Most of us view our pets as a furry part of the family. As a result, pet owners are increasingly considering human-grade food ingredients as an alternative diet for their animals. If fresh ingredients like lean chicken breast, green beans and whole apples are healthy for the human family, then they should be for dogs too right? With the rise in pet owners opting for fresh cooked diets, there is also a proportionate need for scientific testing around these diets. One pioneering study from the University of Illinois at Urbana-Champaign is the first to examine the digestibility of human-grade dog foods1.
Digestibility is the proportion of an ingested foodstuff or nutrient that is absorbed into the body2. It is used as a measure to determine how much of a foodstuff is broken down and utilized by an animal versus how much is simply excreted. To study the digestibility of the human-grade dog foods, six commercial human-grade dog foods from the same company were selected. The diets all differed in their protein and carbohydrate sources. The primary components of each of the diets were a beef/russet potato diet, chicken/white rice diet, fish (cod)/sweet potato diet, lamb/brown rice diet, turkey/whole wheat macaroni diet and venison/squash. Ideally, these diets should be highly digestible.
Before digestibility was determined, the basic nutrient composition of the diets was examined to look at key components like protein, fibre and energy content. To test the degree of digestibility, the diets were fed to cecectomized roosters in two separate groups. Cecectomized animals have a tube surgically inserted into the beginning portion of the large intestine, allowing for easy fecal collection. The researchers claimed that the use of cecectomized roosters allowed for the study of true digestibility without having to consider the influence of intestinal bacteria. The specific goals of this study were to examine true nutrient and amino acid digestibility. Both digestibility calculations were based on the degree of energy or amino acid ingested compared to how much was excreted.
Results of the study showed that all nutrients in the fresh cooked diets met and exceeded the AAFCO levels. The Association of American Feed Control Officials or “AFFCO” is the association which dictates nutritional adequacy in pet food diets. This means that all of the commercial human-grade diets tested were able to meet the nutritional needs of dogs.
Results also showed that the dry matter content (the amount of feed left over after all water has been evaporated) of the fresh cooked diets was more highly digestible than plant protein-based diets used in other studies, ranging from 86.0% to 87.0% in human-grade pet food. Amino acid digestibility, which takes into account the availability of dietary protein, was also higher than plant protein-based diets used in other studies, ranging from 79.0% to 93.4%. However, it was noted that the degree of protein digestibility is greatly influenced by certain factors such as processing and the proportion of muscle to connective tissue in the protein ingredients3. A higher proportion of connective tissue and bone in meat products lowers the overall digestibility of protein ingredients.
The researchers found that fibre digestibility was highly variable between the human-grade foods. This was attributed to the different levels of soluble versus insoluble fibre in the diets. Even with the variability in the fibre digestibility among the diets, it did not negatively affect overall amino acid digestibility. Lastly, the researchers determined that the metabolizable energy content of the human-grade diets was high compared to dry pet foods but more research is also needed to be able to accurately estimate the metabolizable energy of human-grade pet foods.
There were a few limitations in the study. The first being the use of roosters as the species of study as opposed to dogs. This is comparable to the use of rats as a model for humans in human studies. Roosters may have some similar digestive traits to dogs but do not completely replace the same digestive function for dogs. Roosters are a good preliminary model for the study of digestibility in dogs but should be followed up by a canine study as well. Another limitation is the lack of a control dry food in the study. While the researchers make a comparison to literary sources for dry-food digestibility, they cannot make a true conclusion unless a dry food is measured against fresh food in the same study. Lastly, the sample size of the roosters used was quite small. Statistically, a small sample increases the chance of error in the interpretation of data. If a larger sample size was used, there may have been less variability observed among the diets for fibre digestibility. Even with its limitations, this study could still be used as a preliminary study and reference for future canine feeding trials.
Overall, this study by researchers at the University of Illinois at Urbana-Champaign shows that the ingredients used in human-grade pet foods are highly digestible and nutritionally adequate for dogs. As one of the first animal feeding trials involving human-grade pet foods, this study shows promise for superior digestive benefits in dogs fed fresh, human-grade pet food.