Much is made of early temperament testing in rats. Typically, a breeder will perform a number of tests including a “scruff” test, a human approach test (HAT), and a novel object test (NOT) as well as an open door test (ODT).
In the scruff tests, the breeder holds the rat by the scruff of the neck and observes its behaviour. A good score would be given to those rats that go limp and do not struggle. A HAT test is just what it sounds like. A human puts a hand into a cage of rats (usually a tub so they are all on one level) and waits to see which rats approach first. The same would be observed with a novel object. Rats with a “good temperament” will approach the hand or object ahead of the others. One with a very fearful temperament will hang back, unwilling to interact with that hand or object as quickly.
There are a number of shortcomings to such tests. First, most breeders interact with their newly born rat kittens from day one, if only to count them, make sure they have “milk bands”, indicating they are feeding well, and remove any dead kittens if there are any in the nest. They continue to interact with them throughout their very young lives simply because they enjoy their new kittens and also to ensure the kittens have exposure to human scent early so that they are not fearful of people.
Handling varies with breeders. Some handle their baby rats a great deal and owners can pretty much expect tame babies from the time they collect them, though whether this is due to genetics or environments is difficult to determine. The point is that the babies will run to the door of the cage because either they have learned that the hand at the door is safe and/or because they’ve been taught that by doing so they received food treats. The object test won’t do much good because the breeder has placed novel objects in the cage for weeks since the rats were mobile in order to provide a more “enriched” environment for the babies as they grow. It is possible the scruff test would still work out, though the breeder has to be careful that they are doing it the same on each rat and doing it correctly (this is harder than you think) in order to get a worthwhile result.
Some breeders do not do much handling. This is either because they worry about upsetting the mother rat or because they have so many litters being born that they do not have time. Also, they may feel they’ve already “stabilised” temperament within the line of rats that they breed so that the rats are pretty tame even without handling. For these babies, temperament tests may have a role, though even then we run into difficulties assessing what a “good”temperament is.
I have a few friends who breed rats and we all have different ideas about temperament. Some like their rats to be quite naughty and “ratty”, to be active, curious and into everything. Others prefer “lap rats”, those rats who like to sit passively and be stroked like a lap dog. If you were wanting a curious, intrepid rat you might say that the rat that is first to check out new things, always first out of the cage, always the one that climbs fastest and goes furthest from the others has the “best” temperament. However, if you want a lap rat you’d probably look for one that is a little more dopey and slow. I like dopey slow rats, myself, but I have to admit that the personality of my more active rats makes for a great deal of amusement. And who wouldn’t want a rat that jumps from the cage onto your shoulder, practically begging you to take her out and do something fun?
What we do know about temperament in rats is that you can’t determine it entirely at the age of 4 weeks or 5 weeks or even 8 weeks. Sure, you can get a sense of the rat. A very outgoing rat may be obvious at that time. Same with a very shy one. However, what science we do have on temperament in developing rats tells us that the brain is still developing throughout a rat’s adolescence. See below, from Applied Animal Behaviour Science:
A rat that may appear fearful or squeaky at 4 weeks could develop into a very sweet, biddable rat months later if it was handled often. A more confident rat could possibly become more cheeky than you like by the time it has grown up. Can we determine this early on? I’m not sure, though the best source for information may be the breeders, themselves. Breeders who are very interested in temperament (not all are) and who give thought to the development of their rats from birth to death will glean some patterns in what you might look for in a young rat.
For example, they may have a line of rats that are real “potatoes” or “lap rats” and they’ll have determined how those babies behave in comparison to their more active lines, who would perform really well in agility competitions but rarely sit on a lap. I’m new to breeding, but I can tell you that rats change over time, too. My does that were incredibly active, scrambly mad girls at 6 months have often become very docile, quiet rats a year later. Sure, they still like to climb and explore, but they often sit on my lap, too.
I have three 21-month old does who are very active, never sit on my lap, and are always into mischief. However, they race to get to me, climb onto my shoulders and “groom” my hair, love everyone (rat or human) and never fight. Good temperaments? I think so. They were haphazardly bred by someone who was going to feed them to a snake.
There isn’t any real science behind temperament tests for rats, though you get a lot of breeders on youtube behaving as though they have some kind of scientific basis for testing. However, temperament tests may be useful and I continue to keep track of them. As for now, the best source of information is probably the breeders who breed different “lines” and who have done so for many years. That is, if they are particularly interested in temperament.