Distillers grains (DG) are without a doubt one of the most versatile ruminant feedstuffs. Aside from their high concentration of sought-after nutrients (i.e. protein, energy, phosphorus), their impact on the digestibility of other feeds is minimal. In fact, by not interfering with the digestion particularly of structural carbohydrates, they allow for more energy to be obtained from forages. This was corroborated through research conducted at the Dairy and Food Science Department at South Dakota State University. In these experiments, diets for growing heifers and lactating cows with the same protein and energy content, had higher feed efficiency as distillers’ grains in the diet increased from 0 to 30 percent.
When fed to young calves during their first sixty days of life however, efficiency increased up to 28 percent DDGS in the concentrate, then decreased when at 56 percent DDGS. This experiment consisted of three diets (Control, 28 percent DDGS, and 56 percent DDGS) with exactly the same protein (22 percent) and energy (2.1 and 1.6 NEm and NEg, respectively) concentration. There was a difference in ether extract (EE) (2.9, 5.1, and 7.3 for Control, 28 percent and 56 percent DDGS, respectively) result of the higher oil in full-fat DDGS. It is highly unlikely however that diets with a maximum of close to 7 percent oil (Table 1) will cause feed efficiency differences, since the development of the rumen at that age is limited.
Table 1. Nutritional Composition
Recent research elsewhere (Ma et al. 2017), has shown that the fiber (NDF)
to starch ratio in the diet, affected the growth of rumen
papillae in lactating dairy cows. This is significant since these tiny structures determine how much energy the ruminant will obtain from feed fermentation. In that study as the fiber to starch ratio increased, the expression of the gene regulating the growth of papillae decreased. The SDSU study found something similar, the papillae in diets with approximately 20 and 25 percent NDF were shorter (0.19 vs 0.25 cm in the diet with no DDGS). However, there were more papillae per unit of surface in the diets that contained DDGS (75.4 pap/cm2 vs 117 and 98.7 pap/cm2 with 28 and 56 percent DDGS, respectively). This difference between size and density resulted in no differences between dietary treatments in total papillae surface area.
Figure 1. Rumen papillae.
Three sets of rumen papillae photos. The first is labeled C and has several clusters of large, round, papillae. The second is DG1 and has several clusters of small to medium, round, papillae. The last is DG2 and has several clusters of small to medium, round, papillae.
As expected, methionine concentrations improved as DDGS in the diet increased. Lysine content on the other hand, was reduced by 28 and 50 percent between the control and the 28 and 56 percent DDGS diets, respectively. It is likely then that the further decrease in feed efficiency observed between 28 and 56 percent DDGS concentrates resulted from an amino acid deficiency, rather than the effects of the fiber to starch ratio on papillae growth. When DDGS in the concentrate exceeds 30 percent in diets for growing ruminants, there is a need to supplement with protected lysine to improve feed