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June 20, 2011

Celebrating the 30th Anniversary of the Black-Footed Ferret’s Rediscovery - Part V: Breeding Season

The female black-footed ferrets (BFFs) come into estrus starting around March. They are checked weekly for signs of vulvar swelling. Once they are at a certain size, then vaginal washes are conducted. This allows for us to look at the epithelial cells to determine when she is at peak estrus. Samples are collected twice per week until she is ready for breeding.



The slides are stained using the Pap staining technique, which causes the cells to be different colors according to the level of estrus. In the early stages, the cells are round and have a very apparent nucleus. When she is near peak estrus, then the cells become more jagged, turn orange, and don’t have a nucleus. Once the female has 90% of the orange keratinized cells, then she is almost ready for breeding.

Peak Estrus
Early Estrus
An average years number of slides

The female is usually given 5-7 days to allow her to be at full estrus and then she is paired with a male. The males are selected using a Mate Suitability Index 1-6 (1 being excellent and 6 being very bad). This number comes from the inbreeding coefficient, mean kinship, and other genetic values of both animals. It is at this time when things start to get a little tricky. Our female is now ready, but what about the male? Is his sperm count above the 250 million per milliliter? Is he currently paired with a different female? Luckily our studbook keeper and genetic advisor have given optional backup pairing suggestions for when problems like this may occur, or if the male is busy being paired with a different female.

Once all is ready, the female is placed in the male’s enclosure. A camera is placed on the nest box to watch for breeding activity. These are normally solitary animals and if they are placed together at the wrong time, then one of them might be very aggressive toward the other. Usually our science has led us to the correct timing and the breeding goes smoothly. After about 30 minutes, the female is removed to do a vaginal wash. She is placed back quickly and the breeding continues. This wash is to check and see if there is sperm present. The challenge of this check is that there are often only a few sperm that are usually missing tails and there are a lot of other cells on the slide. It is almost like playing Where’s Waldo, but looking for a single sperm head. This can sometimes take over an hour of constant searching on the microscope. If there is no sperm found, then the female is re-paired but with a different male.

Power 10
Power 40


Digital Picture zoomed: a single sperm head

This step is important because BFFs females are induced ovulators. This means that the process of breeding will cause her to ovulate regardless of if there are sperm present. BFFs only come into estrus one time per year so if she ovulates and there are no sperm, then she may become pseudo pregnant. The female will then show all the signs of pregnancy and can even have a false birth and lactate, but no litter is produced. If this happens, then we have to wait an entire year before she can be bred again. BFFs are reproductive from the age of 1-4 for females. They only have 4 chances to reproduce, so we must make each year count.