Pet Food Digestibility

We are surrounded by choices these days as we set out to buy food for our pets. There are many different foods in many different price ranges, all claiming to be just what your pet needs. How do we know what is really best, especially when we do not have quite all the information?

Digestibility of a product is a critical piece of information that is currently not quantitatively stated on pet food bags because, as of yet, there is no centralized or standardized official testing procedure that results in comparable data that can be put on pet food bags. Digestibility is an indicator of how thoroughly a feed is processed and utilized by the animal that eats it, and it is affected not only by the quality of the food but by the health status of the animal eating it. For instance, an animal riddled with intestinal parasites will digest far less of its food than will a parasite-free animal, regardless of the quality of the food. Therefore, extensive digestibility trials with large numbers of animals are required to truly estimate the digestibility of a given feed.

Most of the values shown on a feed tag or bag are derived by chemical analysis of the feedstuff. Chemical analysis, however, does not address the palatability, digestibility, or biological availability of nutrients in a food. Thus it is unreliable for determining whether a food will provide an animal with sufficient nutrients needed for growth, performance, or lactation. For instance, protein analysis is based on the measure of nitrogen in a feedstuff, since nitrogen is a key element in protein. However, merely measuring nitrogen is not indicative of protein quality (meaning amino acid composition), and nitrogen is a component of many other biological compounds, such as amine sugars. The analysis for fat does not indicate what kind of fat it is, and the fiber analysis likewise does not indicate the source or digestibility of the fiber, only that it is there. Technically, it is possible to make a “food” out of lawn fertilizer (nitrogen), motor oil (fat) and w ood chips (fiber) that will have the same protein, fat and fiber analysis as your favorite pet food! The tag would look great, but the feeding value would be horrible!

So how do you really make sure you are buying a quality product? You can fairly easily determine palatability yourself. If your pet doesn’t like the food, it’s not very palatable, at least not to your pet. Digestibility and biological availability can be trickier, but not impossible, to determine. The two are interrelated, as more digestible feeds are made from higher quality ingredients that will provide more nutrients that can be readily absorbed and utilized by your pet. Stool size and consistency are major indicators of feed quality: large, soft stools, perhaps with mucus present, are indicative of poor-quality, poorly utilized ingredients that are resulting in a lot of waste. That which goes all the way through the animal is not available for utilization! Poor growth rates in young animals or weight loss in lactating animals is a clear sign that the feed is not meeting their needs, regardless of the nutrient analysis. Dull coats can be a sign in adult animals that they are not getting what they need. And if your pet needs to eat more of a given food in order to maintain its weight, that’s a sure sign that the food is not a very high quality feed.

Since higher quality feeds made from higher quality ingredients will generally cost more, price can sometimes be indicative of quality (certainly a high price tag can be put on a low quality feed, but seldom will a truly high-quality feed be offered at basement bargain prices). If you’ve always been a price tag shopper, consider this: If you pass up Feed A because it costs $23 for 40 pounds and buy Feed B at $20 for 40 pounds, but your pet must eat 25% more of Feed B in order to get the nutrients it needs, have you saved money? Let’s see. If your dog needs 1 pound/day of Feed A, that is 40 servings at 57.5 cents per serving. Your dog will need to eat 1.25 pounds of Diet B to get the same amount of nutrients, meaning you get only 32 servings from the bag, at a cost of 62.5 cents/serving. Not such a great deal after all! Checking feeding directions to determine estimated consumption can be of some help, but beware – one cup of one food may not weigh the same as one cup of another food, so you may end up comparing apples and oranges when reading recommendations on bags. Weight is a better measure than volume when determining intake.

Reputation is another indicator of quality. Established pet food companies that conduct digestibility trials, as well as maintaining a customer service department to interact with consumers, are more likely to be putting out a quality product that they are happy to stand behind. If there isn’t an 800-number on the bag, then you can probably assume the company isn’t very interested in your comments. If they are not testing their feed but rather formulating based on calculated nutrient content (which is based on chemical analysis), then neither you nor they will really know how digestible it is until you feed it. PMI Nutrition conducts extensive digestibility trials on its pet food to ensure that you are getting the highest quality for your dollar.

Remember that nutrition is a complicated process involving not just the presence of nutrients but also their availability and digestibility and therefore their usefulness to the animal. Long-term subclinical nutritional deficiencies or imbalances due to lower quality foods can take a toll on the longevity and eventual quality of life of pets who may appear to be healthy on the outside. Don’t take shortcuts with your pet’s nutrition!

They give us so much—aren’t they worth the very best?

by Dr. Mikelle Roeder, Ph.D, P. A. S.