Paddock Size and Stocking Density Affect Spatial Heterogeneity of Grazing
Keywordsdeferred rotation grazing
grazing management systems
intensive rotational grazing
time control grazing
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CitationBarnes, M. K., Norton, B. E., Maeno, M., & Malechek, J. C. (2008). Paddock size and stocking density affect spatial heterogeneity of grazing. Rangeland Ecology & Management, 61(4), 380-388.
PublisherSociety for Range Management
JournalRangeland Ecology & Management
AbstractThe claim that intensive rotational grazing (IRG) can sustain higher stocking rates can be partially explained by more even spatial distribution of grazing such that livestock consume forage from a greater proportion of a pasture. To test the hypothesis that utilization is more even at the higher stocking densities of smaller paddocks, mean absolute deviation (heterogeneity) of utilization estimates by plot was compared in paddocks of sizes and stocking densities representing increasing subdivision from two-paddock deferred rotation grazing (DRG) to 16-, 32-, and 64-paddock, two-cycle IRG. These 70-, 4-, 2-, and 1-ha paddocks were grazed for 7 wk, 4 d, 2 d, and 1 d, respectively, at 32 animal unit days (AUD) ha-1 during 2000 and 34 AUD ha-1 during 2001. Within IRG there was no response to the treatment gradient. After one cycle in the IRG paddocks, heterogeneity of use was generally lower than in the DRG paddocks, in both 2000 (3-11% [outlier 18%] vs. 14-19%) and 2001 (9-17% vs. 24-28%). After a second cycle in 2001, heterogeneity in half of the IRG paddocks (17-21%) was nearly as high as the early-grazed (24%), but not the late-grazed (28%), of the DRG paddocks. This lack of a stronger difference between systems was probably due to the fixed two-cycle IRG schedule and lack of plant growth during the nongrazing interval. Across both systems heterogeneity of utilization was strongly positively correlated with paddock size. Because utilization was not severely patchy in the largest treatment, the difference between systems would likely be greater in commercial-scale paddocks. Thus grazing distribution can be more even under intensive than extensive management, but this depends on how adaptively the system, particularly the aspects of timing and frequency, is managed.
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Grazing systems, stocking rates, and cattle behavior in southeastern WyomingHepworth, K. W.; Test, P. S.; Hart, R. H.; Waggoner, J. W.; Smith, M. A. (Society for Range Management, 1991-05-01)Grazing systems and stocking rates are used to influence livestock grazing behavior with the intent of improving livestock and vegetation performance. In 1982, a study was initiated to determine effects of continuous, rotationally deferred, and short-duration rotation grazing and moderate and heavy stocking rates on steer gains, range vegetation, and distance traveled by and activity patterns of steers. Steers were observed from dawn to dark on 12 dates during 1983, 1984, and 1985, and activity recorded every 15 minutes. Eight steers per treatment (system X stocking rate combination) per date were observed in 1983 and 1984, and 10 per treatment in 1985. In 1984 and 1985, map locations of all steers were recorded at the same times as activity, and distance traveled summed from distances between successive map locations. In 1984, activity of 3 steers per treatment was electronically monitored during darkness. Steers grazed approximately 8.6 hr per day during daylight and 1.6 hr during darkness. Steers grazed an average of 8.9 hr/day during daylight under moderate vs 8.1 hr under heavy stocking, but stocking rate interacted with date in 1984 and grazing system in 1985. Steers traveled farther under continuous than under short-duration rotation grazing at both stocking rates in 1984, but only at the high stocking rate in 1985. Steers had to travel farther to water in the continuous pastures, and may have had to cover a greater area in an effort to select a more desirable diet, particularly under heavy stocking. These differences were not reflected in differences in gain among stocking rates or grazing systems.
Grazing systems, pasture size, and cattle grazing behavior, distribution and gainsHart, R. H.; Bissio, J.; Samuel, M. J.; Waggoner, J. W. (Society for Range Management, 1993-01-01)Reduced pasture size and distance to water may be responsible for the alleged benefits of intensive time-controlled rotation grazing systems. We compared cattle gains, activity, distance traveled, and forage utilization on a time-controlled rotation system with eight 24-ha pastures, on two 24-ha pastures grazed continuously (season-long), and on a 207-ha pasture grazed continuously, all stocked at the same rate. Utilization on the 207-ha pasture, but not on the 24-ha pastures, declined with distance from water. At distances greater than 3 km from water in the 207-ha pasture, utilization was significantly less than on adjacent 24-ha pastures, at distances of 1.0 to 1.6 km from water. Cows on the 207-ha pasture travelled farther (6.1 km/day) than cows on the 24-ha rotation pastures (4.2 km/day), which traveled farther than cows on the 24-ha continuously grazed pastures (3.2 km/day). Grazing system, range site, slope, and weather had minimal effects on cow activity patterns. Gains of cows and calves were less on the 207-ha pasture (0.24 and 0.77 kg/day, respectively) than on the 24-ha rotation pastures or 24-ha continuously grazed pastures (0.42 and 0.89 kg/da, respectively), with no differences between the latter. Calculated "hoof action" on the rotation pastures was less than that demonstrated to increase seed burial and seedling emergence. Intensive rotation grazing systems are unlikely to benefit animal performance unless they reduce pasture size and distance to water below previous levels, decreasing travel distance and increasing uniformity of grazing.
Effects of herbage allowance on defoliation patterns of tallgrass prairieJensen, H. P.; Gillen, R. L.; McCollum, F. T. (Society for Range Management, 1990-09-01)Few studies have dealt with measuring individual plant defoliations in the context of intensive grazing management. In May, July, and August of 1987, grazing trials were conducted to quantify the effects of herbage allowance on defoliation patterns of big bluestem [Andropogon gerardii Vitman], Indiangrass [Sorghastrum nutans (L.) Nash], and little bluestem [Schizachyrium (Michx.) Nash]. Herbage allowances of 10, 20, 30, and 40 kg AUD-1 were replicated twice per trial. Tiller height, relative leaf area removed, and lrequency of defoliation were measured every 2 days over 10-day trials. Indiangrass was the most preferred species in all trials. The rate of leaf area removal increased as herbage allowance decreased. Current guidelines which call for rest periods of 30-90 days would result in light to moderate intensity defolia- tion for indiangrass at all herbage allowances. The maximum percentage of tillers grazed only once per trial ranged from 20 to 98% depending on herbage allowance, species, and trial. Selectivity between species was reduced by decreasing herbage allowance but this effect was not large until herbage allowance was below 20-25 kg AUD-1 and selectivity was never completely removed. Grazing all tillers only once in a grazing period, even within a species, is unlikely in a tallgrass prairie community. Leaf area removal was moderate the first time a tiller was defoliated and severe for later defoliations. The goal of grazing any individual tiller at no greater than moderate intensity within a grazing period would he roughly equivalent to grazing any tiller no more than once. However such a goal would require many tillers to go ungrazed.