Maximizing poop production...

I'm starting to think that building beds,providing compost, selling vegetable starts , making biochar, and otherwise serving the needs of gardeners is more my interest than growing my own food!
Fir example my rather old chickens dont lay, but they do process food waste into compost.
We have pet bunnies and I love their poop in the garden.
I want to have more bunnies one day, just for the poop.
It occurred to me that my bunnies are relatively small, being a double mane lion head and a mini rex.
Realistically I'll end up with whatever rescue bunnies I can get my hands on, but I can't help but wonder if bigger bunnies would be better for poop production.
Surely bigger bunnies poop more.
They also need bigger accommodations.
I'm inclined to think two smaller bunnies  would be a better choice than one larger one in the same space,  because of the well being of the animals.

I would like to keep any future bunnies more like livestock than pets.
Our pets get a lot of green food, compared to most house rabbits, but my wife and kid baby them.
They get hay, pellets and cubes of orchard grass.
I want to feed the future bunnies almost entirely from our land.
Nutrient cycling biomass is what I value them for most, though their ability to spark oxytocin is pretty amazing.
Chickens are not the best at dealing with brush, so the more tree hay I can feed to bunnies, the better.

I found 2 rabbits in a shared space led to one getting badly bullied, even though I thought they were getting along well..

I bet that feeding lots of things rabbits really like would increase throughput, maybe at the cost of health..

I also keep my two separately, due to my inability to sex them correctly when they were young....
I think of my bunnies more as biodigesters than pets, eliminating my need for a compost pile. The male is friendly, but the female would be happy to never see any of us humans again. They eat all my kitchen scraps (and most of what we eat comes from fresh food that leaves skins, cores, etc) as well as much of my yard waste. Mulberry prunings, weeds, plants that get ripped out, etc. I buy a bale of alfalfa (they won't touch the grass hay here for some reason) every year as a supplement for some eventuality when there isn`t enough for them to eat and it usually ends up as mulch in the garden.
I do notice that poo production waxes and wanes depending on what they're eating, but beyond just "pellets are less productive than greens" there isn't much logic I can figure out. They eat a very wide variety of stuff, but their absolute favorite thing is leafy weeds. I mean, they'll eat carrots and bananas if they can, but they'd probably go for dandelion-type weeds first.
I haven't even done any meat production, but I don't see myself ever gardening without a few bunnies just for this purpose. The difference in productivity is remarkable. And I've seen larger scale operations where the bunnies are eating community waste, along with chickens, in a "give us your trash and we'll give you fertilizer/eggs/meat" operation. They removed significant amounts from the waste stream and produced protein and fertilizer.

Higher fiber hay will produce more poop. The best types are Timothy and orchard grass, with Timothy being best. If you're really interested in feeding from your land, and very interested in adding more buns, it would probably be of great benefit to them and, as a result, to you, to plant some Timothy. Most buns like the softness of first cutting best, but 2nd and 3rd are progressively higher in fiber, and better for them, but all 3 cuttings are better than other types, including the orchard grass.

And, yup - bigger buns = more poop, lol.

There is a big gap in the conclusions that the house bunny and livestock bunny crowds draw.
The house bunny crowd would have you belive that a bunny without a buddy is liable to pine away, unless YOU become that bunny's life partner 🤣.
I certainly see our two fixed rabbits humping each other, and the female runs away from humans unless food is involved.
Even she succumbs to the joy of petting once you catch her, she just can't help but love it!
But I digress.

My future bunnies will be fixed, and they will get a great natural diet.
Growing Timothy grass?
I just don't know.
Growing grass on purpose  is a hard concept for me to get my head around!
Trimming trees feels like husbandry, haying grass seems like work.
Did I mention I hate cutting grass?
I think I'll feed pruning and weeds with a bake of something as backup.

Feeding mixed food waste is a consideration, but the chickens generally do ok on that.
I am a little torn, I like the idea of feeding the bunnies things my chooks tend to scratch into the compost, like dumpster bread, but I don't want to kill a bunny by inducing GI stasis.
That seems like something that might be overblown by the house bunny crowd, but I am not experienced enough to be sure.

As an aside, as I find mice poop in my house,  I find my self wondering about mice as composters.
Clearly there is nothing they can't eat and thrive on, plus my chickens would  love them.
I mean I could feed the little scamps slightly greasy pizza boxes and they would just keep eating, breeding and pooping.
But my kid would hate me for disposing of them, so , it's never gonna happen.

Instead,long live the bunnies, and their poop!
I look forward to many more years of mutalism with my nibbling friends.

Sadly, I can assure you, GI Stasis is a very real thing, and not a good idea to dismiss. It's what we lost our sweet Lola to, and I know of many other folks who have lost their bunnies to it, as well.

William Bronson wrote:
Feeding mixed food waste is a consideration, but the chickens generally do ok on that.
I am a little torn, I like the idea of feeding the bunnies things my chooks tend to scratch into the compost, like dumpster bread, but I don't want to kill a bunny by inducing GI stasis.

Yeah, this was something the program i saw did well: they trained the "trash donors" to separate their waste, in different bags, and made it clear who ate what. It was simple enough: cooked leftovers and eggshells for chickens, raw scraps for rabbits.  A staff person sorted it at intake and really controlled who got what, and the chickens still had fun.
We may divide a stale heel of bread between the two of them once in a while but we really do stick with greens and weeds.

I like your thinking about maximising fertility for the garden. It was one of the big factors that led me to deep litter composting for our chickens; I wanted plentiful good quality material for the vegetable patch.

As for your thinking about the rabbits, I have no clue about maximising poop without potentially harming the rabbit health. What I can say is that I have a STRONG preference for systems where the livestock feed themselves. The less routine human input of time to a system the better, because every routine job that you do that takes time takes you away from other things. That 15 minutes a day to harvest greens from the garden will be insignificant to start with, but will suck after a few months.

When we are able to, we let our chickens free range. They roam over our whole property eating bugs. When they come back to roost they poop into the woodchips. I harvest the fertility, with minimal labour.

How might a "self-harvesting" rabbit setup look? A rabbit tractor around a field?

I'm glad we cleared up the GI stasis issue and the mixed waste thing.
Self feeding rabbits or chickens are less of an issue when disposing of the  "waste" is the whole point.
My birds used to roam my entire urban backyard.
No annual plant was safe.
Now they only get the perimeter , including the 4' x 20' compost bed.
They still have other places to scratch, but they would live in that bed if they could.
We feed them food scraps, weeds, layer feed , sunflowers and corn, right on top of the bed.
I was feeding them the tree pruning's; they do a great job on the greenery but the twigs and branches don't break down much, complicating the composting process.

Our pet rabbits tend to strip branches of foliage and bark, leaving bare branches behind.
What's left after they are done is good for smoking foods, biochar and wood chips.
I don't imagine ever keeping enough rabbits to keep up with the amount of leafy biomass the yard can produce, but diverting some of that biomass into fast nutrient cycling is very appealing.
I hope to feed them a lot dried sunchoke stalks over the winter, they seem to love them, and they are a common byproduct of fall clean up for me.

From Dealing with Rabbits at home
What Causes GI Stasis?
A rabbit’s intestine can become static for a variety of reasons, including (1) stress, (2) dehydration, (3) pain from another underlying disorder or illness (such as gas, dental problems, infections, or urinary tract disorders) (4) an intestinal blockage or, (5) insufficient dietary crude fiber. Left untreated, the slowdown or complete cessation of normal intestinal movement (peristalsis) can result in a painful death, in a relatively short period of time. If your rabbit stops eating or producing feces for 12 hours or more, you should consider the condition an EMERGENCY. GET YOUR BUNNY TO A RABBIT-SAVVY VETERINARIAN IMMEDIATELY.

It seems to be caused by diet, so it may be easy to prevent.
I have looked at commercial rabbit production and found a few good books;
https://www.booktopia.com.au/raising-pastured-rabbits-for-meat-

Sadly our very first bunny died of what was probably GI stasis.
She has a pretty textbook perfect diet,  but sometimes that might not be enough.
I tend to my sick chickens, wipe vents, hand feed if needed, isolated from the flock of course, but I don't take them to a vet.
I have dispatch two of them to stop their suffering, and it wasn't at all easy.

Thinking seriously about giving bunnies the same treatment gives me pause.
Maybe it shouldn't be different but I can tell it would be for me.
I'm so glad you brought up vet care, because I'm realizing that it will probably be inevitable,  even if it is only at the end of life.
I'm not concerned that I wouldn't give them a great life with an excellent diet, but things still happen.
I will need to decide how much responsibility I can take personally vs. what I can afford financially.

Thank you Carla and all others who spoke up about appropriate diet for rabbits - no, you can't just feed them anything.

Not mentioned is their need for Vit C (?) we used pineapple juice for some reason...

Improper diet leads to more than gut issues, such as dental issues (malloclusion is more common than you would think!) causing the need for regular teeth trimming!

NO rabbit tractors please!!! Buns dig and would escape within a week if not contained on all SIX sides. BUT why not use them on a rotational basis from garden area to garden area? Grow, harvest, buns clean up and fertilize while fallow, then plant??? Assuming the areas were ditch fenced at least two feet down they should be good as long as food supplies didn't run low allowing the "grass to look greener on the other side" of the fence.

They would quasi till the ground digging burrows to live in...Hmmm moving them MIGHT be a challenge....this idea may need more thought...

Larger rabbits are generally meat rabbits (Flemish Giants stand taller than 3 feet!!!) IF you had enough of them would the kids really notice if the numbers ebbed and flowed as the males were culled?

I could see grazing them during the day, in a pen, under watchful eyes.
Having done this before with the pet bunnies,  I noticed their lack of a sense of self preservation.
While the chickens outside the pen got quite and plotted their demise, the bunnies just hppped around oblivious to the danger.
They are definitely ultra domesticated.

My kid would definitely notice any fluctuations in population!
Besides, I've realized by talking about it here that I'm not interested in treating bunnies like I do chickens, and I don't even cull my non-laying chickens.
I'm gonna respect that feeling in me, because I can afford to.
One day it might be different,  but for now my animals are companions of various sorts, not food.
The kid puts it this way "In this family we don't eat animals that we know"
That's more a description of the facts, than an explanation of the reasons behind our choices.
There's a lot of cognitive dissadence evident here, but life is like that.