Research finds dairy cow diets could safely include more DGs
South Dakota State University research shows distillers grains (DGs) can comprise up to 20 percent of the diets (on a dry basis) for lactating dairy cows without negatively affecting milk production. Most dairy farmers currently use only about 10 percent of the ethanol coproduct in rations.
“Farmers tend to think that if they include distillers grains up to 20 percent they will see milk fat depression, but in our research, we could see that it is not the inclusion of distillers grains—it is the low level of forage in diets that causes the depression,” said SDSU doctoral student Sanjeewa Ranathunga.
In order to reach his conclusion, Ranathunga, under the guidance of associate professor Ken Kalscheur, conducted a series of experiments aimed at identifying the dietary impacts of replacing corn with up to 18 percent distillers grains. The researchers evaluated diets containing varying percentages of distillers grains and forage (alfalfa and corn silage) on milk production, ruminal nutrient degradability and feed- sorting behavior. The research concluded that it is the percentage of forage in diets, not the percentage of DGs, which can potentially negatively impact all areas studied. In order for DGs to be digested properly in the rumen, for example, Ranathunga found that high forage diets are best. When evaluating the feed sorting behavior of cows, the amount of DGs was found to have no impact on their behavior. Rather, the cows chose to eat the feed differently depending on the amount of forage included in the diet. In low-forage diets, the cows sought out forage, but in diets containing high levels of forage, the cows sorted for concentrates.
Kalscheur noted that the digestibility of diets containing DGs is very important for dairy farmers because the rumen function affects milk composition. If rumen function is altered significantly, it can negatively impact the percentage of milk fat and protein in milk. Those two components are the most valuable for producers, so a reduction in both, or either, could cut into their bottom line. The good news for dairy producers, and consequently ethanol producers, is that the SDSU research shows that not only can DGs be used at higher percentages than previously thought without impacting milk production; dairy farmers can also cut feed costs by more than $1 per cow per day by substituting DGs for corn at about 20 percent of the diet. Considering the high price of corn in recent history, the researchers expect dairy farmers will appreciate the economic benefits of DGs once they are assured that the product can be safely used at those inclusion rates. Kalscheur said one caveat to the equation, however, is that nutrient composition of DGs can vary considerably and dairy producers need to be aware of its nutrient composition in order to properly formulate diets and ensure that DGs can be used in greater amounts.
Ranathunga was recently recognized for his research by the Midwest branch of the American Dairy Science Association, which presented him with the Young Dairy Scholars Award during the group’s annual meeting. Ranathunga is currently working to complete his dissertation on the subject of DGs in dairy cattle diets and plans to publish several papers detailing his findings in the near future.