Country singer Toby Keith's unbeaten Cactus Ridge has been retired from racing because of an injury to his right front knee that was discovered following a workout in preparation for the Oct. 25 Bessemer Trust Breeders' Cup Juvenile (gr. I). The 2-year-old homebred Hennessy colt was withheld from the Juvenile and retires with four wins and earnings of $187,850.Campaigned in the name of Dream Walkin' Farms, Cactus Ridge figured to be one of the Juvenile favorites because of impressive scores in the Arlington-Washington Futurity Stakes (gr. III), the James C. Ellis Juvenile Stakes by 6 1/2 lengths, and the Canterbury Park Juvenile Stakes by 15 lengths.Cactus Ridge, who was produced from grade I stakes-placed Double Park (by Lycius), is stabled at John T.L. Jones Jr.'s Walmac International near Lexington. A decision has not yet been reached as to where he will enter stud.