According to a survey of EU vets, weight loss and inappetence are one of the most common reasons for cat owners to present their cats to the vet (Dechra, 2018).
Weight loss can represent one of the earliest indicators of chronic disease in domestic cats (Figure 1). For example, weight loss in cats with chronic kidney disease (CKD) can begin up to three years prior to diagnosis, with an average loss of 8.9 percent of the individual’s body weight within one year of diagnosis (Freeman et al., 2016). Weight loss tends to accelerate following diagnosis (Quimby, 2021).
Neoplasia and hyperthyroidism also lead to chronic weight loss in cats, reaching a notable decline from two years prior to death (Perez-Camargo, 2004).
Many chronic disease states in cats are associated with a shift in metabolism and inappetence, resulting in inadequate protein intake. Increased catecholamines, nausea, pain and increased inflammatory cytokines lead to dysregulation of the neurohormonal control of appetite (Freeman, 2012). Reduced renal function also leads to the accumulation of “anorexigenic” hormones such as leptin and obestatin (Quimby, 2021). Thus, hyporexia and weight loss often represent a maladaptive process associated with chronic disease in cats.
As obligate carnivores, domestic cats are especially vulnerable to the negative effects of low protein intake because of their reliance on a protein-rich diet to meet their metabolic needs (Chan, 2009) (Figure 2). Inadequate protein intake in cats can lead to a shift in metabolism, sometimes referred to as a “hyper-metabolic state”. This shift in metabolism is a result of increased energy expenditure, increased protein catabolism, lipolysis and insulin resistance (Chan, 2004; Chan and Freeman, 2006; Freeman, 2012).
Inadequate protein intake can also lead to malnutrition, which involves cachexia, negative energy balance, reduced immune function, coagulopathies and eventually organ failure (Chan, 2004; Chan and Freeman, 2006; Freeman, 2012).
Low body weight or low body condition scores (under 4/9) are associated with a reduced average survival time across a variety of disease states in cats, including cardiac disease and neoplasia (Baez et al., 2007; Santiago et al., 2020). Low body condition is also associated with an increased risk of “all-cause mortality” in cats (Teng et al., 2018).
Furthermore, chronic inappetence and weight loss also negatively impact pet owners. Poor appetite is emotionally distressing to owners and is perceived as an indication of a poor quality of life (Bijsmans et al., 2016; Williams et al., 2017).
Weight loss and hyporexia are non-specific signs that require early therapeutic intervention as well as investigation of the underlying disease process (Quimby, 2021). Due to the negative effects of hyporexia in cats and their susceptibility to developing malnutrition, it is important to act promptly to prevent further deterioration (Chan, 2009). Performing a complete nutritional assessment in every cat with weight loss or a poor appetite assists with quantifying and managing inadequate nutritional intake (Quimby, 2021).
Appetite stimulants can be helpful to meet the increased metabolic demands of illness and restore the balance of orexigenic versus anorexigenic stimulation of central appetite centres (Quimby, 2021). In addition to addressing insufficient calorific intake, cat owners may be more likely to comply with treatment recommendations (from diet changes to administering oral medications) if their cat is eating (Cook, 2020).
Prompt therapeutic intervention to increase protein intake and address hyporexia and weight loss is a fundamental step. It is recommended that treatment for hyporexia is initiated as soon as weight loss or inadequate nutrition is noted, even pending a complete diagnostic work-up (Quimby, 2021).
Mirataz is the only licensed mirtazapine product to support body weight gain in cats experiencing poor appetite. Mirataz is a transdermal ointment that is applied to the inside of the pinna once daily, offering the advantage of avoiding oral administration in the inappetent cat. The drug has a wide licensed indication and successfully achieves weight gain in cats with kidney disease, vomiting, cardiac disease, dental disease, hyperthyroidism and degenerative joint disease, as well as in cats in which a final diagnosis is not yet known (Poole et al., 2019).
Inappetence in hospitalised cats is common, and performing nutritional assessments in every hospitalised cat is of vital importance (Quimby, 2021).
Hospitalisation can lead to stress-associated hyporexia in cats. Taking steps to improve the hospital environment and ensuring that human interactions are cat-friendly may help to reduce stress and improve food intake. Other factors affecting hospitalised cats include pain, dehydration, anaemia, nausea, gastrointestinal dysmotility, electrolyte imbalance and adverse effects of medications.
“Picky eaters” who are recovering from critical illness may benefit from an appetite stimulant; however, in anorexic or critically ill cats, initial management with a feeding tube is often necessary (Quimby, 2021; Chan, 2009).
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