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Females: For the safety of the animal, it is generally recommended to wait until the female is full grown before attempting to breed her. While sexually mature at 5-6 weeks of age, a female is not fully grown until 4 months of age. Most breeders wait until a female is 5-6 months old before breeding a female for the first time. It is also recommended that a rat not be bred for the first time after one year of age. Some books and websites will claim that a rat cannot be bred for the first time after 7 months of age, due to a fusing of the pelvic bones or narrowing of the birth canal. This rumor is untrue, though care should be taken when breeding an older rat. Males: Unlike females, most males can breed from 5-6 weeks of age until the day they die unless their testicles ascend in old age. It is recommended that a male be bred around 1 year of age to insure good health and a non-aggressive temperament.
Female Heat Cycle: Female rats go into heat every 4-5 days, usually at night. An observant fancier may notice his or her female acting strangely one to two times a week, depending on the cycle. The female may seem frantic, hop around, quiver and vibrate her ears when touched, arch her back (lordosis) when touched, or be mounted by a cagemate. If looked at, her vulva will be more open than usual and may appear moist looking as well. Once pregnant, a female will go into heat within 24 hours of giving birth to her litter. Mating Methods: There are two different methods of breeding rats. The first is to have an extra cage available for breeding. On the night that the female goes into heat, the male and female can be placed in the extra cage for the night. The next morning, they can be placed back with their cagemates without any problems. This can be done each heat cycle until the female becomes pregnant and stops undergoing heat cycles. The second method is to place the male and female together for an extended amount of time, usually 10 days. By keeping them together for the extended amount of time, it insures that the female should have gone through two heat cycles. This method can make it difficult when re-introducing the rats back into their appropriate cages. Mating: When in heat, the female will be receptive for 12-24 hours. Female rats ovulate 8-12 hours after she goes into heat, but fertilization can occur for up to 24 hours after heat has begun. It is recommended that the breeding cage by as large as possible and of a single level. Both genders play a role in the courtship, but the female is usually the aggressor in the relationship. She can often be seen sniffing the male's genitals, hopping around, and vibrating her ears to alert the male of her breeding status. Some females, especially inexperienced ones, may zoom around the cage, making it difficult for the male to mount her. Eventually she will slow down and allow the male to mount her. When the male mounts the female she will arch her back (lordosis) and present herself for the male. The mating is short, just a few seconds, and ends when the female runs off and the male leans down to clean himself. Usually mating will occur many times while the female is in heat. Because the litter can be fathered by different males, it is important to ensure that only one male is allowed to mate with the female. The first sign that a mating was successful is a waxy plug, also known as a copulatory or mucous plug, in the vulva of the female. This plug is formed by secretions from the male and is usually visible for up to a day after mating.
Mucous Plug: The first sign that the mating was successful is the presence of a mucous plug in the vulva of the female which appears sometime after mating. This plug is formed by secretions from the male during mating and is meant to keep sperm from other male rats out, thus increasing the chances that he will father the litter. During the next day. the plug falls out and may be seen in the female's cage. Lack of Heat Cycle: Probably the easiest sign that the mating was successful occurs 4-5 days later (depending on the female) when she is meant to go back into heat. By keeping track of your female's cycle and time it can be easy to determine if she is in heat or not. If the female goes back into heat, breeding can be repeated until she does not go into heat. Occasionally a female will skip a heat cycle and then go into heat 8-10 days later (or even later into the pregnancy), most likely due to a reabsorption of the fetuses. Weight Gain: Before breeding, it may be wise to purchase a scale to track fluctuations in the weight of the pregnant female. Not all females will gain weight the same way, but gradual weight gain during the first few days can be a good sign of pregnancy. A full grown female (over 4 months of age) should not normally gain weight over time while a pregnant female may gain small amounts (just grams) each day. During the first week, a slow and steady gain is usually seen, but small decreases or stability are not necessarily indicative of something wrong. Large decreases in weight over several days may indicate that reabsorption is occurring, either partially or entirely. The second week seems to be the slowest in terms of gain, and large amounts of gain are usually seen during the third week. Associated with this gain will be an enlarged lower abdomen. The female may look pear shaped or look like she has swallowed a baseball. The amount of weight gain is determined by the female's body type, her diet, and the number of babies that she is expecting. A female expecting a small litter may have very little gain, while a female expecting a large litter may experience huge amounts of weight gain. The PAR Theory of Estimation Coming Soon Behavorial Changes: Hormones associated with pregnancy can alter a female's normal behavior. An active or aggressive rat (although I do not know why someone would purposefully breed an aggressive rat) may become docile and calm, while a docile rat may become overly active, aggressive, or territorial towards other rats and humans. A pregnant female may show more interest in food as well. It is not uncommon for an expectant female to hoard food from cagemates or be overly protective of it. Cagemates often sense the pregnancy and share more food with the expectant mother or allow her to eat her fill first. Normal female rats are very interested in the scent of a male rat and will eagerly sniff at areas when a male has been, including unwashed hands. A pregnant female will show no interest in males after an initial sniff. Loss of Hair Around Nipples: During the third week of pregnancy (after 14 days) the mother will lose fur around her nipples. This aids in feeding the babies after birth. Nest Building: As the pregnancy continues, hormonal levels in the mother change to bring out maternal behaviors. Nest building can occur anywhere from several days before birth to several hours. Some females build simple nests and others build large and elaborate nests that can block the babies completely from being seen. It is a good idea to provide the female with plenty of different types of nesting materials. Shredded black and white newspaper, toilet paper, tissues, and paper towels are excellent types of materials to use. Cloth is not recommended because the pups can become caught in holes or tangled in strings. Moving the female to an aquarium or single leveled wire cage is also advised so the female can have a quiet place to give birth without fear of injuring the babies on ramps, hammocks, and other things found in a normal adult cage.
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Last Updated: 09/04/06 |