Data collected from one study of 103 groups of pigs in North Carolina during the latter half of the year showed mortality rates due to bleach-outs in the groups at 3.4 per cent. In some herds, clustering of mortalities due to ulcers can be seen and does not always fit a typical bell shaped curve. In one study of 68 close-out groups, running out of feed increased the mortality in the following week by 29 per cent. The humidity level in the air was positively correlated with mortality rates and may explain the seasonality of the problem. Mixing pigs does not have a significant effect on the occurrence of mortality due to ulcers.
Barrows have higher rates of mortality due to ulcers.
The advent of modern grain processing techniques has led to the emergence of ulcers as a major health concern in swine operations. Research at Kansas State University has shown that for each 100 micron decrease in average particle size of corn in swine diets, there is approximately a 1.3 per cent increase in efficiency of gain. It's also been shown that in grow-finish pigs, the incidence of ulcers tends to increase when they are fed cereal grain diets with an average particle size less than 700 microns. However, all the blame cannot be placed on feed manufacturing as the incidence of ulcers has been shown to be affected by grain type and the stressfulness of housing and shipping conditions. However, researchers say more study is needed to justify widespread use in the swine industry.