Many crops are grown with the goal of extracting only part of their nutritional value – like soybeans for oil, corn for oil or alcohol production, wheat for starch (flour).
When those targeted ingredients are extracted, the remainder contains many valuable nutrients. These “left overs” are commonly termed by-products because they are produced during the process of extracting the component of interest. By-products are not just waste. In fact, in many instances their nutritional value is actually enhanced in some way.
Try to picture this process. Let’s say a company wants to produce sunflower oil from sunflower seeds. Seeds are typically about 30/30/30 oil, protein, carbohydrate and the remainder minerals. When the oil is removed the remaining product is higher in protein and other nutrients.
Soybean meal is a familiar example of this. It is a valuable source of concentrated protein high in lysine. It is actually safer to feed than whole soybeans because heat processing destroys factors in soybean that can interfere with protein digestion.
Corn gluten meal is a very high protein feed, typically about 60%. It is not as good a source of lysine as soy, and arginine may not be optimal, but it is a highly digestible protein source. Corn gluten meal also contains very high levels of the xanthophyll pigments lutein and zeaxanthin which are antioxidants very important in eye health.
Distillers/Brewers Dried Grains are produced after corn, sorghum or other grains are used to make beer or other alcoholic beverages. The grains are ground, added to hot water and combined with yeast to ferment the starch content to ethanol. This produces a feed that is very safe for insulin resistant horses because the starch has been fermented. It is high protein, highly palatable and even has probiotic properties from the Saccharomyces yeast fermentation products.
There are even things you would never suspect at first glance have high nutritional value, like soy hulls. Soy hulls are very low fat, sugar and starch but high in easily fermented soluble fiber. Protein is good at 10%. They are so fermentable they actually provide more safe calories than beet pulp or oats. Soy hulls are also very palatable.
Not all by-products are suitable for horses. Oat hulls are very poorly fermented and would be little more than a filler. Cottonseed products should be avoided because of the potential for toxic gossypol. Also avoid ingredients that are nonspecifically listed as “products”, such as forage products or protein products.
The point here is that by-products are not wastes or floor sweepings. (Just for the record, they never hit the ground either!) They are real foods, like skinless chicken, peeled fruit or low fat milk. Their use is also supported by actual feeding trials, not just chemical analysis. When you hear by-product, don’t automatically discount them.
Eleanor M Kellon, VMD