Basic Breeding Systems

There are several different breeding systems- each with advantages and disadvantages. Some breeding systems are designed to produce the maximum number of rats in any given period of time. For the hobby breeder this is not usually the chosen approach.

A good hobby breeder will generally breed monogamous pairs or use a polygamous method to ensure optimum safety for the adults and offspring as well as to ensure proper identification of the parents for pedigree and tracking purposes.

• Monogamous – Monogamous breeding is when an individual male and individual female are put together. This method provides the most accurate breeding data. Once they have been introduced the male can either stay with the female for a few hours, a few days, or until she is full term.

  Some breeders choose the “hand breeding” method which involves putting the pair together only when she is in heat, or simply overnight. This method helps ensure that the rats do not have to be reintroduced to their cage mates. There are times when a male rat, after mating, will exhibit stronger alpha behaviors once he is returned to his colony. Hand breeding can lessen this effect and ensure a more peaceful transition for the male re-entering his colony. If the other males are too interested in the returning rat then a bath may be in order to remove the scent of the female.
  
  Monogamous breeding is the healthiest choice for the female and her offspring. It is also easier to accurately track the pedigrees of the rats being bred using this particular method.
  

• Polygamous – Polygamous breeding is when one male is put in with multiple females to breed. Removing the females as pregnancy becomes apparent ensures that proper pedigree information can be tracked.
  

• Colony – Colony breeding is also referred to as “harem” breeding and consists of multiple females being housed with one male indefinitely. As the litters are born it becomes difficult to track the lines due to mothers rearing each others offspring. Leaving the mothers in with the male often results in postpartum pregnancies. Although this method will produce the maximum number of offspring it is not the healthiest option for the dams or the offspring. Back to back pregnancies are hard on the mother and can drain her physically. This may result in subsequent litters showing a lower rate of growth and survival. It also is not unusual for babies to be killed or harmed (by either the male or the females) in a “harem” breeding environment.

• Mass – Mass breeding is when multiple males and females are housed together indefinitely. This gives the breeder no idea as to full parentage on the offspring and can be highly dangerous to both the adults and the babies.

Communal Mothering

Leaving the females together to raise their litters has a higher incidence of infant mortality particularly if the females were not familiar with each other before mating/birth. This can result in aggression between the females, stealing babies, and injury or death of the babies.

The still pregnant mother may steal the babies after the first litter is born. On the other hand the first mother, who already has had her litter may steal the babies from the second mother as she is birthing, or shortly after.

The stress on either mother may cause them to commit infanticide upon their own or each others offspring. In studies on communal mothering it has been shown that sisters who have been raised together have the lowest incidents of infanticide and aggression.

When two communal mothers have litters that are not close in age there are other issues that can add to the problem. The oldest litter will be larger, stronger, and more apt to get feedings than the newer litter. The younger babies may suffer from malnutrition and dehydration which can cause serious health issues and even death.

Having the mothers raise their litters separately will ensure the highest chance of infant survival.