LEXINGTON, Ky. (AP) — Three Kentucky horse farms are challenging a rule to limit the number of mares a thoroughbred stallion breeds each year. The farms call it an anti-competitive restriction threatening to disrupt the industry. The farms filed suit Tuesday. The Jockey Club says it stands by the rule meant to preserve the long-term health of thoroughbreds. The suit takes aim at the “stallion cap” adopted by The Jockey Club in 2020. The suit says hundreds of millions of dollars of stud fee revenues will be affected. The Jockey Club says that’s speculative because the rule applies to stallions foaled in 2020 or later.