Principle. Ferrets, rabbits, and cats are induced ovulators. When ovulation is achieved without fertilization, pseudopregnancy will occur.24
Method. In rabbit does, the proximity of an intact male, mechanical stimulation of the vagina, or mounting by a female rabbit can
induce ovulation.31 In cats, stimulation of the vagina will result in ovulation.20,25 In ferrets, both vaginocervical stimulation and neck gripping are necessary to induce ovulation.32 Because of this elaborate procedure, it is not practical for owners to try to induce ovulation in jills. As an alternative,
vasectomized hobs are used in the United Kingdom to induce ovulation.23 One mating leads to cessation of estrus in about 75% of ferrets and two matings to cessation of estrus in 85% of ferrets.23
Effect. Estrus is terminated; pseudopregnancy lasts about 42 days.24
Remarks. During pseudopregnancy, jills may display nesting behavior and abdominal and mammary gland enlargement.24 The nesting behavior, which includes dragging cage mates around the cage and increased aggression toward the owners, does
not make this an attractive option. Vasectomized hobs remain aggressive and have a musky odor similar to that of intact hobs.
Administering hCG or Gn-RH
Principle. After mating, a preovulatory LH surge may last to up to 12 hours. This LH surge can be mimicked by administering human chorionic
gonadotropin (hCG) or by stimulating endogenous LH release with the hypothalamic releasing hormone Gn-RH.
Method. Ten days after the onset of estrus, 20 µg Gn-RH or 100 IU hCG is given intramuscularly.23
Effect. About 35 hours after injection, the ferrets ovulate, resulting in the formation of corpora lutea. Vulvar swelling will start
to decrease within one week of injection. Anestrus (pseudopregnancy) will last for 40 to 60 days.1
Remarks. One study found that multiple injections of Gn-RH may sensitize the ferret to the drug, resulting in anaphylactic reactions
shortly after administration.24 Antihistamine administration ameliorates these reactions within minutes. We have not found any adverse reactions to hCG administration.
The consequences of pseudopregnancy have been mentioned in the previous section, and neutering ferrets with hCG or Gn-RH injections
only applies to jills.
Manipulating photoperiod and administering melatonin
Principle. As described above, a ferret's reproductive season starts when there are more than 12 hours of light a day. During the scotophase,
melatonin concentrations in plasma are high.15 It has been speculated that keeping ferrets either under conditions with short photoperiods or giving them melatonin would
suppress the hypothalamic- pituitary-gonadal axis.
Method. Provide a maximum of eight hours of light a day, or administer 1 mg melatonin subcutaneously eight hours after the onset of
Effect. Ferrets kept under eight hours of light and 16 hours of darkness come into estrus only seven weeks later than ferrets exposed
to long photoperiods (14 hours of light and 10 hours of darkness).33 Similar results were seen in ferrets kept under long photoperiods (14 hours of light) after receiving melatonin (1 mg/day)
eight hours after the onset of light, illustrating that melatonin has the same effect as darkness.33 One study found that in the first year after ferrets were blinded, they came into estrus at the expected time, but thereafter
estrus synchrony was lost.34 Estrus in blinded ferrets lasted from just a few weeks to up to 60 weeks.
Remarks. A limited light regimen and melatonin administration do not seem to have a lasting effect on inhibiting the hypothalamic-pituitary-gonadal
axis in ferrets.