In recent years, dog owners have started to demand more transparency from pet food manufacturers (a needed change, in my opinion). Many are interested in selecting new types of foods for their dogs and prefer products that are less highly processed. In direct response to these trends, nutrition researchers have been studying the ingredients that are used in pet foods, including the effects of processing methods, such as rendering, cooking and feeding raw.
For example, let’s look at chicken.
Chicken Ingredients: Chicken is one of the most common animal-source proteins found in commercial dog foods and, like many animal-source proteins, is considered to be a complete protein for dogs. This means that it can supply all of the essential amino acids in proportions that meet or exceed the dog’s daily requirements. The emphasis here is on the word can. As we will see, there is evidence that not all chicken ingredients found in pet foods are created equal.
Extruded (dry) pet foods include chicken in the form of chicken meal, which is produced from the by-products of the human food industry using a process called rendering. (For a detailed explanation of meals, see “What’s the Deal with Meals“). Chicken is also found in pet foods in the form of retorted (canned), cooked or steamed, and raw.
However, before we look at these different forms, we need to clear up a very basic source of confusion concerning the difference between pet grade and human grade (aka “edible”) chicken sources. This is important, so stay with me.
Framing the Issue: The vast majority of animal protein sources that are included in commercially produced pet foods originate as slaughterhouse waste and from food animals that are deemed “not for human consumption” (officially classified as inedible). In the case of chicken, this comes in the form of “chicken frames”, a term that refers to the portion of a chicken’s body that remains after all of the parts destined for human consumption have been removed and processed for the human food supply chain.
No, no, no. Not that.
Pet Food Grade Chicken: Chicken frames are composed of small bits of muscle meat plus a lot of connective tissue and bone. It is these chicken frames, plus varying amounts of internal organs, intestines, heads, and sometimes feet, that are sent to rendering plants and processed into chicken meal. They are also the primary source of the “fresh” chicken in dry dog foods that are marketed as chicken first. Although this labeling trick implies that this is the same chicken as the food that consumers purchase in the supermarket, it is not. Rather, this chicken is also a by-product of the human food industry – frames (and other stuff) – prior to being turned into a dry protein meal. The same applies to commercially produced raw and fresh cooked foods. Unless the producer specifies “human grade” (technically called “edible”), the chicken ingredients of their products are chicken by-products – not supermarket chicken breast and leg meat.
Human Grade Chicken: Some pet owners are aware of this difference and seek foods that use human grade ingredients. This topic is worthy of attention because it is a tricky issue. Current regulations only allow use of the phrase “human grade” on pet food packaging if every ingredient and processing method of the product meets FDA and USDA requirements for producing foods suitable for human consumption. Because only a small number of pet food companies can meet these very stringent criteria, the inclusion of “human grade” on the food’s label itself is relatively rare. However, companies that are purchasing only human grade ingredients but that do not meet the criteria of producing their food in a USDA-inspected human food facility, can (and do) include this information on their websites and via their marketing materials.
Quality Differences? Although human grade ingredients and finished pet foods that can be labeled as such are generally considered to be of higher quality, these foods are relatively rare and tend to be quite high in price point. It is also true that foods that use pet grade chicken meals are not necessarily lower in quality. Chicken meal quality is influenced by cooking time, processing temperature and other conditions. A number of studies have reported vast differences in quality in the chicken meals and by-product meals that are used as ingredients in pet foods (see “Dog Food Logic” for detailed information).
However, until recently, no one has compared the protein quality of different forms of chicken that are commonly included in pet foods. This year, a group of nutritionists at the University of Illinois used multiple measures of protein quality to compare four types of pet grade chicken (1). These were:
- Raw chicken
- Steamed chicken (cooked to 200 degrees F for 10 minutes)
- Retorted chicken (processed as in canned foods; cooked at ~ 250 degrees F for 30 minutes)
- Chicken meal (rendered/dried)
The Study: The researchers used a rooster feeding assay that has been validated for determining protein and amino acid digestibilities. Prior studies have shown that this assay’s results correlate with results from feeding trials with dogs and it has been used to accurately calculate both protein digestibility and an estimate of essential amino acid availability (called DIAA) in a variety of species.
Here is what they found when they compared raw, steamed, retorted and meal:
- Digestibility: The overall (dry matter) digestibility of chicken meal was significantly lower than the digestibility of the other three forms of chicken. This difference was pronounced. Only 60 percent of the chicken meal was digestible, compared with 73 to 76 percent of the other forms. Steamed chicken had the highest digestibility value (76.5 %); this was slightly higher than that of raw chicken (75.9%), but the difference between the two was not statistically significant.
- Amino Acids: Interestingly, digestibility values for all of the essential and non-essential amino acids were highest for steamed chicken – greater than 90 percent for all but two amino acids. These are rock star values, if you were wondering. Raw chicken did well too – but not as well as the steamed ingredient. Across the board the amino acid digestibility values were lowest in chicken meal. Really low.
- Chicken meal inadequacies: The researchers found multiple essential amino acid deficiencies in the chicken meal ingredient. It was deficient in methionine, tryptophan and threonine when compared with AAFCO recommendations for adult dogs. For growth, the chicken meal met AAFCO recommendations for only three of the 10 essential amino acids. (Wow.)
- Raw vs. steamed chicken: The data in this study showed that moderate cooking provided benefit over raw chicken in the form of higher essential amino acid availability in the cooked chicken. When values were compared with AAFCO recommendations for adult dogs, the steamed chicken provided significantly higher amounts of all 10 essential amino acids than raw chicken. However, both forms of chicken met or exceeded the recommended levels and were considered to be high quality protein sources.
Take Away for Dog Folks: In this study, steamed chicken was evaluated as the highest protein quality, followed closely by raw chicken. Retorted chicken was of moderate quality, while the chicken meal, the form of chicken that is included in almost all dry, extruded dog foods, lagged dramatically behind and was found to be an incomplete protein source for both adult and growing dogs.
Chicken meal performed poorly, really poorly, in this study. It had low digestibility and had numerous amino acid deficiencies for both adult and growing dogs. Here is a direct quote from the paper:
“…. our data indicate that if the chicken meal has a low digestibility, it may not meet the minimal recommendations for indispensable [aka essential] AA without supplementation, especially if the diet is formulated to meet the minimum protein requirement of the dog…“
These results are similar to those reported in another recent study, conducted by a different group of nutritionists (replication is important in science). I review this study in “Mind your Peas and Potatoes“.
In my opinion, there are several important points to take away from this paper:
- Raw claims: The belief of many who feed raw diets that raw meat (in this case chicken) provides better nutrition to dogs than cooked meat, is not supported. The moderately cooked chicken in this study was slightly more digestible and provided higher levels of available essential amino acids than did the raw chicken. Moderate cooking improved nutrient availability – it did not reduce it.
- Chicken meal inadequacies: When included as the primary protein source in a food, chicken meal may not provide adequate levels of essential amino acids to growing or adult dogs, While this certainly may not be true of all rendered chicken meals, it was true of the source that was examined in this study.
- Food selection? The problem is that, (and I have beaten this particular drum before), pet owners have absolutely no access to information about the ingredient quality of commercial pet foods. Because so few companies use human grade ingredients and because those products that do tend to be very high in price point, this is not a helpful criterion for many owners. Although some pet food companies regularly measure the digestibility of their ingredients and foods, this information is not generally available to consumers and companies are under no regulatory pressure to provide it. As a result, in many cases, (based upon personal experience), queries to companies for this information go unanswered. This is a sad state of affairs indeed. Ironically, the universal directive from pet food manufacturers is that owners should select a dog food that is labeled as providing “complete and balanced” nutrition. However, if a company is not testing or reporting quality information about their foods, and we know that at least some ingredients are falling far short of being adequate sources of nutrients, how can we trust such advice or know that a claim of “complete and balanced” has been adequately substantiated? We cannot. And this is a problem.
Tastes like chicken? Probably. Nutritious like chicken? Maybe not.
Cited Study: Oba PM, Utterback PL, Parsons CM, deGodoy MRC, Swanson KS. Chemical composition, true nutrient digestibility, and true metabilizable energy of chicken-based ingredients differing by processing method using the precision-fed cecectomized rooster assay. Journal of Animal Science 2019, in press.