Breeding Information
For Short-Tailed Opossums (STO)
By Molly Kalafut
This article explains the steps necessary to learning about and preparing for breeding, then goes into more depth about each area.
Step By Step Breeding Guide
Step 1: Understand the danger and risk involved in breeding short-tailed opossum (including but not limited to a maimed or killed mother, maimed or killed father and/or killed litter.)
Step 2: Understand that female short-tailed opossums are "induced ovulators" and learn how that is different from most animals that go into heat on a regular basis. This helps explain why the pairing process has to be done carefully, how long it will take for the female to enter heat, and why it is important to remove the father after successful (or unsuccessful) mating.
Step 3: Choose the mating pair. Know the ages of sexual maturity for males and females, frequency of litters, inbreeding, and factors in choosing a mating pair.
Step 4: Prepare the cage(s) for breeding, supply nest-boxes, decide how many (if any) exercise wheels to provide, and adjust daylight schedule. Decide whether you will add the male to the female's cage (most common), the female to the male's cage (less common), or hook the two cages together (least common).
Step 5: During daylight hours, put the opossums in the same cage (or hook together two cages). Monitor the pair very closely during the initial introduction - some threatening and chasing is normal, but be sure to separate the pair if excessive aggression occurs. Read about what threatening behaviors are common when first paired together and throughout the mating process. Make a note of what date you placed the pair together - this will be important later for deciding when to separate the pair.
Step 6: Monitor the pair for mating, or mating behavior. Learn to recognize mating, and signs of successful mating. While occasionally mating may take place immediately, most paired STO mate successfully 7-9 days after being placed together.
Step 7: Separate the pair. If you observe mating 6-10 days after they have been placed together, separate the pair immediately. Separate the pair immediately if mating is not directly observed, but the female has suddenly become more aggressive towards the male about 8-9 days after the pairing (a common sign she in no longer in estrus). Separate the pair for sure by 12-14 days after pairing (even if no mating is observed, or renewed hostility).
Dangers
Breeding short-tailed opossums can be difficult and may result in injury or death. Females are notoriously picky about their partners and may grow more aggressive towards mates as they age. If a male is too submissive they may not mate at all. If the female is too aggressive she may be killed by the male. The STO need to be closely monitored during their time together and separated if aggression is too heated. Ear, tail and eye injuries are common even during successful mating. Fathers need to be removed before the babies are born or he may kill them. Excessively stressed females may not conceive, and in severe cases may cannibalize her litter.
Mothers usually manage their litters fine, but there are possible areas of trouble. Litters of 3 or less may be cannibalized by the mother. If more than 13 babies are born, the mother won't have enough nipples for them and the extra babies will die unless immediately fostered to another nursing mother. Sometimes mothers reject runts. Mothers may become stressed by their litters as they grow older and need to be separated from them before she hurts them. Siblings may fight amongst themselves and should be separated before they start ripping each other's ears and tails off.
Choosing A Breeding Pair
Male and female short-tailed opossums reach sexual maturity usually around 4-5 months. Most breeders prefer to wait until at least 5 months before breeding. Females start to decline in fertility as they age and may stop breeding after 2+ years, while males continue to be fertile well past age 3.
Short-tailed opossums can breed throughout the year and at any time in captivity. They can have up to 5 litters per year, generally 4 litters per year in the wild, and 3 or fewer per year in captive breeding programs. Females should have a generous amount of rest (a month or more) after the young are separated from her before breeding again. Breeding is stressful and a mother bred too often can develop a prolapsed uterus.
Adult females over the age of 5 months are best suited to breeding. The pair should be close in age because adult females may reject or injure older or younger males, and stronger males may injure smaller, younger or less experienced females. Finding the right pairing can be difficult as a too-submissive male might never breed with a female, but a too-aggressive male might kill the female.
Breeders often ask about inbreeding issues. Inbreeding is basically inescapable for short-tailed opossums, as Brazil is closed to importation of new breeding stock. The vast majority of opossums in the United States today are from original stock acquired 10+ years ago. Some breeders try to obtain stock from different parts of the country to reduce the amount of inbreeding, but chances are even those STO are most likely closely related. The stock is fairly hardy, and to-date the results of careful breeding have resulted in healthier and longer-living opossums. As I am not an expert in genetics, I consulted several experts who offer the advice just to take care in not breeding animals with bad traits or health problems.
Preparing The Cage For Breeding
Because short-tailed opossums are solitary, the breeding pair is housed separately except for the brief (up to 12-14 days) mating period. For this reason, certain cage preparations are needed before the short tails are paired together.
Cage: Many breeders choose to use a tank or other solid cage for breeding to prevent the young from slipping through wires. Some exchange a handful of bedding between the male and female's cage a few days before the pairing to let them get used to each other's scent, but not all find it necessary. Most breeders and research facilities introduce the male into the female's cage, because females are more likely to breed if they are comfortable and secure with their nest and environment. Some breeders connect both cages to a neutral third cage, and others place both STO into a neutral new cage.
Nest Boxes: Both STO need their own nest box. One important reason is that the two can retreat to their own nest box during fights. Also important is if the female is stressed by not having her own nest box she may not conceive. The vast majority of the time, the male and female sleep separately in their own nest boxes. On rare occasions, a pair may be found sleeping together in one nest box but that usually last only a few days and then they return to separate nest boxes. Regardless, sharing a nest box is an exception, not the rule so both should have their own.
Wheels: Breeders disagree on whether a wheel should be left in during the breeding period. Some say a wheel distracts the pair from mating and can encourage aggression. Others say it distracts the pair from aggression and provides a healthier outlet for their energy. Still others provide 2 wheels so both opossums can run without needing to fight over the wheel. Though, even if there are two wheels available, the short tails (particularly the females) still may fight over the use of them anyway.
Light Changes: Changing light to a cycle of 14 hours light and 10 hours dark can improve successful breeding chances because it mimics the seasonal light conditions of the wild breeding periods. (Do not, however, use a UV light to provide extra light because short-tailed opossums are prone to developing skin cancer from them.)
Mating
Female short-tailed opossums are "induced ovulators" and do not go into heat until several days after they have been paired with a male for breeding. They are usually first placed together during daytime when aggression is least likely. Watch carefully for excessive fighting though some chasing, noises and threatening behavior is normal. The threatening behavior to each other may continue for several days, then the female becomes more receptive as she goes into estrus (stimulated by the scent of the male). Mating occurs usually between days 7-9. When mating, the male usually grabs the female by the neck and they fall on their right sides in a "tie". Several days after mating aggression may flare up again. If the STO are observed mating, the male can be removed afterwards. If mating is not directly observed, they are usually separated after 12-14 days.
Gestation
If the female does not have babies 14 days after separation from the male, breeding can be attempted again. If the female conceives, babies are born about 13-14 days later. The number of babies ranges from 1-16. The litters 3 or smaller may be cannibalized by the mother, and no more than 13 can survive because the mother only has 13 teats. A typical litter is 7-9. Young females tend to have smaller litters than mature females, and there are usually more females than males born. During the gestation period mothers should be provided with a lot of nesting material so they can weave a tight, elaborate nest.
If all goes well and you have a litter, the next area is the raising babies section.
