Australian-born Auckland physicist Graeme Putt also believes Phar Lap won the richest race in the world with an injured hoof which caused him to falter as he entered the turn into the final straight.

He said lateral forces on his split hoof caused him pain and he slowed in the Agua Caliente Handicap in Mexico in 1932. He lost the clear lead he established but once he came out of the turn and into the straight the lateral force came off his hoof and he ''streeted'' ahead to win by about two lengths.

Dr Putt's book, Phar Lap the Untold Story, will be launched formally in Timaru next week when a life-sized statue of the horse is unveiled at Timaru racecourse.

The statue by Auckland sculptor Joanne Sullivan-Gessler of Phar Lap in full stretch showed his enormous stride and racing style.

Dr Putt said when Phar Lap went to America he was fitted with the wrong shoes which broke one of his hooves. He said the broken hoof made Phar Lap's win in Mexico even more remarkable.

Since Phar Lap died in April 1932, theories about what caused his death have abounded, including deliberate or accidental arsenic poisoning, and one that he ate grass from a nearby paddock which had been sprayed with weedkiller.

Dr Putt said he probably died from a bacterial infection, anterior enteritis, and showed no symptoms to suggest arsenic poisoning.

Had it been anterior enteritis it would have been an agonising death from an internal bloating.

''It was agonising, no doubt about that.'' AAP