Is your little mate looking very full in the tummy but not eating or just picking at his or her food? A quick test is to gently palpitate your hands on either side of the bunny's abdomen and see if you can feel a mass of some sort. If you can, then chances are your little mate has got fur blockage or Furball. If you don't want your little mate to die then you will have to take immediate steps to prevent and cure this problem.
During the hot summer weather, the bunnies will be having extra heavy moults and as a result will have a lot fur to get rid of. Consequently, they will have potential furball problems. Symptoms of furball include; their pellets (number twos) will show signs of being strung together like a string of beads, the size of their pellets is smaller and become fewer, and sometimes diarrhea and bloating occurs.
When my bunnies were going through a moult they would favour all the fresh stuff I gave them which included fresh fruit, grass and other plant food and grass hay and leave their pellet mix. When I first saw that they were leaving their pellet mix, I remove it altogether and instead, gave them extra roughage in the form of dead leaves and branches off shrubs plus fresh fruit and veggies to help soften the furball and get it moving through the bunnies system and passed out.
Gently palpate your bunny's tummy just below their ribs and if you feel a mass then it is 100% sure that your bunny has a gut problem and the most common gut problems are furball or gas. The biggest factor with furball is that your bunny becomes dehydrated due to the mass of fur and hence the reason that they need to drink more water to help loosen up the mass, soften it and break it up to get it moving. If you see the tell-tale signs of furball in your bunny's pellets, give him a gentle tummy massage to help break up the mass and initially, some type of dog or cat laxative to help pass the furball as they can't cough it up like a cat or dog. Any good dog or cat laxative will do and you just follow the directions on dosage for puppies or kitten
If you don't catch the furball problem in the early stages, and only notice when the bunny goes off its tucker all together then you will need to medicate your bunny further to help it pass the fur through its system. At this stage your bunny will, more than likely need re-hydrating which is a priority. The best way of helping your bunny pass the furball and to re-hydrate it is to firstly take away the bunny's pellets and any other concentrated foodstuffs that you may be feeding it and replace them with pieces of fresh fruit and veggies in the form of pineapple or papaya, parsley or broccoli etc. Then feed it a small amount of fresh pineapple or papaya juice. It is widely known that the juice of these two fruits in particular have enzyme content which helps loosen up the mass. If it won't take the juice voluntarily you will have to force feed your bunny the juice in a syringe. Refer to the pictures in the health check procedure for method of positioning bunny prior to administering medicine making sure that you feed the liquid through the side of the mouth and don't cram it down the back of its throat. I usually feed about 10mls of juice and give a gentle tummy massage. Then I put it in the playpen to see what it will do. I don't put it into its cage because I want to encourage it to move and hop about. This exercise helps break the mass up and get it moving. If it is put back into its cage it will just sit in a corner and not move.
Sometimes the above strategy is enough to get your bunny drinking juice or water by itself and then start tucking into all the fresh goodies that you have provided it as mentioned previously. If this is the case, your bunny most probably had gas or furball. If your bunny still refuses to eat or drink take it to your pet vet. If the vet is not sure of the bunny's problem he/she will more than likely give your bunny an injection to stimulate its appetite and ask you to return the next day if it doesn't work. Take your bunny home and repeat the juice and massage process and put it back in the playpen to check the progress. In 90% of cases this will get you bunny's bowels moving as the mass is softened and starts dissipating whilst your little mate gets stuck into its tucker and comes back to its normal happy self.
Having a furball may only be part of the problem; there could also be other gut problems such as enteritis, gas build-up, gastrointestinal stasis or constipation. The other 10% will have to be taken to the vet to try and find out the cause and may have to be operated on to remove the obstruction.