Rabbits or jumbo rats

[Sdaji]

I breed a fair few rats and love to experiment, inspect and learn. I haven't measured it exactly using scientific equipment, but I've dissected young and old rats, and I have been surprised to find that the big, old males aren't particularly fatty. I was expecting to see lots of fat on the big old boys like the rumours all say, but the big boys were surprisingly lean.

I've seen pet rats owned by doting people who give them a bad diet (not intentionally, just too many 'treats') which are clearly very fatty (obviously I don't have the opportunity to dissect the beloved pet ones :lol: ). Active breeding rats fed a proper diet seem to stay pretty good though, even into their older age. My males are still young and growing until over 250g, and females up to around 200g. By the time they are past the 'young, lean' stage my males are well over 250g, and to make them 'old and flabby' I think I'd have to retire them from breeding and leave them to sit around doing nothing for a few months. I actually do keep a few favourites as pets after they're retired from breeding, and some of these do end up a bit chubby, although I haven't dissected any of the 'pets' to confirm how fatty they are. The older females are culled immediately after their last litter is weaned, so as Warwick says, they should be quite lean too.

I have been a bit surprised to find that proper research doesn't confirm the truisms about large rats being fatty, and it seems it might be a bit of a myth. Happy to be shown otherwise, but other than rumour and people repeating each other, I can't find anything to back the 'fatty old rat' story up.

 

[Bluetongue1]

As a generalisation, aging mammals do tend to have a higher proportion of body fat than young mammals. I have been wading through various articles and abstracts and I can say that the situation with rats is far from clear. They have been domesticated long enough that we now have many different breeding lines that are no longer representative of wild R. norvegicus. So where the large or old adults of one breed(e.g.Sprague-Dawley rats) can show no significant difference in proportion of body fat compared to young animals, adults in another breed (e.g. Fischer 344 rats) can have nearly twice the amount of body fat (8.67% at 9-10 weeks compared to 14.02% at 22-23months). There is even a line that is genetically obese (Zucker rats). As has been pointed out, quality and quantity of feed has an influence on fat storage, as does the types of activities, their intensity and duration.

With the correct type of breeders and the correct care, there is no truth to the “fat old rat” tale. However, if you are breeding your own from stock you bought at a pet shop, or obtaining frozen from someone who isn’t well versed in what they are doing, there could well be a problem. On the other hand, if you are buying frozen from a good, professional supplier who knows what he or she is about, it will not be an issue. I do suspect that as the hobby has become bigger and more professional, this problem is probably a lot less prevalent than it has been in the past.

I will be changing my future posts to reflect the above information.

Blue