Use of shelter by grazing bulls: effect of climatic factors

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/m(2) 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 degrees 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