What is immunocastration and how does it work?

Immunocastration has been successfully accomplished in research studies for a number of species including; pigs, sheep and horses. The basis of most of the published research deals with immunizing the animal against a reproductive hormone in its own system, called GnRH. GnRH or Gonadotropin Releasing Hormone is a very small molecule that is produced and released by the endocrine (hormone) system. This hormone is produced and released near the base of the brain. GnRH is the hormone that begins the reproductive process by initiating the release of other reproductive hormones which cause activity (hormone production and growth) to occur in the male testicles or the female ovary. Stimulating the animal to produce antibodies against the GnRH molecule is accomplished by altering the natural GnRH molecule slightly or by attaching it to another molecule that is not a normal part of the animal (such as GnRH attached to a protein). After being injected with this strange molecule, the animal’s immune system recognizes this as foreign and builds antibodies against the strange combination molecule. These antibodies can also recognize and bind GnRH by itself. With antibodies attached to the animal’s GnRH, the hormone cannot initiate reproductive processes and hence, in the male, castration is achieved. Most of the results so far, have not been 100% effective due to differences in how each animal’s immune system responds. However, some of the newer methods are reporting somewhat higher rates of success (it is not clear how high).
Part of the problem with this technique in the pig is the different objectives the immunocastration methods are trying to achieve: 1) make the methods practical for on-farm use; 2) achieve physical castration like results (no boar taint in market weight boars); and 3) try to retain some of the growth and carcass advantages of boars versus barrows. As you can probably guess, this is a difficult task because: 1) the strongest immune reactions come from repeated exposure (more injections); 2)GnRH is already recognized by the animal as part of its ?normal? self; 3) vaccination may sometimes fail (and so would the castration effect); and 4) how much testicle activity is needed for optimal growth but not reduced meat quality. Obviously, there is still much work to be done.