According to Normand St-Pierre, Ohio State University animal science professor, the best way to determine the composition for localized by-products is to get the information from the manufacturer.
In an article in Dairy’s Bottom Line, a publication of the Professional Dairy Producers of Wisconsin (PDPW),
St-Pierre lists the following as important composition items, but notes that not all will be used for every by-product: main nutrients, percent dry matter, crude protein, fat, ash (sum of all the minerals), NDF (neutral detergent fiber), lignin, ADF bound nitrogen for roughage, degradable and undegradable protein estimate and effectiveness of fiber.
Source: Integrating Alternative Feed Into Rations, article by Sarah Young, January 2009 issue of Dairy’s Bottom Line (PDPW). Normand St-Pierre, Ph.D., P.A.S., Professor at The Ohio State University, is one of the PDPW’s Annual Business Conference’s featured speakers.