The assessment of the frequency of chews during rumination enables an estimation of rumination activity in hay-fed sheep.

The objective was to assess rumination behaviour and, more specifically, the intra-individual and inter-individual variation of the frequency of chews during rumination (per min) in five Blackhead sheep fed hay at a level of 100% maintenance (experimental period [EP] I), 50% maintenance (EP II) and ad libitum (EP III). Animals ruminated in EP II less (416 min/day) than in EP I and III (558 and 592 min/day, respectively). Mean inter-individual coefficients of variation (CV) of frequency (defined as number of chews/duration of chewing per cycle) were 12.5%, mean intra-individual CV were 2.5%. The respective CVs for the duration of rumination per day were 8.1 and 9.7%, respectively. The level of intake influenced the frequency of chews significantly. It is concluded that the frequency of chews has to be considered in studies investigating chewing behaviour of ruminants. Under the experimental conditions investigated, number of chews during rumination per day could be estimated by the frequency of chewing with nearly the same precision as by using the duration of rumination per day.