The nutritional quality of grazed corn residue is quite high early in the grazing period—approximately 70% TDN and 8% crude protein—but then gradually decreases over time to approximately 40% TDN and 5% crude protein. This reduction is a result of the cattle selecting the highest quality feeds first and a weathering, or leaching, of nutrients from the residue over time. Cattle will first consume any grain that remains in the field. Then they will shift their preference to leaves and husks and finally cobs and stalks.
As the nutritional quality of the corn residue decreases, producers will need to provide supplemental protein. The microbial population requires rumen-degradable protein sources, commonly found in plant proteins, to effectively digest fiber. Non-protein nitrogen sources, such as urea and biuret, should be avoided. These nitrogen sources require the presence of readily fermentable carbohydrates to be utilized effectively. Unfortunately, once the grain has been consumed, the residue is essentially devoid of readily fermentable carbohydrates.
To determine when supplementation is necessary, producers should watch the manure from the cows. As the corn in the manure begins to disappear, it is time to begin protein supplementation. Generally mature, pregnant beef cows should receive 0.5 to 1 lb of supplemental protein from a natural source. Common protein sources include alfalfa, oilseed meals, and various alternative feeds. Commercial protein supplements are also acceptable.
Corn residue is also quite low in most minerals, especially calcium, phosphorus, and vitamin A. As a result, a well-balanced vitamin and mineral mix should be provided free choice. Keep in mind that many of the feeds used as protein supplements will provide significant amounts of calcium and/or phosphorus and may reduce the need for additional supplementation. However, vitamin A and white salt should be provided at all times.
