Increasing utilization efficiency of continuously stocked Old World bluestem pasture
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The objective of this 2 year study was to identify the optimal height to graze Old World bluestem pasture in the Southern Great Plains under continuous stocking during the growing season. We hypothesized that intensely grazing Old World bluestem pasture would increase utilization efficiency by increasing the proportion of live leaf in the pasture, enhance forage quality and animal performance, and animal performance and root biomass would decline if grazing intensity was beyond an optimal level. Pastures were maintained at 3 levels of standing crop using continuous variable stocking. Stock adjustments were made weekly. A disc meter was used to maintain pasture disc heights of short (35-40 mm), medium (41-45 mm), and tall (46-55 mm) levels. Average standing crops of short, medium, and tall pastures were 1,500, 1,900, and 2,400 kg ha-1, respectively. On the short pasture treatments the proportion of leaf and live stem was higher (P<0.05) and the proportion of dead stem was less (P<0.05) than that on the tall pasture treatments. There were no significant differences (P>0.05) in crude protein of forage between treatments during the vegetative growth phase in spring when forage nitrogen levels were fairly high (> 1.3%). When the grass began to produce reproductive organs and when forage nitrogen levels were lower (< 1.3%), forage crude protein was greater in the short pastures (P<0.05). Individual animal performance was greater on the tall than on the short pastures (P<0.10) over all dates. Individual animal performance was greatest when management maximized the proportion of leaf and live stem while minimizing dead stem. Animal performance per hectare was slightly higher on the short and medium height pastures. Both the short and medium height pastures had approximately 70% the root biomass of the tall pastures (P 0.01) at the end of the trial. These results indicate that intense continuous variable stocking of Old World bluestem increases the utilization efficiency, but increases animal production per hectare only marginally, and reduces root biomass to an extent that production may not be sustained from year to year.