Lowering feed costs without altering production can increase dairy producers’ profitability. Nutritionists or dairy producers may be looking for alternative feed sources to reduce feed expenses.
Corn-dried distillers’ grains with solubles are widely available in the U.S. as a feed ingredient for livestock animals. Because corn-dried distillers’ grains contains high protein (30 to 40% crude protein of dry matter), it can be a good protein feed as a substitution for soybean meal. Although the prices of corn-dried distillers’ grains and soybean meal change, usually corn-dried distillers’ grains is much cheaper than soybean meal. Currently, corn-dried distillers’ grains was $240/ton while soybean meal was listed at $443/ton (May, 2023; USDA).
For significant decreases in feed costs and increases in the income over feed cost, 20% or more in a ration on a dry matter basis by replacing mainly soybean meal is necessary if production doesn’t change. However, according to research, negative production responses are somewhat consistent when diets containing 20% corn-dried distillers’ grains or more (dry matter basis) were fed. Among the negative production responses, milk fat depression is the one often significantly impaired by corn-dried distillers’ grains. Therefore, the inclusion of corn-dried distillers’ grains at 20% or more (dry matter basis) in a ration has not been recommended for lactating cows.
As a factor of corn-dried distillers’ grains causing milk fat depression, high-fat content (about 10% on a dry matter basis) in corn-dried distillers’ grains has been recognized. The fat of corn-dried distillers’ grains includes high polyunsaturated fatty acids, which has been known to depress milk fat synthesis in the mammary glands.
However, the polyunsaturated fatty acids from corn-dried distillers’ grains may not be the only factor causing milk fat depression. In our previous study, low-fat corn-dried distillers’ grains (about 6% fat on a dry matter basis) was used in a ration (30% on a dry matter basis) and we still observed milk fat depression. From that experiment, however, we found that the diet with low-fat corn-dried distillers’ grains contained sulfur (0.4%) twice as high as the soybean meal diet (0.2% on a dry matter basis).
Sulfur concentration in corn-dried distillers’ grains is relatively high compared to soybean meal; therefore, replacing soybean meal with corn-dried distillers’ grains in a diet increases dietary sulfur concentration. Excess sulfur decreases dietary cation-anion difference; therefore, adding corn-dried distillers’ grains to a diet decreases dietary cation-anion difference.
Typically, dietary cation-anion difference is about 200 mEq/kg dry matter for a lactating diet if the diet is formulated to meet all minerals. However, a diet containing 20 to 30% of corn-dried distillers’ grains (dry matter basis) reduces dietary cation-anion difference below 100 mEq/kg dry matter. Because milk and fat yields and nutrient digestibility are positively correlated with dietary cation-anion difference, high sulfur in corn-dried distillers’ grains could be another factor causing milk fat depression in lactating cows. If it is true that sulfur is another factor causing milk fat depression, eliminating this factor should alleviate the negative response to feeding a high corn-dried distillers’ grains diet.
In our first experiment, we examined a diet with 20% high protein corn-dried distillers’ grains with and without increasing dietary cation-anion difference with a soybean meal-based control diet. The inclusion of corn-dried distillers’ grains decreased dietary cation-anion difference from about 200 to 60 mEq/kg dry matter. We added cation supplements (sodium bicarbonate and potassium carbonate) to increase the dietary cation-anion difference of the corn-dried distillers’ grains diet up to 200 mEq/kg dry. We found that the corn-dried distillers’ grains diet decreased milk yield (88 v. 92 pounds) and milk fat yield (2.73 v. 3.41 pounds) compared with the soybean meal diet. However, the corn-dried distillers’ grains diet with increased dietary cation-anion difference eliminated the difference statistically (milk yield, 89 v. 92 pounds; milk fat yield, 3.15 v. 3.41 pounds). Therefore, we concluded that a high corn-dried distillers’ grains diet with increased dietary cation-anion difference can alleviate negative production. However, milk yield and milk fat yield for cows on the high corn-dried distillers’ grains diet were still numerically lower when compared with the soybean meal diet.
In our second experiment, we examined a diet with 30% corn-dried distillers’ grains with increased dietary cation-anion difference up to 300 mEq/kg dry matter compared with a soybean meal diet (180 mEq/kg dietary cation-anion difference). In this experiment, the corn-dried distillers’ grains diet did not affect milk yield but decreased milk fat yield (2.73 v. 3.15 pounds) compared with the soybean meal diet. However, the corn-dried distillers’ grains diet with increased dietary cation-anion difference completely eliminated the difference in milk fat yield (3.23 v. 3.15 pounds). According to the current feed and milk prices, the corn-dried distillers’ grains diet largely increased the income over feed cost ($11.36 v. 9.65/cwt) compared with the soybean meal diet. Therefore, although more studies are needed to confirm our results, increasing the dietary cation-anion difference of a diet containing high corn-dried distillers’ grains (> 20%) up to 300 mEq/kg dry matter is a potential strategy to reduce the feed cost and increase the income over feed cost.
