Black Caviar's half-brother, a two-year-old colt affectionately known as Jimmy, appears to be on the mend after a brush with death.

The colt, owned by BC3 Thoroughbreds, reacted violently to antibiotics used in the treatment for a spider bite and has developed the life-threatening hoof disease laminitis.

BC3's Simon Marshall said the horse had a comfortable weekend, was eating well and appeared much happier.

"There has been no deterioration of his condition and he remains stable," Marshall posted on Twitter.

"The plan is to ease his medication gradually and see how he responds."

The disease threatens the racing career of the colt with his prospects of making it to the racetrack after contracting laminitis greatly diminished.

BC3 paid an Australian record $5 million at the Easter yearling sale for the colt who remains at the Werribee Veterinary Clinic.