Pigweed my personal experience ONLY.
rabbits WILL NOT eat it when it is a mature plant.
they will devour it when it is a young plant.
It receives mixed reviews when it is an inbetween plant.
To tell the difference
a young plant has no seed heads AT ALL. NONE.
A inbetween plant will have some seed heads, you are best trying to feed this if you remove the leaves from the plant.. just the small ones, ignore the big ones.
a mature plant will have seed heads.
NOW.. something to keep in mind
it will keep sprouting off.
so if you have a mature plant..cut it off. Harvest the young small plant leaves that will start up, feed those. Cut it off. Eventually you will reach the point of no return...depends mostly on the fortitude of the individual plant.
Now... my rabbits are used to getting a variety of greens.
My rabbits which will NOT eat spinach, swiss chard or beets will NOT pigweed at any stage of development. They simply won't. 99% of these rabbits are ones that have been bought into my herd and had to be taught that greens and hay are good things to enjoy. (these rabbits currently number 3 in my herd) --- though I did catch one buck nibbling on a very small pig weed today....
The rest of the herd, which will eat the fore-a-mentioned plants will treat them in the same regard they do pigweed. young plants yes, older plants no.
This is, may I repeat, my personal experience with this particular plant/weed.