Commercial Ground Corn Grain Samples Vary In Particle Size Metrics And In Situ Rumen Starch Digestibility

Objective: Commercial dry and ground shelled corn is not a uniform feed. Geometric mean particle size (GMPS; mu m) has been related to rumen digestibility, but researchers have specifically sourced or created varied particle size to assess relationships. Researchers have not sourced corn from differing commercial feed manufacturers. The objectives of our work were to assess variation in commercially ground corn sample particle size, prolamin protein content, and in situ rumen starch digestibility. Further, our objective was to relate prolamin protein and particle size measures to in situ rumen starch digestibility for survey samples.Materials and Methods: Commercial dry and ground shelled corn samples (n = 38) were collected from the eastern and midwestern United States and analyzed for starch (% of DM), prolamin (% of DM), GMPS, surface area (cm(2).g(-1); SA), and in situ rumen starch digestibility (% of starch) following 0, 7, and 16 h of incubation in 3 cannulated, lactating dairy cows. Survey data were analyzed using multivariate methods to report correlations, and ANOVA was carried out between starch, prolamin protein, and particle size relative to in situ rumen starch digestibility measures using JMP v14.3 (SAS Institute Inc., Cary, NC).Results and Discussion: Substantial variability was observed for particle size measures; GMPS (mu m) = 715 +/- 233 and surface area (cm(2).g(-1)) = 92.7 +/- 20.8. Further, GMPS and surface area were related to in situ rumen starch digestibility at 16 h (P < 0.01) and 7 h (P < 0.01), respectively.Implications and Applications: Our survey results for commercially ground dry corn samples suggest that substantial variation exists in geometric mean particle size and surface area for corn supplied by commercial feed mills. This suggests that both the mean and SD of these measures is important when evaluating commercial dry and ground shelled corn.