Truth or fallacy: cattle cannot digest whole shelled corn?

Can cattle digest whole shelled corn? To answer this question, we must first have a basic understanding of corn kernel composition and how it travels through the ruminant digestive tract. Relative to other cereal grains, corn is made up of a greater percentage of starch, which is found in the endosperm. A corn kernel contains 60 to 90% starch depending on the variety of corn. During ruminant digestion, starch is fermented into volatile fatty acids (VFA) in the rumen, and to a lesser degree in the large intestine. Starch is digested into glucose in the small intestine to provide the animal with energy. The starch granules inside the corn kernels are protected by a protein matrix and further protected by a thick multi-layered fibrous shell, called the pericarp, that surrounds the entire corn kernel. In order to access and breakdown the starch from inside the corn kernel, the rumen microbes (i.e., bacteria, protozoa, and fungi) and other digestive enzymes must be able to penetrate the fibrous pericarp and protein matrix that protects the starch contained inside of the corn kernel. For ruminal digestion of the starch from an intact corn kernel to occur, the pericarp of the corn kernel must be damaged by either chewing or some type of grain processing, including grinding, rolling, steam-flaking, ensiling, or tempering. 

Research from The Ohio State University set out to answer questions about the digestion of whole shelled corn when fed to beef cattle. Published in the 2005 article, “Effect of cattle age, forage level, and corn processing on diet digestibility and feedlot performance”, by the Journal of Animal Science, the study investigated factors such as animal age, forage level in the diet, time on feed, and grain processing on feedlot cattle performance and starch digestibility.  

Younger calves have been known to chew their feed more frequently than their older counterparts, but this may be because they are less efficient at reducing the particle size of their feed. Therefore, one might expect for younger calves to digest whole shelled corn more efficiently when compared with older calves. However, recently weaned cattle or yearling steer calves did not demonstrate any difference in their ability to digest whole shelled or ground corn provided at 80% of the finishing diet. Further analysis of the manure indicated that only 8 to 9% of the whole shelled corn kernels remained and the age of steers did not influence the digestibility of the starch being consumed.  

According to the 1994 article, “Effects of mastication on digestion of whole cereal grains by cattle”, by the Journal of Animal Science, has shown eating rate can also influence the effectiveness of whole shelled corn being chewed when cattle are limit-fed compared with being full-fed eating as much as they want, as limit-fed cattle eat faster than full-fed cattle. However, cattle that spend more time eating and chewing need to spend less time ruminating, while cattle that spend less time eating and chewing initially, spend more time ruminating to reduce feed particle size. Therefore, differences observed in whole shelled corn digestibility compared with other dry corn processing methods may be largely due to the animal’s ability to effectively chew or re-chew the whole shelled corn kernel. 

The forage to grain ratio of cattle diets can greatly affect the digestibility of the various components, such as protein, starch, fiber, fat, and the total diet itself. Certain rumen microbial communities are better suited to digest either forage- or grain-based diets. Additionally, the inclusion of forage in cattle diets increases digesta passage rate which reduces the amount of time digesta can be digested in the digestive tract. In the case of cereal grains, as grain particles become denser, they sink from the rumen to the reticulum where they continue through the remainder of the digestive tract. For finishing diets, forage is often included to maintain digestive tract health and prevent digestive upsets such as acidosis and bloat. This allows the energy density of the diet to be maximized for a greater growth response. It was hypothesized that because a greater level of forage in the diet increases passage rate, that forage level may negatively affect the starch digestibility and feedlot performance of cattle fed whole shelled corn compared with processed corn.  

To test this, corn silage was fed at either 5 or 18% on a dry matter basis of the finishing diet and corn was either cracked or left as whole shelled corn. An interaction was observed, where steers fed 5% corn silage with whole shelled corn had the greatest average daily gain (ADG) during the beginning of the finishing period. Feed intake was also greatest for steers fed cracked corn compared with whole shelled corn, but particularly with 18% corn silage compared with 5%. Interestingly, steers that required a different number of days on feed because they entered the feedlot at different body weights resulted in different ADG and feed efficiencies when fed either whole shelled corn or cracked corn. Steers that were heavier at feedlot entry and required fewer days on feed had an ADG of 4.1 lb/d compared with lighter weight steers at feedlot entry that had a 3.5 lb/d ADG and required more time on feed when fed cracked corn. Both groups had similar gain to feed ratios. However, when fed whole shelled corn, light weight steers at feedlot entry that required more days on feed had a 3.6 lb/d ADG, which was similar when compared with heavier weight steers at feedlot entry that required less time on feed and had an ADG of 3.9 lb/d. Steers that were lighter weight at feedlot entry had a greater gain:feed ratio of 0.21 lb gain/lb feed compared with 0.19 lb gain/lb feed for heavier weight steers at feedlot entry when fed whole shelled corn. The reduced performance for steers consuming processed corn may be due to the long-term exposure of enhanced ruminal starch fermentation, which could increase the chance or frequency of acidosis occurring and comprise the rumen’s ability to efficiently absorb nutrients. 

Starch digestibility was similar between cracked and whole shelled corn diets with no interaction between forage level and corn processing. Less than 2% of the whole shelled corn kernels were found in the manure from steers consuming either the 5 or 18% corn silage finishing diets. Interestingly, neutral detergent fiber (NDF) digestibility was greater for the 18% corn silage diet compared with the 5% corn silage diet when whole shelled corn was fed, while NDF digestibility was similar between the two different forage levels when cracked corn was fed. Due to greater chewing and salivation when fed whole shelled corn, feeding whole shelled corn compared with processed corn may prevent the rumen pH from decreasing to a level that is unsuitable for a microbial community that is designed to break down forage and fiber.  

Overall, ADG, feed efficiency, and starch digestibility of the corn being fed to feedlot cattle did not differ when fed as whole shelled corn or dry processed corn, regardless of the small appearance of whole corn kernels present in the manure. Therefore, grain processing costs do not appear to be justified without an increased response in feedlot performance and or carcass quality. Whole shelled corn may be more appropriate for low forage finishing diets to help buffer the rumen with additional saliva and prevent the rumen from experiencing a greater and/or more frequent occurrence of acidosis or ruminal damage due to a low pH. In conclusion, research has proven that cattle can digest whole shelled corn.