David L. Morris: Vet Column 7-25-11
Increasing the amount of dried distillers grains in the diet of feedlot cattle results in an increased concentration of sulfur and as a result, an increased risk for polioencephalomalacia, more commonly known as polio. The production of hydrogen sulfide gas when hydrogen and sulfur combine in the rumen and subsequently absorbed through the rumen wall is thought to be the primary cause of polio. Generation of hydrogen sulfide gas may be increased when rumen pH is low and more hydrogen ions are available.
Ionophores, such as monensin, increase trace mineral absorption and are associated with a decrease in available hydrogen. Feeding haylage also decreases the available hydrogen in the rumen because it stimulates increased salivary buffering by adding bicarbonate to the rumen to neutralize excess acid. What if feedlot cattle were fed monensin and haylage along with dried distillers grains? Would it decrease the potential for developing polio? Investigators from The Ohio State University recently published data evaluating this potential alternative when feeding feedlot cattle.
Using 168 Angus-cross steers weighing approximately 610 pounds and randomly divided into 24 different pens, four dietary treatments were administered. Treatment one involved adding no monensin or any haylage to the basic ration provided. Treatment two consisted of adding 15 mg monensin per pound of diet and zero haylage. Treatment three consisted of zero monensin and 10 percent haylage. Treatment four consisted of 15 mg monensin per pound of diet and 10 percent haylage. The remainder of the diet consisted of 60 percent dried distillers grains, 10 percent corn silage, 15 percent supplement, and 5 to 15 percent corn on a dry matter basis.
Adding 10 percent haylage to the basic ration increased average daily gain by 5.7 percent. If 15 mg monensin per pound were added to the 10 percent haylage, average daily gain increased by 13 percent. Adding haylage increased dry matter intake, but it also decreased feed efficiency. Adding haylage increased final body weight as well. These diets did not affect mineral concentrations. There also was no effect on carcass characteristics.
In this study, haylage inclusion did not allow as much acid or hydrogen ion amounts to build up in the rumen. Adding monensin provided even less acid build up in the rumen. As a result, there was less hydrogen sulfide gas in the rumen when monensin was added to the diet.
Dried distillers grains with solubles can be included in cattle diets at 60 percent of the ration on a dry matter basis. Adding forage will improve intake and growth rate. When fed with haylage, monensin increased final body weight and average daily gain. Feeding monensin alone did not affect final body weight or growth rate.
When feeding dried distillers grains, increased rumen acidity is a concern. In this study, it appeared the lowered pH may be due to the sulfuric acid contained in the dried distillers grains rather than from ruminal short-chain fatty acids metabolized in the rumen. Monensin supplementation decreased hydrogen sulfide gas concentration and may decrease the risk of polio for cattle fed high dried distillers grains diets.