Continuous Grazing Treatments Research Articles

Effects of grazing corn plant residue on beef cattle performance, residue characteristics, and subsequent crop yield

Our objective was to evaluate the effects of grazing method on beef cattle performance, residue characteristics, and subsequent corn grain yields. This was a 3-yr study in which strip-grazing (SG), continuous grazing (CG), and ungrazed control (CT) treatments were arranged in a randomized complete block design with 3 replications per year on a continuous corn production system in central Illinois. Strip-grazed plots were divided into subplots (1, 2, 3) in which cattle back-grazed. Thirty-six spring-calving, multiparous, Angus cows were used in the first and second year of the study and 42 winter-calving Angus heifers were used in the third year. Cattle grazed for 42 d each year following corn harvest. Cattle in SG plots were 9.8 kg heavier ( P = 0.05) postgrazing compared with those on CG plots but did not differ ( P = 0.77) in final BCS, indicating adequate performance was maintained regardless of treatment. The SG and CG plots had increased ADF ( P = 0.03) and decreased CP ( P < 0.01) after grazing compared with CT. In year 2 postgrazing, SG and CG had decreased ( P < 0.01) total residue availability, leaves and husks, and cobs compared with CT, suggesting more digestible, nutrient-dense components were selected during grazing. No differences ( P = 0.16) were detected for corn yield among grazing treatments. However, yield was different ( P = 0.05) among strips. Strip 1 had lower yields than strip 2, which may have been due to increased cattle trafficking in this area. Both grazing methods resulted in acceptable performance. Grazing corn residue did not affect subsequent crop yields; however, strip differences in yield within strip-grazed paddocks warrant further investigation.

Collaborative Adaptive Rangeland Management, Multipaddock Rotational Grazing, and the Story of the Regrazed Grass Plant

Frequent, severe defoliation reduces grass production and can alter plant species composition in grasslands. Multipaddock rotational grazing has been proposed as a grazing strategy that may reduce the frequency and intensity of defoliation on palatable grass plants without altering stocking rates. Previous studies evaluated this hypothesis using small, homogeneous paddocks and nonadaptive rotation schedules and found small and inconsistent differences between continuous and rotational grazing systems. Using a stakeholder-driven collaborative adaptive management (CAM) framework, we conducted the first ranch-scale experimental investigation into tiller defoliation patterns in the context of adaptive multipaddock rotational grazing. We monitored tiller defoliation frequency and intensity in 10 paired 130-ha pastures assigned to either a collaborative adaptive multipaddock rotational grazing treatment (CARM, one livestock herd) or a season-long continuous grazing treatment (traditional rangeland management [TRM]; 10 separate herds) in shortgrass steppe. Consistent with previous studies, we observed that frequencies of grazing and regrazing on a palatable, cool-season grass (western wheatgrass, Pascopyrum smithii) were much more sensitive to stocking rate than grazing system. Under moderate stocking rates used in both CARM and TRM treatments, roughly two-thirds of western wheatgrass tillers remained ungrazed annually, regardless of grazing system. Thus, season-long rest is present in season-long continuous and rotational grazing systems. Frequencies of tiller regrazing were low (5−15%) and similar between CARM and TRM treatments. Although defoliation patterns were similar between treatments at the whole-ranch scale, CARM enhanced spatial and temporal heterogeneity in defoliation frequencies among individual pastures. Pastures grazed earlier in the season or for longer experienced more defoliation. Managers implementing adaptive, multipaddock rotational grazing could use this heightened and predictable variability to strategically manage impacts of grazing on western wheatgrass at the individual pasture scale. The CAM model enabled our team to identify and directly address key stakeholder hypotheses and resulted in coproduction of management-relevant research.

Grasshopper populations respond similarly to multiple moderate intensity livestock grazing treatments

Livestock grazing frequently affects grasshopper populations, but no prior studies have simultaneously examined a wide range of moderate intensity livestock grazing treatments in the Northern Great Plains. Grasshopper densities varied significantly between years, but five moderate grazing treatments, including both rotational and continuous grazing treatments, did not differentially affect grasshopper densities or species composition. Grasshopper populations appear resilient to different types of moderate grazing at this Northern Great Plains mixed-grass prairie site.

Evaluation of rotational grazing as a control strategy for Rhipicephalus microplus in a tropical region

Rhipicephalus microplus is the most significant tick of livestock and its control is particularly challenging due to its resistance to commercial acaricides. Pasture rotation is considered a management strategy that could help control R. microplus, however, the literature only contemplates mathematical models and little is known about the effects of this practice in the field. The objective of this work was to determine whether pasture rotation is an efficient method for controlling R. microplus. Two different experiments were performed that involved groups of continuous and rotational grazing bovines. Female ticks measuring 4.5–8.0 mm were counted on animals while larvae in pasture were counted using the flannel drag technique. Treatment for infested bovines was applied when the average group tick count was ≥30 females. The results showed that rotational grazing (with 20-day periods of rest) had a higher tick count on-host than continuous grazing (P < 0.05) and additional bovine treatment was needed. Sixty and 105 days were needed to re-infest and disinfest pasture of R. microplus larvae, respectively. The first treatment of bovines occurred 91 days after the animals were placed in a closed area. The results indicate that rotational grazing is not an efficient way to control R. microplus.

Effects of long-term cattle market conditions on continuous season-long and rotational grazing system revenues

In this study we evaluated the combination of long-term market conditions and the price slide in the cattle market on revenues associated with continuous and rotational grazing systems. A price slide is a market phenomenon in which lighter cattle sell at a higher price per unit of liveweight compared with their heavier counterparts. We used actual herd average starting and ending weights in this market analysis, and analysed the outcome using five years’ data from a continuous and rotational comparative grazing study. Despite consistently lower weight gains with rotational grazing, differences in gross revenues per steer between grazing treatments ranged from US$43.46 to minus $5.72 across the study years. We observed annual differences in the net returns across years between the two grazing systems; net returns were greater for steers in the continuous grazing treatment in three of the five years, one year with net returns that did not differ between systems, and one year in which net returns were lower with continuous grazing. These variable results showcase the complexity in having both differences in end of grazing season weight classes between the grazing systems and the differential effects of price slide among weight classes. Therefore, we argue that it may be a better management strategy for land managers to determine the optimal ending weights and the time of year to market livestock to meet the goals of an operation, rather than trying to determine which grazing system is ‘best’.

Effect of high-intensity rotational grazing on the growth of cattle grazing buffel pasture in the Northern Territory and on soil carbon sequestration

Context Scientific and anecdotal reports conflict on the effects of intensive rotational grazing (IRG) on cattle growth, and very limited objective data are available from cattle grazing in northern Australia that producers can use to decide whether to adopt IRG. Aims This study aimed to compare liveweight gain and sequestration of soil organic carbon when cattle grazed buffel grass (Cenchrus ciliaris L.) under either continuous grazing (CG) or IRG. Methods In each year of this 9-year study, a cohort of Brahman and Brahman-cross weaners was randomly allocated to IRG and CG treatments. They grazed predominantly buffel pasture at Douglas Daly Research Farm from shortly after weaning for about a year, at which time they were replaced by the next year’s group, and the average liveweight gains of the treatments over the post-weaning year were compared each year for 9 years. Soil organic carbon was measured in the topsoil (0–30 cm) twice each year for 5 years (2009–14) and changes in carbon stocks over time were compared between treatments. Key results In each year of this study, the growth of cattle grazing buffel pasture was lower under IRG than CG. In each year, liveweight gain was lower (P &amp;lt; 0.05) per head and per hectare under IRG. Topsoil soil organic carbon stocks did not increase in the IRG treatment over the 5 years of this study. Conclusions This study found that cattle growth, both per head and per hectare, was lower under IRG than CG, and that IRG did not result in any increase in soil organic carbon over time. Implications The lower per head and per area production from the IRG system, combined with the extra infrastructure and operating costs for IRG systems, make it unlikely that adoption of IRG would improve the profitability of cattle-grazing operations on similar pasture systems in northern Australia. However, the findings of this study may not apply to other pasture systems and environments.

Influence of streambank fencing on vegetation and soil of the Mixed prairie component in a complex corridor pasture

A 5 yr (2011–2015) field study was conducted to test the hypothesis that streambank fencing had a significant effect on selected vegetation and soil properties of the Mixed prairie component of a complex corridor pasture. The grazing treatments [ungrazed (UG) – periodic grazing (PG)] inside the corridor pasture were 11 yr (2001–2012) of cattle exclusion (UG), followed by 3 yr (2013–2015) of periodic grazing (PG) when the riparian soil was dry. A control treatment outside the fencing was continuous grazing (CG). Selected vegetation and soil properties were measured over the growing season at 10 paired locations in each treatment (nonreplicated) pasture over 5 yr (2011–2015), and rangeland health was measured in 2011. The UG–PG treatment significantly (P ≤ 0.10) increased the total biomass by 2- to 5-fold in all 5 yr compared with CG treatment and improved the rangeland health score of the UG phase of the UG–PG (63%) treatment compared with the CG treatment (50%) in 2011. It also significantly reduced surface soil temperature by 2.2–5.2 °C, significantly increased volumetric water content of the surface soil by 7%–10% in 3 of 5 yr, and significantly increased surface soil CO2 efflux (instantaneous) by 17%–60% in all 5 yr. Overall, the UG–PG treatment improved rangeland health, increased total biomass, soil water, and soil CO2 efflux of the Mixed prairie, but decreased soil temperature compared with the CG treatment. Excessive dead biomass, greater fire risk, and an increase in noxious weeds caused by cattle exclusion suggested that periodic grazing may be the preferred option.

Vegetation composition and forage mass in grassland with a double structure under two winter grazing regimes

ABSTRACT: Remnant areas of Pampas grassland have a distinct double structure. Efficiency of livestock farming on these grasslands depends on practices that are synchronized with natural variation. This study examined the changes in vegetation composition and forage mass during winter to understand the effects of grazing methods in a natural pasture with a double structure that was grazed by heifers. An experimental area in the municipality of Bagé, Rio Grande do Sul, was subjected to continuous or rotational grazing treatments, with two replicates each. Frequency of the structural composition and forage mass of the lower stratum and animal weight was measured at the beginning and end of the experimental period (June 7 to October 7, 2016, respectively). Data were analysed with PCA ordination, regression and variance analysis. Both structural composition and forage mass changed during the experimental period. Axonopus affinis and Paspalum notatum were characteristic of continuous grazing, while Mnesithea selloana and Axonopus argentinus characterized rotational grazing (the latter had the highest levels of forage mass). Although, grazing methods changed the composition of forage mass in winter, they did not affect average daily gain of the animals.

Grazing weakens temporal stabilizing effects of diversity in the Eurasian steppe.

Many biodiversity experiments have demonstrated that plant diversity can stabilize productivity in experimental grasslands. However, less is known about how diversity–stability relationships are mediated by grazing. Grazing is known for causing species losses, but its effects on plant functional groups (PFGs) composition and species asynchrony, which are closely correlated with ecosystem stability, remain unclear. We conducted a six‐year grazing experiment in a semi‐arid steppe, using seven levels of grazing intensity (0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep per hectare) and two grazing systems (i.e., a traditional, continuous grazing system during the growing period (TGS), and a mixed one rotating grazing and mowing annually (MGS)), to examine the effects of grazing system and grazing intensity on the abundance and composition of PFGs and diversity–stability relationships. Ecosystem stability was similar between mixed and continuous grazing treatments. However, within the two grazing systems, stability was maintained through different pathways, that is, along with grazing intensity, persistence biomass variations in MGS, and compensatory interactions of PFGs in their biomass variations in TGS. Ecosystem temporal stability was not decreased by species loss but rather remain unchanged by the strong compensatory effects between PFGs, or a higher grazing‐induced decrease in species asynchrony at higher diversity, and a higher grazing‐induced increase in the temporal variation of productivity in diverse communities. Ecosystem stability of aboveground net primary production was not related to species richness in both grazing systems. High grazing intensity weakened the temporal stabilizing effects of diversity in this semi‐arid grassland. Our results demonstrate that the productivity of dominant PFGs is more important than species richness for maximizing stability in this system. This study distinguishes grazing intensity and grazing system from diversity effects on the temporal stability, highlighting the need to better understand how grazing regulates ecosystem stability, plant diversity, and their synergic relationships.

Better management of intensive rotational grazing systems maintains pastures and improves animal performance

Grazing management has been identified as a means of increasing livestock production and improving the composition of perennial pastures. The benefits of intensive rotational grazing have been the subject of much debate, but few studies have evaluated contrasting management of intensive rotational systems. A grazing management experiment was established on a pasture with cocksfoot (Dactylis glomerata L., varieties Porto and Kara) as the dominant species, to investigate different stocking rates, paddock numbers and rotation speeds, and a flexible treatment that adjusted grazing time, rest periods and stock numbers for optimal pasture utilisation. Data were collected on pasture composition and diet quality assessed by using faecal analysis, animal weight changes and pasture characteristics. Animal production per hectare was greatest for fast rotations (56 days’ rest) at high stocking rates (HStR, 13.6 dry sheep equivalents (DSE) ha–1), but continuous grazing (CG) was equally productive. Although flexible grazing based on the 3–4-leaf stage was proposed as the best balance between pasture production and quality, this treatment had lower stocking rates (9.2 DSE ha–1) and was not as productive. No treatment negatively affected pasture composition over the 4-year period. Area of bare ground was highest for the HStR CG treatment; however, the 30-paddock rotations were able to limit bare ground at the same stocking rate. The results indicated that intensive rotational grazing could be effectively managed by using green herbage allowance. In spring, green herbage allowance needed to be 1–1.5 kg green dry matter (DM) DSE–1 day–1, which increased to 5 kg green DM DSE–1 day–1 as the quality of green DM decreased, to allow selective grazing to enhance diet quality.

The Effects of Patch-Burn Grazing on Vegetation Structural Heterogeneity in the Northern Tallgrass Prairie of South Dakota

Patch-burn grazing was developed as a grazing system to increase vegetation structural heterogeneity in managed grasslands of the central Great Plains. To evaluate this system in northern tallgrass prairie, we compared the structural response of vegetation following patch-burn grazing to that of continuous season-long grazing at two sites in eastern South Dakota. We established two pastures at each site and randomly assigned one pasture at each site to a patch-burn grazing treatment and the other to a continuous season-long grazing treatment. We allotted cow-calf pairs to each pasture during the summers of 2007 through 2009. We burned one patch of the patch-burn grazing pastures each spring for three years, leaving one patch not burned at the end of the study. We measured foliar cover of major plant functional groups, litter cover, and visual obstruction at the end of each grazing season and measured forage quality three times during the final summer. Ordination of principal component patch means showed greater vegetation structural heterogeneity for patch-burn grazing than season-long continuous grazing each year. Our results suggest that patch-burn grazing is a strategy that has potential to increase vegetation structural heterogeneity in northern tallgrass prairies and should be tested at other northern locations.

Livestock grazing and vegetative filter strip buffer effects on runoff sediment, nitrate, and phosphorus losses

Livestock grazing in the Midwestern United States can result in significant levels of runoff sediment and nutrient losses to surface water resources. Some of these contaminants can increase stream eutrophication and are suspected of contributing to hypoxic conditions in the Gulf of Mexico. This research quantified effects of livestock grazing management practices and vegetative filter strip buffers on runoff depth and mass losses of total solids, nitrate-nitrogen (NO₃-N), and ortho-phosphorus (PO₄-P) under natural hydrologic conditions. Runoff data were collected from 12 rainfall events during 2001 to 2003 at an Iowa State University research farm in central Iowa, United States. Three vegetative buffers (paddock area:vegetative buffer area ratios of 1:0.2, 1:0.1, and 1:0 no buffer [control]) and three grazing management practices (continuous, rotational, and no grazing [control]) comprised nine treatment combinations (vegetative buffer ratio/grazing management practice) replicated in three 1.35 ha (3.34 ac) plot areas. The total 4.05 ha (10.02 ac) study area also included nine 0.4 ha (1.0 ac) paddocks and 27 vegetative buffer runoff collection units distributed in a randomized complete block design. The study site was established on uneven terrain with a maximum of 15% slopes and consisted of approximately 100% cool-season smooth bromegrass. Average paddock and vegetative buffer plant tiller densities estimated during the 2003 project season were approximately 62 million and 93 million tillers ha⁻¹ (153 million and 230 million tillers ac⁻¹), respectively. Runoff sample collection pipe leakage discovered and corrected during 2001 possibly reduced runoff depth and affected runoff contaminant mass losses data values. Consequently, 2001 runoff analysis results were limited to treatment comparisons within the 2001 season and were not compared with 2002 and 2003 data. Analysis results from 2001 showed no significant differences in average losses of runoff, total solids, NO₃-N, and PO₄-P among the nine vegetative buffer/grazing practice treatment combinations. Results from 2002 indicated significantly higher losses of runoff and total solids from 1:0 no buffer/rotational grazing and 1:0 no buffer/continuous grazing treatment combination plots, respectively, compared among other 2002 season treatment combinations. The 2003 results showed significantly higher runoff and total solids losses from 1:0 no buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and from 1:0.1 vegetative buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and with respective 2002 treatment combinations. However, the 2003 results indicated effective vegetative buffer performance with significantly lower runoff, total solids, and NO₃-N losses from the larger 1:0.2 buffer area compared among the smaller 1:0.1 buffer area and 1:0 no buffer treatment combinations. The 2003 results also indicated a highly significant increase in losses of NO₃-N from 1:0.1 buffer/no grazing treatment combination plots compared among other 2003 season treatment combinations and with respective 2002 treatment combinations. Overall results from this study suggest a shift from significantly higher 2002 season plot losses of continuous and rotational grazing treatment combinations to significantly higher 2003 season losses of no grazing treatment combinations. We speculate this shift to significantly higher runoff and contaminant losses from no grazing treatment combination plots during 2003 reflects the variability inherent to a complex and dynamic soil-water environment of livestock grazing areas. However, we also hypothesize the environmental conditions that largely consisted of a dense perennial cool-season grass type, high-relief landscape, and relatively high total rainfall depth may not necessarily include livestock grazing activities.

Responses of a Remnant California Native Bunchgrass Population to Grazing, Burning and Climatic Variation

This study examined the interactive effects of grazing intensity and burning on a remnant population of the California native bunchgrass Nassella pulchra. We measured growth, reproduction and mortality of permanently marked bunchgrasses and measured bunchgrass seedling recruitment and density in permanent quadrats. We burned half of the treatment plots in late spring 1998. Grazing treatments were implemented in 1998, 1999 and 2000 at four different intensities: ungrazed, light rotational grazing (31% average biomass removal), heavy rotational grazing (42% average biomass removal), and continuously grazed. Both burning and grazing affected the bunchgrass population. Bunchgrass mortality was 10% higher in burned vs. unburned plots but was not significantly different among grazing treatments. Seedling density was 100% higher in burned vs. unburned plots 2 years after the burn, however seedling densities never attained preburn levels. Seedling densities did not differ significantly among grazing treatments, but grazing reduced the height and reproduction of the mature bunchgrasses. Adult bunchgrass density did not differ significantly in any of the treatments but experienced a five-fold decrease over the 4 years of the experiment. Although the continuous grazing treatment reduced the number of culms produced per plant by 75% from the baseline year, the effect on culm production in the continuous grazing treatment was not consistently greater than the rotational grazing treatments. The interaction of grazing and burning had no significant impacts on the N. pulchra populations except on the diameter of adult bunchgrasses which was highest in the lightly grazed, unburned treatments 2 years following the burn. All response variables except bunchgrass height followed a similar pattern in time over the 4 years of the experiment regardless of treatment, peaking in 1998 and then declining in 1999 and 2000. We believe the above average rainfall and below average temperatures experienced late in the growing season in 1998 provided conditions that favored the native bunchgrasses. Overall, we found few interactive effects of grazing and burning but the separate treatments did affect bunchgrass growth, reproduction and mortality, and these effects were modulated by the ubiquitous effects of climatic fluctuations.

Impacts of grazing systems on soil compaction and pasture production in Alberta

Livestock trampling impacts have been assessed in many Alberta grassland ecosystems, but the impacts of animal trampling on Aspen Boreal ecosystems have not been documented. This study compared the effects of high intensity [4.16 animal unit month per ha (AUM) ha-1] short-duration grazing (SDG) versus moderate intensity (2.08 AUM ha-1) continuous grazing (CG) by wapiti (Cervus elaphus canadensis) on soil compaction as measured by bulk density at field moist condition (Dbf) and penetration resistance (PR). Herbage phytomass was also measured on grazed pastures and compared to an ungrazed control (UNG). The study was conducted at Edmonton, Alberta, on a Dark Gray Luvisolic soil of loam texture. Sampling was conducted in the spring and fall of 1997 and 1998. Soil cores were collected at 2.5-cm intervals to a depth of 15-cm for measurement of bulk density (Dbf) and moisture content. Penetration resistance to 15 cm at 2.5-cm intervals was measured with a hand-pushed cone penetrometer. The Dbf and PR of the top 10-cm of soil were significantly (P ≤ 0.05) greater by 15 and 17% under SDG than CG, respectively, by wapiti. Generally, Dbf in both grazing treatments decreased over winter at the 0-7.5 cm and 12.5-15 cm depths, suggesting that freeze-thaw cycles over the winter alleviated compaction. Soil water content under SDG was significantly (P &lt; 0.05) lower than CG. Total standing crop and fallen litter were significantly (P ≤ 0.05) greater in CG treatment than the SDG. The SDG treatment had significantly (P ≤ 0.05) less pasture herbage than CG areas in the spring (16%) and fall (26%) of 1997, and in the spring (22%) and fall (24%) of 1998, respectively. The SDG did not show any advantage over CG in improving soil physical characteristics and herbage production. Key Words: Bulk density, Cervus elaphus, moisture content, penetration resistance, pasture production

Morphology of white clover during development from seed to clonal populations in grazed pastures

Following germination, the ontogeny of white clover is characterized by two distinct morphological growth phases, a seminal taprooted stage followed by a clonal growth stage. Death of the seminal taproot and primary stolon initiates a process of fragmentation of the taprooted plant into a variable number of independent clonal fragments (plants) which comprise the initial population of the clonal growth stage. The objective of this study was to characterize the plant morphology of field-sown white clover populations from germination through to established clonal populations. Populations of eight white clover cultivars were assessed when sown with perennial ryegrass or tall fescue in pastures established under a common grazing regime for 16 months prior to imposition of continuous or rotational grazing treatments. One year from sowing, taprooted plants attained maximum size, with a mean plant branching order of 3·35, stolon DW of 460 mg and lateral spread of 250 mm, with some individuals having 6th order branching, 3·5 g stolon DW and 1m lateral spread. These taprooted plants were 4–5 times the size of plants in the subsequently formed clonal population. Nine months after sowing, the first individual taprooted plants fragmented into clonal plants. Twelve months from sowing, fragmentation processes were occurring at a linear rate, eliminating 6% of the original taprooted population each month. This resulted in a 12–15 month transition period when the white clover population comprised both taprooted and clonal plants. During this transition period, the initial clonal fragments produced from taprooted plants were large, and this maintained a larger mean plant size in the clonal plant proportion of the transition population than measured in the later fully clonal population. This process was also considered to act to prevent the development of the expected differences between grazing managements, as it was not until the third year when all taprooted plants had disappeared that the clonal populations developed characteristics reflecting the expected influence of grazing management. Variation due to white clover cultivar and companion grasses was minor. The substantial differences in plant size and branching structure between taprooted and clonal populations has significant implications for the evaluation of breeding lines.

Evaluating Stocking Rate Impacts in Rangelands: Animals Don't Practice What We Preach.

paper session 29: Molecular biology - forage quality. In: Proc. XVII International Grassland Congress, pp. 1105-6. Keeling and Mundy Ltd., Palmerston North, New Zealand. United States Department of Agriculture. (1980). Report and recommendations on organic farming. U.S. Government Printing Office, Washington, DC. VanTassel, L. W., Heitschmidt, R.K. and Conner, J.R. (1987). Modeling variation in range calf growth under conditions of environmental uncertainty. J. Range. Manage. 40: 310-4. Walker, B.H. (1993). Stability in rangelands: ecology and economics. In: Proc. XW International Grassland Congress, pp. 1885-90. Keeling and Mundy Ltd., Palmerston North, New Zealand. Walker, J.W. (1994). Multispecies grazing: the ecological advantage. Sheep Res. J. Special Issue: 52-64. Walker, A.B., Frizelle, J.A. and Morris, S.D. (1994). The New Zealand policy framework for sustainable agriculture and some implications for animal production research. Proc. N. Z. Soc. Anim Prod. 54: 369-72. Walker, J.W., Heitschmidt, R.K., DeMoraes, E.A., Kothmann, M.M. and Dowhower, S.L. (1989). Quality and botanical composition of cattle diets under rotational and continuous grazing treatments. J. Range Manage . 42: 239-42. Whitson, R.E., Heitschmidt, R.K., Kothmann, M.M. and Lundgren, G.K. (1982). The impact of grazing systems on the magnitude and stability of ranch income in the Rolling Plains of Texas. J. Range Manage .35: 526-32. Wight, J.R. and Hanson, C.L. (1993). Simulation models as decision aids for management of rangeland ecosystems. In: Proc. XVII International Grassland Congress, pp. 770-1. Keeling and Mundy Ltd., Palmerston North, New Zealand. Wilson, A.D., Harrington, G.N. and Beale, I.F. (1984). Grazing management. In: Management of Australia's rangelands (Eds G.N. Harrington, A.D. Wilson and M.D. Young) pp. 129-40. Commonwealth Scientific and Industrial Research Organization, Australia. Wood, W.R. and Thiessen, T.D. (Eds) (1985). Early fur trade on the Northern Plains: the narratives of John Macdonnell, David Thompson, Francois-Antoine Laraocque and Charles McKenzie. University of Oklahoma Press, Norman, Oklahoma. Manuscript received 4 April 1996, accepted 30 July 1996. Rangel. J. 18(2) 1996, 216-43 EVALUATING STOCKING RATE IMPACTS IN RANGELANDS: ANIMALS DON'T PRACTICE WHAT WE PREACH A.J. Ash1 and D.M. Stafford Smith2 'CSIRO Division of Tropical Crops and Pastures, PMB, Aitkenvale, Qld 4814 2CSIR0 Division of Wildlife and Ecology, PO Box 2111, Alice Springs, NT 0871 Abstract Stocking rate is the most important management variable affecting productivity and stability in rangelands. In this paper we examine the relevance of stocking rate research to the complex and highly variable ecosystems that make up most rangeland enterprises. We review a number of stocking rate experiments that have been conducted in both rangelands and more intensively grazed, improved pastures and demonstrate a fundamental difference in the nature of the stocking rate - animal production relationship between the two environments. Animal production in rangelands is less sensitive to increases in utilisation rate than in improved pastures, at least in the short to medium time frame of most experiments. These differences can largely be explained by factors relating to the much greater spatial and temporal variability of rangelands such as: inter-annual and seasonal fluctuations in vegetation composition and quality; long-term vegetation changes; and spatial and temporal patterns of diet selection in complex vegetation. Together, these factors limit the application of linear stocking rate models to complex rangeland environments for prediction of animal production responses. We suggest that dynamic simulation models, which incorporate the spatial and temporal variability of rangelands, may be the best way of developing simple but useful management principles for setting stocking rates that are more appropriate than simplified regression relationships.

Grazing impacts on bulk density and soil strength in the foothills fescue grasslands of Alberta, Canada

Alberta foothills fescue grasslands are very productive ecosystems but there is concern that the traditional season-long (continuous) grazing regimes may be leading to soil deterioration due to compaction and increased soil strength. The objectives of this study were to quantify grazing effects on soil bulk density and soil strength of sloped areas in the Alberta foothills fescue grasslands at the Agriculture Canada Stavely Range Substation. The effects of two grazing intensities (heavy and very heavy) for two treatments (short duration and continuous) on these two parameters were compared to an ungrazed control. Soil bulk density and soil water to a depth of 7.5 cm were measured with a surface water/density gauge. Soil strength was measured with a hand-pushed cone penetrometer to a depth of 45 cm. Cone index, the maximum penetration resistance in a given depth interval, was used as a measurement parameter for soil strength.Grazing affected both soil bulk density and penetration resistance. Even short-duration treatments affected these soil properties, although their effects were similar for both heavy and very heavy grazing intensities. Distinction between heavy and very heavy continuous grazing treatments was clear for both bulk density and penetration resistance, with the very heavy treatment having the greatest detrimental effect on these two soil parameters for all treatments. Bulk density and soil strength values were always lowest in the spring after snowmelt and highest late in the growing season, reflecting the water status of these ecosystems. Identical treatment rankings were obtained using bulk density and penetration resistance, but cone index was a more sensitive indicator of the effects of grazing than bulk density. Key words: Grazing, fescue grasslands, bulk density, soil strength

Nutrient Intake of Cattle on Rotational and Continuous Grazing Treatments

Many benefits have been obtained from rotational grazing, including management flexibility and livestock distribution, but long-term positive effects on plant and animal production have been inconsistent. The purpose of this cast study was to investigate nutrient intake of animals in 2 production scale grazing, treatments. The study site was the Texas Experimental Ranch located in Throckmorton County, in the eastern portion of the Rolling Plains of Texas. Treatments were a 465-ha, 16-paddock, 1-herd, cell designed rotational grazing system (RG) stocked at a heavy rate (3.7 ha . cow-1 . yr-1) and a 248-ha continuously grazed (CG) treatment stocked at a moderate rate (6.2 ha . cow-1 . yr-1). Size of RG paddocks was varied to create different livestock densities to simulate rotational grazing at a 14 and 42 paddock level. Comparisons were made to determine the effect of type of grazing system (RG vs. CG) and the effect of livestock density within the RG system on nutrient intake. Nutrient intake of esophageally fistulated steers was determined by daily dosing them with ytterbium nitrate-labeled forage and collection of fecal samples plus collection of fistula extrusa samples for crude protein and in vitro organic matter digestibility determinations. The only difference caused by different livestock densities was a higher (P < 0.001) intake of forage crude protein in the simulated 42 paddock system. Nutrient intake of steers in the CG treatment was greater (P < 0.001) than those in the RG treatment. Differences between treatment were attributed primarily to differences in stocking rate rather than grazing system.

Effects of Strip Versus Continuous Grazing on Diet Parameters and Performance of Steers Grazing Eastern Oregon Native Flood Meadows

Native flood meadows in the northwestern U.S. are typically managed for hay production. However, management for use by grazing livestock is receiving increased interest. Irrigation water is primarily supplied by surface runoff from snowmelt occurring at higher elevations surrounding the meadows. This experiment was conducted to compare strip (SG) and continuous grazing (CG) effects on livestock diet quality and subsequent performance. On May 1, groups of 20 steers (253 kg) were randomly allotted to two replicates of SG and CG treatment pastures (5.6ha each). Animals in SG pastures were confined by electric fence to an area large enough to provide approximately 65% utilization after a 5- to 7-d grazing period. Average strip size was .5 ha, and varied from .23 to 1.15ha. Herbage allowance was between 305 to 1131 kg/AU under CG, and 72 to 198 kg/AU for SG treatments, as measured on d 1 in each strip.Biweekly esophageal extrusa samples and total fecal collections showed that over the grazing season, average CP of extrusa samples from CG tended to be higher than SG (P = .14), at 13.9 and 10.9%, respectively. Crude protein declined signifi-cantly between May and September. Diet IVDDM varied between treatments (P = .07), at 64.6 and 60.7% on CG and SG, respectively. Grasses were more frequent in extrusa samples from SG than CG (P = .06), at 49 and 35%, respectively. Meadow foxtail was the most common grass on the meadows and was more frequent in SG extrusa samples (P = .05). Forage intake was similar (P = .42) for both treatments, at about 2.1% of body weight per day. Steers were weighed biweekly. Steer average daily gain was greater under CG (P = .09) (1.16 kg/day) than SG (.77 kg/day).

Cow/Calf Production and Economic Returns from Yearlong Continuous, Deferred Rotation and Rotational Grazing Treatments

Livestock production from grazing is an integrated measure of the quantity and quality of forage produced and consumed. Research was conducted over 6-yr to assess the effects of four yearlong grazing treatments on cow-calf production (382 cows Bos taurus) and economic returns under extensive rangeland conditions (4637 acres). Treatments were heavy (HC) and moderate (MC) stocked continuous (1-pasture; 1-herd), a moderate stocked 4-pasture, 3-herd deferred rotation (DR); and a very heavily stocked 16-pasture, 1-herd rotation (RG). Averaged across years, stocking rates were approximately 12, 16, 15, and 10 acres/cow-year for the HC, MC, DR, and RG treatments, respectively. From 1982 through 1987, conception rates averaged 89, 93, 95, and 89%; weaned calf crops averaged 80, 83,86, and 80%; weaning weights averaged 579, 574, 593, and 550 lb; production/cow averaged 466, 467, 508, and 439 lb; production per acre averaged 40, 31,35, and 45 lb; and residual returns to land, management and profit averaged $60.81, $69.57, $93.12, and $62.72/cow and $5.35, $4.46, $6.47, and $6.63/acre for the HC, MC, CR, and RG treatments, respectively. Results show that stocking rate was the major factor affecting differences among grazing treatments in cow/calf production and economic returns and that, as stocking rate was increased, production stability decreased.