The ability to quantify consumption in free-ranging large herbivores remains a challenge in extensive landscapes. To date, activity sensors built into geographic positioning system (GPS) collars offer a means to estimate foraging and resting behaviors based on head position (i.e., up or down). This advancement for GPS collars, however, does not provide a way to separate foraging behaviors such as searching, chewing as well as actual consumption (i.e., biting). A solution may be the use of automatic jaw movement recording devices that detect and record multiple foraging behaviors in real-time. Outside of the dairy industry, jaw movement recorders have experienced little use. Here, we employed automatic jaw movement recorders to quantify daily time spent grazing, number of grazing bouts, and grazing bout length of three yearling steers (Bos taurus) in three pastures in shortgrass steppe rangeland representing a gradient of forage availability during September 2019 at the USDA ARS Central Plains Experimental Range.
Results/Conclusions
The number of grazing bouts was lower in Loamy soil pasture co-dominated by midgrass and shortgrass communities (Loamy soil: mean ± SE: 5.2± 0.2 bouts) and Loamy soil pasture dominated by short grass (Heavy stocked, Loamy:5.4± 0.3) than pasture co-dominated by midgrass and shrubs (Sandy:7.0±0.4;linear mixed-model, random intercept: animal ID, p=0.04). In contrast, grazing bout length was marginally shorter in Sandy pasture (90.0±7.0 min) than Loamy pasture (132.0±7.9) and Heavy stocked, Loamy pasture (117.0±6.4; p=0.11). The daily time spent grazing did not differ among pastures (Loamy:10.0±0.16 hrs, Loamy, heavy density:9.8±0.3, Sandy:9.5±0.2; p=0.66). Instantaneous intake rate (bite rate x bite size=g per min) derived from ten-minute continuous bite monitoring observations (n=10/steer) during morning foraging bouts revealed that sensor-equipped steers in Loamy pasture (6.8±0.4 g/min) consumed more forage during 10-min foraging bouts than steers in Heavy-stocked, Loamy pasture (4.1±0.1; Tukey’s pairwise comparison p=0.03), but not more than steers in Sandy pasture (5.6±0.4; p>0.2). Our combination of jaw movement sensor-derived foraging effort data and in-field continuous bite monitoring data suggest steers in shrub-laden Sandy pasture, where average daily gain was highest among our study pastures, meet intake requirements through a foraging strategy of taking large bites and more bouts per day but of shorter duration than steers in more forage limited environments. The next steps include assessing the ability of jaw movement sensors to accurately represent instantaneous intake rate, which will be validated by daily weight gains of individual steers.