Nathan Tinkler's Patinack Farm will offer around 350 horses for auction later this year.
Magic Millions will host the reduction sale of a selection of two-year-olds, racehorses and broodmares in conjunction with its Horses in Training sale from October 30 to November 2.
Patinack Farm chief executive Peter Beer said the time was right for a reduction of the massive operation.
"Patinack Farm operation is now one of the biggest in the world, with a very strong broodmare band," Beer said.
"We have reached a point where we need to reduce our numbers and we regret losing some of our best stock, but a decision had to be made."
"The sale will be filled with quality entries and will be a genuine reduction."
Vin Cox, from Magic Millions, said a large number of the expected 200 mares to be sold would be in foal to a Patinack stallion including leading young sires Casino Prince and Husson.