Correlation between median and mean irregular particle sizes and degradation kinetics in barley genotypes

Barleys, a major source of feed, are all coarsely dry-rolled before feeding beef and dairy cattle in North America. The shapes of coarsely dry-rolled barley particles are not round but very irregular. The model for geometric mean is not suitable for determining irregular barley particle size. In a previous study, we tested four different published models to determine the mean and median particle sizes of coarsely dry-rolled barley with irregular particle size shapes and found that the Pond's model with 0 mm=100% was the best model to compute mean and median particle sizes of the coarsely dry-rolled barley samples expressed as per cent cumulative weight oversize. However, we still did not know which parameter, median or mean particle size, was the best indicator to predict rumen nutrient degradation and availability. This information is badly needed. The objective of this study was to study the relationship between the mean and median irregular particle sizes and nutrient availability of various barley varieties which were coarsely dry-rolled. The results revealed a stronger correlation between the median irregular particle size (not mean particle size) and the rate (K(d) ) and extent (ED) of rumen degradation of dry matter (K(d) : R= -0.78, p= 0.065; EDDM: R= -0.89, p= 0.016), starch (K(d) : R= -0.96, p= 0.003; EDST: R= -0.95, p= 0.003) and crude protein (K(d) : R= -0.59, p= 0.215; EDCP: R= -0.89, p= 0.019). In conclusion, it is the median but not mean particle size that has stronger correlation with rumen degradation kinetics. The 79.9%, 78.3% and 91.0% of variation of effective degradability of dry matter, crude protein and starch, respectively, could be explained by the median irregular particle size.