Dr Martin de Scally – BVSc, Hons MMedVet (Med)
Sonja Maricevic – Technical director
Veterinarians are often faced with the task of comparing pet food labeling in order to choose the best diet for their patients. This article will give you some simple rules of thumb useful when scrutinizing front of bag claims, ingredient lists and guaranteed analysis panels of foods as well as highlighting some common tricks used by pet food manufacturers.
Front of bag claims
The product name can be a key factor in the consumer’s decision to buy the product. For that reason, manufacturers are often tempted to emphasize a particular aspect of the product, usually an ingredient considered desirable to consumers such as chicken, ostrich, or lamb. Product wording is regulated and relates to overall presence of the highlighted ingredient in the food. These terminology differences are subtle while ingredient percentage differences are not and this can mislead unsuspecting consumers:
- Chicken Dog Food –needs to be made with at least 65% chicken
- Chicken Formula/Diner/Entree for Dogs –26% chicken or more
- Dog Food Rich in Chicken – at least 14% of this ingredient
- Dog Food With Chicken – only 4% chicken
Chicken Flavoured Dog Food – Under the “flavour” rule, a specific percentage of the ingredient is not required at all, provided the product contains an amount sufficient for detection. Pet foods often contain “digests,” which are materials treated with heat, enzymes and/or acids to form concentrated natural flavors. Only a small amount of a “chicken digest” is needed to produce a ”flavoured” food, which need not contain any actual chicken. Some companies disclose the actual percentage of the ingredients the food is made with, either amongst the front of bag claims or vignettes, or in the ingredient list, which you will find on the back of the packaging.
All pet foods must list the ingredients present in the food in descending order of pre-cooked weight. The biggest contributors are first and the smallest last in the ingredient list. A good rule of thumb is that the ingredients before the first “fat ingredient” – e.g. animal fat or chicken fat, tend to make up the bulk of the food. Vitamins and minerals are added to supplement natural sources if needed. Other ingredients might include colourings, preservatives, or stabilisers.
Ingredients can range from clearly labeled ones like “ fresh chicken meat” to more vague “bulk” ingredients like “meat and bone meal” which do not specify which animal or parts of animal the meal is made from.
Meals are created by a rendering process, where the materials are subjected to heat and pressure, removing most water and fat and leaving primarily protein and minerals. Meat meals vary greatly in protein quality and overall mineral content, ranging from highly digestible meat meals supplying superior amino acid balances to poor quality by-product meals with high bone content.
Plant protein sources are not as balanced or nutritionally available as the protein from high quality animal sources but are more consistent in protein quality and mineral content and can therefore be preferable to very poor quality animal sources.
The weights of ingredients are determined as they are added in the formulation, including their inherent water content. This latter fact is important when evaluating relative quantity claims, especially when ingredients of different moisture contents are compared.
One pet food may list “chicken” as its first ingredient, and “pea protein concentrate” as the next protein ingredient. The manufacturer doesn’t hesitate to point out that it has chicken as the main ingredient, however, chicken is very high in moisture (approximately 75% water). On the other hand, water and fat are already removed from pea protein concentrate (what’s left is mostly protein and minerals). Realistically you may find that the majority of protein in the food, a dehydrated end product, will be supplied by the pea protein concentrate, and not the chicken.
Be careful of another tactic used by some manufacturers to disguise less desirable ingredients. Breaking an ingredient into several different smaller ingredients and listing them individually is used to lower these undesirable ingredients farther down the ingredient list.
An ingredient list could contain chicken, ground corn, corn gluten, ground wheat, corn bran, wheat flour, wheat middling, etc. If we were to group all of the corn ingredients as one, they would probably far out-weigh the amount of chicken.
The guaranteed analysis shows the minimums or maximums of nutrients in the final product. The food ingredients and various additives listed in the ingredient list supply these. SA regulations require a pet food manufacturer to guarantee the following:
- crude protein – minimum %
- crude fat – minimum %
- crude fiber – maximum %
- moisture – maximum %
The “crude” term refers to the specific method of testing the product, not to the quality of the nutrient itself. The maximum percentage of ash (the overall mineral component) is also often shown. There is no minimum requirement for carbohydrates for dogs or cats, and the carbohydrate content is not disclosed in the guaranteed analysis, although it can constitute up to 60% of dry pet food. If you are looking for a low carbohydrate diet for a patient, and need to calculate the overall “as-fed” carbohydrate content of a diet use the following equation:
100% – % protein – % fat – % fiber – % ash – % moisture = % carbohydrate
While the guaranteed analysis is a start in understanding what’s in the food, be careful about relying on it exclusively. The guaranteed analysis does not provide the exact nutrient quantities or make a judgement as to the digestibility or quality of the food and ingredients. A pet food manufacturer made a mock product that had a guaranteed analysis of 10% protein, 6.5% fat, 2.4% fiber, and 68% moisture, similar to what you see on many canned pet food labels. The only problem was, that the ingredients were old leather boots, used motor oil, crushed coal, and water!
How to compare different foods
Guaranteed analysis is declared on an “as fed” or “as is” basis, that is, the amounts present in the product as it is found in the can or bag. When comparing the guaranteed analyses between dry and canned products, you will notice that the levels of crude protein and most other nutrients are much lower for the canned product. This can be explained by looking at the relative moisture contents.
Canned foods typically contain 75-80% moisture, whereas dry foods contain only 10-12% moisture. To make comparisons of nutrient levels between a canned and dry product we need to mathematically “remove” the water from both foods, and convert the guarantees for both products to a moisture-free or dry matter basis (DM). The percentage of dry matter of the product is equal to 100% minus the percentage of moisture guaranteed on the label.
100% – %moisture = % dry matter (DM)
A dry food is approximately 88-90% dry matter, while a canned food is only about 20-25% dry matter. To convert an “as fed” nutrient guarantee to a dry matter basis, the percent “as fed” nutrient should be divided by the percentage of the dry matter, and then multiplied by 100.
(% “as fed” nutrient / % dry matter) X 100 = % nutrient on a DM basis
- A canned food guarantees 8% crude protein and 75% moisture (or 25% dry matter).
- A dry food contains 27% crude protein and 10% moisture (or 90% dry matter).
Which has more protein, the dry or canned?
Calculating the dry matter protein of both, the canned contains 32% crude protein on a DM basis (8/25 X 100 = 32), while the dry has 30% on a DM basis (27/90 X 100 = 30). Thus, although it looks like the dry has a lot more protein, when the water is counted out, the canned actually has a little more. An easier way is to remember that the amount of dry matter in the dry food is about four times the amount in a canned or frozen product. To compare guarantees between a dry and canned food, multiply the guarantees for the canned food times four first.
The impact of portion size
High moisture content in canned or frozen food dramatically increases the daily recommended portion size needed, where up to 8 times food by weight needs to be fed when compared to the recommended portion size of a dry food for the same pet.
Recommended portions sizes for different dry foods can also vary by as much as 100%. The lower the quality, digestibility or caloric density of the food is, the bigger the recommended portion size will be. To make meaningful comparisons between different diets with varying amounts of moisture, calories or digestibility, you would need to first work out the daily amount of nutrients ingested by weight.
- as fed nutrient X daily portion size = daily amount of nutrient ingested
We were looking for a diet that is moderate in calcium for a patient. We select two foods of the shelf that both show 1,4% calcium “as fed” in their guaranteed analysis panels. But do the foods supply the same amount of calcium?
The recommended daily portion size of the first food selected is 310g which translates to 4,3g calcium ingested per day. (1,4% x 310g = 4,3g). The recommended portion size of the second food is 185g for the same dog and this diet will only supply 2,59g calcium per day. (1,4% x 185g = 2,59g).
Even though the “as fed” percentages on the bags are the same, the second food supplies significantly less calcium overall.
The bag label contains a wealth of information, if one knows how to read it correctly. The front of bag claims, guaranteed analysis, ingredient list and feeding guidelines all tell part of the story, but need to be read in conjunction with each other in order to paint the full picture. Certain companies can provide full guaranteed analysis of their products including EPA, DHA and individual amino acid, mineral and vitamins levels. Check the website, or contact the manufacturer, if you would like more information than is provided on the label.
*The guaranteed analysis does not provide the exact nutrient quantities or make a judgement as to the digestibility or quality of the food and ingredients.
References available on www.vet360.vetlink.co.za