Abstract
The behaviors and growths of dairy heifers were studied at three levels of grazing intensity under rotational grazing with six paddocks. Diurnal behaviors were traced in spring (June 10-12), summer (August 12-15) and autum (September 17-20). Body weight of heifers were also measured at three hours intervals from 6a.m. to 6p.m. on each day. The results are summarized as follows. 1. Average herbage weights of eight rotation were 631, 970, 1251kg per 10 are and utilization percentage were 72.9, 56.8, 46.6% at heavy, moderate and light grazing intensity, respectively. Herbage of heavily grazed pasture was high in DCP and TDN contents and at all grazing intensities herbages were lowered 2.6-3.8% in DCP and 2.7-3.8% in TDN after grazing. The nutritive values of herbage were lowered in mid-summer and growths of heifers were slowered in this period. The proportion of orchardgrass was maintained higher in light grazing and perennial ryegrass in heavy grazing. 2. Average daily gains of body weightr were 434, 653 and 611g at heavy, moderate and light grazing, respectively. Average amounts of dry matter intake per animal per day were 1.94, 2.02 and 2.48% of body weight at each intensity and they tended to decrease with advancing season. 3. The time spent by heifer in grazing was longer in heavy and moderate grazing probably due to deficiency of pasture allowance, but judging from their performace this was not enough to compensate less amounts of pastures in heavy grazing. Grazing intensity had greater effects on rumination than grazing, as the time spent on rumination by heifer of heavy grazing was half that of light grazing. Animals appeared to have a dull grazing when amount of herbage was bellow the critical point and decreased their grazing time at the last day of each rotation. Behavior, especially ruminating, varied markedly by season. Then the behavioral patterns of heifers were similar at same season in spite of the differences of their grazing intensity. Rainfall of 18mm per day had little effects on their fundamental behaviors, but the proportion of lying down form markedly decreased in the rainy day. In a day, heifers had three peaks of grazing of which the peak from 9a.m. to 1p.m. was very sharp and in autumn heifers spent almost their time for grazing during this period. 4. Liveweights increased from morning to evening every day, but its maximum values were shown at the first day of each rotation. Therefore, values during afternoon decreased linearly from the beginning to the end of each rotation and seasonal growths of heifers were indicated as accumulated values of gains of each rotation, not as gains of day. From periodical liveweight changes, intake by heifers was very large in the first day of rotation and peak of grazing was only one time from 9a.m. to 12a.m. each day. Behaviors and liveweight changes suggest that heifers learned not only the periodicity of rotation but also the moveing time to the next paddck. 5. The growth of heifer had a positive correlation with the time spent on rumination, but negative correlations with the time spent on grazing and the number of drinking.
