Nonstructural Carbohydrate and Digestibility Patterns in Orchardgrass Swards during Daily Defoliation Sequences Initiated in Evening and Morning

Abstract

Herbage soluble carbohydrate (SC) levels vary diurnally and livestock intake can be higher for herbage harvested or allocated to animals in the evening than in the morning. Few assessments of SC and digestibility patterns have been made during sward depletion in rotationally stocked orchardgrass (Dactylis glomerata L.). We tested the hypothesis that simulated evening daily pasture allocation increases 24-h mean herbage SC and digestibility levels relative to morning allocation. Total nonstructural carbohydrate (TNC) and in vitro true dry matter digestibility (IVTDMD) levels were compared during 24-h clipping sequences initiated at 1900 h (PM) and 0700 h (AM). Sward height was progressively reduced from 40 to 8 cm at 6-h intervals in October, June, and August. Successively lower horizons from defoliation sequences and also from control areas that were not under progressive defoliation were analyzed. Digestibility and TNC levels varied diurnally and seasonally, and were often higher for PM sequences, but differences among 24-h means were small. Daily mean TNC levels for defoliation sequences initiated in PM and AM were 138 vs. 132, 93 vs. 88, and 72 vs. 60 g kg' in October, June, and August, respectively. In all periods, digestibility decreased from approximately 920 to 800 to 890 g kg' during sward depletion and displayed similar patterns between defoliation sequences. Patterns of TNC and digestibility during sward depletion may not be represented by those in intact swards, and PM allocation of daily herbage may not increase 24-h mean dietary TNC density relative to AM allocation. Daily quantities of ingested TNC could be higher for PM herbage allocation if livestock consume proportionately more herbage in the PM than we simulated. M ANAGEMENT OF GRAZING SYSTEMS for high animal performance includes facilitation of high intakes of pasture dry matter (DM) by livestock. Constraints to grazing animal performance include sward structural and herbage compositional factors that determine rates and concentrations of dietary energy intake (Orr et al., 1997;Vazquez and Smith, 2000;Barrett et al., 2001). Herbage SC and digestibility concentrations, two indices of dietary energy density, usually vary diurnally according to daily patterns of photosynthesis, respiration, and translocation of SC. In temperate climates, herbage SC concentrations are generally highest in evening and low-

Herbage intake and ruminal digestion of dairy cows grazed on perennial ryegrass pasture either in the morning or evening

“…Griggs et al . () demonstrated that photosynthate concentrations in orchardgrass leaves exhibited greater diurnal fluctuations than stems and pseudostems. As most of the herbage samples in this study were plucked from the upper plant portions, the fluctuations in chemical composition was likely quite pronounced.…”

“…; Griggs et al . ). Moreover, dairy cows appear to increase their grazing behavior and herbage intake during dusk (Orr et al .…”

“…Some studies have improved nitrogen utilization efficiency in grazing dairy cows by altering the timing of concentrate supplementation (Vaughan et al 2002;Trevaskis et al 2004). However, time of day could influence the effects of supplementation on nitrogen utilization and herbage intake because herbage chemical composition is not consistent across the day; in particular, water soluble carbohydrates increase later in the day (Delagarde et al 2000;Griggs et al 2005). Moreover, dairy cows appear to increase their grazing behavior and herbage intake during dusk (Orr et al 1997;Gibb et al 1998;Taweel et al 2004;Gregorini et al 2007).…”

Effect of increased concentrate allotment before evening grazing on herbage intake, nitrogen utilization and rumen fermentation in dairy cows grazed on perennial ryegrass pasture

“…; Griggs et al . ). The time of concentrate supplementation in grazing dairy cows could alter herbage digestion, ruminal metabolism and amino acids supply for milk production.…”

“…Some studies have shown improved nitrogen utilization efficiency in grazing dairy cows by altering the time of carbohydrate supplementation (Vaughan et al 2002;Trevaskis et al 2004;Mitani et al 2005). Timing of supplementation could influence nitrogen utilization because herbage chemical composition is not consistent across the day; water-soluble carbohydrates increase later in the day (Delagarde et al 2000;Griggs et al 2005). The time of concentrate supplementation in grazing dairy cows could alter herbage digestion, ruminal metabolism and amino acids supply for milk production.…”