The quality of pet food ingredients can vary widely based on the food you buy. Many dogs will dictate ingredients to avoid by not tolerating them, but there are some ingredients that should always be avoided.
Wheat and Corn
Most dog food allergies are caused by grains such as wheat and corn. If that isn't enough a reason to avoid them, dogs can't digest wheat or corn. Thus, they are unnecessary ingredients which are just used as a cheap filler for dog food. No high-quality brands of food utilize wheat or corn, so these ingredients are a good indicator that the food you are buying isn't as high quality as you expected.
The first three ingredients listed on the food label make up a high percentage of the its ingredients. If wheat and corn are listed in any form in the first three ingredients, avoid this food. This means it contains very little meat, which your dog needs to be healthy.
There are many grain-free foods available, but there is debate among the pet nutrition community whether grains should be excluded completely from food. Healthy grains such as barley and oats may provide your dog with some nutrition when given in small amounts.
Meat Byproducts
There are a wide variety of protein sources available for dog food, such as beef, chicken, turkey, pork, rabbit and venison. The first three pet food ingredients should be protein or protein meal, so it's a very important part of your dog's diet. Protein is the ingredient most likely to cause allergies after wheat and corn, so your dog largely dictates which protein type you purchase. If your dog does poorly on one protein, try another.
However, any type of meat byproduct should be avoided. Meat byproducts are the parts of the protein source that have very little nutritional value and can even include the feathers, hooves and other unhealthy pieces. In addition, if the protein source is just listed as "meat," avoid this product. This means that many different protein types have been compiled to the point where they can't really be recognized. This will likely be unhealthy for your pet and should be avoided.
Dyes and Preservatives
Dogs don't distinguish the different shapes and colors of their food. The only reason food is made colorful is to appeal to humans. These ingredients can even be unhealthy to your pets.
Preservatives are put in the food to make it last longer. However, this ensures that the ingredients aren't as fresh or healthy for your dog. In addition, many of the dyes and preservatives are thought to be carcinogens to pets, increasing the likelihood they will contract some type of serious illness as they get older.
If you buy a high-quality food, you will not find any of these pet food ingredients. These foods have an expiration date and are meant to be consumed quickly when the ingredients are fresh and provide the most nutritional value. A good general rule of thumb is that if you aren't sure what an ingredient is, you shouldn't put it in your pet's body.