First, the residual component of feed and residual use appears to vary considerably from year to year. This is illustrated by the variation in the magnitude of feed and residual use per unit of livestock production. 

The USDA estimates the number of grain consuming animal units for each corn marketing year. That estimate is based on an estimate of the number of animals fed by species, weighted by the amount of grain required per animal in each species.

In the previous six years, the estimate of grain consuming animal units has ranged from 91.6 million to 95.5 million and the magnitude of feed and residual use of corn per animal unit has ranged from 47.1 to 61.9 bushels. 

Some of the variation in feed and residual use of corn per grain consuming animal unit is explained by the variation in the magnitude of feed and residual use of other grains, particularly wheat. Still, the magnitude of feed and residual use of all grains per grain consuming animal unit has varied by 20 percent over the past six years. 

The USDA acknowledges this variation and attributes much of the variation to crop size, with larger residual use associated with large crops and vice versa. The large variation illustrates the difficulty of anticipating quarterly feed and residual use of corn based on estimates of the number of livestock fed during the quarter.

A second reason for the difficulty in anticipating the magnitude of quarterly feed and residual use of corn is that apparent use during any particular quarter has varied substantially more in recent years. This variation has been most notable in the first and last quarters of the marketing year when estimated use is influenced by the amount of “new crop” corn that is harvested before Sept. 1.   

However, there has also been considerable variation in the estimates of use in the second and third quarters of the marketing year. From the 2006-07 marketing year through the 2012-13 marketing year, the estimate of feed and residual use varied by more than 500 million bushels for each quarter of the year. 

In contrast, the range in the seven marketing years from 1999-00 through 2005-06 did not exceed 275 million bushels for any quarter.