Relationship between behaviour and heart rate as an indicator of stress in domestic sheep under different housing systems

Four adult Bergamasca rams were used in three types of housing: (1) common enclosures, consisting of a wooden paddock of 3 m X 7 m, partially covered by a shed; (2) metabolic cages of 57 cm X 135 cm; (3) fixed housing, with the animals tied by a rope about 1 m in length to a ring fixed on a wall. Heart rate was measured by means of a biotelemetric system during free standing, free lying, restrained standing and restrained lying, feeding, mastication, ruminating and drinking. The results show that rams, housing system and the interaction between behaviour and housing system affected heart rate (P < 0.001) during restrained standing and restrained lying. Heart rate in metabolic cages was lower (P < 0.001) than in other housing systems. Behaviour (considering only restrained standing and restrained lying) did not affect heart rate. Nevertheless, the interaction between behaviour and housing system showed that, within each housing system, heart rate during restrained standing was always higher than during restrained lying (P < 0.001). In all types of housing systems, a higher heart rate was observed in the second measurement (P < 0.001), which implies a state of greater agitation in the animals, probably due to the absence of a constant and familiar figure in the present experiment. From a methodological point of view, this study underlines the importance and efficacy of the determination of heart rate as an indicator of the reactive state of sheep.