The male ferret (hob) can weigh as much as 2 kg when intact, with an average weight of 1.2 kg when neutered. The female (jill) can weigh as much as 1.2 kg when intact, with an average weight of 0.8 kg when spayed. Sexual maturity is reached at 4–8 mo and occurs in the first spring after birth. The vast majority of ferrets are spayed or neutered before 6 wk of age, primarily because females are induced ovulators and can develop severe hyperestrogenemia if not bred. Ferrets also have less of the musky smell that is characteristic of Mustelids if they are gonadectomized early in life. The anal scent glands are usually removed at the time of the neuter or spay. Most physiologic data for ferrets are similar to those of the domestic cat, except that creatinine should not be >0.9 mg/dL in ferrets. Ferrets require high levels of fat and protein in the diet and should be fed commercial ferret food or high-quality cat or kitten food. Most adult ferrets have a large spleen. This is usually caused by extramedullary hematopoiesis and is nonpathogenic; ultrasonography and aspiration can be used for a definitive diagnosis.
Ferrets are vaccinated annually for rabies and canine distemper. There is one FDA-approved rabies vaccine for ferrets in the USA. It should be given to ferrets >16 wk old and repeated annually. If this vaccine is unavailable, a recombinant vaccine should be substituted. Canine distemper vaccines for ferrets should be of chick embryo or recombinant origin. Vaccines of mink or ferret culture (eg, most multivalent vaccines for dogs) should not be used, because they may cause seroconversion and disease. There is currently one FDA-approved distemper vaccine in the USA for ferrets. Ferrets should be vaccinated at ~8, 10, and 12 wk of age and then yearly. Vaccine reactions occur frequently in ferrets; vaccinated animals should be monitored for 20–30 min after vaccination, and only one vaccine (ie, rabies or distemper) should be given at a time. Ferrets raised commercially are often vaccinated for Clostridium botulinum type C at 6–8 wk old.