**3. Results**

. (1)

Forage productivity can be estimated using the grazing stick method:

24 Forage Groups

**Figure 1.** Pasture condition before (A) and after (B) a 24-hr mob grazing event at Chamberlain, SD.

Forage productivity = (average standing forage height − 10 cm) × 79 kg ha<sup>−</sup><sup>1</sup> cm<sup>−</sup><sup>1</sup>

which is the conversion value for a cool season, mixed species pasture with about 90% cover [30]. The 10 cm is subtracted from the height to account for remaining leaf and stubble after grazing. In preliminary data sets, Myer compared grazing stick method to clipping forage biomass at >40 sampling points and found these two estimates were within 15% of each other [29].

#### **3.1. Chamberlain**

Estimated forage biomass before mob grazing was 6100 and 2840 kg ha−<sup>1</sup> in 2013 and 2014, respectively (**Table 3**). Stocking density was greater and individual paddock size larger in 2013 (67,200 kg ha−<sup>1</sup> on 5 ha) than 2014 (43,680 kg ha−<sup>1</sup> on 2 ha). Harvest utilization (consumed + trampled) in mob-grazed areas were similar and >90% each year. Harvest efficiency (amount consumed) was also similar and >60% each year.


second sampling (*P* = 0.43). In 2014, WS plants were reduced in volume by about 19% (from

occurred prior to the first sampling. This was due to a large grasshopper infestation in the area.

**Figure 2.** Percent (±SE) of western snowberry with smaller volume post-graze by grazing system (A), and percent (±SE)

(B). Numbers above bars represent the average volume reduction of western snowberry plants in the respective category.

and >6500 cm3

) by grazing system

of western snowberry with small volume post-graze based on initial size (<6500 cm3

) between the first and second sampling dates (*P* = 0.01) even though grazing

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8850 to 7050 cm3

\*\*\*Significant at p<0.0001, \*significant at p<0.1

a Utilization = forage consumed and trampled, calculated by [(pre-graze) - (post-graze) / (pre-graze) x

b Efficiency = forage consumed, calculated by [(pre-graze) - (post-graze + trampled forage) / (pre-graze)

c Rotationally grazed in 2012

dBoth sampling dates occured after rotational grazing

**Table 3.** Impact of pasture management on forage at Chamberlain (Chamb.) and Selby, SD experimental sites in 2013 and 2014.

The comparison pasture was not grazed in 2013 but had been rotationally grazed in 2012. On June 19, forage biomass was estimated at 1190 kg ha−<sup>1</sup> , whereas on August 8, biomass increased to 2690 kg ha−<sup>1</sup> (**Table 3**). Between the first and second sampling there was >200 mm of rainfall. In 2014, the comparison pasture was grazed at a stocking rate of 250 kg ha−<sup>1</sup> from May to mid-June, which was prior to the first sampling. Forage biomass on July 9 and September 13 was similar (*P* = 0.1), averaging about 1800 kg ha−<sup>1</sup> . The apparent lack of growth may be explained by dormancy of the dominant cool season species, lack of rainfall (<12 cm) between sampling dates, and a grasshopper (*Caelifera* sp.) infestation that consumed forage regrowth.

Response of WS plants to mob grazing was similar in both years, with data combined over years. About 95% (±4%) of the measured plants were reduced post-grazing by an average of 63% (**Figure 2A**). Forage near WS plants was consumed (about 75% less biomass present), rather than trampled, and WS appeared to be browsed (stems and leaves removed). WS plant response in the 2013 ungrazed pasture indicated no difference in WS plant volume between the first and second sampling (*P* = 0.43). In 2014, WS plants were reduced in volume by about 19% (from 8850 to 7050 cm3 ) between the first and second sampling dates (*P* = 0.01) even though grazing occurred prior to the first sampling. This was due to a large grasshopper infestation in the area.

The comparison pasture was not grazed in 2013 but had been rotationally grazed in 2012.

**Table 3.** Impact of pasture management on forage at Chamberlain (Chamb.) and Selby, SD experimental sites in 2013

Utilization = forage consumed and trampled, calculated by [(pre-graze) - (post-graze) / (pre-graze) x

Efficiency = forage consumed, calculated by [(pre-graze) - (post-graze + trampled forage) / (pre-graze)

of rainfall. In 2014, the comparison pasture was grazed at a stocking rate of 250 kg ha−<sup>1</sup> from May to mid-June, which was prior to the first sampling. Forage biomass on July 9 and

may be explained by dormancy of the dominant cool season species, lack of rainfall (<12 cm) between sampling dates, and a grasshopper (*Caelifera* sp.) infestation that consumed forage

Response of WS plants to mob grazing was similar in both years, with data combined over years. About 95% (±4%) of the measured plants were reduced post-grazing by an average of 63% (**Figure 2A**). Forage near WS plants was consumed (about 75% less biomass present), rather than trampled, and WS appeared to be browsed (stems and leaves removed). WS plant response in the 2013 ungrazed pasture indicated no difference in WS plant volume between the first and

(**Table 3**). Between the first and second sampling there was >200 mm

, whereas on August 8, biomass

. The apparent lack of growth

On June 19, forage biomass was estimated at 1190 kg ha−<sup>1</sup>

September 13 was similar (*P* = 0.1), averaging about 1800 kg ha−<sup>1</sup>

increased to 2690 kg ha−<sup>1</sup>

Rotationally grazed in 2012

\*\*\*Significant at p<0.0001, \*significant at p<0.1

dBoth sampling dates occured after rotational grazing

regrowth.

and 2014.

26 Forage Groups

a

b

c

**Figure 2.** Percent (±SE) of western snowberry with smaller volume post-graze by grazing system (A), and percent (±SE) of western snowberry with small volume post-graze based on initial size (<6500 cm3 and >6500 cm3 ) by grazing system (B). Numbers above bars represent the average volume reduction of western snowberry plants in the respective category.

### **3.2. Selby**

Forage at Selby averaged about 1940 kg ha−<sup>1</sup> each year prior to mob grazing (**Table 3**). After the 24-hr grazing event, forage remaining was 1110 kg ha−<sup>1</sup> in 2013 and 240 kg ha−<sup>1</sup> in 2014. Forage consumption and utilization were estimated at 15 and 42%, respectively, in 2013. In 2014, efficiency and utilization were estimated at 48 and 88%, respectively. The three-fold increase in forage consumption (efficiency) in 2014 compared to 2013 may have been due to timing of the grazing. Forage was likely more mature and less palatable for cattle in late September (2013) compared to late July (2014). The increase in both consumption and utilization may have also been due to the slightly higher stocking density in 2014 compared to 2013 (**Table 2**). In the 2013 rotation-grazed pasture, the forage biomass averaged 2690 kg ha−<sup>1</sup> pregraze and about 790 kg ha−<sup>1</sup> post-graze, with an estimated 70% consumption and utilization, as very little newly trampled biomass was present. In 2014, the ungrazed comparison pasture had about 470 and 2920 kg ha−<sup>1</sup> at the first and second sampling, respectively.

**4. Discussion**

Cattle in NGP mob-grazed settings were more competitive for available forage, and were less selective in consumption, eating vegetation that would normally be avoided in a less intense grazing. The high stocking densities also resulted in more trampling and greater animal impact (e.g. dung deposition, data not shown) per unit area [29]. Other studies have reported similar results in other intensive-grazing systems although terminology [e.g. ultra-high stocking density [23]; intensive stocking [34]; cell-grazing [35]; high intensity, low frequency grazing [36], stocking rates, grazing duration, and seasonal timing often differ. High stocking densities have been shown to maintain animal performance if carefully managed [36]. Lush regrowth during the rest period following an intense grazing event increased forage crude protein (from 8.9 to 10.2%) and digestibility (from 44.6 to 54.7%) compared with more mature forage in lessintensively grazed areas [36]. Timing of grazing events, both within and among seasons on the same parcels, must be carefully controlled as repeated grazing when grass is at a vulnerable

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Other studies have reported that cattle graze less palatable, weedy species when grazing intensity is high. For example, cattle have browsed prickly pear (*Opuntia macrorhiza*) [39], absinth wormwood [29], and thistles [40], species that are typically avoided in low-intensity grazing. The least desirable species at Australian sites, purple wiregrass (*Aristida ramose*) and gray tussock-grass (*Poa sieberiana*), decreased 45% in basal diameter in a cell-grazing treatment with a

observed in continuously grazed sites [35]. These results suggest that during mob-grazing events, animals will browse less desirable species. In addition, mob-grazing, or similar high stocking-density, low frequency grazing management, has been suggested to maximize forage use [21], aid in maintaining a balance of desirable and undesirable vegetation [41] and may enhance nutrient cycling in the paddock with minimal to no risk to animal gains if properly managed [42, 43]. However, mob-grazing should be strictly managed with recovery periods for forage regrowth to ensure adequate feed. Returns to management can be low for mob-grazing [45] if high stocking densities for long periods reduce average daily gain per animal [46] and

Size of WS plants influenced the efficacy of mob-grazing for weed management. In contrast to absinth wormwood (*Artemisia absinthium*) (AW) where small patches and plants were most affected by mob-grazing [44], larger WS plants were most impacted. Larger WS plants may have leaves closer to the cattle's face, which may facilitate browsing strictly due to convenience, even though the stems are woody. Smaller AW plants, which have herbaceous rather

Mob-grazing with cattle reduced forage selectivity and utilized undesirable plants compared to low stocking density rotational grazing. Long-term benefits of mob-grazing, while difficult to quantify in short-term studies, can be positive and numerous SD ranchers have adopted

than stiff woody stems, may be more easily trampled and/or consumed.

and moved every 1–3 days compared with <5% decreases

growth stage can result in rangeland degradation [37, 38].

stocking rate of about 35,000 kg ha−<sup>1</sup>

may degrade range resources and resilience.

**5. Conclusions**

Volume data from WS plants were combined for the 2013 and 2014 mob grazing treatment, with 66% (±8%) of the tagged plants decreasing in volume by 46% after grazing. In the rotational-grazed area, pre- and post-sampling volumes were similar and averaged 15,000 cm3 . However, 43% of these sampled plants had a 45% reduction in volume, but the remaining plants increased in volume by about 90%. Basal stem counts (data not shown) indicated that WS plants in mob-grazed areas had fewer stems (*P* = 0.001) after grazing, whereas no difference in stem number was observed in rotational-grazed plots. In the 2014 ungrazed pasture, 74% of the tagged plants increased in volume by an average of 5000 cm3 , a 3000% increase from the first to the second sampling.

#### **3.3. Initial WS plant volume and grazing impact**

Initial WS plant volume impacted final volume after mob grazing. Mob grazing data, combined by location, indicated that the median plant size was about 6500 cm3 . When initial plant volume < 6500 cm3 , 73% (±7%) of these plants had a 42% reduction in volume. However, about 87% (±5%) of the larger plants were reduced in volume by about 62%.

In the early spring rotationally-grazed paddock at Chamberlain (2014), initial volume did not impact final size (*P* = 0.46). About 66% of all plants increased in size an average of 168% (±81%). In the late-season rotation treatment at Selby in 2013, about 50% (±13%) of the small plants were reduced in volume by about 52% (**Figure 2B**), with the remaining plants increasing in volume an average of 150%. About 44% of the large plants were reduced in volume by about 38%, with the remaining plants increasing an average of 37%. While the plant size reduction in the less intensively grazed rotational treatment was similar between the large and small plant classes (*P* = 0.46), the increase in size of the small plants was greater than the size increase of the large plants (*P* = 0.02). This may be due to smaller plants being trampled and stems spread apart thereby increasing the final volume (i.e. plants lost vertical height but both horizontal lengths increased), whereas larger plants may have been more difficult to trample.

These data indicate that WS plants were more impacted by mob grazing compared with plants in paddocks rotationally-grazed early or later in the season. Larger plants in mobgrazed areas tended to be more damaged than smaller plants.
