A student used his teeth to castrate a pig during an agriculture science class, and officials fired the teacher who told him how to do it. After a 3 1/2-hour hearing, the Harmony School Board voted 7-0 Thursday to dismiss teacher Dick Pirkey, who was suspended without pay May 4. He said he would appeal to the state education commissioner. The 16-year-old student, who was not identified, orally castrated the pig around Oct. 1, and the teacher took before-and-after photos of the pig, according to testimony before the board. Pirkey, 41, said he had told the student about an oral castration technique that he was taught in college but repeatedly told him not to do it. Dr. Robert Wilson, a veterinarian, testified by videotape that the student risked exposure to disease.