How to fatten an underweight rabbit

Hi all, my bunny Mochi has been given a clean bill of health after a bout of gut issues (not stasis, just not eating well and poo not round golden shaped since Christmas) His blood test is ok too so it’s on the road to recovery.

However he is underweight at the moment and doctor is looking at at least 300-500gr increase going forward.

Do any of you have any great advices/tips to fatten him up [emoji4] Thank you so much!

View attachment IMG_9764.jpg

View attachment 4406211B-D1E0-4122-B104-759C7564D626.jpg

Sorry wrong pic attached [emoji28][emoji28][emoji28] him just back from vet look, obviously not v happy [emoji28][emoji28][emoji28]

If he is recovered and eats normally, he should gain weight pretty quickly. Rabbits get fat easily. You can increase a bit 'root vegetables' like carrots and parsnip or pellets, but I wouldn't risk messing with his guts by giving too much (and risk him eating less hay) or trying too hard to find fattening things he is not used to eating if it's not a case where gaining weight will be a forseeable issue. Gaining weight too quickly is never very good anyway, so I would just let him go back to his normal routine and keep an eye on his weight.