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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.

The objective of this study was to determine the effect of drought stress on neutral detergent fiber (NDF) and lignin (LIG) concentrations and on in vitro dry matter digestibility (IVDMD) and in vitro neutral detergent fiber digestibility (IVNDFD) of leaf blades and stem internodes of corn for silage. Eight plots were blocked (i.e., 4 blocks) and randomly subjected to a watered (W) or non watered (NW) treatment. Within each block, plots were split into 7 sub-plots, to which 1 of 7 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 225 and 360 mm of water pre-tasseling and post-tasseling, respectively. Stem internodes and leaf blades from the second phytomer below (LOWER) and the second phytomer above (UPPER) the ear insertion were collected to determine tissue composition and digestibility. Drought stress increased the concentration of NDF in both leaf blades (628 vs. 613 mg NDF/g DM) and stem internodes (625 vs. 572 mg NDF/g DM). Drought stress decreased IVDMD in stem internodes (0.575 vs. 0.525 IVDMD) but had no effect on IVDMD of leaf blades (0.561 IVDMD). Similarly, drought stress decreased IVNDFD in stem internodes (0.422 vs. 0.391 IVNDFD) but had no effect on IVNDFD of leaf blades (0.536 IVNDFD). Drought stress increased the concentration of lignin in the cell wall of leaf blades (161 vs. 141 mg/g CW) but had no effect on stem internodes (266 mg/g CW). Under the conditions of this study, water supply had a minimal effect on lignin concentration in the cell wall and did not increase the in vitro digestibility of fiber in corn for silage. The latter observation is contrary to the general industry belief that water stress increases fiber digestibility in forages. Virginia Tech and University of Idaho through the multistate project USDA-NIFA [NC-2042, VA-136291, IDA01613]; National Forage Testing Association; Western SARE This is a collaborative project between Virginia Tech and University of Idaho through the multistate project USDA-NIFA NC-2042 Management Systems to Improve the Economic and Environmental Sustainability of Dairy Enterprises (USDA-NIFA Multistate Project VA-136291 and USDA-NIFA Multistate Project IDA01613, respectively). This project was partially funded by the National Forage Testing Association (Project title: Holistic analysis of forage cell wall composition and its relationship with undigested neutral detergent fiber) and by Western SARE (Project title: Transferring knowledge to trainers on water conservation practices and their effects on forage quality to ensure environmental and economic sustainability of livestock production systems).

`HiMag' tall fescue (Festuca arundinacea Schreb.) was selected for high Mg concentration to reduce grass tetany risk to ruminants, but neither animal preference nor consumption of HiMag were known. The objectives were to evaluate methods of quantifying preference and to determine intake and preference by cattle (Bos taurus L.) of HiMag relative to seven other tall fescues. All entries were free of a fungal endophyte [Neotyphodium coenophialum (Morgan-Jones & Gams) Glen, Bacon & Hanna] that reduces cattle performance. The experimental design was a randomized complete block with three replications of eight cultivars nested within each of three test pastures. Six heifers grazed the vegetative to boot-stage pastures for 48 h in May, June, August, and September of 1993 and 1994. The pastures, located at 1200 m elevation, were furrow irrigated. Pre- and post-grazed forage were clipped and weighed to determine yield and utilization (48-h utilization < 50%). Preference scoring of 0 to 10 (0 to 100% of forage eaten) was done by four trained observers at 24, 30, and 48 h. The heifers quickly learned to distinguish between cultivars, and their order of preference was Kenhy > KY 31 > HiMag = Barcel = Cl = Stargrazer > M096 = Mozark. The cultivar x trial(year) interaction for preference indicated that cultivars responded differently to weather conditions, which in turn affected animal preference. Preference scoring had high repeatability and ranked cultivars similarly to the clip-and-weigh method of measuring utilization. Preference scoring was accomplished with 27% of the experimental error and only 6% of the time required for clip-and-weigh. Only 44% of the variation in preference score (PS) was explained by the model: PS = 8.8 - 1.1(Mg DM yield ha-1). Estimated dry matter (DM) intake of HiMag was 6.4 kg (animal unit day)-1. Consumption and preference of HiMag by cattle are satisfactory relative to other tall fescue cultivars.