One of the disturbance factors of human on the grassland is grazing. Livestock grazing affects grasslands through defoliation and trampling and there have been many reports about the effect of grazing on grasslands under normal weather conditions. However, animal behavior may change in the situation of rainy days and the impacts on grasslands may be different. This is especially relevant in China where the herd persists in grazing as of old even after a drencher.
A study was conducted to determine differences in grazing effects between rainy and rainless days. The experimental design was as follows: a pasture of 2800m2 was divided into three parts, the first part with 1200 m² was further divided into three plots of 400 m² each for the rainy day grazing treatment, the second part with 1200 m² was also divided into three plots of 400 m² each for the rainless day treatment, and the last part with 400 m² was used as the control without grazing for the rain day treatment. Each plot was grazed by 80 sheep for different time levels (30, 60 minutes and 90 minutes) with grazing rates of 10, 20 and 30 sheep•h/100m², respectively. In this paper we adopted the special parameter of ingestion type to describe sheep intake in the plant modulars. Two new indices, ingestion loss and trampling breaking rate, were proposed for the first time. The ingestion loss of sheep was used to indicate the waste mass during sheep foraging and the trampling breaking rate of plant was to measure activity intensity of sheep.
We compared changes such as ingestion type, ingestion loss, trampling loss, water content and bulk density in a rainy day and in a rainless day. We concluded that (a) the proportion of ingestion type for Leymus chinensis decreased, and the proportion of top-clipping, a major ingestion type, increased with increasing grazing intensity although it didn’t occupy the most proportion any longer in a rainless day, (b) the difference in ingestion loss mass for L. chinensis under between grazing intensity was not significant, but for the preferred plants such as Phragmites communis and Kalimeris interifolia, it was much higher than that in a rainless day, (c) sheep reduced their movement in a rainy day, and trampling breaking rate for L. chinensis was similar between grazing rate while it increased with increasing grazing intensity for P. communis, similar to that in a rainless day, (d) soil moisture in three layers (0～5cm, 5～10cm, and 10～15cm) after grazing was less than that of control, indicating that trampling could reduce water availability in the soil, and (e) bulk density was significantly reduced by grazing（p<0.05）and increased with increasing grazing intensity.