A P Valentine, who has been retired from stallion duty at Ashford Stud near Versailles, Ky., because of fertility problems, has arrived at Dr. Phillip McCarthy's Watercress near Lexington. A reproductive specialist, McCarthy hopes to identify A P Valentine's problem. Five years earlier, he dealt with the infertility of Horse of the Year Cigar, who also stood at Ashford."We're going to fully examine him, and send the semen samples to labs across the country," McCarthy said. "We're going to investigate what caused the problem and take the appropriate steps to try to solve it."Cigar's fertility problem never was corrected, and he was sent to the Kentucky Horse Park.