The grazing behaviour and heat production of Japanese black cattle grazed on mountainous range(115a）and on tame pasture(118a) were investigated in summer. For two 24-hr periods in each experimental period, contiinous observations were made with two cows in a herd. Heat production was estimated from the hear-rate measurment in a cow which was recorded continuously by telemetory. No supplementary feed was given at any periods.
The mean grazing time of cows on range was a little longer than on tame pasture, but ruminating time was shorter on range as against on tame pasture. Difference in resting time or loafing time was not observed between on range and pasture. The number of bites per minute of the forages in range and pasture were 19-38 and 41, respectively Lower rate in grazing and not so much longer time spent in grazing on range as compared with on pasture suggest that cows could not secure sufficient intake on range.
The heat production of grazing cow, calculated from the regression equation Y = 0.042X - 1.766 (Y:Cal/kg B.W./hr., X：heart-rate) was 23.4 Cal/kg/24 hr. on range and 18.3 Cal/kg/24 hr. on pasture.