Cats will often present at the veterinary surgery after losing their appetite. Feeding is a focal interaction for owners and their cats, and anorexia can be the first sign of a number of disease processes. The cat who communally feeds ad libitum may have pronounced anorexia and weight loss before a problem is noticed by the owner.

Anorexia describes a loss or lack of appetite. Anorexia may be partial or complete; inappetance or hyporexia describe a reduction in appetite. Prolonged anorexia causes systemic complications due to immunosuppression, reduced hepatic function (detoxification) and intestinal dysfunction.

Forms of Anorexia

There are two forms of anorexia.

True Anorexia

This is due to decreased appetite; the animal has no interest in food.

 Primary anorexia:

 Neurological diseases reducing cerebral arousal; cranial trauma; anything affecting the appetite centre in the hypothalamus

 Anosmia. Cats are highly dependent on smell to stimulate appetite

 Behaviour, e.g., environmental (change in housing/family members/furniture), psychological (fear, anxiety)

 Secondary anorexia. Due to disruption of endocrine, cytokine or neurological control of appetite:

 Systemic disease

 Pain (abscess, fractures, osteoarthritis, periodontal disease, neoplasia, foreign bodies)

 Neoplasia

 Neurological diseases

 Chemotherapeutics causing nausea and opioids inhibiting the orexigenic (appetite-stimulating) network

 Upper respiratory tract/nasal disease reducing the ability to smell

 Lower respiratory tract disease causing difficulties in breathing

Pseudoanorexia

This is anorexia secondary to other factors. The animal will still be hungry, but be unable to eat. Most commonly associated with oral pain preventing prehension, chewing or swallowing of food. Also may be related to unpalatable diets or environmental stress.

Diagnosis

Unfortunately, anorexia is a syndrome and cannot be used to diagnose the underlying or causative disease. Treatment of anorexia lies in identifying and managing the underlying disease whilst supporting the cat's fluid and nutrient balance until appetite resumes.

A thorough clinical examination of all organs, including the eyes, will help define a tighter differential diagnosis list. The diagnostic work-up should be directed by the clinical findings. Useful additional tests to routine biochemistry and haematology may include feline pancreatic lipase immunoreactivity to investigate pancreatic inflammation and cobalamin to assess vitamin B12 deficiency secondary to pancreatic, hepatobiliary or gastrointestinal disease.

Intervention

Feeding an anorexic sick patient can help to avoid or miminise the impact of malnutrition. This enhances recovery rates and reduces morbidity and mortality. Intervention should occur early once fluid and electrolyte imbalances are corrected. Intervene when weight loss is greater than 10% (including obese patients) or when there has been partial (< 85% calculated energy requirements) or complete anorexia for more than 3 days. Additionally, support those patients in a catabolic state (burns, severe inflammation, major surgery or trauma).

Treatment is based on identifying and treating the underlying cause. Adequate analgesia, for example sublingual buprenorphine 0.01–0.02 mg/kg q6–12h, should be provided for any painful condition or suspicion of pain/discomfort. Although the exact time of intervention may vary depending on the case in question, a good general rule is to consider placing a feeding tube in any cat that has been partially or completely anorexic for at least 3 days. Hepatic lipidosis is becoming more widely recognised in the UK and may complicate or exacerbate the underlying clinical condition. Additionally, a sick cat needs good nutrition to strengthen its immune system and recover from disease. Avoid appetite stimulants until the underlying disease has been treated. If a feeding tube is in place, there is no need to worry about the cat meeting its own nutritional requirements. In nauseous cats with systemic disease, do not tempt to eat until the patient is stabilised and recovering. Offering food items early in disease can contribute to food aversion and make it more difficult to get the cat eating subsequently. Once the cat is feeling better, it will often start eating voluntarily.

Tempting a cat to eat should be done with small food items, which can be warmed to enhance smell. Syringe-feeding cats can be stressful and encourage food aversion. Sometimes placing food in the mouth or on the lips can stimulate the cat to eat, but only use this method in those cats that are stable and improving, as again this can encourage food aversion and heighten stress. Some cats respond well to food hides; other cats prefer company and encouragement to start to eat. Getting a cat to eat within a hospital environment is difficult due to the limitations of space and food placement.

All cats should have their weight monitored daily and a regular assessment of body condition score. Assisted feeding of anorexic cats is a method that frequently fails to provide sufficient daily food intake; consequently, clinicians should be prepared to abandon it in favour of a more reliable means of nutritional support if nutrient requirements are not adequately met.

Feeding Tube Placement

Feeding tubes enable enteral nutrition and utilise either part or all of the gastrointestinal tract. Enteral nutrition is preferable to parenteral ('intravenous feeding') as enterocytes derive 50% of their nutrients directly from the intestinal lumen. If the enterocytes are starved, the intestinal mucosa becomes hypoplastic and hypofunctional with increased permeability. Parenteral nutrition is technically difficult, requires good asepsis and should be reserved for malabsorption syndromes, acute severe pancreatitis and severe persistent vomiting. The choice of feeding tube will depend on length of support and the site of the disease (tubes should be placed distal to the problem area).

Short-Term Support

 Naso-oesophageal tube. For patients without oral, nasal, pharyngeal or oesophageal disease and who are not vomiting:

 Advantages: quick and easy to place, does not require general anaesthesia.

 Disadvantages: short duration of use; liquid diet choice is limited; some cats do not like having the tube on their face.

Longer-Term Support

 Oesophagostomy tube. Very useful and well tolerated in cats. Suitable for cats with oral and nasal disease; do not use in vomiting cats or those with oesophageal disease. A wider-bore tube can be used, making feeding easier. The tube is bandaged at the neck and does not affect whiskers or grooming. The main potential complication is infection at the stoma. A two-stage placement procedure is usual, where the tube is first inserted through the stoma in a retrograde direction and then subsequently redirected down the oesophagus.

 Gastrostomy tube. Most practical for long-term feeding and suitable for prolonged use. Contraindicated for gastroduodenal disorders especially persistent vomiting. Occasional complications include tube dislodgement (and possibly peritonitis) and infection at the stoma site. Placement techniques include:

 Coeliotomy. Invasive, but useful to place at the same time as an exploratory laparotomy.

 Percutaneous endoscopically placed gastrostomy (PEG) tube. If equipment and expertise is available, this is the simplest, and perhaps safest, method of placement.

 Blind placement. Using an applicator passed per os. Greater potential for complications because the placement of the tube cannot be directly observed.

 Jejunostomy/enterostomy tube. Rare indications, such as gastric disorders or pancreatitis where small intestinal function remains normal. As the stomach is bypassed, the patient is more prone to complications such as vomiting, diarrhoea and abdominal pain. Continuous food infusions are required. Enterostomy tubes are usually placed surgically, although laparoscopic-assisted and endoscopic approaches are described.

Feeding Guidelines

How Much Should I Feed?

Food requirements are based on energy, the most important factor to support. For critical care patients, the daily requirements are best calculated from estimated resting energy requirement. The current controversy is over how much RER differs in critical illness. Correction factors used to be applied, but there is no validation for these factors. A better approach is to work with RER, monitor the patient's weight and body condition and adjust the intake as necessary.

 RER = 70 x (current bodyweight in kilograms)^0.75 (for > 5 kg)

 RER = 30 x BW_kg +70 (for < 5 kg)

What Diet Should I Choose?

Use a commercial diet to satisfy energy, protein and micro-nutrient requirements. A high-energy, high-protein, easily digestible diet is recommended, though this may be manipulated depending on the underlying disease. Liquid enteral diets (such as Fortol) are best for small-diameter tubes. Larger-bore tubes can carry liquidised prescription diets. As enteral diets are low residue, there will be little faecal matter produced, though the cat should be monitored closely and hydration kept optimal to ensure against constipation.

How Long Do I Feed?

Patients should be supported until their voluntary intake is > 85% of maintenance requirements. Gastrostomy and enterostomy tubes must remain in place for at least 7–10 days to allow a seal to form with the abdominal wall. Oesophagostomy and gastrostomy tubes can be managed on an out-patient basis, allowing owners to feed their cat at home This is particularly useful for hepatic lipidosis patients or those with severe rostral trauma.

Appetite Stimulants

See Figure 1.

Figure 1. Appetite stimulants.