Bugs Bunny and Peter rabbit may well live on a diet of juicy carrots and big lettuces, BUT this is not all that rabbits eat.
A rabbit has a very delicate digestive system that can be upset relatively easily by eating the wrong things leading to diarrhoea among other things. In the wild, rabbits evolved in areas with lots of low quality vegetation. They had to spend a lot of time eating and have a digestive system that would extract maximum goodness out of what they ate. Your pet rabbit is the same and so its diet should consist mainly of grass and hay.
Don't worry though, it's not all as complicated as it may seem! Follow the simple rule of not making any sudden changes to diet, so if you buy a different brand of rabbit mix for instance, Mix it with your old one for a couple of weeks before switching completely.
Rabbits love getting their teeth into hay
Pellets / Mixes
These are 'complete' solutions and contain everything your rabbit needs in terms of nutrients and vitamins. Young rabbits i.e. younger than five months old are growing fast and may need feeding twice a day but after that once a day is fine. The amount that you feed your rabbit is to some extent common sense as it varies massively between different breeds. So if your rabbit seems to be getting a bit fat, reduce the quantity of feed, if your rabbit tries to eat your hand as well as the food when you feed it, increase the quantity!
There can be a drawback with a rabbit mix. Although it looks more interesting than the extruded foods or pellets, some rabbits can be a bit fussy and not eat all of the mix leaving it deficient. If this is the case then a pelleted food is a better option. It may look boring to us but rabbits tend to like them.
Don't be tempted to buy feed that is meant for another animal, that bag of hamster or goat food may look nice, but different animal have different needs and the wrong food could cause your rabbit's problems.
What is the point of hay if you are using a 'complete' mix? It provides the roughage / fibre that the rabbit needs. Make sure you have a plentiful supply of fresh hay. Unless you can get hay from a farming friend, petshops sell hay in handy 'pillows' or small bales. The hay also plays an important role in keeping the growth of your rabbit's teeth in check by wearing them down.
Water as with any animal is very important. Try to make sure that the water is kept fresh by replacing it every couple of days (if they haven't drunk it already!) When winter comes check that the water hasn't frozen over. If you aren't able to check very often, then move the water container inside the rabbits' hutch, where it should keep above freezing. If your rabbits get dehydrated they are less able to withstand the cold so won't last long with an icy crust on their water.
Unlike children, all rabbits love to eat their greens as part of their diet. You can try adding things like broccoli, kale, and fresh herbs as part of their diet but do so one at a time. Too many items on the menu will confuse the rabbits' digestive systems. Rabbits should not eat lettuce or other vegetables like cucumber and tomatoes. Don't forget that grass and hay should be the major part of their diet.
As with any new food that you give your rabbits, don't make any quick changes.
Although it might look revolting, your rabbit will actually eat some of its own (what looks like) poo! A rabbits food goes through two stages of digestion. If you look carefully at what comes out of the back end of a rabbit, you will see that there are two different kinds of pellet. One type of pellet is round and relatively dry, this is a poo. The other type known as a caecotroph is actually the result of the first phase of digestion and is full of goodness, so don't try and stop your rabbit doing this it is all part of the process of extracting all the goodness possible from grass.
A reason to introduce more vegetables and hay to your rabbits diet is 'sticky bottom syndrome.' Basically this occurs from a diet that is too rich and can easily be seen as the rabbit will be producing excess caecotrophs.
As with people, most rabbits have a sweet tooth! Even though it can seem kind to give them treats they can get fat very easily. Avoid human treats like sweets altogether - these can be very dangerous.