Research from the University of Illinois is helping to determine the quality of protein in wheat middlings and red dog -- two co-products of the wheat milling process that can be included in diets fed to pigs and other livestock.

Red dog consists mainly of the aleurone layer that lies between the bran and the endosperm, along with small particles of bran, germ and flour. Wheat middlings are granular particles of the wheat endosperm, bran and germ that contain about three times as much dietary fiber as red dog.

"We have information about the digestibility of crude protein in some wheat co-products produced in Canada and China, but only very limited information about the nutritional value of wheat middlings and red dog produced in the U.S.," said Hans H. Stein, professor in the University of Illinois department of animal sciences. "In addition, because wheat co-products vary in terms of the conditions under which they are produced, their nutritional value may vary as well."

Stein and doctoral candidate Gloria Casas procured wheat middlings from 10 suppliers in Colorado, Iowa, Illinois, Kansas, Michigan, Minnesota, Ohio and Pennsylvania, along with red dog from a supplier in Iowa, and fed them to growing pigs.

Despite the variety in the sources of wheat middlings, the concentration and standardized ileal digestibility (SID) of crude protein were generally consistent. However, there was variation in the digestibility of most amino acids among the sources of wheat middlings, Stein and Casas said.

Red dog contained slightly less crude protein than wheat middlings: The mean protein concentration was 17.67% for the wheat middlings samples and 17% for red dog.

However, the SID of crude protein and all but three amino acids — arginine, histidine and serine — was greater in red dog than in wheat middlings.

According to Stein, "The SID of amino acids is probably greater in red dog because it contains less fiber compared with wheat middlings. It's also possible that excessive heat was used in the processing of the wheat middlings, causing heat damage."

The SID of lysine, the amino acid most susceptible to heat damage, was 72.3% in red dog but averaged only 46.2% in wheat middlings.

Stein said the results of this study provide guidance to producers who hope to incorporate wheat co-products into diets fed to pigs.

"The amino acids in red dog are well digested, so there should be no problem with incorporating them into swine diets," he said. "However, we would advise anyone feeding wheat middlings to add crystalline amino acids or other protein sources so that the diet will have sufficient digestible amino acids."

The paper, "The Ileal Digestibility of Most Amino Acids Is Greater in Red Dog Than in Wheat Middlings When Fed to Growing Pigs," appeared in the June 2017 issue of the Journal of Animal Science. The National Pork Board provided funding for the study.