Maximizing pet nutrition with apples

Nearly 16 million tons of apples are processed annually, and the residual pulp has plenty of utility in veterinary diets. However, this has left some pet owners confused. How does apple fiber benefit their pet’s health?

What is apple pomace?

Approximately 80% of an apple is used in the juicing process, leaving behind a fibrous substance known as apple pomace that consists of skin and pulp (95%), seeds (2-4%) and stems (1%). Analysis by the Teagasc Food Research Centre in Dublin found soluble and insoluble carbohydrates to account for 84.7% of the dry weight, with low amounts of protein (2.37%) and fat (2.27%).

More importantly, apple pomace contains bioactive polyphenols that provide antioxidant, anti-inflammatory and hypolipidemic properties. This is in addition to the high mineral content of calcium, potassium and magnesium required for metabolic processes to function efficiently.

Although a by-product by definition, apple pomace provides a rich source of nutrients that should be utilized in veterinary diet formulations.

Multifunctional filler

The term ‘filler’ is surrounded by negativity. While apple pomace is primarily used as such, its roles are multifunctional and support pet health when used correctly. Advantages include:

1. Prevention of chronic kidney disease (CKD)

In kidney disease, protein absorption in the small intestine can be impaired, leading to an excess of proteins reaching the colon. This has been associated with the overgrowth of proteolytic bacterial populations that digest proteins and produce uremic toxins, further damaging the kidneys. A study led by the College of Veterinary Medicine at Oregon State University found that consuming apple pomace effectively reduced fecal concentrations of many uremic toxins and increased secondary bile acids in cats with CKD.

2. Support for the gut microbiome

Gut microbes feed on fermentable fibers and produce short-chain fatty acids (SCFAs) that provide about 7% of the metabolic energy that dogs require. Among the SCFAs, butyrate is the preferred energy source for more than 90% of colonocytes, and it is needed to maintain colon integrity. When 16 dogs were fed diets containing 9% apple pomace, butyrate concentrations and fecal microbial diversity increased.

3. Source of polyphenols

Recent chemical, chromatographic and spectrophotometric analyses performed at the Department of Veterinary Medicine in Perugia, Italy have confirmed the presence of anti- inflammatory polyphenols in apple pomace. Several studies support these findings, including research conducted by Hill’s Pet Nutrition. Of particular interest are quercetin derivatives, antioxidative and anti-inflammatory flavonoids that act directly on systemic inflammation in cats and dogs.

4. Potential palatant

Fiber is not particularly palatable. Research at Kansas State University found that adding sugar cane or wheat bran fiber significantly reduced the palatability of dry kibble compared to that of the control. Alternatively, limited studies using apple pomace as the fiber source have found promising results. When cats were offered 0% and 9% apple pomace diets, the intake ratio was significantly higher in those consuming apple pomace. For dogs, dietary formulations with 9% apple pomace did not affect palatability. As long as palatability is not reduced, this is a significant advantage for future applications of apple pomace.

5. Improvement in water-binding capacity

Apple pomace naturally has a ratio of insoluble and soluble dietary fibers (around 2:1) that favors water-binding and gelling properties. This is useful in veterinary diets when a firm texture is desired, but high water content is required (e.g., kidney disease).

Everything in moderation

Like anything, apple pomace needs to be used in moderation.

Its high fiber content dilutes the nutritive value of a diet. While this is useful in obese pets, it also means more food must be eaten to reach an appropriate caloric intake. Further, a recent study by the Federal University of Paraná in Brazil reported decreased apparent total tract digestibility in dogs with increasing concentrations of apple pomace. This poses a problem in unregulated diets that are not complete, balanced and formulated by animal nutritionists.

Moving forward, more research is required to understand the utility of apple pomace and the best way to incorporate it into pet diets