Regarding the greens —  I am assuming they are still babies/youth so that is why you are asking about introducing greens?   (Or are they adults that never had them before?)  IF they are young – then here is a great resource for how to start introducing greens. http://rabbit.org/faq-diet/

The above link will also help give you information about if you are feeding enough.  Some rambunctious young bunnies need more food as their body is growing and they have tons of energy.

If she is not under 7 months and/or you are feeding her the recommended amount,  and she still seems to skinny (that even the vet recognizes), then it is something to keep an eye on and have a rabbit-savvy vet monitor. 

Did your vet say why he thought antibiotics would help? If her poop looks normal and she’s eating and doesn’t seem sick at all, I think it was good that you took her off the abs. Excess antibiotics should be avoided in bunnies because all abs disrupts the bacterial flora to some extent, and rabbits are so very dependant on a healthy gut flora. Medication is sth you should ask your vet about though.

Sometimes an under-weight bunny benefits from a probiotic like Benebac. While lactobacillus rarely survive the GI tract of a bunny and aren’t part of their normal intestinal flora, there are many other bacteria that can be used as probiotics in bunnies. Benebac has one of those bacteria, enterococcus faecium. Here’s a rather long but informative article on use of probiotics in rabbits: http://www.vettimes.co.uk/article/beneficial-bacteria-in-pet-rabbits/

Not much experience with babies here, but I do know it’s best to wait until 12 weeks to begin gradually introducing fresh greens/veg/fruit. It takes that long for a kit’s gut flora to develop properly. I believe that alfalfa pellets & alfalfa hay are the ticket at the moment.

Ok, then I see why your vet gave her the abs!

I’m pretty sure your not doing anything wrong. She may have a malabsorption problem. The reason could be one of several. Did the vet test for intestinal parasites? Or say anything about the possibility of worms?

As Q8 says, it’s recommended to hold off on greens/fruit until around 12 weeks, unless the bun has had greens from the start at the breeder’s and does well on them, of course. Alfalfa pellets and alfalfa hay has good protein that a growing bun needs.

I think you should ask your vet if you should put her back on the abs. Abs can do a lot of good, but it can also be harmful. Abs kill all bacteria that are sensitive to them, good bacteria as well as bad. That leaves the field open for other bacteria (and yeast) to colonize the intestines, and sometimes, that opportunity get seized by some really bad bugs that are normally present in small numbers and kept from proliferating wildly by the other bacteria. That’s why abs should be used in moderation with bunnies (with people too actually but we don’t have quite as sensitive tummies as buns do). So I think it’s best if you ask your vet, that way you don’t have to make a medical decision yourself.

It’s good that you don’t see any worms. Worms are not common in house bunnies and it’s absolutely not the first thing you suspect if a bun isn’t eating, so your vet was right in treating the inappetance/gas first. I was just trying to figure out some reason for her being a bit under-weight in spite of a hearty appetite.