Monitoring and assessment of ingestive chewing sounds for prediction of herbage intake rate in grazing cattle.

Accurate measurement of herbage intake rate is critical to advance knowledge of the ecology of grazing ruminants. This experiment tested the integration of behavioral and acoustic measurements of chewing and biting to estimate herbage dry matter intake (DMI) in dairy cows offered micro-swards of contrasting plant structure. Micro-swards constructed with plastic pots were offered to three lactating Holstein cows (608±24.9 kg of BW) in individual grazing sessions (n=48). Treatments were a factorial combination of two forage species (alfalfa and fescue) and two plant heights (tall=25±3.8 cm and short=12±1.9 cm) and were offered on a gradient of increasing herbage mass (10 to 30 pots) and number of bites (~10 to 40 bites). During each grazing session, sounds of biting and chewing were recorded with a wireless microphone placed on the cows' foreheads and a digital video camera to allow synchronized audio and video recordings. Dry matter intake rate was higher in tall alfalfa than in the other three treatments (32±1.6 v. 19±1.2 g/min). A high proportion of jaw movements in every grazing session (23 to 36%) were compound jaw movements (chew-bites) that appeared to be a key component of chewing and biting efficiency and of the ability of cows to regulate intake rate. Dry matter intake was accurately predicted based on easily observable behavioral and acoustic variables. Chewing sound energy measured as energy flux density (EFD) was linearly related to DMI, with 74% of EFD variation explained by DMI. Total chewing EFD, number of chew-bites and plant height (tall v. short) were the most important predictors of DMI. The best model explained 91% of the variation in DMI with a coefficient of variation of 17%. Ingestive sounds integrate valuable information to remotely monitor feeding behavior and predict DMI in grazing cows.

A note on using a laser-based technique for recording of behaviour and location of free-ranging animals.

We developed a precise, remote (up to 300m) observation system to record animal location and behaviour that requires no animal handling or disruption of the normal environment. Our system, combining a survey laser and a laptop, also allows recording of observed animal behaviour from seconds to hours, with accuracy of 1m or better. Up to one individual per second can be located, which supports data collection of large numbers of animals not possible with other methods. The laser system was used to track a halter-broken heifer led in an arc beginning and ending about 50m from the laser with a maximum distance of about 150m. We recorded the location of the heifer at 35 points along the arc using the laser, a global positioning system (GPS), and a nylon tape. There was an average linear difference of 1.16m (S.D. 0.63) between the laser data and the GPS data. The laser was potentially more accurate than GPS for this application because the laser averaged only 0.21m (S.D. 0.24) linear difference from the tape. Tests of the laser to relocate points in the field to within 0.20m and 0.1 degrees, averaged 0.42m (S.D. 0.29) from the original points. Our technique allows precise location of behaviour and navigation to grazed sites, potentially revealing how animals interact with the resources they exploit and showing the effect of landscape spatial heterogeneity on foraging and habitat use patterns.