Feline Malnutrition Study Guide

Overview and Clinical Importance

Malnutrition in cats encompasses a spectrum of disorders resulting from inadequate, unbalanced, or excessive nutrient intake. Unlike dogs, cats are obligate carnivores with unique metabolic requirements, making them particularly susceptible to specific nutritional deficiencies. On the NAVLE, feline malnutrition questions frequently focus on hepatic lipidosis, taurine deficiency, thiamine deficiency, refeeding syndrome, and protein-energy malnutrition (cachexia). Understanding these conditions is essential for successful board examination performance.

Cats have several metabolic adaptations that impact their nutritional requirements, including higher protein needs, an inability to synthesize sufficient taurine and arachidonic acid, and limited ability to convert beta-carotene to vitamin A. These unique characteristics predispose cats to malnutrition when fed inappropriate diets or during periods of anorexia.

Nutritional Assessment in Cats

Body Condition Scoring (BCS)

The WSAVA recommends a 9-point body condition scoring system to assess body fat stores. For cats, a score of 4-5 out of 9 is ideal. Scores of 1-3 indicate underweight conditions, while 6-9 indicate overweight to obese.

Muscle Condition Scoring (MCS)

MCS is independent of BCS and evaluates lean body mass. Cats can be obese yet have severe muscle wasting (sarcopenia/cachexia). The WSAVA recommends a 4-point MCS system: Normal, Mild muscle loss, Moderate muscle loss, and Severe muscle loss.

Key palpation areas: Epaxial muscles over spine, temporal muscles, scapulae, lumbar vertebrae, and pelvic bones. Early muscle loss is often first detected in the epaxial muscles.

Feline Hepatic Lipidosis

Hepatic lipidosis (fatty liver syndrome) is the most common acquired liver disease in cats in North America. It occurs when triglycerides accumulate in greater than 80% of hepatocytes, increasing liver weight by more than 50% and causing intrahepatic cholestasis.

Pathophysiology

When cats become anorexic, peripheral fat stores are mobilized to provide energy. Unlike other species, the feline liver has limited capacity to export or oxidize fatty acids. This leads to hepatocyte cytosolic expansion with triglyceride stores, impairing liver function and causing cholestasis. The condition typically develops after 3-7 days of complete anorexia or prolonged reduced food intake.

Risk factors: Obesity (most significant), middle age (median 7 years), recent stressful event (moving, new pet, boarding), underlying disease causing anorexia (greater than 90% of cases have concurrent disease: diabetes, pancreatitis, IBD, cancer, kidney disease).

Clinical Signs

• Anorexia (preceding condition development by days to weeks)
• Weight loss (often greater than 25% body weight)
• Jaundice/Icterus (present in majority of cases)
• Hepatomegaly on palpation
• Vomiting, diarrhea, or constipation
• Depression and weakness
• Ventroflexion of the neck (suggests concurrent hypokalemia or thiamine deficiency)

Diagnosis

Treatment

Nutritional support is the CORNERSTONE of treatment. Average time to voluntary eating is 6-7 weeks, requiring feeding tube placement.

Taurine Deficiency

Taurine is an essential amino acid for cats because they cannot synthesize sufficient amounts. Taurine is required for bile acid conjugation, cardiac function, retinal integrity, and reproduction. Since 1987, commercial cat foods are required to contain adequate taurine levels (AAFCO), making deficiency less common but still seen with inappropriate diets.

Causes

• Dog food fed to cats (inadequate taurine for feline requirements)
• Home-cooked diets without supplementation
• Vegetarian/vegan diets
• Heavily processed or overcooked commercial diets (taurine degradation)

Clinical Manifestations

Diagnosis and Treatment

Diagnosis: History of inappropriate diet, clinical signs, and measurement of whole blood or plasma taurine levels (low). Electroretinogram (ERG) for retinal function; Echocardiography for DCM.

Treatment: Taurine supplementation (250-500 mg PO BID) until symptoms improve, then transition to complete and balanced commercial cat food. DCM may improve within weeks of supplementation. Retinal lesions are IRREVERSIBLE but further degeneration is prevented.

Thiamine (Vitamin B1) Deficiency

Thiamine (Vitamin B1) is a water-soluble vitamin essential for carbohydrate metabolism and nervous system function. Cats have high thiamine requirements and cannot store significant amounts, making them susceptible to deficiency within 1-3 weeks of inadequate intake.

Causes

• Raw fish diets (contain thiaminase enzyme that destroys thiamine)
• Over-processed/overheated commercial foods (thiamine heat-labile)
• Sulfur dioxide preservatives (inactivate thiamine)
• Prolonged anorexia
• Commercial food recalls (inadequate thiamine levels)

Clinical Signs

Neurological signs appear 30-40 days after transitioning to a thiamine-deficient diet and progress rapidly.

Early signs: Anorexia, vomiting, salivation, weight loss

Neurological signs: Ventroflexion of the neck (pathognomonic), vestibular signs (head tilt, ataxia, nystagmus, falling), mydriasis, vision loss, seizures, progression to coma

Diagnosis and Treatment

Diagnosis: Based on clinical signs, dietary history, rapid response to treatment, and MRI findings (bilateral symmetrical hyperintense lesions in vestibular nuclei, caudal colliculus, lateral geniculate body on T2-weighted images).

Treatment: Thiamine supplementation - 10-25 mg/cat IM/SQ q12-24h until signs resolve, then 10 mg/kg PO daily for 21 days. Clinical improvement typically within 24-48 hours of starting treatment. Feed complete and balanced commercial diet.

Refeeding Syndrome

Refeeding syndrome is a potentially fatal constellation of metabolic derangements that occur when nutrition is reintroduced to a severely malnourished or starved patient. It is characterized by electrolyte shifts, particularly hypophosphatemia, along with hypokalemia and hypomagnesemia.

Pathophysiology

During starvation, the body shifts from using carbohydrates to fat and protein for energy. Total body stores of phosphorus, potassium, and magnesium become depleted, though serum levels may remain normal. When carbohydrates are reintroduced, insulin is released, causing rapid intracellular movement of these electrolytes, leading to severe serum depletion and life-threatening complications.

Risk Factors

• Anorexia for greater than 7 days
• Severe weight loss (greater than 25%) or emaciation
• Obese cats with rapid weight loss (hepatic lipidosis)
• Chronic malabsorptive conditions
• "Missing" cats found after prolonged starvation

Clinical Signs

Prevention and Management

Vitamin A Disorders

Cats cannot convert beta-carotene to vitamin A and must obtain preformed vitamin A (retinol) from animal sources. Both deficiency and toxicity can occur, with toxicity (hypervitaminosis A) being more clinically significant in cats.

Hypervitaminosis A (Vitamin A Toxicity)

Cause: Excessive liver in diet (raw liver treats), cod liver oil, or vitamin A supplements. Chronic ingestion over months leads to toxicity.

Clinical Signs: Cervical spondylosis with new bone formation at tendon/ligament attachments, cervical spine fusion, reluctance to move neck, inability to groom, lameness, pain, weight loss, poor coat, constipation. Neurological signs from spinal cord compression may occur.

Diagnosis: History of liver-rich diet, radiographs showing exostoses on cervical/thoracic vertebrae, elevated serum vitamin A.

Treatment: Stop liver/supplements; feed balanced commercial diet. Bony changes may be IRREVERSIBLE. Pain management with analgesics. New bone formation ceases after dietary correction.

Hypovitaminosis A (Vitamin A Deficiency)

Rare in cats on commercial diets. Clinical signs include: night blindness, conjunctivitis, corneal keratinization, skin changes (squamous metaplasia), reproductive failure, growth retardation in kittens. Treatment: dietary correction and vitamin A supplementation under veterinary guidance to avoid toxicity.

Protein-Energy Malnutrition and Cachexia

Cachexia is the loss of lean body mass and body weight that occurs secondary to chronic disease (cancer, CHF, CKD, FIP). Unlike simple starvation where fat is primarily lost, cachexia involves muscle breakdown driven by inflammatory cytokines (TNF-alpha, IL-1, IL-6). Nutritional support alone cannot fully reverse cachexia.

Starvation vs. Cachexia

Clinical Significance

Cats with cancer and BCS less than or equal to 4/9 have median survival of 3.3 months compared to 16.7 months in cats with BCS 5/9 or higher. Nutritional support should include: high-protein diet (greater than 5 g/kg BW for cats), increased caloric density, omega-3 fatty acids (may reduce inflammatory cytokines), and treatment of underlying disease.

Nutritional Support Strategies

Calculating Energy Requirements

Resting Energy Requirement (RER) = 70 x (Body Weight in kg)^0.75

For hospitalized cats, start with RER and adjust based on response. Critically ill cats may require only RER initially; do not over-feed.

Feeding Tube Options