To know when a female rat is coming into or already in heat is pretty easy if you know what you are looking for. For basic anatomy here is a link to see what I am talking about Sexing Rats. The female's vaginal opening is directly below her urethra. Many people mistake females for males because they think the urethra is a penis. Here is a picture of our Ariel, being hairless you can see her nipples (only female rats have nipples - 12 in all) you can also see her urethra. The vaginal opening is directly below that. I wish I had a better shot of it but with the link above and Ariel's picture it should help you know more about rats then you ever wanted. When a female rat is in heat the vagina is open. Sometimes it becomes discolored, a blue or purple hue. Which often shows up in our darker rats. When a female is not in heat, the hole is tightly closed. With tracking our rats they seem to go into heat every 5-6 days. Usually a female in heat will also behave a bit different. If you scratch her back she may arch it. She may also be more jumpy, darting and sometimes spinning around. To tell the male she is interested, she will even stiffen her legs and lift her tail. With our new girl, Pumpernickel, we will even be able to see her ears vibrate when she is in heat. The dumbo mutation prevents female dumbo ears from doing this.
It is possible for a female to get pregnant from a single mounting. However, during courtship, they will mount many times before the male can complete the act. Usually the female is in heat for about 10-12 hours at night but this is not always the case. Our EmmaOreo went into heat around 10 am. I have read, it is very important not to let your male rats 'play' with your female even if she is not in heat, the male might stimulate her to come into heat. What I find amazing, is how a female in heat is also VERY determined to procreate. Rats will usually synchronize their heat cycles. This helps them in the communal living to take care of each others offspring like many other animals in the wild. A friend's new females actually chewed through their cage and chewed out the male (YES, it pays to watch CSI - the fragments were on the outside of the male's cage) Both females became pregnant. My friend knew right away for one because she saw a mucus plug. It is a waxy plug in the vulva of the female. It is formed by the secretions from the males and can be visible for up to a day after mating. This prevents other males from breeding her. Like dogs, superfecundation, is one way to keep the genetics diverse within a colony.
How We Pair
There are a couple different methods for breeding rats. We usually use our single level cage. On the day the female goes into heat, we place them both together into the cage. Often it is immediate but we will leave them in the cage together overnight. In the morning, we put them back with their cagemates, usually without any problems. Occasionally the male is still a little amped up, so we often provide some yummy extra food as a distraction as he settles back into the boys dormitory. The second method, usually used by larger scale breeders, is a bit longer and less involved with the 'humans'. They will place the male with one or two females for about 10 days. This method, insures that the female has had at least two heat cycles. However, it does sometimes make it difficult when reintroducing the rats back with their cagemates. For this reason they usually keep the females in the cage or tub until after the babies are weaned. The male will need to be bathed and slowly reintroduced to his old cagemates to prevent any posturing or aggressive attacks.
Now many of you know, I am a bit OCD when it comes to weighing our rats. This habit has come in handy for me to see that a rat has lost weight quickly over a weeks time. Might not look visible at first but if a healthy buck drops 15 grams in one week that is usually a sign that something is off. We weigh our juveniles and adult rats once a week. We weigh dams daily, starting from day of pairing. This has been a valuable resource helping us and others in knowing if there are complications, predicting how many babies, and overall just plain fun! Once the babies are born depending on the size of the litter we will usually weigh the largest and the smallest the first few days. If we have runts we have even weighed them before and after us feeding them to insure they 'swallowed' formula. As for determining weight gain for a female. We notice right away a weight gain of 8-12 grams then slowly 2-10 grams a day during first few weeks. The last week there are usually huge daily gains. We have tracked up to a 24 grams gained in just 1 day with our litter of 18 (Spring 2015 'X-Men' Litter)!
Is She Expecting?
As for Lil Miss Aurora, her weight has fluctuated so far. Last week before pairing her weight was 324g. The next morning it was 214g. The following days it went back up to 324g, yesterday it was 326 and today it is 330. I am tracking her heat cycle to see if she comes back in. We do hope she took last week. If not, this week we will continue with her evening 'playdates' with Apollo.