Anorexia is a common manifestation of many illnesses including upper respiratory tract disease, oral disease, renal disease, pancreatitis, liver disease, GI disease, cardiac disease, anaemia and neoplasia. Acute or chronic pain, nausea associated with systemic disease, delayed gastric emptying and medication are also important causes of inappetance.

Nutrient intake is an important consideration in any hospitalised patient, and can easily be overlooked in a busy practice setting. Adequate nutrition is necessary to provide energy for cellular function, substrates for protein synthesis and vitamins and minerals for daily metabolic processes and maintenance of homeostasis. Failure to meet nutritional requirements will result in reduced immune system function, increased risk of sepsis, reduced tissue repair and delayed healing, muscle weakness, reduced gastrointestinal function and altered drug metabolism.

Cats can also be very susceptible to development of hepatic lipidosis following even short periods of anorexia. Hospitalised patients are often in a hypermetabolic state which when combined with starvation quickly leads to protein depletion and protein energy malnutrition, which can be a major contributing factor in multiple organ failure.

Inadequate food intake may result from inability to eat, inability to digest or absorb food, reluctance to eat as a result of stress, anorexia associated with illness or not being offered adequate palatable food. Food aversion is a particularly important component of anorexia in hospitalised cats, for example, offering food or force feeding whilst a cat is feeling nauseous will often result in persistent refusal to eat that food. Finally, in many feline patients the change in environment and stress of hospitalisation alone will result in significant inappetance.

Appropriate housing and nursing care is an essential part of managing any anorexic cat, and for those that have been inappetant for less than a couple of days, are capable of ingesting food, and have no evidence of systemic illness then the following may be enough to restore a normal appetite before more invasive assisted feeding techniques need to be considered:

 Reduce environmental stressors (e.g., dogs, noise).

 Make sure the cats food bowl is as far away from its litter tray as possible.

 Offer food that the cat is used to as cats are strongly influenced by habit in their selection of foods.

 Increase palatability (e.g., adding flavours, increasing fat/protein content, warming to improve aroma, changing texture and consistency).

 Tempting - smearing a small amount of food on the paws or face usually stimulates a licking response that may result in continued ingestion of food.

 Wide shallow feed bowls should be used to avoid the cats' whiskers touching the sides.

 Offer small frequent meals, removing the food bowl in-between.

 Gentle stroking will often stimulate eating.

 Draping a towel over the cage, or placing the food in a cardboard box or similar, where the cat can hide can be useful.

 Some cats like a lot of TLC and handfeeding, whereas others prefer to be left alone and undisturbed in a quiet place.

The following points should also be considered in all anorexic cats, particularly those with persistent inappetance:

 Clinical examination should in particular include a thorough oral assessment for evidence of oral/dental disease, assessment for nasal discharge and upper respiratory tract noise, looking at mucous membranes for signs of pallor or icterus, cardiac and thoracic auscultation, palpation for a goitre, abdominal palpation including careful assessment for pain, evaluation for skin wounds and abscesses, rectal temperature.

 If the cat has undergone any surgery, all surgical sites should be evaluated for pain and signs of infection.

 Consider any medication that the cat is receiving as some drugs can cause nausea/inappetance (e.g., metronidazole).

 Additional assessment should include a minimum of routine haematology to look for evidence of infection/inflammation and anaemia, biochemistry to evaluate electrolytes, renal and liver parameters (ALT, ALP, bilirubin) and T₄ if appropriate.

 If no abnormalities are detected, submitting serum for feline pancreatic lipase immunoreactivity (PLI) may be warranted, since anorexia may be the only sign of chronic pancreatitis, which can be very difficult to diagnose.

 Abdominal ultrasound may be indicated to further assess for evidence of intra-abdominal pathology.

 Careful attention should be paid to pain control where this may be a contributing factor. Pain is difficult to recognise in cats and the only manifestations may be very subtle behaviour changes and/or inappetance. The authors therefore recommend a trial treatment with opioid analgesics such as buprenorphine (0.01–0.02 mg/kg IM or sublingual every 8 hours) to try and exclude pain as a cause of the clinical signs.

 Fluid and electrolyte imbalances (e.g., hypokalaemia) should be corrected by intravenous fluid therapy.

 Nutritional requirements should be calculated and the amount of food being eaten daily should be closely recorded.

 All hospitalised cats should be body condition scored and weighed daily.

 If an inappetant cat is discharged from the hospital, it is essential that the owners understand the seriousness of their cat not eating, and that they know to bring the cat back in the following day if the anorexia persists. The longer a cat is left with inadequate nutrition, the more problems that will arise, and the more difficult it will be to manage. However, it is often preferable to discharge the cat for a trial at home as most cats are more likely to eat at home compared to in the hospital.

Appetite Stimulants

Appetite stimulants can be useful when the above recommendations have failed, and the cat is not systemically ill or in very poor body condition. The most commonly used appetite stimulant is mirtazapine. Mirtazapine is a serotonergic drug licensed as an anti-depressant treatment in people. It also has anti-emetic properties and so can be very useful for cats that may be inappetant because of nausea. The other useful aspect of mirtazapine is that it usually only needs to be administered every 48–72 hours (1/8th of a 15 mg tablet per cat, PO), although recent pharmacokinetic studies suggest it can be given daily.

Enteral Assisted Feeding

More severely or persistently anorexic cats may require more aggressive nutritional support through enteral assisted feeding such as an oesphagostomy or gastrotomy tube. Enteral assisted feeding should be considered in any patient that has not been consuming resting energy requirements for 3 or more days, if there has been loss of 10% bodyweight or if there are increased nutrient demands (e.g., trauma, surgery, illness) that are not being met by voluntary food intake.

Various methods of assisted feeding are available, the main indications/contraindications and advantages/disadvantages are summarized in Table 1.

Diets used for enteral feeding should be highly digestible and high in energy density. Hypermetabolic states are supported primarily by fat oxidation and protein breakdown, and therefore fat and protein are particularly important energy sources for the critical patient. Cats also have several nutritional idiosyncrasies, which need to be addressed, including high protein requirements and taurine, arginine, arachidonic acid and vitamin A requirements. The simplest and most effective way of meeting specific nutritional requirements is to use commercially prepared formulations. Human baby preparations or soups should not be used since in addition to not meeting essential nutrient requirements they often contain onion powder which causes oxidative damage to feline red blood cells, resulting in haemolytic anaemia.

Table 1. Enteral feeding techniques

Calculating Food Requirements

 BER (Basal Energy Requirements)

 > 2 kg = (30 x BW_kg) + 70

 < 2 kg = 70 x BW^0.75

 Total daily requirement (ml)

 BER

 ME (Where ME = metabolisable energy of food)

 Additional water requirements

 50 ml/kg/day minus water provided by food

Food should be introduced gradually and spread out into 4–5 meals throughout the day

 Day 1 - Feed 1/3 total daily requirement of food mixed 1:2 water

 Day 2 - Feed 2/3 total daily requirement of food mixed 2:1 water

 Day 3 - Feed total daily requirement of food undiluted