Oh, I feel your pain! Sometimes, and it seems to come in waves, if it's not one thing, it's another! I'd like to say it's that steep learning curve when you're just starting out, but honestly, between my breeding partner and me, we have a combined history of about four decades of rabbit raising, and we're still
encountering some new mystery pretty much every single year!
I usually think about retiring breeding does at around 3-4 years, but that's because they start having occasional missed conceptions and much smaller litters. It really does depend on the line and the particular rabbit. The mini breeds seem to be reproductively fit for longer than the bigger meat breeds, but I did have a Satin doe that was still giving me litters of 6-8 well into her fourth year.
Are you sure your does are not overweight? Most of the issues you're describing sound like what I've seen with overweight does. It has been my experience that the older does get, them more likely they are to put on extra fat. That interior fat really messes with breeding interest, conception rates and successful kindling. Even if they are the "right" weight for their breed they may be fat. Look for that telltale sign of softness/flab around their shoulders.
That would not, however, really explain her lack of interest in taking care of the nest and kits. That sounds more like there's something that's bugging her. It could environmental, it could be a health issue, and/or it could be her diet. Here are some thoughts:
1) Stomping the kits, in my barn, always makes me think of mice. Most does have a serious problem with mice, and are willing to kill the kits in an effort to kill the mice.
2) Having failed litters in November and January might explain it a bit. I quit breeding for December-Januaury litters because, although most litters did fine, a very large proportion of litters I did lose occurred in those months. My theory is that even though you can get the rabbits to breed, their hormones are at a natural low, so some of them are not getting the proper chemical instructions from their body to do what they need to do. This might be especially true of an older doe, whose hormones are presumably ramping down a bit anyway.
She could be carrying some kind of sub-clinical parasite load that's disrupting things. I've had more than one judge advise giving the rabbits a dose of fenbendazole (SafeGuard for horses) for mysterious out-of-condition episodes. I have used used it several times and I must admit, the turn-around sometimes looks miraculous - both their appearance and their vigor improved dramatically.
In another thread I described our battle to identify what turned out to be a Vitamin E deficiency, which completely wreaks havoc on reproduction:
I’ve had successful fall offs but no kits. The girls aren’t over weight or sick. Anyone else had this problem???? Also I have a buck who refuses to breed….he isn’t even remotely interested in the opposite sex lol. Both issues buns are mini rexes. (I have two mini rex does who I can’t seem to...
also talk briefly about vitamin deficiencies here:
Absolutely not! Split between 5 bucks. This got me laughing, thinking that must be one vigorous buck.
It seems a shame to sell two proven does in exchange for unproven first-timers, who can have their own issues. Since they're both having problems (and 2 years old is not
old for a breeding doe), I'd be inclined to try to figure it out if you can; and it certainly cold be more than one thing.