Abstract
In the public-run farms of northern Tohoku, we have generally sown pastures with orchardgrass (Dactlis gromerata L.) or perennial ryegrass (Lolium perenne L.). However, Kentucky bluegrass (Poa pratensis L.), introduced before and naturalized, frequently replaced those grasses as a dominant species throught grazing use year after year. We conducted this experiment to evaluate the real animal productivity of Kentucky bluegrass dominant pastures subjected to rotational grazing by Japanese shorthorns in Morioka during 2002 and 2003. High grazing capacity about 600 CD (Cow day) per hectare could be obtained with 200-day grazing periods from late April to early November in both the years. Furthermore, the grazing capacities before and after August were similar. Herbage yields were kept uniform from spring to late autumn, enabling the same number of grazing heads to be raised throughout the grazing periods. In addition, herbage nutrition analysis revealed sufficient levels to sustain animal growth and health with high CP, Ca, Mg, P, TDN and mineral balance like K/Ca+Mg(meq.) ratio and NO_3-N concentration, although the K content was high. Kentucky bluegrass had been regarded as a low-productivity species. However, Kentucky bluegrass pastures examined in rotational grazing use in the northern Tohoku exhibited high ability to raise breeding cows with productivity and quality of nutrition of herbage as well as mineral content.
