Diurnal behavior patterns of feedlot bulls during winter and spring in northern latitudes.

The diurnal behavior patterns of feedlot bulls were investigated at 52 degrees N during winter and spring. Two trials were conducted during periods when the daylight portion of the day increased by over 7 h. In trial 1, 324 bulls were observed hourly for 24 h on nine occasions at 2-wk intervals. The average proportions of bulls eating, drinking, standing and lying were 9.8, 1.9, 27.4 and 60.0%, respectively. Major periods of eating, drinking and standing were associated with the times of sunrise and sunset and shifted with seasonal changes. Initiation and termination of the afternoon period of eating was greatly affected by changing times of sunset and not by the daily addition of feed, which always occurred at approximately 1600 h. A significant period of eating, involving up to 15% of the bulls at one time, occurred near midnight during the longer winter night but decreased in duration and intensity as day-length increased. In trial 2, continuous observations for 24 h were made at 2-wk intervals on two groups of nine bulls. When the spread in time between morning and evening activity increased due to longer daylength, bulls were active at midday. This became more pronounced on days when the photoperiod exceeded 10 h. Minor periods of activity were evident at night. Mounting and agonistic encounters increased dramatically in frequency near sunset and in general were associated with the major periods of eating and standing.(ABSTRACT TRUNCATED AT 250 WORDS)