Principle. Several reports on using Gn-RH vaccines in mammals are available.35-38 Depending on the species, these vaccines prevent conception, prevent boar taint, or control hormone-dependent cancers, including
breast and prostate cancers. In ferrets, a Gn-RH vaccine would serve two goals: inactivate gonads in both sexes and lower
plasma concentrations of gonadotropic hormones.
Method. Depending on the study, Gn-RH inoculations were performed intramuscularly, subcutaneously, or intranasally.35-38
Effect. Decreased plasma gonadotropic hormone concentrations have been reported in male rats after immunization against Gn-RH.36 Testosterone concentrations decreased in bulls, boars, male rats, and dogs after immunization,35-37 while in female mice a sterilizing effect was seen.38 Reduced testes size has also been reported in boars and rats after immunization against Gn-RH.36,37
Remarks. In a pilot study conducted at Utrecht University, eight out of 12 ferrets immunized against Gn-RH became lethargic and anorectic
after subcutaneous vaccination. Long-term supportive care did not result in any improvement, and the eight affected animals
had to be euthanized (Schoemaker NJ, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands: Unpublished
data, 1998). Postmortem examination disclosed nonspecific lymphocytic-plasmacytic infiltrations in multiple organs (liver,
kidney, lung, and intestines), suggesting a nonspecific immune reaction. In the same experiment, 24 control ferrets were used
(12 surgically neutered and 12 intact). Since these ferrets had not received any component of the Gn-RH vaccine, had been
kept in the same area, and had not shown any signs of disease during the vaccination trial, it is assumed that a component
of the vaccine was responsible for the nonspecific immune reactions. To confirm this assumption, further studies are necessary.
Such a vaccine should not be used before the cause of these reactions has been unraveled.
Principle. Inhibit LH secretion by immunization with heterologous LH.39-41
Method. Heterologous LH is injected intramuscularly or subcutaneously.
Effect. Injecting bovine LH causes a 90% reduction in the weight of rabbit testes, genital atrophy in female rabbits, and loss of
receptiveness to males.39 In another study with male rabbits, LH and testosterone plasma concentrations decreased significantly after immunization
against LH; however, FSH concentrations increased significantly.40 Similar but less consistent effects of LH immunization were seen in dogs.42 In ewes, estrus and pregnancy were prevented for two years after immunization against LH, although plasma LH concentrations
were not lower than those in control ewes.41 In these ewes, FSH concentrations were also increased.
Remarks. So far, no reports of LH vaccination in ferrets exist. Since not only LH but also FSH may influence the development of hyperadrenocorticism
in ferrets, there is reason for caution with LH immunization in ferrets, especially since plasma LH concentrations were not
reduced in the control ewes.
Immunizing with LH receptor
Principle. Induce LH receptor dysfunction by immunization with heterologous LH receptor.
Method. Bitches were immunized with 0.5 mg bovine LH receptor encapsulated in a Silastic subdermal implant on the fifth day of vaginal
bleeding, followed by intramuscular booster injections, which were given based on antibody titers.43
Effect. In bitches, immunization with bovine LH receptor suppresses serum progesterone concentrations for about one year, while serum
concentrations of estradiol and LH are not affected. Although stimulation with Gn-RH in immunized dogs leads to a LH surge,
serum progesterone concentrations do not increase. Thus, bitches immunized with bovine LH receptor do not ovulate or produce
active corpora lutea.43