In this study, we examined days open（DO）of Japanese Black cattle in order to examine the hypothesis that animals reduce DO due to acclimatization to sensible heat stress. DO was calculated based on calving records of heifers and cows from 2008 to 2016 in Okinawa. DO of 22 d to 50 d was set to 50 d, DO of 250 d or more was set to 250 d and DO of 21 d or less was excluded from the data set. Target areas were Okinawa Island and Yaeyama Islands. The hot season with high sensible temperatures was divided into two: a rising period and a falling period, and the rest of the season was set as a thermal neutral period. This classification was implemented with reference to the temperature humidity index（THI）at each location. Assuming that DO during the falling period was a reaction to acclimatization after the rising period, DO of the rising period was compared with that of the falling period. In the linear model analysis, root mean square error（RMSE）was calculated to compare linear models and to estimate deviations from the rising period to the falling period. As a result, animals in the rising period had approximately seven THI higher than those in the falling period. This study indicates that further research focusing on the rising period of the heat stress is needed to improve DO to accomplish reproductive cycle with single birth per year.

Many yaks（Bos grunniens） and sheep（Ovis aries） are fed in native pastures of the Qinghai-Tibet Plateau. These pastures have serious issues, such as ongoing decreases in herbage mass formations of bare land and livestock body size reductions. To develop an effective grazing management plan in this region, it is important to understand the pasture-degradation factors. Therefore, we designed a grazing experiment during the warm season to estimate the effects of livestock species (yak and sheep) on bare-land formation. The experiment was conducted in a pasture approximately 4350 m above sea level in Qinghai Province, China. In May 2014, immediately after the snow melted, approximately 6 ha of grassland was divided into six equal plots, allocated to three yak-grazing plots (5.5 sheep/ha as the animal units of sheep) and three sheep-grazing plots (4.7 sheep/ha). In August 2014, May, June, July, and Aug 2015, and May 2016, the vegetation was investigated in each of the six plots using the fixed quadrat method. This procedure resulted in 37 quadrats per plot, totaling 222 quadrats. In addition, 37 fixed quadrats were set outside of the grazing experiment plots where both animal species were grazed throughout the year. A three-way analysis of variance (ANOVA) was performed to estimate the effects of the livestock species, investigation time (month and year), and plot location on the bare-land formation. The results showed that the type of grazing livestock (sheep vs yaks) had very little influence on bare-land formation but that the investigation time and plot location effects were significant. The bare-land rate only decreased during the warm-season grazing treatment, whereas cold-season grazing increased the bare land. These results suggested that the reduction of grazing density, especially during the cold season, is critical for the recovery of degraded pasture vegetation in this region.