A good criterion to evaluate the quality of a balanced food

In the pet food industry there is a wide variety of brands that provide enough of each of the essential nutrients to meet the rating of “complete and balanced” food. But, not all of them have ingredients of the same quality or nutritional value in their formulas to adequately meet the requirements of dogs and cats.

In this sense, the technical criterion of evaluating the degree of digestibility of a food is a useful analytical tool to objectively and qualitatively weigh a balance. And also to compare the nutritional quality between different commercial brands.

In simple terms, the digestibility of food can be defined as the percentage that is absorbed and used by the body of the total that enters the digestive system of an animal in a certain period. Conventionally, it is determined by subtracting from the total amount consumed of a certain nutrient, the amount of it excreted with the feces.

This way of calculating the digestibility of a complete food, although simplistic, is also valid to establish the assimilation of some of its nutrients in particular, such as proteins.

Quality indicator

Although the digestibility of a balanced food is not the only parameter to establish its nutritional value, it is a good quality indicator. Taking into account that it measures the degree of use of nutrients, its value influences both the quality of the fecal matter of the dog or cat and its health and well-being.

When a pet consumes a low-quality balance, and low protein digestibility, the animal manifests it by presenting a poor fecal score (bulky and moist feces that do not conform  properly), bad smell in its stools and sometimes flatulence.

But the greatest impact is in the medium term on the health and well-being of dogs and cats. If the degree of use or assimilation of the nutrients contained in a balanced diet is low,  the organism of the pet that eats this food is affected since it does not adequately cover its nutritional requirements by not being able to assimilate well what is consumed.   

From the digestibility value of a dry balanced food, it is possible to establish which quality segment this product belongs to. Thus, a balance that has a digestibility value of 75% or less is considered low quality. Those whose value is between 75 and 82% occupies the standard or moderate quality segment, while those balanced with more than 82% digestibility make up the group of high quality: premium and super premium.

In vivo and in vitro

The determination of the digestibility of a balance can be done  through two types of tests: in vivo and in vitro. In the first case, it is carried out on a certain number of dogs or cats taking into account the amount of balanced, or protein,  ingested and excreted by each animal in a certain period. There are standardized protocols, such as those of the Association of American Feed Control Officials (AAFCO) that indicate how to perform this type of test.

When considering the digestibility coefficient as the difference between the nutrients ingested and excreted, it is necessary to bear in mind  that not all the material that makes up feces is actually undigested food. One part is made up of enzymes, substances secreted into the intestine and epithelial desquamation cells. For this reason, the values ​​obtained through this type of test allow us to know the apparent digestibility of the food. This differs from true digestibility, in that the latter considers the endogenous nutrient losses of the animal.

For its part, the in vitro determination is carried out through laboratory analysis where the proteins of the balance are digested using pepsin, an enzyme that is secreted in the stomach of higher mammals.

In general, the value of protein digestibility in vitro is higher than the result obtained in the analysis of the same nutrient through an in vivo test.

Protein digestibility

The digestibility of the main source of animal protein in a feed is another good indicator of the nutritional quality of a food. There are differences in this value according to the supplier animal species considered. According to the results of a research published in 2016 by Danish scientists from the University of Copenhagen, lamb meal has a significantly lower protein digestibility value than chicken and fish meal and is also deficient in the contribution of the essential amino acid methionine. The Nordic researchers fed 3 groups of dogs with extruded feedstuffs whose main sources of animal protein were provided in each case by lamb, chicken and fish meals. After determining the digestibility in vivo, they obtained that the lamb meal had an assimilation value of 71.5%, the chicken meal of 80.2% and the fish meal of 87%.

These results lead us to reconsider the concept, currently quite widespread in the pet food industry, which states that lamb meal is a high-quality protein source.

Fresh meat vs flour

In another study, the same team of researchers from Denmark evaluated the in vivo digestibility of two dry balanced food whose protein sources were, in each case, fresh chicken meat and chicken meal. As expected, prior to the extrusion process, the digestibility of fresh meat yielded a significantly higher result than that of flour: 88.2% versus 80.9%, respectively.

However, when the digestibility of both food was measured after extrusion, the results were almost similar: 81.3% for fresh chicken meat versus 80.3% for flour. 
Scientists speculate that the proteins in fresh chicken meat are probably more susceptible to deterioration due to exposure to heat during extrusion compared to the already processed proteins provided in the form of chicken meal.

According to the results of this research, the digestibility of a balanced food that contains fresh chicken meat in its formula does not improve protein assimilation or the availability of amino acids, compared to another that provides chicken flour. This result calls into question another statement that is quite widespread today in the pet food industry regarding the quality assessment of both protein sources.

Factors that affects it

The digestibility of a balanced food is influenced by different factors: those inherent to the composition of the food, or the quality of its raw materials, and others related to variables outside the product such as: the animal species and age of the pet that consumes it , the industrial manufacturing process, among others.

In the specific case of the digestibility of proteins in a pet food, it must be taken into account that sources of animal origin present, in general, better assimilation than vegetable sources.  But also, that there are significant differences in terms of digestibility between the different proteins of animal origin used in the formulation of pets food.   

In cats, protein digestion is usually very efficient, and the apparent digestibility of protein is similar to that in dogs. The digestive capacity of the young cat is lower than that of the adult animal, either due to physiological immaturity of the digestive tract, or due to the enzymatic modulation induced by feeding.

In dogs, no significant difference is observed in the digestibility of the same diet administered to specimens of different breeds / body sizes beyond the tendency, already known in dogs of greater physical size, to present more moist feces compared to the specimens smaller in size.

The way in which some of the industrial steps of preparing a dry balance are developed also conditions the final digestibility of the food, regardless of the quality of its formula. A good grinding as well as a correct handling of the preconditioner and the extruder are fundamental conditions for  a correct cooking of the ingredients of the mixture and to achieve a good expansion of the croquettes, attributes necessary to obtain a product with good digestibility.