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Effect of drought stress on fiber digestibility of corn for silage.

G. Ferreira




Effect of drought stress on fiber digestibility of corn for silage.
G. Ferreira*, C. L. Teets. Department of Dairy Science, Virginia Tech Blacksburg, VA.

The objective of this study was to determine the effect of drought stress on ruminal in situ neutral detergent fiber digestibility (NDFD). Five corn varieties were seeded in pots (6 replicates) and grown in a greenhouse. After seeding (5/13/19), replicates were allocated to a water-sufficient treatment (W) or a water-insufficient treatment (D). From seeding to harvesting, W and D pots were watered with 598 and 273 mm of water, respectively. Silking date (date at which 50% of the plants showed silks) occurred on 8/12/19, and harvesting occurred on 9/4/19. At harvesting, 3 internodes and 3 leaf-blades from the bottom of the plant and from the phytomers above the insertion of the ear were dissected and composited by tissue. After drying, tissues were ground to pass through a 2-mm screen (cyclone mill), and 0.25 g was put into Ankom F57 porous bags previously rinsed with acetone to perform in situ digestibility in 3 cows. All tissues of each of the 3 replicates per treatment and variety were incubated within a same cow, so cow was considered a blocking factor. All bags were placed simultaneously into the rumen and incubated for 0, 3, 6, 9, 12, 18, 24, 48, 96, and 240 h. In situ disappearance parameters were determined using Proc NLIN of SAS according to the model ISNDFD = B � [1-e(-k � T)], where B is the potentially digestible NDF and k is the fractional digestion rate of B. We also measured fraction C at 240 h (i.e., uNDF240). Kinetic parameters were contrasted using a mixed model that included the effects of cow (random), treatment (fixed), hybrid (fixed), treatment � hybrid (fixed), and the residual error. For the lower stems, drought stress did not affect fractions B (65.0%; P = 0.22) and C (35.0%; P = 0.22) and did not affect k (5.3%/h; P = 0.34). For the upper stems, drought stress did not affect fractions B (76.3%; P = 0.30) and C (23.8%; P = 0.30) but tended to increase k (4.5 vs. 5.2%/h; P = 0.09). For the upper blades, drought stress increased fraction B (82.5 vs. 84.3%; P < 0.02) and reduced fraction C (17.5 vs. 15.7%; P = 0.02) but did not affect k (3.9%/h; P = 0.42). In conclusion, under the conditions of this study, drought stress had minimal effects on NDFD.

Keywords: drought, corn silage, fiber digestibility.