Poor harvest year may alter US corn quality

The US produced a bumper corn crop last year, but wet conditions during part of the growing season and harvest may have impacted its overall nutritional value, according to the Poultry Science Association (PSA).

In addition, nutritionists who rely on bushel weight as a prime factor for assessing quality may be missing an important part of the quality-evaluation picture, said PSA.

"Adverse growing conditions and the potential for reduced bushel weight are one component of the corn quality equation. Unfortunately, determining a precise relationship between variability in bushel weight and the nutritional value of corn is problematic," said Mike Lilburn, a poultry nutritionist in The Ohio State University's Department of Animal Sciences.

In a given harvest year, the presence of poor growing conditions is often reflected in variations in the bushel weight or test weight of corn. A common measure used for pricing purposes, bushel weight represents a composite of factors affecting bulk density and assumed quality of the grain.

The standard bushel weight for No. 2 Yellow corn is 56 pounds per bushel, but for years like 2009, with significant variability in the growing season, much of the corn coming out of the field may be well below this industry standard. Drying the corn, a process which takes place after harvest, can increase bushel weight, but the drying process may have other effects on the overall feeding value of the crop.

According to Lilburn, nutritionists have long been aware of the variability in commodity grains and use routine analytical testing (moisture, fat, protein, etc.) to adjust their nutrient matrix values accordingly. These analytical tests, however, do not reflect what nutritional value the animal actually derives from a particular ingredient.

Corn harvested with above average moisture content may require more extensive drying prior to storage. According to Lilburn, the drying conditions, particularly the drying temperature, may contribute to quality issues.