Joseph O'Brien admits it is impossible to predict how long his career in the saddle will last.

Backed by the might of father Aidan's formidable Ballydoyle juggernaut, O'Brien has been Irish champion jockey for the past two seasons.

However, as one of the taller jockeys in the weighing room, he does not ride below 9st and acknowledges his size may eventually get the better of him.

O'Brien said: "I'll ride as long as I can, whether it's another year or 10 years I don't know.

"My weight is pretty much the same as it has been the last couple of years. I keep fit and healthy.

"I don't do less than 9st and try and kill myself.

"Realistically I'm not going to ride until I'm 50 but hopefully I can get another couple of years. I'll keep going as long as I can."

O'Brien will soon have more competition for rides from within his own family.

Joseph's sisters, Sarah and Anna, have already had a taste of racecourse action and his younger brother, Donnacha, will receive his riding licence in the near future.

The jockey said: "Donnacha is well able to ride and I might have to give up when he starts as he's a better rider than I am!

"He's been riding work as long as I have. He gives me plenty of stick and he'll get plenty when he starts riding."