I have been successfully breeding rats for years to feed my snakes but am having problems over the last six months with less pregnancies, smaller litters and more stillborns. We have introduced some new stock but the problem persists. They are fed lots of fruit/vege scraps as well as a dry mix of rat pellets and dog biscuits (which hasn't changed over the years). We recently found some of the pellets had weevils in them...could this be the problem? I would have thought that would not bother the rats. Any suggestions on what we could do to increase our breeding success?
There is no need to mix rat pellets with other things like dog food. I see people writing this time and time again and it makes no sense. That would be like me saying I feed my cat cat food mixed with guinea pig food LOL. Rats need what is in rat food. A good quality rat pellet has perfect nutrition for rats to grow and breed at full potential. Feeding a bunch of other things along side it, including a lot of fruit and veg scraps, does not improve anything for breeding or health, and can actually make things worse. Rat pellets such as Cummins and Lauke Mills, have the correct ratio of nutrients for rats to get the most out of their food. Really good quality rats can do well on any diet, even the worst diet, but rats that are sick or have weaker genetics will start to loose condition and have reduced reproductive success if the dietary needs aren't spot on.
Rats will naturally have less reproductive success as they get older and become seniors, although I am guessing that you have not been breeding the same pairs the whole time, so it is probably something else
If you are adding new rats and the same thing is happening to the breeding groups of new rats, it is obviously due to an aspect of husbandry, which could be any number of things, including time of year/temperature. It would not be the weevils, I would only worry about mouldy food, not bug infested food, as rats would love to eat bugs anyway.
Improving genetic traits relating to reproductive success, through outcrossing, inbreeding and selective breeding, can take multiple generations, and you may have accidentally been selecting towards smaller litter sizes and less milk production and ability to hold condition, over the years. If this is the case and it isn't about husbandry, then it may be easier to just start again to save time and resources. Although if you were attached to the lineage, you could work on it and make progress.
