"When I was at school I was always in the top-end classes and thought about being a lawyer, even though I have always preferred being outside compared to inside," says McKay as he prepared for today's big occasion.
"When I started riding work I'd take two or three days a week off as work experience because by then I'd decided horses were for me.
"My teachers didn't like the idea I was taking so much time off studying, but I was determined and by that stage I was sold on racing."
Jacob took over more responsibility in the stable run by his father Peter and this season the pair created a training partnership. Jacob has an amateur jockey's licence and has enjoyed admirable success.
"I've got no regrets, I'm extremely happy with the job I chose and not a lot of people can say that. It's not a job, it's a lifestyle.
"It's not all glory, there are some hard times, but they just make the good times better."
He has already had great thrills in the last three months by producing Puccini to take the Great Northern Guineas, Waikato Guineas and Avondale Guineas. Puccini has led and run his opposition breathless to win the last two of those Guineas races, but faces a tougher task today.
The colt is not the fastest out of the barrier stalls and in his more recent starts has been allowed to work forward by rider Michael Walker and take the front 300m to 400m after the start. From the No3 gate today Puccini could well be smothered by runners outside him that have jumped quicker and come across him before he can get into stride.
"That's probably the key to the race," says McKay. "If he can ping and get the front he'll be fine, but if he gets crossed and gets hemmed back on the rail he might start over-racing and may not see out the (2400m) trip.
"It's exciting going into a race like this knowing you have a horse that can win, but that you need luck with."