Classifying cattle jaw movements: Comparing IGER Behaviour Recorder and acoustic techniques

Abstract

The identification and classification of jaw movements is essential to a mechanistic understanding of the intake process. Two methods for the detection and classification of jaw movements in grazing dairy cattle were compared: the IGER Behaviour Recorder (IBR) and acoustic monitoring (ACM). Ten-minute grazing sessions were recorded for six cattle wearing both devices. Sound was detected by a microphone mounted against the cow's forehead with signals transmitted to a camcorder. Data from the IBR were post-processed by the Graze Analysis Program, which generated a time-stamped record of bites and chews. The acoustic record was analysed aurally to classify sound bursts into bites, chews and chew-bites and these events were time-stamped by an event recorder. The IBR and ACM timelines of unclassified jaw movements were brought into alignment and movements that occurred within 0.4 s of each other on the aligned timelines were assumed to correspond and the degree of correspondence in their classification was examined. With the exception of one animal, there was broad correspondence between the two methods in the identification of unclassified jaw movement events. The IBR method classified 73% of events as bites and 27% as chews, whereas the ACM method gave the proportions of bites, chews and chew-bites as 6, 39 and 52%, respectively. Error rates for the IBR and ACM methods during head-up chewing bouts were 22 and 1%, respectively. Jaw movements classified by IBR as chews ( n = 1156) were predominantly (90%) classified as chews by ACM. Jaw movements classified by ACM as bites ( n = 219) were almost always (96%) classified as bites by IBR. Of 2092 ACM jaw movements classified as chew-bites, 92% were interpreted as bites by IBR. However, of 1599 ACM jaw movements classified as chews, 35% were interpreted as bites by IBR. Further development of the IBR system should include the recognition of chew-bites and an improved identification rate of chews. The ACM method requires automation of the sequencing process to become a practical tool.