2016 Volume 62 Issue 2 Pages 63-69
The effects of difference of growth stage and canopy structure on grazing behavior and intake of hydrogen cyanide potential (HCNp) during the early grazing period were determined on Sorghum pasture under different growth stage (before heading : BH and after heading : AH). The growth stage was flag-leaf stage on BH pasture and first heading stage on AH pasture, respectively. The canopy height was 166.3cm on BH pasture and 191.7cm on AH pasture, respectively. It was clarified that grazing animals intake up to the top of canopy from the position of about 60% of the plant height from the base regardless of the plant height. HCNp intake for a few hours after putting animals on AH pasture showed a tendency to increase as compared with BH pasture. The vertical distribution of HCNp showed a different tendency with growing stage and HCNp in strata located at 60-70% of plant height from the ground level remarkably increased in first heading stage. It indicated that the HCNp contents and their vertical distribution in the canopy structure of Sorghum pasture influenced on intake of HCNp by grazing animal. The heading stage of Sorghum showing high productivity and nutritive value is an adaptive growing stage for grazing utilization in Sorghum pasture. Therefore, it should be investigated details of the changes of HCNp contents during heading stage for restricting the increase of HCNp ratio in herbage intake.
