A thoroughbred appraiser has set Curlin's market value at $US20 million ($A30.79 million) and recommended shares of the richest North American racehorse in history be consolidated under primary owner Jess Jackson.The complicated ownership dispute focuses on a 20 per cent interest of the reigning Horse of the Year controlled by William Gallion and Shirley Cunningham Jnr.The two disbarred lawyers have been ordered to sell their interest in Curlin to satisfy a $US42 million ($A64.66 million) civil

A thoroughbred appraiser has set Curlin's market value at $US20 million ($A30.79 million) and recommended shares of the richest North American racehorse in history be consolidated under primary owner Jess Jackson.

The complicated ownership dispute focuses on a 20 per cent interest of the reigning Horse of the Year controlled by William Gallion and Shirley Cunningham Jnr.

The two disbarred lawyers have been ordered to sell their interest in Curlin to satisfy a $US42 million ($A64.66 million) civil judgment won against them by clients they were accused of bilking in a settlement over the diet drug fen-phen.

Circuit judge Roger Crittenden is trying to sort out whether their share of the horse should be sold back to Jackson, who owns the other 80 per cent, and for how much. He could rule as early as December 1, when the parties will next appear in court.

A company owned by Jackson has bid $US4 million ($A6.16 million) to buy out the remaining shares, and bloodstock appraiser Ric Waldman testified on Monday he believed that was fair market value and that the sale should go through.

But Andre Regard, a lawyer for Cunningham and Gallion, said the price was far too low for one of the most successful racehorses of the modern era.

He said Jackson had been responsible for driving down the value by failing to clarify when the horse would be retired to stud.

"How does anybody bid on something if they haven't retired him?" Regard said.

"If you're going to lay out money, you want to know you're going to get some kind of return for your money now."

On Sunday, Jackson issued a statement announcing Curlin would be retired to the breeding shed next year, perhaps after running one last race.

It wasn't clear whether the horse's future home would be at Stonestreet Farms, owned by Jackson, or a prominent breeding operation elsewhere.

Waldman said he put a $US30 million ($A46.19 million) value on Curlin over the summer but scaled back his numbers due to the economic downturn that has led to sagging thoroughbred prices.

His $US20 million estimate assumes Curlin will be sent to 120 mares next year and command a stud fee of $US75,000 ($A115,465). Those numbers would drop to 80 mares and $US50,000 ($A76,976) by year four, he said.