Visual damage levels were determined and data on initial moisture, initial test weight, and test weight after drying to 15.5 percent were recorded for each sample. Statistical techniques were used to determine which variables affected the change of test weight when shelled corn is dried and to predict the final test weight of wet corn samples. It was shown that by far the most important factors were initial moisture and damage levels. On the basis of these results an adjustment table was developed showing the increase in test weight that would occur as corn of various moistures and damage levels was dried to 15.5 percent moisture.

IS TEST WEIGHT A MEASURE OF QUALITY?

There have been many tests and studies conducted to determine the value of test weight as an indicator of feeding value or general quality for corn. The detailed reports of these experiments are available using the references at the back of this publication. The results of the most relevant ones will be summarized. In a USDA publication dated 1933 the following statements appeared. “Pound for pound the utility value of high test weight corn for livestock feeding or for use in so called corn products industries is usually not considered much if any greater than that of low test weight corn, with the possible exception of immature corn that is of very low test weight. So far as the utility value of corn for livestock feeding is concerned, feeding tests of high test weight corn have shown sometimes that the low test weight corn was of superior value because of its relatively high protein quality." Also, "Variations in the test weight per bushel of corn do not correlate with utility values of anywhere near the same extent as they do in the case of wheat in which test weight is important as an index of flour yield" [7].

In November 1974 the USDA Northern Regional Research Lab in Peoria, Illinois published the results of milling trials in "Milling Properties of Corn After Field Shelling and Artificial Drying." In the summary of results they state "There appears to be no correlation between test weight and the recovery of oil or starch" [1].

A report in the Thirtieth Kansas Formula Feed Conference Proceedings talks about test weights and their relevance in grain standards. Although the tests were done using grain sorghum, the results contribute to the overall pattern. "Test weight should not be used to indicate feeding value except under those conditions where test weights are reduced below approximately 45 ppb" [3].

Feeding trials were conducted with hogs at the University of Illinois and with lambs at the University of Minnesota.

At the University of Illinois tests, two diets were prepared that were identical except that one utilized 51 ppb corn and the other used 63 ppb corn. The pigs fed the diet of light-weight corn gained 1.08 pounds per day with a feed efficiency of 48 pound of gain per pound of feed fed. The pigs fed the diet containing the 63 ppb corn gained 1.04 pounds per day with a feed efficiency of .45 pound per pound of feed fed. The two diets were equally well accepted and no significant nutritional difference was indicated between 51 and 63 ppb test weight corns. The results are summarized in Table 2.

TABLE 2.-COMPARISON OF FEEDING PERFORMANCE OF SWINE FED CORN OF DIFFERING TEST WEIGHT 1

1 The 2 test weights were obtained by harvesting the same variety at different maturities. The 51 ppb was harvested at 48-percent moisture and dried to about 9-percent moisture. The 63 ppb was harvested at 19-percent moisture and dried to 8-percent moisture. There was 4 replicates of each treatment. None of the differences in the table are statistically significant.

The report by Thorton, Goodrich, and Meiske of the University of Minnesota states that the maturity of the corn is one of the major factors affecting the composition and properties of corn. It goes on to state first that "physiological maturity of corn grains occurs at kernel moisture levels ranging from 30 to 44 percent," and that secondly "test weight may be related to physiological maturity" [4]. It is important to note therefore, that in all studies involving test

weight, the factor of the maturity of the corn should be considered. Corn of different qualities may have similar levels of kernel damage and initial moisture but different test weight because of differences in the maturity of the corn.

Chemical analyses of corn with differing test weights have shown no significant differences and no pattern of variations except for extremely low test weights resulting from immature corn. The gross energy and crude protein were determined for eight samples at the University of Illinois. These samples were selected to represent a range of test weight from 39.9 ppb to 59.8 ppb. All samples except A1 and A2 were ear corn hand shelled and dried with 170° air. Samples A1 and A2 were obtained from an elevator after drying. The results (Table 3) show no correlation or pattern. The sample coded X53 with a test weight of 58.5 ppb has a gross energy value slightly less than that of X7L with a test weight of 43.5 ppb. The crude protein of samples coded A1, P27, and A2 have nearly identical crude protein levels despite their respective test weights of 59.8 ppb, 49.8 ppb, and 39.9 ppb.

TABLE 3.-GROSS ENERGY AND CRUDE PROTEIN OF CORN OF DIFFERENT TEST WEIGHTS

At Minnesota an analysis of a single variety harvested at four stages of maturity showed a general increase in fiber content and a decrease in protein content as the corn matured. Corn harvested 17 days after silking had a dry test weight of 35 ppb and a crude protein content of 15.49 percent compared to mature corn of the same variety with a test weight of 58 ppb and crude protein of 10.77 percent [4]. Differences between corn harvested in mid-dent stage at 55 ppb test weight and mature corn at 58 ppb were slight and often in favor of the lighter corn. Digestibility coefficients did not differ significantly on the samples from 47 ppb to 58 ppb.

A more extensive chemical analysis of corn with varying test weight was made by the Subcommittee on Feed Composition, National Academy of Science (Table 4). Variation in fiber, carbohydrates (N-free extract), and energy were very small and did not follow a consistent pattern as test weight decreased. Crude protein increased slightly as test weight declined. Digestibility of the protein also showed a tendency to increase with lighter test weight. The analysis of samples of corn ranging from 47 ppb to 56 ppb provided no evidence of any relationship between feeding value and test weight.

TABLE 4.-NUTRITIONAL COMPARISONS OF CORN OF VARIOUS TEST WEIGHTS 1

1 Source: "Atlas of Nutritional Data on United States and Canadian Feeds," National Academy of Sciences prepared by Subcommittee on Feed Composition, Washington, D.C., 1971, p. 253-255.

* Energy values for sheep were not determined for the 54-lb corn.

The differences in chemical composition or feeding value that have been found in immature corn are not consistent with grade standards or discounts. For example, the Minnesota study identified differences between 35.2 ppb corn and 55 and 58 ppb corn. However, grade standards identify differences between 56, 54, 52, 49, and 46. Discounts in common use consider 53-pound corn to be worth less than 54—a distinction clearly not supported by research.

RECOMMENDATIONS FOR THE TEST WEIGHT DISCOUNT

Although more evidence and research are needed to establish the limitations of test weight as a measure of quality, enough studies have been completed to determine that test weight is not a good measure of feeding value, especially for normally mature corn. It will be difficult to ever establish test weight as a measure of corn quality because light-weight corn may be caused by any of a great many factors, including high moisture, mechanical damage, immaturity, kernel shape, and air spaces within the kernel. Some of these may be important but most are not.

As long as test weight is retained in the grades and standards, it should be adjusted for the two major factors affecting test weight-moisture and mechanical damage to the kernel. The adjustment table (Table 5) was used by many elevators in 1973 and results were generally satisfactory. However, during the fall of 1974 the tables apeared to overestimate final test weight.

TABLE 5.-TEST WEIGHT ADJUSTMENTS TO 15.5-PERCENT MOISTURE BASE FOR CORN WITH NORMAL LEVELS OF MECHANICAL DAMAGE

To determine the accuracy of the tables, 70 samples of ear corn from Illinois, Ohio, Indiana, and Michigan were selected with special attention to obtaining samples that appeared to be light weight but with minimal mechanical damage. These samples were subjected to the same drying procedures as the 1970, 1971, and 1972 samples. The same pattern of increased test weight during drying was observed in all samples. Final test weight of each sample was compared to the test weight that would have been estimated using the adjustment table. The chart below shows the + or error for each sample plotted against beginning moisture. For samples below 30 percent (the limit of the adjustment table) the average actual test weight is almost identical to the estimated test weight.

The apparent inaccuracy of the test weight adjustment table was due to two factors (1) the moisture levels of delivered corn were often above 30 percentoutside the range of the table and (2) nearly all the corn harvested at high moisture was also damaged by the combine. The simple one-column table (Table 5) did not allow for higher damage levels. As shown in the more complete adjustment table (Table 6) many of the high damage samples would not have received a test weight adjustment according to the table. For example, 26 percent moisture corn with 35 percent of the kernels sustaining combine damage will not increase in test weight when dried.

TABLE 6.-ADJUSTMENT TO BE ADDED TO WET HARVEST TEST WEIGHT TO OBTAIN EXPECTED TEST WEIGHT LEVEL AFTER DRYING TO 15.5-PERCENT MOISTURE

1 Percent damage is the weight of kernels and pieces of kernels in a 100-gr sample that show any type of break in the seed coat, cuts, or chipped pieces.

The table needs to be extended to higher moisture levels if reliable relationships can be obtained. The 1974 data are being analyzed to establish these relationships for a more complete table.

REFERENCES

[1] Anderson, R. A., E. L. Griffin, and C. Vojnovich, Wet Milling Properties of Corn after Field Shelling and Artificial Drying, Northern Regional Research Laboratory, U.S. Department of Agriculture, Peoria, Illinois, Nov. 74, page 1.

[2] Atlas of Nutritional Data on United States and Canadian Feeds," National Academy of Science, prepared by the Subcommittee on Feed Composition, Washington, D.C., 1971, page 253.

[3] Cole, C. W., "Do Grain Standards Relate to Feed Usage?," Thirtieth Kansas Formula Feed Conference Proceedings, Kansas State University, Manhattan, January 13, 1975, pages 1-1 through I-3.

[4] Goodrich, R. D., J. C. Meiske, and J. H. Thorton, "Digestibility of Nutrients and Energy Value of Corn Grain of Various Maturities and Test Weights," Journal of Animal Science, Vol. 29, No. 6, Dec., 69, pages 983–986.

[5] Hall, Glenn and Lowell D. Hill, Test Weight as a Grading Factor for Shelled Corn, Department of Agricultural Economics, Agricultural Experiment Station, University of Illinois at Urbana-Champaign, September, 1973, AERR 124. [6] Hill, Lowell D., Robert B. Schwart, and L. F. Stice, Corn Quality and Discounts in Illinois, 1974, Department of Agricultural Economics, University of Illinois at Urbana-Champaign, Cooperative Extension Service and Agricultural Experiment Station, January 27, 1975, AE-4368.

[7] U.S. Department of Agriculture, Proposed Revised Federal Grain Standards, Miscellaneous Publication No. 173, 1933, page 153.

Senator CLARK. The hearing is adjourned.

[Whereupon, at 3:40 p.m., the subcommittee adjourned, subject to the call of the Chair.]