American Fancy Rat & Mouse Association

This article is from the WSSF 2014 AFRMA Rat & Mouse Tales news-magazine.

Breeding & Stuff

When And Why To Cull

By Karen Robbins

Mouse on soap box

QI am trying to be as informed about breeding rats as I can, and I had a question on culling. I’ve done some searching on the subject and can’t find much information. The technical books that I have read all say it must be done, where the pet rat sites that I have visited all say it is cruel to do so. These pet sites all refer to culling only as eliminating (killing) the very young, but in reading the technical books it is eliminating non breeding-quality stock which can happen when the animal is much older either due to poor conformation, health, or other physical problems that come up.

If one were to cull a litter of babies very young, when would you do so and why? In the older rats, are these also killed? Couldn’t they be placed into pet homes or the breeder just keep them? I’ve even looked on mouse sites for information and they seem to be more for culling than the rat sites.

So far in the few breedings I have done, my rats have all had litters around 8–10 and the moms seem to feed and care for them just fine and they are in good weight. I have been able to place any that I don’t want into pet homes but on occasion have kept those that did not sell. I do have a fellow breeder near me that her rats continuously have huge litters (14–16) and they always seem much smaller and not as thrifty as the babies from my females.

Hope I’m not opening up a can of worms by asking this question, but I want the best for my rats.

AThank you for being brave enough to ask this question and be informed about the animals you are working with. Culling is essentially just eliminating animals from the breeding population. If you look the word up in the dictionary, it simply means to pick out from others, select. It can include those that are runts, poor-doers, sickly, poor type, not the correct specimens for their particular type, those that have genetic flaws in the line, temperament issues, or those that show up with health issues later on. It can include humanely euthanizing those with health or temperament problems, to placing unwanted ones into pet homes, to the breeder keeping them at their facilities rather than risking them being bred and continuing a line that should not be perpetuated. No one should ever sell off rats from lines with serious genetic defects as there is too much of a risk of those getting bred by a pet owner because they are too cute or they have such nice temperaments even if the new owner is told they must never breed them because of the genetic defects.

In the short answer, it depends on the mom and the litter as to when and why to cull very young babies. Not every litter needs to be culled and not every breeder that culls will cull every litter. Breeders that cull will do so for the health and welfare of the mom and the litter. Babies that are small, malnourished, injured in some way, or showing some defect, have a good chance of dying on their own if the breeder did not step in, and these are usually euthanized. I’ve seen some babies where the mom was overzealous in her cleaning of the newborns and ate parts of the baby. It’s one thing to eat the end of a tail, it’s another to eat the side out of the baby or part of the head or face or an entire limb. Eaten tail tips should heal fine and these can be placed into pet-only homes if they do not meet the requirements of the breeder. Those with more serious injuries should be humanly euthanized rather than letting them slowly die on their own. Other breeders will cut down a litter to what they can comfortably place into responsible pet homes. Breeders in the show community that cull will euthanize sickly, thin ones, ones with defects or injuries, etc., and may also cull (euthanize or place into pet-only homes) those that do not meet the minimum standards set by the club they are members of. Health and temperament are a given part in breeding for show and should not be the only reason to breed. In every show-bred litter there will be a number of pet quality animals that can be placed into pet homes due to their type or color/markings not being up to breeding/show standards, but it doesn’t make them any less of a wonderful pet.

Breeding animals should be more than just putting two together to make more. Having a goal in breeding to improve the animals overall should be the norm. Those that don’t participate in shows miss out on knowing what correct conformation looks like as well as getting their animals critiqued to know if they are being bred to standards (there is more than one part that makes up the animals) or if they are even worth breeding. All breeders should be involved with a local club if possible and show their animals no matter what they breed for so they are producing the best possible animals overall. Showing shouldn’t be just to win ribbons (though that is a nice bonus!) but to get feedback on how their breedings are progressing and where they still need to make improvements. It also gives breeders a chance to share their love for the animals with others of the same passion.

The signs that a litter may need to be cut back are both in the mom and the babies. Rats are known for trying to raise more than they can handle and because they are prolific breeders by being prey animals designed to feed other species, over the years they have been selected to have large litters. In the wild, natural selection takes place and rats from smaller litters have a better chance of survival. A mom that is continuously trying to get out of the cage away from her babies or splits the litter into two or more piles is saying she is stressed and can’t handle that many babies. Now, some moms can handle 12 babies with no problems— everyone is well taken care of, gets plenty to eat, have good weight on them, are all growing at the same rate, are in the same nest, and mom is content with the number she has. On the other hand, I have seen moms that only birth 6 or 8 and display the signs of being stressed (splitting the litter and constantly wanting out) and the litter needs to be cut back to 3 to 4—the number that rat is most comfortable with. Some moms are just plain not good moms (barely caring for their kids, just going in to feed them and ignoring them otherwise, etc.) and these should not be bred again. Also, babies in very large litters (usually over 12) will normally not get their fill to eat and it is a mad scramble for mom every time she is near. They will also be very vocal from not getting their fill at each mealtime, which in the wild would signal predators. This can occasionally be seen in litters of 12 or less if mom is a poor milker and doesn’t have enough for everyone. Oftentimes in large litters there will be those that are much lighter weight than their siblings and these should always be placed into pet homes. Even with only a few to start with, there can be runts and ones that don’t get enough to eat. Whether you euthanize the babies or foster them onto another female better equipped to care for the numbers she has, is up to you and all depends on why you are breeding in the first place. Sometimes you need to foster babies from a large litter because you need to see what the color/markings are. As long as you have other litters the same age and they have smaller numbers with the moms able to care for more, then you can foster some from large litters and evenly divide up the numbers between everyone (it is recommended to breed at least two at a time so you not only have a possible foster mom in the other rat, but in case one dies or is unable to care for her babies, you can have another mom that can help out). You also have to take into consideration the health of the baby—is it small or thin for any reason other than just not getting enough to eat? Runts are runts for a reason—they usually have a health issue that may not be visible but will show up when they are much older. You may get a call months later from the pet owner that took the runt saying their rat is now not doing well or has suddenly died. Occasionally there will be babies that have something wrong with them and not doing well and it is unrealistic to try and save them. The quality of life of these babies must be considered and it is better to humanely euthanize them. So culling does not only mean euthanizing the young as you say the pet rat sites refer to it as. Just remember, a rat can only nurse 12 at a time so should never be expected to raise more than that herself.

In regards to culling older rats (weaning age or older), no, these are not necessarily killed. Most are placed into pet-only homes or kept by the breeders as non-breeding animals. If there are any that show physical, health, or temperament issues that makes them unplaceable into pet homes or a detriment to the well-being of the rat or breeder, then these may be euthanized as their quality of life would be in question. Animals with health or temperament issues have no place in a breeding program let alone to be sold as pets.

With mice it is a little different in regards to culling. There is no demand for pet mice as there are for rats, and male mice have a natural musky odor making it next to impossible to find people willing to have the smell in their house. Also, male mice do not get along together as do rats so even if you do find homes for the boys, they are sold as single pets only. For mouse breeders, they cannot keep a large tank of unplaceable boys as they could with unsold rat babies, instead any unsold male mice would have to be housed individually once they started fighting with each other which can be as soon as 4 weeks of age.

Mouse breeders that are in the show world may cut a litter back to a particular sex, the color of the type they are breeding for, or just eliminate any with defects, runts, small ones, type issues, etc., with the desired number of 4–6 left for the mom to raise. Some mice have been known to have as many as 18–22 babies. That is like two litters as a female mouse is only able to nurse 10 at a time. A lot of females will self-cull if the breeder does not step in and in doing so may well kill off the one baby that showed the traits you were breeding for. With mice, culling normally refers to euthanizing the young as fostering to another mom is usually not as easily undertaken as with rats. Older mice that do not meet the requirements of the breeder or the written standards the breeder is breeding for, are either humanely euthanized or kept by the breeder as non-breeding stock depending on their sex. If females, they can then be placed into pet homes.

Culling in larger animals usually means killing, as livestock that is not up to breeding standards can be eaten. Since rats and mice are not used as a food source for humans but rather reptiles, there are those breeders that choose not to use that route for their culls, but rather look to place their non-breeding stock into pet homes as companion animals. Most breeders will not sell to pet shops as they cannot be guaranteed that these animals will not be bought and further bred or used as a live food source for reptiles.

Thirty years ago the options breeders had for selling their excess stock were to pet shops with no distinction of pets vs. feeders, at club events, through advertising in their local papers or in local establishments, or through word-of-mouth. Nowadays, most pet shops will have separate cages for their fancy vs. feeders, although the large chain stores will only buy from brokers; there are more clubs around the country to sell your stock through; with the Internet you can not only put up your own web site to sell your stock from, but there are lots of forums, message boards, lists, classified sites, and social sites to advertise on.

As you have noticed, the rat babies born to your females are bigger and do better than your friends. Those that have a better start in life by being born larger (not necessarily huge) and with less in the litter will generally be bigger and healthier than those born very small to litters with large numbers. These bigger kids can also be sold as pets (if that is your intent) at the usual 6 weeks, where babies from huge litters will need to wait until sometimes 8–10 weeks before they are doing well enough to go to new homes. Babies from large litters where the litter is cut back to a more manageable number will never be as big at the same age when in the nest through weaning age as those born bigger, but they will be much healthier and be in better weight and size because they are getting plenty to eat. They will be ready to go to pet homes at the normal age and can meet the minimum size for their age in kitten classes. My experience has been that those smaller in the nest will always be smaller as adults compared to their bigger siblings. However, you should never keep or sell runts or small ones as breeding stock.

While we don’t have inspectors critiquing our animals prior to breeding to determine if they are of breeding quality like they have for some species in other countries, it is up to each breeder to learn all they can about the animal they are breeding, the genetics, background and pedigrees, breeding techniques used, the written standards for their particular animal, etc., and from this knowledge determine which individuals should be culled from the breeding population. Other countries will have inspectors grading individuals, scrutinizing pedigrees, and require certain titles or tests be met before an animal can be considered for breeding. They can also advise on which animals should be paired up. Animals that are not deemed breeding quality are either euthanized, or altered so they cannot be bred and then placed into pet homes. By having breedings strictly controlled, you don’t have the problem of overpopulation or casual breeders breeding inferior animals. *

Back to top

July 14, 2017