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Q: I have heard there are differences in the effect of various milling by-products like distillers' grains and wet corn gluten feed in helping with acidosis in feedlot cattle. Can you explain some of the differences?

A: First it would be useful to give some brief background information on what causes acidosis in feedlot cattle. Generally speaking, acidosis in feedlot cattle is caused by rapid consumption of high-starch (i.e. high-grain or "hot") diets. Because starch is rapidly fermented in the rumen, the fermentation end-products and organic acids are produced at a rate faster than they can be removed from the rumen. This causes an accumulation of these organic acids in the rumen which leads to a decrease in rumen pH. It is thought that this leads to a condition that can be best described to be like heartburn, which can cause feed intake to decrease substantially. When the acidotic event subsides and the cattle begin feeling better, they are usually very hungry because they have not eaten much over the last day or two and will again consume a large meal that can lead to another acidotic event, which will in turn lead to reduced intake again. This cycle repeats itself and is the reason that large day to day variability in feed intake is indicative of acidosis. Good bunk management practices are the best way to prevent acidosis, but grain milling by-products can also help. In general, corn milling by-products do not completely prevent acidosis in feedlot cattle, but cattle fed diets high in milling by-products seem to be less susceptible to acidosis. This is because nearly all of the starch has been removed in grain milling by-products and therefore they have a higher content of fiber than the grain they were made from. It appears that wet corn gluten feed is better at alleviating acidosis than distillers' grains, and this difference is most likely due to differences in size of the fiber particles in the two products. Wet corn gluten feed generally has a greater particle size and therefore may be retained in the rumen longer than distillers' grains. This is important because fiber is digested more slowly in the rumen than starch and its presence will decrease the overall rate of ruminal digestion. This will lead to a slower accumulation of organic acids in the rumen and thus a reduction in acidosis. Other concepts have not been thoroughly studied, but may be important. In short, it appears that the "effective fiber" content of corn gluten feed is greater than that of distillers' grains and thus it is better suited to help with bunk management. Generally speaking however, distillers' grains contain more energy than corn gluten feed, and local supply may dictate which by-product is most economical to use in any particular situation regardless of any potential effects on acidosis.