The cool summer, slow maturation of the corn crop and the late harvest
have created challenges for corn growers and pork producers this year. The
end result is that pork producers have poor quality corn to feed this coming year that is low in test weight and may be contaminated with molds and mycotoxins. As test weight declines, concentration of protein, fiber and minerals usually increases and concentrations of starch and fat decrease. These changes result in a higher protein, lower energy grain compared with corn of normal test weight (54-56 Ib/bushel). Since corn's
primary contribution to swine diets is energy, we generally think that low test weight corn is of lower feeding value than normal test weight corn.
Several years ago at the West Central Research and Outreach Center, we
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. The old corn contained 0.2 percent lysine while the low test weight corn contained between 0.25 and 0.26 percent lysine. There was no statistically significant difference in daily gain, feed intake or feed efficiency between normal and low test weight corn.
Researchers at Michigan State University studied the effects of corn test
weight on performance of growing pigs. Test weights evaluated ranged from 42 to 59 lbs/bu. Like our study in Minnesota, they reported no effect of test weight on growth performance of pigs. Likewise, other workers in South Dakota using growing-finishing pigs and Canada using nursery pigs could not demonstrate any consistently negative or positive effects on pig performance of corn ranging in test weight from 40 to 58 lb/bu. Researchers at South Dakota State University 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. Fortunately, reports of low test weight corn in 2009 have not reached the severity of that reported in this South Dakota study.
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.
Dr. Lee Johnston is a swine scientist at the West Central Research and Outreach Center in Morris, MN,