Black Caviar half-brother put down

The half-brother of unbeaten Australian world champion sprinter Black Caviar has lost his fight for life after being bitten by a spider.

The colt, known as Jimmy, was the most expensive yearling in the Southern Hemisphere when sold at auction this year for Aus$5 million (US$4.7 million) to Australian bloodstock firm BC3 Thoroughbreds.

Jimmy was euthanised on Sunday at a veterinary clinic in Victoria state, Mark Webster, managing director of auction house William Inglis, said on his blog.

"At approximately 11am this morning ... Jimmy was euthanised on humane grounds at the Melbourne University Veterinary Hospital in Werribee Victoria," he said.

"Jimmy was suffering from laminitis, a painful hoof condition that impacts on the mobility of horses."

Inglis held security over the colt after the collapse of BC3 Thoroughbreds.

Born to Redoute's Choice, Jimmy was reportedly bitten by a white tail spider at the end of October and suffered a reaction to the antibiotic treatment.

This caused diarrhoea, which in turn led to laminitis, a disease that affects the hoof and can prove fatal.

Jimmy's bloodline to Black Caviar was the selling point but BC3 defaulted on payment for the colt and several other horses which are now for private sale by Inglis.

Champion mare Black Caviar was unbeaten in all 25 races she ran before retiring in April and is widely considered the best female sprinter the world has seen.