. I'm currently trying to think of a way to engineer a small gap to allow the sweeping out of loose hay
I love the idea of being able to sweep out hay, but there are two issues: 1) if hay can fall out, so can a newborn kit that has been drug out of (or never made it into) the nestbox. 2) Hay will be in all directions and doesn't like to fall neatly down a slot, sadly.
I use those thinner plastic vented sitting boards as emergency floor repair until the pen bottoms can be replaced. They tend to build up manure much, much quicker than wire. Makes a good inducement to repair the pen flooring quickly, though.
As to wire flooring being expensive: I am still using wire pens made of good quality heavy wire that I purchased used thirty years ago. I have also purchased new some of those ready-to-pop-together wire cage kits from the feed store that were junk, after only a few years they had major issues. Investing in good wire is worth the money.
The biggest problem with wire flooring is allowing manure to build up in the first place, the urine acids eat through the wire quickly, especially on thin wire. I find a stiff brush on a long handle lets me remove any shed fiber easily, before it can accumulate manure (with angora rabbits, this can be an issue). Keeping the rabbits groomed when they start to molt also keeps the fiber off the wire, preventive maintenance.
Over the years I've even moved away from even having anything under the cage. I had cages resting on pipes and even those rounded surfaces collect hair, poop and urine.
I so agree with this. We started with two 2x4" boards spread between two sawhorses to set the rabbit cages on. The rest of the pen would be clean, but where the wire rested on the boards for support got messy easily. Suspended cages are so much easier to deal with, and so much easier to clean under.
I have used pens with the dropped nest boxes in the floor, and did not like them. The weight of the growing rabbits pulled the floor down in the middle, and the rabbits were much more likely to escape the nestbox. I thought they would be safer, as they could more easily wander back into the nestbox, but they actually ended up OUTSIDE the nestbox more often. It also puts the kits in a more dangerous position beneath the pen, as far as predators go, instead of safely in a secure strong box inside the pen. If you have no predator issues, be very thankful. For those of us with a wide array of potential predators, it becomes an issue.
I just use some of that very thick plastic for shelving in the pantry, like they use for milk crates. Seemed so sturdy. It not only bent under the pressure, it cracked. I find plastic has issues of its own, scratching, and yes, cracking in cold weather. Of all the things I've used in the last forty years for rabbits, nothing has beat good old fashioned heavy duty wire. It lasts for me, and is easy to handle.
Just another thought, I realize that there are folks that sanitize constantly, but I've found that the rabbits seemed to be healthier when I wasn't constantly killing off the good/neutral bacteria, leaving behind only the small percentage of bad bacteria that now had no competition. I haven't found all that sanitizing to be beneficial, except when you are cleaning a pen that has been exposed to a live disease.
I also have found that constant washing leaves a very humid environment, which can be difficult on respiratory systems, and make it harder to feel cool and comfy in the hot weather. Hot and humid is much harder to take than a dry heat.
Sometimes we make a lot more work for ourselves than necessary. It has been much easier to simply go down the pens once a week or so with a scrub brush to remove any little loose hair or debris. If you end up with a manure build-up starting, the quicker it gets dealt with, the easier it will be to handle. If you find a rabbit that is much messier than the others, I consider that a ding against using that rabbit as a future breeder, it may have some trait that is encouraging the problem.
Scrubbing anything in the winter cold is unpleasant. Your hands get quickly chilled, rubber gloves can be difficult to work in, and they don't keep you warm. The warm and also waterproof gloves I've tried have been much too bulky to try to pick up pieces of hair from the flooring.
My rabbits love to chew on wood, so I avoid wood pens when possible, they're also much heavier to move around. Yes, over the years I've used many different systems and many different materials, and so far, heavy gauge all-wire pens have been the best choice. I actually like the same 1/2" x 1" flooring as sides and roof as well, to keep rodents/snakes/weasels out of the pens completely (they go right through the 1" x 2" normal sides.)
Of course, I have a friend that swears by the colony system, and it works really well for her. That eliminated all of the cages, end of problem. My barn is not sufficiently predator proof to permit that, but maybe someday. . .I have had successful colonies in the past, and do appreciate NOT having to deal with pens at all.
If they really are used in production facilities in china, I can't imagine they are too bad, that seems like it would make them pointless pretty quick otherwise. Commercial operations usually prioritize efficiency, right?
