All breeders try to breed for a “good temperament” but not all breeders agree on what a good temperament is! Some breed for rats that are active and always on the move. Others may wish for “lap rats” that tend to be more mellow and cuddly. All breeders agree they want their rats to be happy, relaxed animals. They want rats that enjoy interacting with humans and other rats without any concerns about injury.
Genetics influence temperament in all sorts of ways. I recall reading something from long-time breeder, Jemma Fettes, of Isamu Stud, a very well known rat stud in the show world. She talked about how an orphan rat was put into a group of babies and grew up among them with (presumably) the same maternal care as the biological offspring to the mother. Even though he was raised exactly as the others, his temperament was far different. He wasn’t a “bad” rat, but a very active, cheeky rat, and far more trouble than his adopted brothers and sisters! Jemma was convinced the difference in his temperament was due to his genetics, not his environment.
When it comes to rat temperament, epigenetics come into play. That is, not everything about the DNA of a rat result in a particular temperament. “Mother rats spend a lot of time licking, grooming, and nursing their pups. Others seem to ignore their pups. Highly nurtured rat pups tend to grow up to be calm adults, while rat pups who receive little nurturing tend to grow up to be anxious…Through her licking behavior, a mother rat can write information onto her pups’ DNA in a way that completely bypasses eggs and sperm. In a sense, her nurturing behavior tells her pups something about the world they will grow up in. Mom’s behavior actually programs the pups’ DNA in a way that will make them more likely to succeed.” (Genetics Science Learning Centre).
In fact, researchers at McGill University have determined that maternal care in the form of licking and grooming “changes hundreds of genes” in the babies at once. In their laboratories, rats that were “poorly licked” were anxious and harder to handle. Those who were licked a lot were easy to handle. The tendency toward high levels of maternal care may be genetically linked, of course, but the point is that stress responses can be changed in a single generation. This has important ramifications for breeders. While they are unlikely to lose “type” or “colour” quickly, they can lose temperament simply because a doe isn’t attending to her offspring properly.
Having rats with low levels of anxiety is important. Anxious rats are more likely to bite. They are also more likely to become ill, lead shorter lives, and suffer from problems with mites. It’s important to breed relaxed rats and I know all breeders are trying to do so but understanding the mechanism for good temperament is trickier than it looks. And while breeders can do their best to socialise baby rats, handling them and creating a good environment for them with plenty of “enrichment” (toys and climbing and foraging opportunities), it looks like the basics of temperament depend largely on the mum!