The time spent under a shelter by eight grazing fattening bulls of the Belgian Blue breed in each of 3 years consecutively for a total of 48 days was recorded using a time-lapse recorder with infrared illumination.
During one grazing period, data were collected over 35 days (experiment 1). Observations were divided into 166 h with rain (20%) and 674 h without precipitation (80%). The average occupation rates were 15·4 (s.e. 29·1) % for the hours with rain and 4·5 (s.e. 14·8) % for the hours without precipitation (P < 0·001). The effect of intensity and duration of rain on the occupation rate was significant from 0·4 l/m2 or from 2 h.
Experiment 2 (13 days of observation) examined the influence of temperature and solar radiation on the use of shelter. The occupation rates were 21 (s.e. 23) % during the daylight hours (07.00 to 19.00 h), 6 (s.e. 8) % during the night (19.00 to 07.00 h) and 14 (s.e. 14) % during a 24-h period. The occupation rate between 07.00 and 19.00 h was significantly correlated to the mean daily temperature (r = 0·75), the maximum daily temperature (r — 0·86) and the direct solar radiation time (r 0·60). When the maximum daily temperature exceeded 20°C, the use of the shelter increased from 10 to 49% of the daylight hours.
There was no significant difference between the live-weight gains of animals from the observed group and those of other bulls on an adjacent pasture without shelter. Nevertheless, these observations suggest that a shelter may improve the welfare of grazing cattle.