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Effect of water status (drought) on in situ starch digestibility of corn for silage.

G. Ferreira




Effect of water status (drought) on in situ starch digestibility of corn for silage.
G. Ferreira*1, C. Teets1, L. Martin2, S. Hines3, G. Shewmaker4, M. de Haro-Marti5, M. Chahine2. 1Virginia Tech Blacksburg, VA, 2University of Idaho Twin Falls, ID, 3University of Idaho Jerome, ID, 4University of Idaho Kimberly, ID, 5University of Idaho Gooding, ID.

The objective of this study was to determine the effect of irrigation on in situ starch digestibility (ISSD) of corn for silage. The study was performed in Kimberly (ID) during the 2018 growing season. Five commercial corn hybrids were planted in a split-plot within a randomized complete block design with 4 blocks. Experimental treatments consisted of a control treatment with furrow irrigation at planting and 3 more times during crop growth (watered, W) and a non-irrigated treatment with furrow irrigation only at planting (drought, D). When the corn was between 1/4 and 3/4 milk-line stage of maturity, ears from 3 plants were harvested from each plot and shelled by hand. After drying (55�C) to constant weight, kernels were ground to pass through a 4-mm screen of a cutter mill and placed in porous Dacron bags (3.6 g DM/bag). At 9:30 a.m. of the test day, bags were immersed within the rumen of 3 cannulated cows fed a totally mixed ration (40% corn silage, 7% alfalfa hay, and 53% concentrate mix; DM basis) and incubated for 0, 4, 8, 12, 24, and 48 h. Once dried, all bags were weighed and opened, and the residues were re-ground to pass through a 1-mm screen of a cyclone mill before starch analysis. In situ starch disappearance parameters were determined using NLIN procedure of SAS according to the model ISSD = A + B � [1-e(-k � T)], where A is the digested starch at time (T) zero, B is the potentially digested starch, and k is the fractional starch digestion rate. Undigestible starch (C) was also determined. Kinetic parameters were contrasted using a mixed model that included block (random; 3 df), treatment (fixed; 1 df), block � treatment (random; 3 df), hybrid (fixed; 4 df), treatment � hybrid (fixed; 4 df), and the random residual error. Whole-plant dry matter concentration was greater for D corn than for W corn (36.9 vs. 30.3%; P < 0.01). Water status did not affect fractions A (20.3%; P = 0.16), B (75.9%; P = 0.36), or C (3.8%; P = 0.19), the fractional starch digestion rate (6.7%/h; P = 0.96), or the half-life of starch (7.4 h; P = 0.21). In conclusion, under the conditions of this study, water stress had no effects on in situ starch digestibility of corn for silage.

Keywords: drought stress, corn silage, starch digestibility.