Katharine Merryman, who raced homebred Maryland Horse of the Year Twixt, died Nov. 15 at her farm, The Orebanks, near Sparks, Md., of Alzheimer's disease. She was 79.Merryman and her late husband, John, bred Twixt and raced her in partnership with Mrs. John M. Franklin. Twixt won 26 races, including the grade I Top Flight Handicap in 1975 and several other graded races, and earned $619,141. The couple's daughter, Katy Voss, trained Twixt. Voss was one of five of six siblings who became trainers.Katharine Merryman was no stranger to farm life and outdoor activities. She was raised on a 3,000-acre estate in Howard County, Md., and once married took charge of the family's livestock operation. Much of her enjoyment came in assisting the mares in foaling and helping break yearlings.The Merryman operation was responsible for more than a dozen homebred stakes winners, some in her name, some in his, and some together in partnership with others. Both John, who died in 1993, and Katherine were members of the Maryland Horse Breeders Association.In addition to Voss, Merryman's survivors include daughters Ann Merryman, Elizabeth Hendriks, and Frances Merryman (who did not become a trainer), and sons John Jr. and Edwin. Donations may be made to the Copper Ridge Institute, an affiliate of the Johns Hopkins School of Medicine, 710 Obrecht Rd, Sykesville, Md. 21784.