Incorporating virtual fencing to manage yearling steers on extensive rangelands: spatial behavior, growth performance, and enteric methane emissions

Abstract

We examined the spatial movement behavior, growth rates, and enteric CH₄ emissions of yearling beef cattle in response to spatial distribution management with virtual fencing (VF) in extensive shortgrass steppe pastures. Over the 110-d grazing season (mid-May to early September), 120 British-breed stocker steers (~12 months of age; mean body weight [BW] 382 kg ± 35) were grazed with VF management (active VF collars) or free-range (non-active VF collars) in two pairs of ~130 ha physically fenced rangeland pastures (i.e., VF-managed vs. control). One pair was associated with a diverse mosaic of soil types supporting alkalai sacaton (Sporobolus airoides [Torr.] Torr.), blue grama (Bouteloua gracilis [Willd. Ex Kunth] Lag. Ex Griffiths), and needle-and-thread (Hesperostipa comata [Trin. &Rupr.] Barkworth), while the other pasture-pair was associated with the Sandy Plains ecological site, primarily hosting western wheatgrass (Pascopyrum smithii [Rydb.] Á. Löve), needle-and-thread, and blue grama. Within each pair of pastures, one herd was rotated among sub-pastures using the VF system, which focused grazing on varying native plant communities over the growing season. In control pastures, steers had access to the entire pasture for the grazing season. Spatial distribution management with VF maintained steers within desired grazing areas occurred 94-99% of the time, even though five of the 60 VF-managed steers consistently made short daily excursions outside the VF boundary. In all four pastures, an automated head-chamber system (AHCS, i.e., GreenFeed) measured the enteric CH₄ emissions of individual steers. Steers that met the criteria of a minimum of 15 AHCS visits in each of at least two VF rotation intervals were analyzed for spatial behavior, growth performance, and enteric CH₄ emissions. Screening based on AHCS visitation requirements resulted in 15 steers (nine VF, six control) in the diverse mosaic pasture pair, and 39 (17 VF, 22 control) in the Sandy Plains pasture pair. VF management significantly reduced growth rates for all steers across both pasture pairs by an average of 9%, resulting in steers that were 7.3 kg lighter than unmanaged steers at the end of the grazing season. VF management effects on enteric CH₄ emissions varied among rotation intervals and pasture type. In the diverse mosaic pair, VF management significantly reduced CH₄ emissions during the first rotation interval, when VF steers were concentrated on the C₃ grass-dominated plant community, but increased emissions in the second and third intervals when VF steers were concentrated on C₄ grass-dominated areas. In the Sandy Plains pasture pair, where cattle were rotated between sub-pastures with and without palatable four-wing saltbush (Atriplex canescens [Pursh] Nutt.) shrubs, VF management reduced CH₄ emissions in three of four rotations as well as over the full grazing season. CH₄ emissions intensity increased with VF management in the diverse mosaic, but not in the Sandy Plains pastures. Overall, our findings show VF management (1) controlled animals spatially within sub-pastures, (2) did not improve growth performance but rather decreased it, (3) did not consistently reduce enteric CH₄ emissions, and (4) tended to increase emissions per kg of product via lowering steer growth performance. While some have posited that VF is a potential tool to reduce enteric emissions, our findings suggest VF management is not a straightforward solution for mediating the relationships between forage resources, growth performance, and enteric CH₄ emissions of stocker steers on extensive rangeland. Furthermore, our fusion of animal GPS tracking, growth rates and AHCS data indicated that differences in spatial behavior and weight gain were consistent between VF-managed and control steers irrespective of their AHCS-acclimation status, supporting the perspective that AHCS-based gas flux measurements are a valid means of estimating enteric emissions in extensive rangelands.

Keywords: GPS and AHCS; animal distribution; data fusion; rangeland enteric emissions; shortgrass steppe; spatial distribution management; virtual fencing technology and GreenFeed.

Figure 1

Remotely sensed daily time series of herbaceous biomass (kg/ha) in diverse mosaic pastures, with control and three sub-pastures, showing a general decline and recovery trend (A) and Sandy Plains pastures, with control and two sub-pasture groups, also depicting fluctuations (B) at the USDA ARS Central Plains Experimental Range, 2024. The legend identifies lines by color. Solid colored lines depict biomass when steers were present in the grazing area, while dotted colored lines show biomass when steers were not present.

Figure 2

Boundaries of ~130 ha barbed-wire fenced pastures and virtual fence sub-pastures at the USDA ARS Central Plains Experimental Range near Nunn, Colorado, USA. Satellite maps A–C depict diverse mosaic pasture-pairs and D,E depict Sandy Plains pasture-pair for each rotation interval and hectarage of grazing area, illustrating changes in grazing management.

Figure 3

Satellite maps of locations of virtual fence-managed steer #7E23 (blue dots) and control steer #7C5D (red dots) across the three rotation intervals (A–C) in VF-managed and control pastures of the diverse mosaic pasture pair. Light blue circle denotes location of water tank and automated head-chamber system (AHCS) location.

Figure 4

Satellite maps of locations of virtual fence-managed steer #7C52 (blue dots) and control steer #7C58 (red dots) across the four rotation intervals (A–D) in VF-managed and control pastures of the Sandy Plains pasture pair. Light blue circle denotes location of water tank and automated head-chamber system (AHCS) location.

Figure 5

Comparisons of mean ± SE daily distance traveled (m/hd/d) and daily area explored (ha/hd/d) for VF-managed and control steers over the study period in diverse mosaic-associated pastures (A,C) and Sandy Plains ecological site-associated pastures (B,D). Mean ± SE for automated head-chamber system (AHCS)-acclimated and all steers are depicted. Asterisks denote significance at p < 0.05 for means comparison of AHCS-acclimated steers; see text for all steer results.

Figure 6

Comparisons of mean ± SE enteric CH₄ emissions (g/hd/d) for VF-managed and control steers over the study period in diverse mosaic-associated pastures (A) and Sandy Plains ecological site-associated pastures (B). Asterisks denote significance at p < 0.05 for means comparison.

Figure 7

Variation in average daily gain (kg/hd/d) and enteric CH₄ emissions (g/hd/d) of yearling steers in relation to their previous production environment (A) and management with vs. without virtual fence (B) in the shortgrass steppe of northeastern Colorado.