Evidence of Oxidative Injury in Pigs With Melanosis Coli

Melanosis coli is a dark discoloration of the colon due to accumulation of pigment-laden macrophages in the lamina propria. Three case submissions were received where rectal discoloration was reported at slaughter in pigs from separate production systems and melanosis coli was confirmed microscopically. Tissues from affected and unaffected cohort pigs were evaluated for evidence of oxidative damage using immunohistochemical staining for 3-nitrotyrosine, 4-hyroxynonenol, and malondialdehyde. Affected colons had significantly greater immunolabeling for all 3 target compounds than unaffected colons (P ≤ .001, all analyses). Hepatic vitamin E levels were low in both affected and unaffected pigs, and there was a trend toward lower values in affected pigs. Given the limited number of slaughter-collected samples available for this investigation, further study is warranted to elucidate the possible association between low vitamin E concentrations and oxidative damage in cases of melanosis coli in pigs.