bioavailable & digestible

*Bioavailability refers to how efficiently and effectively the body absorbs and uses a given nutrient (e.g. macronutrients, micronutrients, like vitamins and minerals).


01 vegetable diets have a better average digestibility (bioavailability) then meat-based diets

Hegsted et al (1964) found that the apparent digestibility of proteins in an all-vegetable diet containing white bread, corn, rice, potatoes, lettuce, carrots, onions, tomatoes, and applesauce was 80.0 (plus or minus 7.7%). James and McCay(1953) reported that the apparent protein digestibility of commercial, dry-type food, containing both vegetable and animal proteins, ranged from 67 to 82% for adult dogs. Kendall and Holme (1982) reported the apparent crude protein (Nx6.25) digestibility coefficients for textured soy protein, extracted soy meal, full-fat soy flour, and micronized whole soybeans ranged from 71 to 87%. Moore et al.(1980) reported apparent digestibility values of soybean meal, corn, rice, and oats by mature Pointers to be in the range of 77 to 88%. Their data revealed that normal cooking procedures did not significantly influence the digestibility of rice, oat, or corn protein. Their data also indicated that increasing the fat content of the diet from 10 to 20% did not alter the digestibility of nitrogen in a corn-soybean-based diet. Burns et al (1982) showed that the apparent digestibility’s of lactalbumin, casein, soy protein, and wheat gluten are 87, 85, 78, and 77%. Clapper et al(2001) compared the canine digestibility of five soybean protein sources to that of poultry meal and found the soy protein to offer a viable protein source.

KENDALL, P.T., HOLME, D.W. and SMITH, P.M. (1982), Comparative evaluation of net digestive and absorptive efficiency in dogs and cats fed a variety of contrasting diet types. Journal of Small Animal Practice, 23: 577-587.

James & McCay. 1950. In National Research Council. Nutrient Requirements of Cats. Washington, DC: National Academy Press. 1986, 12.


02 dog’s ability to digest plant protein

The domestication of dogs was an important episode in the development of human civilization. The precise timing and location of this event is debated, and little is known about the genetic changes that accompanied the transformation of ancient wolves into domestic dogs. Here we conduct whole-genome resequencing of dogs and wolves to identify 3.8 million genetic variants used to identify 36 genomic regions that probably represent targets for selection during dog domestication. Nineteen of these regions contain genes important in brain function, eight of which belong to nervous system development pathways and potentially underlie behavioral changes central to dog domestication. Ten genes with key roles in starch digestion and fat metabolism also show signals of selection. We identify candidate mutations in key genes and provide functional support for an increased starch digestion in dogs relative to wolves. Our results indicate that novel adaptations allowing the early ancestors of modern dogs to thrive on a diet rich in starch, relative to the carnivorous diet of wolves, constituted a crucial step in the early domestication of dogs.

Link to article : Axelsson, E., Ratnakumar, A., Arendt, ML. et al.  (2013) The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature 495, 360–364. 


03 various studies on the digestibility of high starch diets for dogs

Study 1: Cereal grains represent 30 to 60% of the DM of many companion animal diets. Once incorporated into a diet, the starch component of these grains can provide an excellent source of ME. However, crystallinity and form of starch are variable and can cause incomplete digestion within the gastrointestinal tract. Diets fed in this experiment included one of six high-starch flours as the main source of carbohydrate. The flours originated from barley, corn, potato, rice, sorghum, and wheat. The diets were extruded and kibbled. Starch fraction concentrations of flours consisted of nearly 100% rapidly digestible starch (RDS) and slowly digestible starch (SDS) combined. Starch fraction concentrations of diets paralleled concentrations in flours. The starch component of all diets was nearly completely digested (>99%). Total tract digestibility of DM and OM was lowest for sorghum (80 and 84%, respectively) compared to all other diets. Crude protein digestibility was highest for corn (87%). Any of these flours could be used without negative effects on digestion at either the ileum or in the total tract.

Link to article: Murray SM, Fahey GC Jr, Merchen NR, Sunvold GD, Reinhart GA. Evaluation of selected high-starch flours as ingredients in canine diets. J Anim Sci. 1999 Aug;77(8):2180-6.


Study 2: The effects of six extruded diets with different starch sources (cassava flour, brewer’s rice, corn, sorghum, peas or lentils) on dog total tract apparent digestibility and glycemic and insulinemic response were investigated. The experiment was carried out on thirty-six dogs with six dogs per diet in a completely randomized design. The diets containing brewer’s rice and cassava flour presented the greatest digestibility of dry matter, organic matter and gross energy (p < 0.05), followed by corn and sorghum; pea and lentil diets had the lowest. Starch digestibility was greater than 98% in all diets and was greater for brewer’s rice and cassava flour than for lentils and peas diets (p < 0.05). Dogs’ immediate post-prandial glucose and insulin responses (AUC £ 30 min) were greater for brewer’s rice, corn, and cassava flour diets (p < 0.05), and later meal responses (AUC ‡ 30 min) were greater for sorghum, lentil and pea diets (p < 0.05). Variations in diet digestibility and post-prandial response can be explained by differences in chemical composition of each starch source including fibre content and starch granule structure. The nutritional particularities of each starch ingredient can be explored through diet formulations designed to modulate glycemic response. However, more studies are required to support these.

Link to article:  Carciofi AC, Takakura FS, de-Oliveira LD, Teshima E, Jeremias JT, Brunetto MA, Prada F. Effects of six carbohydrate sources on dog diet digestibility and post-prandial glucose and insulin response. J Anim Physiol Anim Nutr (Berl). 2008 Jun;92(3):326-36. 


04 digestibility of minerals in animal vs. vegetable based dog food

The objective of this study was to determine the apparent digestibility and true digestibility of macro and trace minerals in canines fed either animal or vegetable based adult maintenance diets. We hypothesized that dogs fed the animal ingredient based diet would have higher mineral digestibility as compared to dogs fed the vegetable ingredient based diet. There was no difference in apparent digestibility of calcium between dogs fed vegetable vs. animal diets; however, dogs fed the vegetable based diet had greater true digestibility of calcium (P = 0.0143) as compared to dogs fed the animal based diet. The apparent and true digestibility phosphorus and iron were greater in dogs fed the vegetable based diets as compared to animal based diets (P < 0.001). There were no differences in apparent or true digestibility of potassium, copper, and zinc between dogs fed the animal and vegetable based diets (P > 0.05). These results suggest that apparent and true digestibility do not result in similar conclusions, and digestibility of endogenous minerals are similar or greater in dogs fed diets that are largely vegetable based.

Link to article: C. L. Cargo-Froom, A. K. Shoveller, M. Z. Fan, 227 Apparent and true digestibility of minerals in animal and vegetable ingredient based adult maintenance dog food, Journal of Animal Science, Volume 95, Issue suppl_4, August 2017, Page 112.


05 digestibility of plant-based protein

The objective of this study was to evaluate macronutrient apparent total tract digestibility (ATTD), gastrointestinal tolerance, and fermentative end-products in extruded, canine diets. Five diets were formulated to be isocaloric and isonitrogenous with either garbanzo beans (GBD), green lentils (GLD), peanut flour (PFD), dried yeast (DYD), or poultry by-product meal (CON) as the primary protein sources. The high inclusion of legumes and yeast in extruded diets was well-accepted by dogs throughout the study. The analyzed serum chemistry and CBC were all within normal ranges for healthy adult dogs for the duration of the study. No negative effects were observed in fecal quality and all diets were highly digestible for all macronutrients. Dogs fed the experimental diets had greater SCFA concentrations than dogs fed CON. In particular, dogs fed DYD had high butyrate concentrations. Therefore, it can be concluded that these proteins are viable novel sources that can safely be included in canine diets, with inclusion levels over 40% for garbanzo beans and green lentils, and near 30% inclusion levels for peanut flour and dry yeast.

Link to article: Reilly LM, He F, Rodriguez-Zas SL, Southey BR, Hoke JM, Davenport GM, de Godoy MRC. Use of Legumes and Yeast as Novel Dietary Protein Sources in Extruded Canine Diets. Front Vet Sci. 2021 Jun 4;8:667642.


06 respectable pet food brand will score at least 80% digestibility on average

Popular brands of dog food have average digestibility percentages for protein, fat and carbohydrate of 81 per cent, 85 per cent and 79 per cent respectively. Although nutrient digestibility may be higher in premium brands and lower in economy products, the majority of dog foods from reputable manufacturers will deliver apparent digestibility values within a range of 80 per cent to 90 per cent.

Link to article: T. Watson (2011), Breaking it Down - Measuring Food Quality and Digestibility. Vet Times.


07 oat, groats, barley, wheat, corn, rice al exceed 80% digestibility of nutrients

The dogs appeared to digest the cereals with quite a high efficiency. The apparent digestibility coefficients showed that low fiber cereals provide great amount of digestible nutrients and energy to dog diets. Known protein content and energy value of the cereals offer useful information for diet formulation. Any of the cereals tested can be used in dog diets without major negative effects on digestion. Oat groats were also found to have mainly positive effects on nutrient digestibility. Since recent studies in humans have shown that oats are low gluten and suitable for diets of adults with celiac disease, the possibilities of using oats in hypoallergenic diets of gluten-sensitive dogs also need to be studied further

Link to article: Kempe, Riitta & Saastamoinen, Markku & Hyyppä, Seppo & Smeds, Kurt. (2004). Composition, digestibility and nutritive value of cereals for dogs. Agricultural and Food Science. 13. 5-17. 10.2137/1239099041838067.