Heat-Damaged Protein Supplements and Amino Acid Nutrition

A common way of measuring heat damaged protein is to analyze a feedstuff for acid detergent insoluble nitrogen (ADIN). This measures the amount of nitrogen that is bound to the indigestible part of the feed. ADIN is then used to calculate the bound or unavailable protein. As ADIN increases in a forage, the protein digestibility decreases. There is always a portion of the crude protein that is unavailable but that percentage will increase if heating has occurred. Forages with a ratio of bound protein to crude protein of over 12% have experienced significant heating and the available protein value should be used to formulate rations.

The ADIN analysis is widely accepted as a good measure of heat damage in forages. It does not, however, appear to be a good measure of heat damage in non-forage protein sources such as dried distillers grains (DDG). Both animal research and laboratory work shows very little correlation between ADIN and protein digestibility. In fact, with non-forage protein supplements, heating appears to increase their value. Undoubtedly, severely damaged DDGs have lower feeding values but this type of damage does not occur routinely. At this time, animal digestion trials appear to be the only means of determining protein damage in non-forage protein sources. Until a laboratory procedure is developed, good judgement and use of past experience with a protein source is recommended.

In DDG, a darker color is often associated with a higher ADIN but keep in mind that color is also related to the type of grain the DDG comes from. DDG from wheat will have a darker color than DDG from corn.

Amino Acids Typically Lacking in Manitoba Diets

Typical Manitoba diets can be low in many different amino acids. Alfalfa and barley based diets are likely to be most deficient in histidine and leucine. After these, lysine appears to be most limiting.

Suggested Protein Supplements

Keep in mind that estimates of amino acid supply to the small intestine are based on very complex biological processes. Every amino acid has at one time been shown to be the most limiting amino acid. To cover all your bases, feed several different protein supplements. Canola meal is a better source of histidine than SBM. If your ration consists of corn silage and corn grain, do not choose a corn based protein supplement as your main protein supplement.

For further information contact:

Karen Dupchak
Farm Production Extension, Animal Nutritionist
Manitoba Agriculture Food, and Rural Initiatives
204-545 University Crescent
Winnipeg, MB R3T 5S6
Phone: 204-945-7668
Fax: 204-945-4327