The variation of rumination responce in cows fed a same amount of hay was investigated. With three adult cows of the Japanese Black Breed, ruminating behaviour was measured continuously during a 7-days period by pen-writing recorder, using the wire resistance strain gauge connected on a leather head-harness and strain amplifier.
The rumination activity in terms of time spent ruminating showed great variation among animals or days. Average ruminating times per day of respective animals were 381, 487, and 342 min., and the maximum difference between days appeared in one animal was 124 min. for seven days.
As well as the ruminating time, actual time in chewing cud showed large variation, and percentage of actual chewing time spent in ruminating time was from 86 to 92 % on individual average.
The daily number of chewing in rumination was approximately 17,000 to 27,000 with large individual difference. The number of boluses regurgitated daily was highly correlated to the time spent ruminating, but the time spent on each bolus differed significantly among animals and was fairly constant on every day in each of the animals. The average rate of chewing per minute was not variable among animals or days.
Rumination was distributed within a day with marked circadian pattern, which were quite alike on each of the animals.