Sawdust is not a good substitute for food. It’s a great additive but I wouldn’t feed it alone as a meal. Dogs may get constipated. Sawdust naturally acts a bit like glue that they add to commercial kibble.
SDC Talk! - Sawdust for dog yard surface
Nearly every major dog food includes some variety of grain, including corn, soy, rice, wheat and even sawdust and mill waste. Despite being advertised as nutritionally significant, grains added to dog food are used indisputably as bulk fillers, low-cost ingredients with no added value. While cited as important sources of energy, these simple carbohydrates are not the natural energy producers for canines. Those roles should be filled by quality proteins and fats. In addition: Grains, and even certain vegetables, are digestively strenuous. Digestion takes up the most energy in any living being and the dog’s short and simple digestive tract is not designed to breakdown high-starch carbohydrates.
Natural Diet for Dogs – Web Resources
Understanding the composition of the food you are feeding your dog is only one aspect of choosing a good food. It is imperative to also understand the dangers, risks, and nutritional availability of its ingredients. Many ingredients in pet foods are typically not even biologically recognized as nutrients to dogs, such as flaxseed. Flaxseed is added for its omega-3 properties however they are about as absorbable as sawdust. The reason that dogs and humans receive little to no nutrition from the ALA omega-3s in flaxseed is because they do not contain EPA or DHA omega-3s that are found in fish oil. Omega-3s are called essential fatty acids because the body does not produce them and must acquire them through diet. In a nutshell, the flaxseed omega-3 fatty acids (ALA) have chemical chains that are simply too short to fill an animal’s nutritional requirements, therefore it is often not recognized as a nutrient. Another very important thing to keep in mind is that Omega fatty acids are so volatile that whether they are already contained in the meat or if they are added afterwards, they are completely inactive because the heat from extrusion and cooking destroys the oils.
How much Sawdust? - Page 2 - German Shepherd Dog Forums