Breeding Hamsters

Sooner or later, after a little experience with feeding and general care, one’s thoughts turn to the subject of breeding. Why not, indeed, for much of the enjoyment of hamster keeping is in the expectation of babies. Young hamsters are just as much fun as adults— more so in the opinion of many people. The only trouble is that they grow up so quickly!

Age for breeding

Hamsters will breed at a very tender age if allowed but this is definitely unwise in the case of the female. The young are often born undersized and the mother may be physically incapable of feeding them properly. Only really well grown females should be bred as early as eight weeks of age. A breeding age of twelve weeks would be better for the majority. Males may in fact be bred a week or so earlier (if necessary) because they do not have the strain of rearing the litter and the act of mating is not harmful. If a male is not sexually mature, he will not mate, it is as simple as that.


Since hamsters have to be housed individually, breeding is not simply a case of leaving the male and female together, as with gerbils or mice, for example. The two sexes have to be placed together and the mating supervised. The male . is normally always ready for mating but the female is not. She will only accept the attention of the male every fourth day and then only rather late in the evening. This is the heat period, as it is termed, and, while some females will come on heat early in the evening, others do not until quite late. The heat period lasts for most of the night, so the later the mating is attempted, the greater the chances of finding the female “on heat”.

The most straightforward method of determining whether or not a female is in heat is by placing her with the male. This may be done on a convenient table top, in an open box, empty pen or, most effectively in the male’s cage. Never put the male in the cage of the female—even females in heat have been known to attack the male because of the intrusion. When the two come together, the male will investigate the female. If the female is ready, she may move about for a few moments in an hesitant sort of way, pursued by the male, and then she will “freeze”. This posture is unmistakable, the female will crouch slightly with head pointed forward, body and hind legs extended and tail pointing upwards. Should she move about excessively but not attack the male, the mating posture can often be induced by lightly tickling the female’s back with the tip of a finger nail.

An experienced male will promptly mate the motionless female. This is done by the male climbing onto the back of the female from the rear. Successful matings are shown by the male drawing his body up strongly, followed by an immediate dismount. He will wash himself briskly, perhaps lick the female briefly, and promptly mount her again. This process will be repeated many times, with short intervals of rest. The female will be unmoving unless she is disturbed liy a sudden noise. The mating should be permitted to continue for about ten minutes or stopped sooner if either the male loses interest or the female unfreezes and starts to attack the male. A male who has not mated before may mount the female from the front or even from the side but eventually he will find the correct position and the mating will then proceed smoothly.

If the female is not in heat, she will react vigorously towards the male; prancing around with a high stepping walk, rearing on her hind legs or turning on her side, probably snorting the whole time. She may also press her hind quarters firmly against the floor. A fight will ensue if the male persists in his attentions. The two hamsters, should be separated at once. Young males have been known to become shy of mating because they have been savaged by females. Older males will fight back. If you have tried the female early in the evening, she could be re-tried later on, just in case she is one of those which does not come in heat until late. The female should be placed with the male on successive evenings until she eventually accepts the mating.

Failure to Breed

Most female hamsters will accept matings every four days without bother. However, there are exceptions and these may be due to different causes. The most common cause is over-fatness. A well-fed female which has not been bred from until she is six months of age or more has had time to fatten up. Had she been bred from at three months, the fat would have gone on feeding her babies. This is not to say that all young females must be bred from, nor to imply that all females will become over-fat. Not at all, the point is that an older female has had time to accumulate excess fat.

The same thing can happen to a female which has had one litter but none for some months. She too, can become over-fat. One can only persevere with her, day after day. The cereal content (and mash, if fed) of her diet should be reduced and fresh young green leaves substituted. Males also can become over-fat but this rarely interferes with their mating ability.

The season of the year can modify the heat periods of a female. The short days of autumn may bring about a cessation which can last throughout the whole of the winter. Breeding during the winter months is not always good policy although, with centrally heated houses, this is not the problem it used to be. The “winter pause” can sometimes be overcome by exposing the female to electric light as soon as daylight starts to fade. An extra four hours or more may be required and even this may not be successful. Do not be surprised if you have to wait for the arrival of the longer days of spring before a female becomes ready for breeding.

Another aspect is that a female which has never been bred from may become prematurely sterile. Hamster females can breed until they are about fourteen months of age. An unbred female may become sterile at twelve months or earlier due to a combination of over-fatness and attempts to reduce her fat. The act of reducing fatness by semi-starvation is not wise. Yet another cause is that the female is unable to have any heat periods. This form of infertility, however, is rare but could be the reason for persistent refusal to mate when all other possibilities are excluded.

All of the above explanations for a female not coming into heat assume that the animal is in good condition —too good if fatness is the cause. A female may not accept the male because she is out-of-condition or thin. It is not fair to breed from a thin female and it has been assumed that you would not attempt to do so.

Not all matings necessarily result in a litter. Should the stomach of the female not be swollen by the twelfth day of pregnancy, this may indicate either a small litter or that the mating has not been successful. One can wait until the seventeenth or eighteenth day, when the arrival or non-arrival of a litter will decide the issue. However, if you are anxious for a litter, the female can ‘be tried daily with the male. If the mating has failed, the female nearly always comes into heat again about the twelfth to fourteenth day and, thus, a few days’ delay can be saved.

The Expected Litter

The gestation period—time between mating and birth of young—is sixteen days; one of the shortest periods among mammals. By about ten days, the mother-tobe should be swelling in the tummy and one can soon tell if she is pregnant or not. By 15 days, females which are due to have large litters are almost like walking tennis balls. This does not inconvenience them and it is surprising how agile they can be. The average size of litter is between six to eight babies but a large healthy female may have as many as sixteen (even more, on rare occasions).

Proud owners are apt to boast how their pet has brought up a fine litter of fourteen or more young. It is certainly an achievement but one which imposes a considerable strain on the female and it may be wondered if it is always wise. A newborn litter may be briefly examined by removing the mother from the cage and opening the top of the nest with a ball-pen or similar object. The babies may be roughly counted. Most females can rear up to nine young comfortably. Over this number, you should consider reducing the litter. If you can arrange it, the smallest babies should be painlessly destroyed by a vet. Many mothers with large litters do in fact eat a few babies. This is nature’s way of taking care of excess numbers.

Be careful how you handle a pregnant female. Accidents do happen and a fall could result in the regrettable loss of the unborn babies and perhaps the mother. In fact, the female should be left alone for the last few days of pregnancy. She will be busy making a cosy nest for her young and you can help by providing plenty of soft meadow hay or woodwool. The cage should be cleaned out, prior to the arrival of the litter since it is advisable not to disturb the female more than absolutely necessary for the next fortnight. These precautions are not so necessary if you have made a fuss of your pet and he is used to you. But, beware of allowing strangers to handle her and particularly, to touch the young.

The babies are born naked and pink in colour, with their eye-lids tightly sealed. They also have teeth which is unusual for baby rodents. Depending on the variety, the skin darkens with pigment, within a few days for the golden, longer or not so intensely for others. The skin of the albino and cream never darkens. The eyes open by about the twelfth day and by this time the little toddlers will be venturing from the nest. Their walk is very unsteady and wobbly. The mother is often beside herself on these days, running around, picking up her wandering babies and trying to bundle them back into the nest. No sooner has she turned her back, than they are out again!

The female will eat voraciously while she is suckling and she should be given all that she needs. The young begin eating before they leave the nest, obtaining nourishment from the food which the mother takes back to the nest. As soon as they are able to toddle around on their own, the food consumption will increase, so be careful not to be caught napping. Be lavish, for it is impossible to over-feed either the mother or the young at this time. The cage will require frequent cleaning and uneaten food can be removed. Mashes made with milk, or bread soaked in milk, can be given as special treats for the young but, in general, it will be found that they are capable of eating the same food as the mother.


The young hamsters are frisky and well able to look after themselves by three weeks of age. They can be weaned at this time although many people delay weaning to four weeks. However, they should not be left with the mother too long because she may turn on them. This may seem curious but hamsters are solitary creatures and the mother seems to feel that she has

done her bit and it is time for the young to fend for themselves. The youngsters themselves will live together happily until about six to eight weeks before fighting becomes serious. However, fighting could start sooner and one must be on the alert.

Rearing a litter places a strain on a female and it is not surprising that she often loses weight and becomes thin. She will do this in spite of a satisfactory diet and extra food. It is quite natural and is simply a reflection that most of the food is passed on to the babies as milk. Once the young are weaned, the female should rapidly regain her former condition. She should not be re-mated too soon after the weaning of the young. It is better to wait until the female has regained herself. A couple of weeks ought to be sufficient but be guided by the animal’s condition rather than by the calendar. The other side of the coin is that if you wait too long before deciding to have another litter, the female may become over-fat for easy breeding.


Young hamsters of mixed sexes should not be left together for long, otherwise unexpected litters will make an appearance. The separation must be done by six weeks or earlier if possible. Juvenile hamsters are more difficult to sex than adults. The simplest method is direct examination of the sex organs. The hamster should be upturned in the palm of the hand. In the female, two small openings (vulva and anus), sited just in front of the tail, can be seen, almost touching, with no hair in between. Whereas, in the male, there is only one opening (the anus) but a small pimple a quarter of an inch or so from the anus and separated by hair. In addition, when the animal squirms in the hand, two ball-like glands can often be seen moving under the skin on each side of the vent in the male.

The female has fourteen nipples in two rows of seven down each side of the stomach. These can easily be seen as prominent “teat spots” in the very young hamster but are less obvious as the fur grows. They can still be seen, however, in older animals by gently blowing apart the hair. Nipples are completely absent in the male and this method of distinguishing the sexes is reasonably reliable. As the hamster becomes older, the sex differences become more pronounced. The female always has a rounded appearance at the rear; while the tail region in the male becomes more and more elongated as the male sex glands develop into two definite pouches.

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