Theme 5: Drought--Oral Sessions

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Limited information exists about the impact of drought stress on corn silage digestibility. The objective of this study was to determine the effect of irrigation on in situ NDF digestibility of corn tissues grown under controlled conditions in a greenhouse. Five commercial corn hybrids were planted in pots and grown in a greenhouse. Pots were subjected to an abundant or restricted irrigation regime. Leaf blades and stem internodes were collected from the upper and bottom portion of each hybrid. Tissue samples were incubated in the rumen of 3 rumen-cannulated cows for 0, 3, 6, 12, 24, 48, 96, and 240 hours. Drought stress did not affect the concentration of undigested neutral detergent fibre (uNDF) in upper or bottom internodes but slightly decreased in leaf blades (17.5 and 15.7% for abundant and restricted watering, respectively). The concentration of uNDF varied substantially among corn hybrids in upper internodes (13.4 to 28.3% uNDF), bottom internodes (21.5 to 42.3% uNDF), and blades (11.6 to 20.1% uNDF). Drought stress did not affect the fractional digestion rate (kd) of fibre in any tissue. The kd of fibre varied substantially among corn hybrids in upper (3.8 to 6.6%/h) and bottom internodes (4.2 to 6.7%/h) but did not vary in blades (3.8%/h). Significant interactions existed between irrigation treatment and corn hybrid for the effective ruminal degradation (ERD) of upper and bottom internodes. This interaction did not exist for blades. The ERD of fibre varied substantially among corn hybrids in blades (32.5 to 39.1%). The conclusions of this study are that drought-stressed corn had a marginal increase in fibre digestibility of blades but not in internodes, that drought stress had no effects on ERD of fibre within hybrids, and that the effect of drought stress on fibre digestibility of corn for silage is still inconclusive.

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Effect of Drought Stress on Fibre Digestibility of Corn for Silage

Limited information exists about the impact of drought stress on corn silage digestibility. The objective of this study was to determine the effect of irrigation on in situ NDF digestibility of corn tissues grown under controlled conditions in a greenhouse. Five commercial corn hybrids were planted in pots and grown in a greenhouse. Pots were subjected to an abundant or restricted irrigation regime. Leaf blades and stem internodes were collected from the upper and bottom portion of each hybrid. Tissue samples were incubated in the rumen of 3 rumen-cannulated cows for 0, 3, 6, 12, 24, 48, 96, and 240 hours. Drought stress did not affect the concentration of undigested neutral detergent fibre (uNDF) in upper or bottom internodes but slightly decreased in leaf blades (17.5 and 15.7% for abundant and restricted watering, respectively). The concentration of uNDF varied substantially among corn hybrids in upper internodes (13.4 to 28.3% uNDF), bottom internodes (21.5 to 42.3% uNDF), and blades (11.6 to 20.1% uNDF). Drought stress did not affect the fractional digestion rate (kd) of fibre in any tissue. The kd of fibre varied substantially among corn hybrids in upper (3.8 to 6.6%/h) and bottom internodes (4.2 to 6.7%/h) but did not vary in blades (3.8%/h). Significant interactions existed between irrigation treatment and corn hybrid for the effective ruminal degradation (ERD) of upper and bottom internodes. This interaction did not exist for blades. The ERD of fibre varied substantially among corn hybrids in blades (32.5 to 39.1%). The conclusions of this study are that drought-stressed corn had a marginal increase in fibre digestibility of blades but not in internodes, that drought stress had no effects on ERD of fibre within hybrids, and that the effect of drought stress on fibre digestibility of corn for silage is still inconclusive.