Effect of drought stress on in situ ruminal starch degradation kinetics of corn for silage

Abstract

The objective of this study was to determine the effect of drought stress on the in situ ruminal starch degradation kinetic parameters of corn for silage. Five commercial corn hybrids for silage were utilized. The experiment was designed as a split-plot within a randomized complete block design with 4 blocks. Eight plots were blocked and randomly subjected to a watered (W) or non-watered (NW) treatment. Within each block, plots were split into 5 sub-plots, to which 1 of the 5 corn hybrids were randomly assigned. Before planting, all plots were irrigated with 150 mm of water to ensure a consistent emergence of corn seedlings. After this pre-planting irrigation, NW plots were not irrigated ever again. After planting, W plots were irrigated with 75 mm of water when the crop showed 2 visible leaves, 6 visible leaves, and pre-tasseling and with 45 mm every week, thereafter, for a total of 8 weeks (360 mm post-tasseling). Three ears from each subplot were collected when corn crops were between the 1/4 and 3/4 milk-line stage of maturity. Kernels were shelled by hand and dried. The in situ ruminal starch degradability was determined on ground (4-mm) grain samples placed in Dacron porous bags. All bags were immersed within the rumen of 3 rumen-cannulated cows fed a totally mixed ration containing 32 % corn silage, 3 % alfalfa hay, and 65 % concentrate mix (DM basis). Bags were incubated for 0, 4, 8, 12, 24, and 48 h. Water stress did not affect the fraction of instantly degraded starch (203 mg/g), the fraction of potentially degraded starch (759 mg/g), the fraction of undegraded starch (38 mg/g), or the differential starch degradation rate (0.0669/h). Corn hybrids did not affect any of these degradation kinetic parameters and no interactions existed between irrigation treatment and corn hybrid. In conclusion, drought stress had no effect on the in situ ruminal starch degradability of corn for silage.