Introduction

The concentration of protein, fibre and minerals usually increases and concentrations of starch and fat decrease as test weight of corn declines. This results in a higher protein, lower energy grain compared with corn of normal test weight (54-56 pounds per bushel; lb/bu). Research conducted with chickens has demonstrated that reductions in test weight did result in a slight reduction in the true metabolizable energy content of corn (Dale and Williams, 1993).

Since corn's primary contribution to swine diets is energy, it is generally thought that low test-weight corn is of lower feeding value than normal test-weight corn. The cool growing season and harvest challenges of 2009 have created increased concerns over test weight of corn.

This is not the first time University of Minnesota scientists have had this concern. In the early 1990's, several research groups evaluated the effects of low test weight corn on pig performance. So, it seems wise to review what we know about this issue.

Research Results

At the West Central Research and Outreach Center, they compared corn harvested in one year having a test weight of 57 lb/bu with corn harvested the next year dried to three moisture levels. Test weight of the second-year corn ranged from 47.5 to 49.5 lb/bu. Standard grower and finisher diets were formulated to contain 0.78 and 0.63 per cent total lysine, respectively. The old corn contained 0.25 per cent lysine while the low test-weight corn contained between 0.25 and 0.26 per cent lysine. Pigs began the experiment at an average weight of 77 lb and ended the experiment at 229 lb. There was no statistically significant difference in daily gain, feed intake or feed efficiency between normal and low test-weight corn (Table 1).

Researchers at Michigan State University (Rozeboom et al., 1993) studied the effects of corn test weight on performance of growing pigs. Test weights evaluated ranged from 42 to 59 lbs/bu. Pigs began the four-week trial weighing 29 lb. They reported no effect of test weight on growth performance of pigs (Table 2). The diet containing corn with a test weight of 47 lb/bu did significantly reduce growth rate and daily feed intake. However, retrospective analysis of corn revealed vomitoxin contamination of 2 ppm, which probably was responsible for the depression in feed intake an growth performance associated with this diet.

Others workers in South Dakota using growing-finishing pigs (Rudolph, 1993; Table 3) and Canada using nursery pigs (Patterson et al., 1993; Table 4) could not demonstrate any consistently negative or positive effects of low test-weight corn on pig performance.

Researchers at South Dakota State University (Iverson and Thaler, 1996) found that adding fat in the form of extruded soybeans or soy oil to corn-based diets containing very low test-weight corn (36 or 44 lb/bushel) had no effect on daily gain but did improve daily feed intake and feed efficiency of growing-finishing pigs (Table 5). Fortunately, reports of low test-weight corn in 2009 have not reached the severity of that reported in this South Dakota study.

Conclusion

Assuming corn is not contaminated with mycotoxins, and other factors are not compromising quality of the corn, low test-weight corn seems to be comparable in feeding quality to normal test weight corn for pigs. It appears that corn with test weight as low as 45 lb/bushel, and maybe as low as 40 lb/bushel, can support pig performance similar to corn with test weights of 56 to 59 lb/bushel.

References

Dale, N. and W.P. Williams. 1993. Research provides insight into value of low test weight corn. Feedstuffs, April 12, p17.

Iverson, D.M., and R.C. Thaler. 1996. Low-quality soybeans and corn as feedstuffs for swine. J. Swine Health Prod. 4:15.

Patterson, R., J. Tuitoek and L. Young. 1993. Nutritional value of immature corn of different bulk density for young pigs. Ontario Swine Research Review p24.

Rozeboom, D.W., D.A. Nelson and E.R. Miller. 1993. Influence of corn test weight (lb/bushel) on the performance of growing pigs. Michigan State Univ. Anim. Sci. Newsletter, p6.

Rudolph, B. 1993. Feeding value of light test weight corn for pigs - Better than expected. Feedback, GTA Feeds, Sioux Falls, SD.

January 2010