Rabbits make excellent companion animals and may be the pet of choice for families unable to commit to a cat or dog. However, like their higher-maintenance counterparts, rabbits are susceptible to certain potentially fatal diseases. A basic knowledge of rabbit care will get you far in terms of keeping your rabbit healthy and happy, but there are some symptoms that warrant an immediate call to your vet. Always remember that because rabbits are prey animals, they may not show obvious signs of suffering, pain or discomfort. That's why it's so important to be vigilant and recognise changes in your rabbit's habits as soon as possible.This article will outline some of the most common signs that your rabbit's health may be at risk or in decline. Even if you do not regularly take your pet for health checks, make sure that you are registered with a local rabbit-friendly vet just in case one or more of the following symptoms arise. A rapid response can make a big difference towards the intensity of treatment required, as well as it's success.1. Sudden lack of appetiteRabbits have a complex, efficient digestive system designed to extract nutrients from their low-quality fibre-based diet. Being natural foragers, wild bunnies eat a variety of plants, including weeds, leaves, grass, and even bark. Healthy rabbits eat at least twice per day, everyday and may nibble intermittently between feeds. A lack of appetite or cessation of normal eating habits is linked to a potentially fatal condition called gastrointestinal stasis, in which the rabbit's gut becomes inactive. This condition may cause blockages in the intestinal tract, eventually leading to collapse or death. Recognising the threat posed by gastrointestinal stasis is the first step in saving your rabbit. Just a few days of inappetence can be fatal. A sudden lack of appetite can also be a sign of a myriad of other serious problems, and so it is important you speak to your vet if you notice any changes in your pet's eating habits.Be aware that rabbits may become selective eaters and only consume certain elements in a mixture of loose or crude food products. Fussy eating can cause health issues down the road, as picky bunnies may be missing out on essential nutrients. A potential solution is to offer baked or kibble-based foods to be sure your pet's diet is balanced.2. Changes in faecal production A sudden absence of faecal pellets in the rabbit's hutch can be another sign of gastrointestinal stasis. Misshapen, undersized, or loose droppings are also hallmarks of disease, and so it is important that you clean your rabbit's hutch regularly to detect any changes. Even if you are unsure whether your rabbit is eating or not, a lack of faeces may indicate that something has gone wrong in the gut. Conversely, the presence of loose faeces, especially if caked around the rabbit's bottom, is also a cause for concern. Healthy rabbits are steadfast groomers and will normally remove loose stool by themselves. A build-up of faecal matter is not only a sign of poor health, but it also puts the rabbit at risk of developing a horrifying condition called flystrike. Maggots, attracted to soft, warm stool, burrow into a rabbit's faeces, eventually entering the rectal cavity and consuming the host's flesh. Regular handling and grooming of your rabbit can help you detect signs of flystrike early, as can good cage hygiene. Bottom line: any changes in faecal texture or quantity should be reported to your vet as soon as possible.3. Respiratory or breathing problemsEnvironmental stresses can make your bunny more susceptible to bacterial infection, hence the development of cold-like symptoms. Unlike in humans however, rabbit "colds" can be indicative of serious health problems and may rapidly worsen without proper attention. Any wheezing, sneezing, or mucous membrane discharge should be reported to your vet immediately, as it could be a sign of pasteurella. Pasteurella is linked to tooth-rot, head-tilt, and pneumonia so it is important that your vet catches the infection early. Treatment may involve the use of antibiotics, fluids, or hospitalisation. Be sure to note any recent changes in temperature, humidity, or ventilation within your rabbit's living space and discuss these with your vet.4. Skin swelling or bumpsRed swollen patches on the skin can occur due to parasite infection or viral disease. In addition any hair-loss, discharge, or ulceration around the affected site should be reported to your vet. Take careful notice of any other symptoms that may be concurrent with the development of swollen patches.Perhaps the most worrisome disease associated with skin swelling is Myxomatosis, a virus that spreads rapidly from rabbit to rabbit and also causes lethargy, respiratory distress, and eventual blindness. Myxomatosis is usually transmitted via blood-sucking parasites, and initially concentrates itself around the eyes, nose, genitals, and anus of the rabbit. Therefore, swelling in these areas should be treated with extreme caution: isolate any affected rabbits and call a vet immediately. Swelling can also occur as a result of trauma, as is usually the case with abscesses. Inflammation to the eye tissue could be indicative of conjunctivitis. Prolonged infection may eventually inhibit gut mobility, and could lead to further complications. In any case, bring any lumps or bumps to your vet's attention.5. Unusual behaviourRabbits are known for their gentle demeanors, however aggression can occur as a response to territorial threats, hierarchical issues, or as a consequence of sexual maturity. Since rabbits are social creatures and do best when housed in groups, conflicts between herd-mates may breakout from time to time. While some forms of behavioural change are a result of social dynamics, a previously docile rabbit suddenly turning aggressive or fearful towards a human handler is cause for concern. Sudden displays of aggression can be a sign of underlying health problems, especially in response to the handling of a painful area or other disturbance. General discomfort or pain may also cause lethargy, or an unusually reserved stance. Be sure to contact your vet if your rabbit's temperament changes unexpectedly.