86. The Use of Virtual Fencing to Manage Yearling Heifers on Montane Riparian Pastures.

Abstract The implementation of grazing management strategies on western rangelands poses the issue of effectively managing beef cattle herds in a manner that promotes beef production and rangeland forage resources. Virtual fence technology allows for increased flexibility to fully customize grazing strategies. Although grazing management strategies have been developed to effectively manage cattle, little is understood about the combination of virtual fence technology and grazing system strategies on forage resources and heifer performance in montane riparian pastures. Therefore, this study evaluates the effects of season-long grazing and short duration rotational grazing utilizing virtual fence, on riparian area forage resources and heifer performance. Eighty yearling Angus based heifers (average 263 kg) were fitted with virtual fence collars and grazed on a ∼90 ha montane riparian pasture in southwest Montana (2 blocks, ∼45 ha/block; 2 treatments/block). We utilized a randomized block design to contrast the following treatments: 1) short duration rotational grazing and 2) season-long grazing. Heifers were weighed and body condition scored (BCS) by two trained technicians, following a 16-hour shrink, at the initiation of the study, day 42 and 84. After the initial BW and BCS, heifers were stratified by BCS and BW, and, within stratum, randomly assigned to blocks and grazing treatments. Throughout the 84-day study, forage samples were taken weekly. The continuous treatment averaged 0.9 percentage points of crude protein higher than the rotational treatment, (P < 0.01; 7.64 versus 6.74, respectively) and 1.47 percentage points of neutral detergent fiber lower than the rotational treatment, (P = 0.03; 59.53 versus 61.00, respectively). For heifer performance, average final weight was 13.34 kg higher for the continuous treatment than the rotational treatment, (P = 0.04; 375.80 versus 362.46, respectively). Average total weight change was 12.53 kg higher for the continuous treatment than the rotational treatment, (P = 0.01; 112.52 versus 99.99, respectively) and average total BCS change was 0.23 points higher for continuous treatment than the rotational treatment, (P = 0.01; 0.69 versus 0.46, respectively). In summary, our data suggests that continuous grazing of cattle had greater heifer performance and better forage resources. These results reflect the first year of a two-year study that will also measure hair cortisol levels, grazing distribution and grazing behavior. Overall, this work will aid the development of refined grazing management strategies, virtual fencing and their combined impacts on cattle performance and vegetative communities in montane riparian areas.