Nutrient Composition of Unprocessed Grains and Processed Grains

Nutrient composition of commercial corn grain appears to have changed little in the last 10 to 15 years. Although the data for sorghum grain and barley are more limited, no dramatic changes in nutrient composition were apparent. Flaking corn appears to reduce the crude protein concentrations, perhaps because water used for starch gelatinization is not released during drying. Harvesting and storing corn grain as high-moisture increases the protein solubility and rumen degradation of corn grain protein. In contrast, flaking corn decreases protein solubility and ruminal protein degradation. Flaking corn may increase phosphorus availability by increasing ruminal phytase activity. INTRODUCTION Nutrient composition of grains can be quite variable. Although the variation is less with grains than with forages or byproduct feeds, grains comprise the majority of most feedlot diets so small changes in nutrient composition become very important. The sources of variation in nutrient composition can be divided into processing and nonprocessing factors. Most of the processing effects relate to energy value of the grains. Because several speakers have discussed how processing variables affect the energy values of different grains, that topic will not be discussed here. Effects of processing on protein and mineral availability will be discussed later. NON-PROCESSING VARIATION Non-processing factors that can affect the nutrient composition of grains include, but are not limited to, year, variety, fertilization, and management factors. In the last 10 to 15 years grain producers have made substantial changes in varieties (genetics), fertilization programs, and management practices. This review will examine whether such changes have altered grain composition. Grain nutrient composition data collected for the 1996 Beef NRC publication (NRC, 1996) were from grains produced in the early 1990s. Data were collected from approximately 40 different laboratories in North America. Grain samples from most states and Canadian provinces were included in that database. The Dairy One feed analysis laboratory in Ithaca, New York provides excellent public access to a database that can be used to examine nutrient variation. This laboratory receives grain samples from throughout the United States and Canada. These data have not been screened to remove outliers, so the standard deviations are greater than found in other data sources. The Dairy One data base is robust because it contains a large number of samples analyzed for many nutrients that were received between May 2000 and June 2006. All nutrients are expressed on a dry matter basis and can be accessed at http://www.dairyone.com/Forage/FeedComp/disclaimer .asp. Through comparing the nutrient composition data from the 1996 Beef NRC and the current Dairy One database, large changes in nutrient profile over the last 10 to 15 years can be detected. Corn is the primary grain fed to cattle and has the largest number of samples in the data base. With over 3500 samples in both data sets, corn in the Dairy One data set averaged 9.51% crude protein; in the early 1990s corn averaged 9.80% protein (Table 1). Whether this is a trend or just random variation, is impossible to determine. However, when we select corn varieties for increased yield or alcohol production, a decrease in protein concentration would not be surprising. Based on more than 2200 samples, corn NDF values also have tended to decrease (10.8% vs. 9.78%) during the past 15 years. Since most of the fiber is in the seed coat, it is possible that as we select for increased yield, kernel size could increase resulting in the seed coat being a smaller fraction of the weight.