races and Museum, who landed the colts triple crown. O'Brien, though, is more than likely going to have to win all five with five different animals.

Since the man himself is congenitally indisposed to headline-friendly utterances along "bring it on" lines, it's probably more significant that bookmakers betting on the grand-slam have cut their odds from 5 to 2 to just 6 to 4.

"If you take the view that he has Yeats, Septimus and any number of those three- year-olds like Frozen Fire, who could all run as well, then you're thinking that O'Brien must be 1 to 3 or 1 to 4 to win the Leger. At this stage only the filly Anna Pavlova looks like coming over and you would expect Septimus or Yeats to beat her," says the Cashmans spokesman, Joseph Burke.

However, there is a wider context to tomorrow's race that will resonate around the world. Europe's top races are grouped for pattern purposes throughout the different countries, with Group One being the very top.

In America they use Grade instead of Group but whatever the description, these prizes are the sports crème de la crème.

In 2001 O'Brien announced himself to the racing world with a staggering 23 Group One successes, a new record that looked set to last for a long time. In fact it only lasted only two years. The Los Angeles-based trainer Bobby Frankel enjoyed a dominant 2003 with Heat Haze's Matriarch Stakes victory bringing the final Grade One tally to 25. Now it looks like the record might be coming back to Ireland.

In fact after his scintillating start to the season, which puts him ahead of his 2001 schedule, O'Brien is now rated as low as 4 to 6 by some bookmakers to break Frankel's total. Apparently there have been some takers at that price too, which in a roundabout way is a helluva compliment to the Irishman's talent.

Leaving aside the reality that Frankel belongs to a generation of American horse-players whose achievements have taken place against a back-drop of drug issues that are only now starting to be addressed by federal government, there is also a question of simple scale.

"The very best American trainers have satellite yards on the East Coast, the West Coast and maybe in Kentucky too. They also race all year round. In terms of scale it's like trying to compare a British champion jockey with an American in terms of winners. One can win with two 200 winners. The champion in America could ride 500," says Ireland's senior flat handicapper, Garry O'Gorman.

"There's also the question of range of opportunities. There may be three or four times more Grade One races in the US so it's not a level playing field in that context," he adds.

No doubt Frankel fans will argue that O'Brien will have the option of competing outside of Europe later in the year with trips to the US, Hong Kong and maybe even Australia in the offing. But that's negated by the fact that some handicaps carry Grade One status in America, a development that usually allows the best horses run off encouraging weights set by accommodating racing secretaries.

No doubt there are those who will argue that interest in such a scenario will only be confined to statistical anoraks who in turn will poo-poo the entire concept since the Group-Graded race pattern is only in operation for the last 35 years.

But underneath it all, the Coolmore-Ballydoyle operation is far too competitive a beast to ignore the chance of a new record if it looks like being on. For that to be the case, the fortunes of O'Brien's juvenile squad are going to be of paramount importance.

In 2001, 11 of the 23 winners were in two-year-old races. They included the remarkable Johannesburg, who won four in four different countries.

Is there a similarly powerful team waiting to go in 2008? Or will the older horses do the job themselves?

Finding out will be a fascinating sub-text throughout the rest of the year. So, no pressure then, Moonstone!