Effects of fungal infested steam-flaked corn on characteristics of ruminal and total tract digestion in steers

Four Holstein steers (407 ± 4 kg) with cannulas in the rumen and proximal duodenum were used in a 4×4 Latin Square design experiment. Treatments consisted of a 755 g/kg steam-flaked corn-based finishing diet in which fungal infested steam-flaked corn replaced 0, 150, 300, and 450 g/kg of the control flaked corn. The yeast and mold counts averaged 2.9×102, and 1.2×104 CFU/g, respectively, for control flaked corn, and 7.0×105, and 6.2×106 CFU/g, respectively, for fungal infested flaked corn. There were no treatment effects (P>0.10) on ruminal pH or volatile fatty acids molar proportions. Ruminal digestion of organic matter (OM; linear component, P<0.10), and feed N (linear component, P<0.05) decreased with increasing levels of fungal infested flaked corn in the diet. There were no treatment effects (P>0.10) on net microbial N synthesis. Amino acid intake increased linearly (P<0.01) as fungal infested flaked corn was augmented, and amino acid flow to duodenum was increased (P<0.01) with the highest fungal infested flaked corn level. Total tract digestion of OM, N and energy decreased (linear component, P<0.05) with increasing SFM. Ruminal and total tract digestion of ADF and starch were not affected (P>0.10) by treatments. It is concluded that mold infestation diminishes the feeding value of steam-flaked corn. The consequence was not related to effects of fungal growth on characteristics of digestion, but rather, to loss of readily digestible nutrients (starch) through the spoilage process, and to a lesser extent, decreased N digestibility. On the other hand, the metabolizable protein value was greater for fungal infested flaked corn.