Validation of the Lifecorder Plus device for accurate recording of the grazing time of dairy goats

Abstract

Few portable devices that record grazing time have been tested on goats. The Lifecorder Plus is a commercial device, based on a single-axis accelerometer, that calculates and stores in memory the average activity level (range: 0–9) every 2 min. Previous studies determined that activity levels greater than or equal to 0.5 were specific to grazing, while those less than 0.5 could be considered as other activities. The aims of the present study were to determine the threshold value that minimised the prediction error and to validate the ability of the Lifecorder Plus device to record goat grazing time at vegetative temperate pasture under rotational grazing management. Twenty goats (5 in 2015 and 15 in 2017) were fitted with the Lifecorder Plus on their neck and had access to pasture for 8−12 h/d. The device was evaluated by comparing 2-min visual observations of trained observers to the activity level recorded at the same time by the device, resulting in a total of 187 h of observations. Two analysis methods were used to assess the device’s accuracy: a confusion matrix and the mean squared prediction error. Lifecorder Plus recorded grazing time with 93 % accuracy, 95 % precision, 97 % sensitivity and 73 % specificity. Relative prediction errors calculated at the hour and day scales were low, averaging 0.09 and 0.05 of actual grazing time, respectively. Overall, there was no confusion between grazing and other goat activities. Lifecorder Plus overestimated grazing time by 3%, probably due to other activities of goats (lack of specificity). Placing an additional Lifecorder Plus on a leg may help identify non-grazing activities (e.g. long-duration walking, running) and thus reduce this slight overestimation. No bias due to sward height was detected. In conclusion, for rotationally grazed vegetative temperate pastures, Lifecorder Plus detects grazing activities of goats with high accuracy and precision and is suitable for studying variations in grazing time, particularly at the day scale in small paddocks.