INFLUENCE OF GENOTYPE AND ENSILING OF CORN GRAIN ON IN-SITU DEGRADATION OF STARCH IN THE RUMEN

This trial was conducted to determine the influence of genotype and en siling of corn grain on the rate and extent of ruminal starch degradat ion. Two cultivars of corn that differed in texture of the endosperm, dent (Zea mays ssp. indentata) or flint (Zea mays ssp. indentura) were harvested at 30% whale-plant dry matter (DM). After separation from s tover and cob, the kernels were coarsely chopped and ensiled or not en siled. Grains were oven-dried at 40 degrees C and either ground throug h a 3-mm sieve or left unground. Ruminal Dill and starch degradabiliti es were determined using the in situ technique. The proportion of star ch lost through the pores of the bag without degradation was also dete rmined. Mean ruminal DM and starch degradabilities were higher for gro und grains than for chopped grains, which could be related to the prop ortion of DM and starch lost through the pores of the bag. For unensil ed, chopped grain, ruminal starch degradability was higher for dent co rn than for flint corn (72.3% vs. 61.6%). The ensiling process increas ed ruminal starch degradability, averaging 5.8 percentage units. The d ifference in ruminal starch degradability between dent corn and flint corn remained constant whether the corn was unensiled or ensiled (10.7 vs. 11.6 percentage units).