Relationship between ruminal starch degradation and the physical characteristics of corn grain

The objectives of this study were to determine the range of variation in th e rate and extent of in situ ruminal starch degradation of 14 corns differi ng in vitreousness and to predict ruminal starch degradability by physical characteristics of corn grains. This study was conducted with eight dent an d six flint corns. Ruminal starch degradability was determined by an in sit u technique on 3-mm ground grains. Physical characteristics of corn grain w ere measured: hardness by grinding energy and particle size distribution, a pparent and true densities, and specific surface area. Ruminal DM and starc h degradabilities averaged 50 and 55.1% and varied from 39.7 to 71.5% and f rom 40.6 to 77.6%, respectively. Ruminal starch degradability averaged 61.9 and 46.2% in dent and flint types, respectively. The proportion of coarse particles (61.9 vs 69.6% for dent and flint, respectively), the apparent de nsity (1.29 vs 1.36 g/cm(3) for dent and flint, respectively), and the spec ific surface area (.13 vs .07 m(2)/g for dent and flint, respectively) vari ed with the vitreousness. Ruminal starch degradability could be predicted a ccurately by vitreousness (r(2) = .89) or by the combination of apparent de nsity and 1,000-grain weight (R-2 =.91), a measurement faster than the dete rmination.