By Phillip Lancaster
In the last decade corn ethanol co-products have replaced a large portion of corn in diets of growing and finishing cattle due to availability and price. However, the price of corn has decreased considerably in the last year making it a cost-effective feedstuff in cattle diets again. A recent study evaluated replacing modified distillers grains with solubles with dry rolled corn in high roughage growing diets. Additionally, the study compared brome hay: sorghum silage with baled corn stalks as the forage source in the diet.
The study used 120 individually-fed steers weighing 620 lb at the start of the study. The steers were fed for 84 days and growth, feed intake and feed efficiency were measured. The diets consisted of 56% forage, 40% a combination of distillers grains and dry rolled corn, and 4% supplement. The main part of the study was to evaluate replacement of modified wet distillers grains with dry rolled corn. There were 4 diets with modified distllers grains at 40, 32, 24, and 16% of the diet dry matter. Dry rolled corn was then included at 0, 8, 16, and 24% of the diet dry matter. As distillers grains decreased in the diet and dry rolled corn increased, there was a linear decrease in gain and feed efficiency such that steers on all diets at the same amount of feed but gained differently (Figure 1).
A probable reason for the decreased gain of steers fed more dry rolled corn could be the decrease in protein in the diet. The protein was 17, 15, 13, and 12% for diets with 40, 32, 24, and 16% distillers grains. In the diets with 24 and 16% distillers grains, urea was added to maintain protein levels at 12%. All diets were evaluated using a nutrition model and results indicated that all diets met requirements for metabolizable protein; however, true protein from distillers grains and microbial protein synthesis from urea may not have been equivalent.
The second part of the study was to evaluate brome hay: sorghum silage versus corn stalks as the forage source in the diet. The brome hay: sorghum silage had crude protein of 7.8%, neutral detergent fiber of 67% and digestibility of 54% compared to 4.0%, 77%, and 49% for the corn stalks indicating that the corn stalks were of lesser nutritional value. The corn stalks were included at 56% of the diet dry matter; the same as the brome hay: sorghum silage such that diets with corn stalks likely had lesser net energy for gain values. Steers fed corn stalks gain 1.76 lb/day compared to 2.89 lb/day for steers fed brome hay: sorghum silage. Interestingly, feed efficiency was the same between forage sources indicating that the lesser gain of steers fed corn stalks was due to lesser feed intake, and not necessarily lesser digestibility of the diet.
In conclusion, when dry rolled corn replaces large amounts of modified distillers grains in forage-based growing diets, a true protein source like soybean meal may need to be added to the diet. Replacing brome hay:sorghum silage with corn stalks may decrease feed intake and growth in backgrounding diets.
