Changes in biting characteristics recorded using the inertial measurement unit of a smartphone reflect differences in sward attributes

Accurate monitoring of grazing activity at individual cow level would provide useful information to farmers to improve the management of their animals and pastures in intensive dairy systems. Pasture attributes, starting with sward height, influence grazing behaviour and bites characteristics. In an attempt to link sward height to an individual automated detection of biting behaviour, a series of recording sessions of 4×3 days were realized on a ryegrass pasture with two contrasting heights (5 and 15 cm) over the grazing season (from July to October) with 4 dry red-pied cows equipped with the inertial measurement unit (IMU) of a smartphone on a halter, recording acceleration data at 100Hz. The behaviours were video-recorded. The number of grazing bouts performed during grazing trends to increase when the grass is highest. Fourier transforms of acceleration data showed that grazing bouts were characterized by a distinctive acceleration peak which frequency ranged between 1.02Hz and 1.46Hz whatever the sward height. It corresponded to the uprooting of grass frequency in the biting movement when compared with the observation in the video recordings and it could be used to improve automated grazing behaviour detection and to remotely characterize bites. These results show that some bite characteristics are influenced by sward height and automated individual monitoring of grazing behaviour is possible. An extension of this methodology should allow analysing more deeply the grazing behaviour of cattle in order to determine number of bites and possibly to link it to biomass intake.