Interpretive Summary: Increasing dietary proportion of heat grain in finishing diets containing distillers’ grains: impact on nitrogen utilization, ruminal pH, and digestive function 

By: Dr. Emily Taylor

The use of Dried distillers’ grains with solubles (DDGS) in ruminant diets has increased drastically over the last ten years. This alternative feed resource offers a product that is very high in crude protein (CP). Unfortunately, when trying to achieve a dietary inclusion concentration that lowers feed costs, overfeeding DDGS is an easy occurrence. This results in the ruminal loss of ammonia-nitrogen being excreted as urea-N in the urine. In addition, increasing the fermentable energy supply can enhance ruminal use of N; however, it also may lead to acidosis, which can compromise digestive function and animal performance. Therefore, the objective of this study was to examine the effects of partially replacing dry-rolled corn grain with 20- or 40% dry-rolled wheat grain in finishing diets containing 15% corn DDGS on nutrient intake and digestion, ruminal fermentation characteristics, measures of N utilization, and blood metabolites. 

Dietary treatments were either corn (73% of diet DM; CON), 53:20 corn: wheat blend (20W), or 33:40 corn: wheat blend (40W) as the major fermentable energy source. Dry matter intake was lower for heifers fed the 40W when compared to the CON and 20W treatments. An increase in NDF was seen in the wheat grain diets compared to the CON; however, there was no effect on apparent total tract DM and NDF digestibility. A mean and minimal pH decreased, pH duration increased, and a tendency for an increase in the area and acidosis index for pH when feeding wheat grain. Nitrogen intake did not differ among treatments. There was no effect on ruminal ammonia-nitrogen concentration and estimated microbial N flow; however, feeding wheat-containing diets did decrease the urine urea-N excretion. Although, fecal and total N excretion did increase with the addition of wheat grain. Apparent N retention was lower for the 40W heifers when compared to the other treatments. 

In conclusion, while some parameters did show desirable results, feeding wheat grain in corn DDGS-containing diets increased the acidotic conditions in the rumen and maybe the reason for the reduced DMI in the 40W heifers. In addition, the harmful apparent N retention for heifers of the 40W treatment also suggests a decrease in nutrient supply which could decrease feedlot performance. Authors suggest more research is needed to evaluate N transactions across the portal drained viscera, anabolic use of recycled urea-N, and growth performance and carcass characteristics.

This article is available in the Journal of Animal Science.