This article is from the WSSF 2010 AFRMA Rat & Mouse Tales news-magazine.

By Karen Robbins

Amanda Brewer, Bloomingfield Rattery, CA, e-mail
Q I’m about to the point where I’m sure Pyrite, my male Siamese rat, is sterile, but I’d like your thoughts. He has been in with a B.E. Siamese (she got a good evaluation score card) doe for nearly 2 months until I finally switched her mate. I then put him with Golden Birdie, my Russian Blue Agouti, since she just turned 5 months, and despite being in for about 2 weeks I’ve seen nothing happen. I know sometimes it takes a few tries and heats to get things going, but the thing that caught my eye is that even when she was obviously in heat, he showed no interest in her at all. I don’t know if you have any thoughts on that.

A Try the female with a male that has produced and the male with a young female that has produced. Also, you can try a younger female (4 months) but don’t put her with him until the day (evening) she is in season. If the first female (BES) gets bred right away with a different male and a female that has produced a litter does not get pregnant with Pyrite after several weeks, then he could be sterile—though it is rare, I can’t recall ever having a sterile rat—some males are slow about breeding and the females take weeks to get bred where other males get them bred right away. If nothing happens after several weeks, then splitting them up for a few days/week then reintroducing when she is in season may help. Sometimes an aggressive female will intimidate a young male (especially if she is put in with him not in season) and cause him to not want to have anything to do with females after that. I normally don’t breed my males until they are at least a year old—you get past the 6–8 month mark where possible aggression shows up and you therefore won’t have produced any babies that they then may have issues when they get older, plus he is more mature to deal with females. Sometimes placing another female in season in the mix helps. Place them in a breeding cage (such as an aquarium or plastic tote—one that doesn’t have levels) with no houses or hidey things. Also, diet could be a factor—for breeding animals you need something like the Harlan Teklad 8604 lab blocks with 24% protein, 4% fat (or 6% fat in the breeding formula). Sometimes weather has an influence—hot weather is not good and they won’t breed very well if they are kept too warm.

One other thing to add: overweight females are harder/impossible to get bred. Also, older females will sometimes take longer to get bred and are more prone to having problems with the pregnancy/litter/smaller litter size.