Reproduction in Domestic Animals

Reprod Dom Anim 43 (Suppl. 2), 150–156 (2008); doi: 10.1111/j.1439-0531.2008.01155.xISSN 0936-6768Reproduction of the Female Ferret (Mustela putorius furo)H LindebergUniversity of Kuopio, Department of Biosciences, Kuopio, FinlandContentsThe domestic ferret is a seasonally polyoestrous species.Females reach puberty at the age of 8–12 months. Femalesexhibit a constant oestrus between late March and earlyAugust if they are not bred. Increasing tumescence in thepink-coloured vulva is a sign of pro-oestrus. Oestrus canpersist for up to 5 months, but once ovulation is induced,either pregnancy or pseudopregnancy ensues. Folliculardevelopment and atresia overlap in such a manner that thereis a recent cohort of follicles available for ovulation whenevercopulation might occur. Copulation may last from 15 min to3 h, the average being 1 h. Ovulation is induced by pressureon the cervix associated with copulation. After sufficient LHrelease, the pre-ovulatory follicles mature and an average of12 oocytes (5–13) per female are ovulated 30–40 h aftercopulation into the ovarian bursa. The ferret oocytes aremost capable of being fertilized up to 12 h after ovulation,i.e. 42–52 h after copulation. Ferret oocytes ovulate at themetaphase of the second meiotic division (MII) embedded inthree layers of corona radiata cells. Embryos enter the uterusover a period of several days starting on day 5 after mating.Between days 12 and 13 after mating, the embryos havebecome implanted in the endometrium. Implantation in theferret is central with rapid invasion of the uterine epitheliumby the trophoblast over a broad area that eventually becomesa zonary band of endotheliochorial placenta. Gestationlength is 41 days (39–42 days). The domestic ferret givesbirth to an average of eight kits (1–18 kits), which weigh6–12 g at birth.IntroductionMustelids are polytocous carnivorous species demonstratinga variety of unique reproductive characteristics.The reproductive physiology of some species has beenquite thoroughly studied, while less is known aboutother species. This literature review was partly publishedas the PhD thesis of the author (Lindeberg 2003), and itconcentrates on the results obtained with the domesticferret. For comparative purposes, when necessary,results concerning other mustelids and carnivores arealso included.Photoperiods and seasonalityThe domestic ferret is considered to be a seasonallypolyoestrous species, but females exhibit a constantoestrus between late March and early August if they arenot bred (Mead 1989). Marshall (1904) classified the ferretas a mono-oestrous species. Offspring born the previoussummer reach puberty by the following spring at the ageof 8–12 months (Fox and Bell 1998). Initiation of thegonadal activity is totally dependent on the light-darkcycle, which stimulates or inhibits reproduction throughtransmission of information about the day length to thebrain (Bissonnette 1932; Turek and Van Cauter 1988).The ferret’s gonadal response to a given photoperioddepends both on the duration of the photoperiod andon the previous photoperiodic experience. Ferrets, likeother ‘long-day’ seasonal breeders, need alternatingperiods of increasing duration of daylight (long days),at which time they are sensitive to light, and days ofdecreasing duration of daylight (short days), duringwhich time they are insensitive to light, so that theannual cycle recurs normally (Herbert 1989). The stateof temporary unresponsiveness to photic stimuli isreferred to as the ‘photorefractory’ condition (Elliottand Goldman 1981), and it is required to induce areturn to the photosensitive state (Forsberg 1992).Ferrets exposed to artificially changing long and shortdaylight conditions (long days: 16 h light and 8 hdarkness; short days: 8 h light and 16 h darkness) startshowing oestrus approximately 3 weeks after the changefrom short days to long days (Fox and Bell 1998), andcease showing oestrus about the same time after achange from long days to short days. The repeatedchange from long days to short days after every6 months causes one period of gonadal activity peryear similar to a natural breeding season when theanimals are exposed to natural outdoor light conditions.A change in light conditions every 4 or 2 months causestwo or three periods of gonadal activity a year,respectively (Herbert 1989). Through the use of reverselight cycles, ferrets can be induced to breed any timeduring the year (Harvey and MacFarlane 1958).Oestrous cycle and vaginal cytologyThe increasing tumescence in the pink-coloured vulva isa sign of pro-oestrus in the ferret. The vulva enlarges upto 50 times its normal size during a 2- to 3-week periodat the beginning of the breeding season (Hammond andMarshall 1930), which extends from March to August(Marshall 1904). No change in the turgidity of the vulvaoccurs up to 36 h after copulation (Hammond andWalton 1934), but 3 or 4 days after mating, the vulvastarts regressing and regains its normal size in2–3 weeks. If the vulva does not recede, ovulation hasprobably not taken place, and the female may need to beremated (Lagerqvist 1992). Oestrus can persist for up to5 months, but once ovulation is induced, either pregnancyor pseudopregnancy ensues (Hammond andMarshall 1930).In conjunction with the vulval swelling during oestrus,there is a thickening of the uterine endometrium, andfollicles develop in the ovaries. The pattern of folliculardevelopment during a prolonged oestrus is unknown,but it is assumed to be continuous (Robinson 1918). Inthe absence of copulation, which results in a prolongedÓ 2008 The Author. Journal compilation Ó 2008 Blackwell Verlag