Immunocastration of colts and immunospeying of fillies

A series of experiments using an ovalbumin conjugated gonadotrophin releasing hormone was used to stimulate antibody production, suppress testosterone secretion and depress testicular function in yearling and 2 year old colts and fillies. In the preliminary experiment, an injectable oil-based formulation was administered to yearling colts. Testicular development and testosterone secretion were retarded for a period of approximately 28-32 weeks while antibody titres were greater than 1:1000. An implant and water-soluble vaccine (200 and 400 mg) is presently being tested in 2 year old colts. Testicular dimensions and testosterone concentrations decreased following vaccination. Preliminary results indicate that the effects of the implant are reversible and last for approximately 30 weeks. The water-soluble vaccine produced effective antibodies for 10-19 weeks. Plasma testosterone of all colts was reduced to gelding levels (0.2 ng/mL) while antibody titres were greater than 1:1000. Semen evaluation, morphometric analysis and daily sperm production data indicate that the testes recovered normal function. These experiments are continuing and more definitive data on the vaccine and its reversibility will be available at their conclusion. Ovarian activity of the treated fillies (200 and 400 mg) ceased soon after vaccination. Their progesterone concentrations have remained below 1 ng/mL for 20 weeks. The untreated control fillies have continued to cycle normally as determined by ovarian ultrasonography and progesterone concentrations.