Why are Digestibility Studies Important in Pet Food?

When formulating pet foods, it is common to utilize the nutritional information of individual raw ingredients and to combine those ingredients at specific levels, so that the finished product will deliver the required levels of macro and micronutrients. Of course, depending on the pet food format, processing plays a role in the formulation as well. The Association of American Feed Control Officials (AAFCO) has established levels of required nutrients for adult maintenance as well as for growth and reproduction.

Once the pet food formulation is finalized and produced, a complete nutrient analysis should always be performed to ensure that the diet is meeting all regulatory requirements for the macro and micronutrients, based on levels specified in AAFCO’s official publication. Feeding studies are a great way to substantiate the safety of the diet. A previous article was published discussing extended AAFCO feeding studies and the importance of those studies which measure detailed health parameters on dogs eating a study diet for six months.

Something that may get overlooked is conducting digestibility studies. Digestibility can be defined as the number of nutrients that are available to the body after consumption. Pet food can be formulated to meet all the nutritional requirements but may be an issue if the nutrients are not bioavailable to the pet consuming them. This is done via digestibility testing and the good news is that digestibility studies are not complicated, long, or expensive. Six dogs or cats will eat the diet for 10 days, exclusively. For the last five days of the study, all stool is collected from each individual animal. The diet and the stool collected from each animal are then analyzed at a reference laboratory for protein, moisture, fat, ash, and fiber. Through a series of calculations, the percent digestibility of the diet is determined.¹

The digestibility results are usually calculated for dry matter (total) digestibility, protein digestibility, fat digestibility, and caloric digestibility. Each calculation represents important information about the diet and each one considered collectively can give a well-rounded picture of how a certain diet performs when fed to pets. Protein and fat digestibility are usually higher than total digestibility when using this methodology and that is because those calculations do not consider the fiber and ash components of the pet food. Ash is defined as what is left in pet food when the protein, fat, fiber, carbohydrates, and moisture are all removed. When comparing diets with fresh meat or meat meals, diets with higher levels of fresh meat generally have higher protein digestibility because the ash content of fresh meat is relatively low. However, fresh meat contains much more moisture than meat meals, so to reach the same protein level much more fresh meat will need to be added to the diet when compared to meat meals.

It is important to remember that no diet is 100% digestible. If they were there would be no waste.  Many factors can play into the digestibility of a diet, including the type of manufacturing process, protein source, insoluble fiber levels, as well as percent gelatinization, more commonly known as “percent cook”. Gelatinization of starch is important in pet food as non-gelatinized (not sufficiently cooked) starches are not as bioavailable to pets.² Another commonly overlooked factor in pet food may be anti-nutrient factors that can be contained in some grains and legumes. Anti-nutrient factors, such as lectins, tannins, saponins, phytate, and protease inhibitors can also negatively affect digestibility.² Many manufacturing processes can help limit anti-nutrient factors, such as milling to small particle size, soaking in water, germination along with fermentation, and even microwave treatment.

Other common factors that may play into the digestibility of pet foods are the amount of insoluble fiber and ash levels. When it comes to dogs and cats, insoluble fiber is not able to be easily broken down into energy sources. However, some insoluble fiber does benefit pets for improved stool quality, lowering caloric density, increasing satiety (feeling full), and may help with stool regularity.⁴ There is also always going to be ash content in pet food as ash is mostly made up of the minerals our pets need.

There are many important factors that can affect pet food digestibility, but BSM Partners can help implement, manage, and interpret digestibility testing results. BSM Partners even offers “in-home” dog digestibility testing for clients. Our expertise in animal nutrition and pet food testing can help clients understand their results, to help make pet food as digestible and healthy as possible for all pets.

References:

1. American Association of Feed Control Officials, 2022 Official Publication.
2. Gibson M. & S. Alavi., Pet food processing-understanding transformations in starch during extrusion and baking. Materials Science. Cereal Foods World. 2013.
3. Smitya et al., Plant food anti-nutritional factors and their reduction strategies: an overview.  Food Production, Processing and Nutrition. 2020. 2:6
4. de Godoy MRC. et al. Alternative dietary fiber sources in companion animal nutrition. Nutrients. 2013. 5(8).

 

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About the Author

Dr. Bradley Quest, DVM, is the Principal Veterinarian at BSM Partners. He has practiced clinical veterinary medicine, developed and tested hundreds of pet food and health products, performs extensive animal health research, and helps navigate pet food ingredient approval for clients.