Tute Sweet
Is he still eating his other vegetables/leaves, or is he only eating hay?
It might be worth mixing some of his chopped fresh favourite treats in with his gruel to encourage him to eat it, especially strong-smelling foods such as fresh herbs.
I had a similar but opposite problem with my boy (he's a reluctant hay-eater) and mixing his daily veggies and herbs/leaves in with his hay made the world of difference.
If that doesn't work, this might be of some use to you:
Pellet free diet
It would be tricky, especially with such a big breed of rabbit, so probably only as a last resort but if you really can't get your bun to eat them, it might be worth discussing the possibility of going pellet-free with your vet, or at least ask them for advice for exactly how to replace the nutrients in the meantime until he does start eating them again.
Actually he eats the hay voraciously.
But we figured out the problem. He is a very picky eater, and I bought the wrong pellet food. There are two different color bags, which are different flavors, and I bought the wrong one.
Went out, got the right food, he dug in immediately. Also I started to give him some banana mixed with oatmeal, which my vet recommended for a short time to help him gain some weight faster.
He ate the greens happily, but not mixed with the other pellet food. I normally stick with kale, bok choy, and broccoli, and he loves all three of those. But he went nuts over the banana oatmeal mix.
I'm so relieved I finally got him to eat, since the syringe was not working at all. And I'm sure he is a happier bunny now that he got the stuff that he likes eating!
Vet said it was probably due to stress from the move. It's a big life change for him, as well as us. But thank you for the advice! I will keep it in mind for the future. Now to just make him gain about seven pounds!