Sources of variation in the grazing behaviour of dairy cows

Measurements of grazing, ruminating and idling time and number and duration of bouts of these activities were made on cows grazing a perennial ryegrass-white clover sward on a number of different occasions between 8 May and 10 July 1990 at the North Wyke Research Station, Devon, UK. Repeatabilities, calculated using the residual maximum likelihood method, were low for all measurements, the highest being for idling time. Coefficients of variation were generally lower between periods than between animals for total activity times and ruminating and idling bout duration but were higher for the number of bouts of all activities and for meal duration. Grazing time and meal duration increased significantly as the season progressed, while the number of bouts of all activities declined. Behaviour was not significantly correlated with meteorological conditions. There were no significant correlations between production traits and mean behaviour of cows across periods.