Mitchell B. Stephenson

Effect of terrain heterogeneity on feeding site selection and livestock movement patterns

Feeding site selection is a critical part of livestock foraging that can constrain and/or increase the choices available during diet selection. When livestock choose new feeding sites, vegetation and nutrient profiles can differ from other areas, especially in heterogeneous environments with rugged terrain. Correspondingly, livestock should remain longer in feeding sites in rugged heterogeneous pastures than in homogeneous pastures where animals may alternate among feeding sites to facilitate diet mixing and to prevent satiation. The objective of this study was evaluate how terrain and corresponding heterogeneity may affect the sequence and pattern of feeding site selection of free-roaming livestock. Grazing patterns of mature cows were evaluated on six ranches located in Arizona, Montana and New Mexico. In total, 11–19 cows were tracked for 1–3-month periods at each ranch by using global positioning system (GPS) collars. Positions were recorded at 10- or 15-min intervals and used to identify where cows grazed during the early morning (0500 hours to 1000 hours). Pastures (336–9740 ha) at each ranch were divided into seven to nine sections (48–1082 ha) as an indicator of feeding sites. Classification was based on cattle density and topographical and vegetation types. Sequences of daily section selection were evaluated using transition matrixes. For all ranches, the sequence of section selection differed from what would be expected by chance, indicating that the section selected on the following day depended on the section selected on the previous day. For ranches with relatively gentle terrain, cattle selected different feeding sites ~70% of the tracking period. In contrast, cows at the ranch with the largest pasture and enclosing both mountainous and gentle terrain stayed in the same feeding site for over 10 successive days for 42% of the tracking period. Smaller pastures with only mountainous terrain were intermediate. Cows grazing gentle topography and relatively homogeneous vegetation alternated among feeding sites (sections in the present study) more frequently than cows grazing pastures with more rugged topography and more heterogeneous vegetation. This pattern could help livestock mix forages and select a more diverse diet.

Targeted Grazing in Southern Arizona: Using Cattle to Reduce Fine Fuel Loads☆☆☆★

ABSTRACT Managing the risk of wildfires is a growing concern in the western United States. Targeted grazing, or managing livestock grazing to achieve specific vegetation goals, is one possible tool to treat fuels, but few studies have evaluated its efficacy. The goal of this study was to test the effect of targeted grazing on herbaceous fuel loads and fire behavior by 1) implementing targeted grazing in a field experiment and 2) using a fire model (BehavePlus) to evaluate changes in fire behavior resulting from treatments. We applied targeted cattle grazing using low-stress herding and strategic placement of low-moisture block supplement on rugged rangelands in southwestern Arizona using a herd of 58 Red Angus cows and two bulls. Six of the cows were initially fitted with global positioning system collars. We tested two grazing treatments: 1) herding and supplement versus 2) no herding and no supplement on two pairs of study sites and replicated this for 2 years. Herding and supplement affected both the distribution of cattle and herbaceous fuel loads. Despite light utilization (26%) in treated sites, the BehavePlus fire model predicted that herding and supplement reduced fire rate of spread by more than 60% in grass communities and by more than 50% in grass/shrub communities. Fuel treatments dropped flame lengths below a 1.2-m critical threshold under the moderate fuel moisture scenario in grass communities and below a 2.4-m critical threshold in grass/shrub communities under both moderate and extreme fuel moisture scenarios. These results suggest that targeted grazing could reduce the potential cost of fighting fires in conditions similar to this study site. However, implementing this type of treatment on other sites will require careful calibration of animal numbers, supplement amounts, and length of herding periods relative to the specific context and goals.

Grazing Method Effect on Topographical Vegetation Characteristics and Livestock Performance in the Nebraska Sandhills

Abstract A study was conducted on upland range in the Nebraska Sandhills to determine differences in plant species frequency of occurrence and standing crop at various topographic positions on pastures grazed with short-duration grazing (SDG) and deferred-rotation grazing (DRG). Pastures within each grazing treatment were grazed at comparable stocking rates (SDG = 1.84 animal unit months (AUM) · ha−1; DRG = 1.94 AUM · ha−1) by cow–calf pairs from 1999 to 2005 and cow–calf pairs and spayed heifers from 2006 to 2008. Plant frequency of occurrence data were collected from permanently marked transects prior to, midway through, and at the conclusion of the study (1998, 2003, and 2008, respectively) and standing crop data were collected annually from 2001 to 2008 at four topographic positions (dune top, interdune, north slope, and south slope). Livestock performance data were collected during the last 3 yr of the study (2006 to 2008). Positive change in frequency of occurrence of prairie sandreed (Calamovilfa longifolia [Hook.] Scribn.) was 42% greater on DRG pastures than SDG after 10 yr. Total live standing crop did not differ between DRG and SDG except in 2001 when standing crop was 23% greater on DRG pastures. Standing crop of forbs and sedge was variable between grazing methods on interdune topographic positions depending on year. Average daily gain of spayed heifers (0.84 ± 0.05 kg · d−1 SE) did not differ between SDG and DRG. Overall, SDG was not superior to a less intensively managed grazing method (i.e., DRG) in terms of vegetation characteristics and livestock performance.

Time of Grazing Effect on Subsequent-Year Standing Crop in the Eastern Nebraska Sandhills☆

ABSTRACT Rotational grazing methods provide range managers opportunities to alter the time when grazing occurs on pastures in consecutive years. The effect of time of grazing on subsequent-year standing crop was evaluated within four pastures (42 ± 1 ha) rotated annually within a deferred rotation using a modified Williams design that included mean times of grazing within different pastures from 16 May to 14 June, 13 June to 20 July, 20 July to 29 August, and 27 August to 7 October (i.e., stages of grazing A, B, C, and D, respectively). Subsequent-year standing crop of different plant functional groups was collected from 2001 to 2008 at four topographic positions (i.e., north slopes, south slopes, dune tops, and interdunes) in mid-June and mid-August harvests. During the mid-June harvest, standing crop of subsequent-year warm-season grasses was 51 ± 24 to 117 ± 41 kg·ha-1 greater (P < 0.1) when grazing occurred during stage A compared with when grazing occurred during stages B and C on north- and south-facing slopes and at the pasture level. During the mid-August harvest on south-facing slopes, subsequent-year warm-season grass standing crop was 265 ± 105 and 341 ± 113 kg·ha-1 greater (P < 0.03) when grazing occurred during stage A compared with stages B and C, respectively. Overall, grazing on pastures during stage A tended to provide greater amounts of subsequent-year standing crop for warm-season and cool-season graminoids at specific topographic positions. Given that the effect of time of grazing on subsequent-year standing crop varied among topographic positions for different functional groups, a deferred grazing rotation provides a viable management tool to alter the yearly sequence of grazing on pastures to avoid negative effects of grazing Nebraska Sandhills vegetation at critical times in consecutive years.

Factors Affecting the Efficacy of Low-Stress Herding and Supplement Placement to Target Cattle Grazing Locations

ABSTRACT Success of targeted grazing is strongly influenced by the ability of livestock managers to focus grazing livestock on a specific area. Targeted cattle grazing using low-stress herding (LSH) and strategic supplement placement was conducted at four study sites to evaluate management factors that affected our ability to focus cattle grazing on small areas of large pastures. Simple linear regression was used to evaluate relationships between the time Global Positioning System—tracked cattle spent near supplement placement sites and four factors: 1) intake of low-moisture block (LMB) protein supplement, 2) perennial grass standing crop, 3) horizontal and vertical distance of LMB from water, and 4) slope near LMB. Repeated measures were used to evaluate time cattle spent near LMB in different years at study sites in Arizona and New Mexico. Intake of LMB supplement was a moderately good predictor (r2 = 0.60; P < 0.01) of time cattle remained within 250 m of LMB supplement. When cattle consumed recommended amounts of LMB, they tended to stay near LMB longer if supplement was placed in areas with greater perennial grass standing crop (r2 = 0.34; P = 0.07). No relationships were detected (r2 < 0.15; P > 0.17) between time cattle were near supplement and the horizontal and vertical distance of LMB from water and slope near LMB. The combination of LSH and strategic LMB placement was an effective method to target cattle grazing when cattle consumed recommended amounts of LMB. However, efficacy of LSH and LMB to target cattle grazing may be influenced by environmental factors such as drought and yearly differences in forage standing crop and quality. Changes in cattle grazing behavior in years following initial LSH and LMB treatments also may influence cattle remaining near LMB.