Optimal Stocking Rates Research Articles

Effects of stocking rate, supplementation, genotype and their interactions on grazing dairy systems: a review

The main effects of, and the interactions between, stocking rate (SR), supplementation and genotype on dry matter (DM) intake, herbage utilisation, milk production and profitability of grazing dairy systems have been reviewed. The SR determines the average herbage allowance (HA) per cow and therefore has a major effect on herbage intake (HI) and on the productivity of grazing dairy systems. In this review, the effect of HA on HI is presented separately for two groups of studies: those that measured allowance at ground level and those that measured allowance at a cutting height of 3–5 cm above ground level. HI and milk yield per hectare usually increase as SR increases. However, there is generally an associated reduction in HI and milk yield per cow because of the decrease in average HA at a higher SR. The dual objectives of adequate level of feeding per cow and high herbage utilisation per hectare can be achieved through the inclusion of supplements. The milk response to supplements depends mainly on the size of the relative energy deficit between potential energy demand and actual energy supply. The relative energy deficit determines both energy partitioning within the cow and substitution rate. The relative energy deficit is increased by either a high demand for energy within the cow or by a deficit of dietary energy available to meet the demand. Cows of different genotype differ in their potential for milk yield. Cows with high genetic potential for milk yield undergo higher relative energy deficits under grazing dairy systems, resulting in lower substitution rates, higher milk responses to supplements, but also lower body condition score, which, in turn, leads to lower reproductive performance. Whole-farm experiments in many countries have demonstrated that the inclusion of supplements, with a concomitant increase in SR, can have synergistic effects in improving the productivity of grazing dairy systems. Overall, the level of supplementation required per cow and the optimum SR depend on the genetic potential of the cow, the size of the responses to supplement, the value of milk and the costs of feeding supplements.

Nitrogen use efficiency: A potential performance indicator and policy tool for dairy farms

Abstract Escalating fertilizer and feed costs, declining product prices, and increasing regulations to reduce environmental pollution have created new pressures to improve nutrient use in agricultural production. This study provides an overview of factors and processes that impact nitrogen use efficiency (NUE) in dairy production, identifies practices that may bridge gaps between actual-NUE obtained on commercial farms and potential-NUE obtained under experimental conditions, and explores the possibility of using NUE as a performance indicator and policy tool for dairy production. Actual feed-NUE varies from 16% to 36% and is impacted by of a range of dairy practices; manure/fertilizer-NUE varies from 16% to 77% and is very site-specific; and whole-farm NUE varies from 8% to 64% and declines as stocking rates increase. Optimal stocking rate and manure nitrogen (N) crediting can enhance NUE, increase farm profits, and reduce N loss from dairy farms. NUE could be used to further engage dairy producers in collaborative assessments of gaps between their actual N use and the biological potential of N use, to develop performance goals for N use in various production components, and to monitor and evaluate the impacts of alternative feed, manure and fertilizer management practices on N use, profitability, and environmental outcomes.

Optimal management of fertiliser and stocking rate in temperate grazing systems

Phosphorus (P) fertilisers are one of the key tools available for increasing pasture production and the profitability of grazing enterprises. However, recent rapid changes in fertiliser price have increased the importance of developing optimal management strategies for applying P fertiliser and setting stocking rates. We applied a novel combination of process-based grazing systems modelling and randomised cash flow analyses to examine how changes in fertiliser price affect optimal fertiliser application rates and stocking rates for sheep grazing systems in south-eastern Australia, simultaneously taking into account long-term economic viability and environmental sustainability. We used ‘GrassGro’, a grazing systems decision support tool, to simulate three sheep enterprise types (Merino wethers, Merino ewes, crossbred ewes) at two locations (Hamilton, Victoria; Bookham, New South Wales). Gross margins from each year simulated in GrassGro (1966–2007) were randomised 500 times and input to a cash flow analysis that identified the financially optimal stocking rate for a range of fertiliser applications and the financial risk frontiers (combinations of stocking rate and fertiliser input for which the enterprise becomes financially unviable). For all enterprises examined at both locations, the optimal combinations of stocking rate and fertiliser application rate did not vary markedly as fertiliser price changed. Regardless of enterprise type or location, the fertiliser application rate at which the highest gross margins were achieved provided the greatest range of stocking rates that were both financially viable and environmentally sustainable. Increases in fertiliser price reduced the combinations of stocking rate and fertiliser application rate that were viable in the long term, emphasising the importance of well informed grazing management decisions.

Sustainable rangeland management using fuzzy logic: A case study in Southwest Iran

While there is no consensus on a definition, it is widely recognized that the concept of sustainability has economic, environmental and social dimensions. We used fuzzy logic as a well-suited tool to handle the vague, uncertain, and polymorphous concept of sustainability. For recognizing the major important indicators in defining sustainability in range management, several semi-structured interviews with an open-ended questionnaire in three different areas of the Fars province in Southwest Iran were held. Pastoralists’ experts recognized that sustainability in range management is a function of three major components (inputs) which are the stocking rate in a pasture, the amount of plantation density per hectare, and the number of pastoralists who live in a pasture where the output of the model is the Right Rate of Stocking. Based on pastoralists’ insights we developed a model called Equilibrium Assessment by Fuzzy Logic (EAFL) which provides a mechanism for assessing sustainability in rangeland management. The EAFL model exhibits three important characteristics. First, it permits the combination of various aspects of sustainability with different units of measurement. Second, it overcomes the difficulty of assessing certain attributes or indicators of sustainability without precise quantitative criteria and, third, the methodology is easy to use and interpret. An important outcome of the EAFL model is that all the pastoralists’ experts agree with this conclusion that the current, real stocking rates are much higher than the optimal stocking rates.

Economic Returns for Purchased or Contract‐Grazed Stockers on Marshall Annual Ryegrass

Output and profitability of stocker production depend largely on stocking rate, but the optimal stocking rate may be different for contract grazing and traditional ownership of cattle (Bos taurus). Little previous research has been conducted on economic returns under contract grazing for different stocking rates. Data from a grazing experiment performed at the E.V. Smith Research Center (Macon County, Alabama) in 2004 were used in an analysis of the economic benefits of contract grazing vs. traditional ownership. In the experiment, the highest stocking rate (SR) resulted in the maximum gain ha−1 (G) but not always the maximum return ha−1. For traditional ownership, returns ha−1 were highest at 6.17 steers ha−1 under typical price margins. Under contract grazing, the highest experimental stocking rate (7.41 steers ha−1) produced the highest returns. If resources to purchase cattle are not limited, traditional ownership was superior to contract grazing under all but extremely unfavorable price margins. If capital to purchase stockers is limited, contract grazing may provide higher total returns. Shrinkage level can influence the relative profitability of contract grazing versus traditional ownership. Contract grazing may be preferred in some situations with high expected shrinkage, where ownership would be preferred with lower expected shrinkage.

Towards sustainable grassland and livestock management

SUMMARYGrasslands are one of the world's major ecosystems groups and over the last century their use has changed from being volunteer leys, or a resource on non-arable land, to a productive resource equal to any crop and managed as such. Many grasslands are now being acknowledged as having a multifunctional role in producing food and rehabilitating crop lands, in environmental management and cultural heritage. However, grasslands across the globe are under increasing pressure from increasing human populations, reduced areas with increasing livestock numbers, and declining terms of trade for livestock production, and they are managed to varying degrees of effectiveness. The complexity of grassland uses and the many aspects of grassy ecosystems require a framework wherein solutions for better management can be developed. The present paper discusses a generic approach to grassland management to satisfy these multiple objectives. A focus on ecosystem functionality, i.e. on water, nutrient and energy cycling and on the biodiversity required to sustain those functions, provides a means of resolving the dilemmas faced, through the intermediary, management-related, criteria of herbage mass, which also relates directly to animal production. Emphasis is placed on the opportunities to satisfy multiple objectives. A consideration of the basic relationships between stocking rate and animal production shows that the longer-term, economically optimal stocking rate is associated with improved environmental outcomes. There may be environmental objectives that go beyond economically sustainable limits for livestock producers and in those cases direct payments from the government or others will be needed. These are likely to be where degradation is clearly apparent. The achievement of desirable outcomes in grassland management that satisfy multiple objectives will require new areas of research that seek viable solutions for farmers and society.

Impact of Low Catfish Prices on Economically Efficient Feeding and Optimal Stocking Densities of Channel Catfish, Ictalurus punctatus, in Multi-Batch Production in the U. S. South

ABSTRACT Channel catfish, Ictalurus punctatus, prices fell to historically low levels in 2002 in the U.S., but little economic research has been done on optimal farm management during times of very low prices. A Just-Pope catfish production function was used to estimate minimum catfish prices and maximum feed prices at which various feeding rates would be economically efficient. Optimal stocking and feeding rates were estimated for very low catfish price levels. Low catfish prices require lower stocking and feeding rates to operate at profit-maximizing levels. However, results showed that the very low prices of 2001–2002 would require farmers to stock at densities less than 10,000/ha to be able to feed at 2% of the pond biomass. Even maintenance feeding (1% of pond biomass) is not economically efficient at prices below $1.43/kg. However, stocking rates below 10,000/ha will not generate adequate revenue to cover debt-servicing requirements for long-term capital investment loans. Thus, farmers must adopt management strategies that will satisfy the multiple business requirements of servicing debt and meeting fish-delivery schedules. The results of this analysis provide guidance on the relationships among prices of catfish and feed, with stocking and feeding rates, to provide a basis for these difficult decisions.

A market-driven approach to the optimal stocking problem on African game ranches

As the growing game ranch industry in Africa becomes more sophisticated so the demand grows for tools and techniques that help achieve greater profits. Within the constraints imposed by the need to meet ecological and other requirements in these multispecies systems, there is scope for manipulating the balance of species to meet economic objectives. A new model and approach centred on marketable packages is proposed to address much of the inadequacies of current practice and previous approaches to the problem. The solution method uses column-generation techniques to generate optimal hunting and live sales packages. Optimal stocking rates for each species then follow. The procedure is illustrated for a typical 4000 ha game farm in a semi-arid region.

The logistic model-generated carrying capacities, maximum sustained off-take rates and optimal stocking rates for Kenya's commercial ranches

This paper deals with the derivation of logistic models for cattle, sheep and goats in a commercial ranching system in Machakos District, Kenya, a savannah ecosystem with average annual rainfall of 589.3 ± 159.3mm and an area of 10 117ha. It involves modelling livestock population dynamics as discrete-time logistic equations with fixed carrying capacities. The fixed carrying capacities are generated endogenously using time-series ranch data, covering a period of 15 years, from 1987 to 2001, in a commercial ranching enterprise. The model incorporates interaction parameters, generated endogenously. The estimation of the logistic models involves estimation of econometric models for each livestock species, followed by the recovery of the logistic models mathematically. Optimisation procedures are employed to determine the optimal stocking levels and the optimal off-take levels. The model-generated carrying capacities are 2 985, 791 and 201 animal units (AUs) for cattle, sheep and goats, respectively. Optimal stocking levels are 1 369, 154 and 69 AUs for cattle, sheep and goats, respectively, while the optimal off-take levels are 857, 88 and 63 for cattle, sheep and goats, respectively. This shows that the logistic models-based system analysis is applicable to the management of mixed-species commercial ranching enterprises.

Determining Optimal Stocking Rates Using a Stock–Recruitment Model: An Example Using Walleye in Northern Wisconsin

AbstractWe propose that stock–recruitment models can be used to estimate optimal stocking rates. Data to estimate the optimal stocking rates can be obtained in a relatively short amount of time by sampling similar populations over a few years. Whether the goal of stocking is endangered species recovery or supplementation of recreational fisheries, accurately determining the optimal stocking rate is of ecological and financial importance. As an example, we applied this approach using a Ricker stock–recruitment model to walleye Sander vitreus stocking in northern Wisconsin lakes. Using June stocking data and fall age‐0 survey data for 39 lakes over a 14‐year time period, we found that the stocking rate resulting in the greatest number of age‐0 walleyes was 60 age‐0 walleyes/ha. Similarly, using June stocking data and fall age‐1 survey data in 18 lakes over a 9‐year time period we found that the stocking rate resulting in the greatest number of age‐1 walleyes was 75 age‐0 walleyes/ha. About 16% of the variation in fall age‐0 walleye density was explained by the stocking rate, and 28% of the variation in fall age‐1 walleye density was explained by the stocking rate. Density‐dependent survival was apparent and significant, as low and high stocking densities resulted in lower age‐0 and age‐1 juvenile walleye densities. The lake surface area explained a significant amount of the residual variation in the age‐1 stock–recruitment relationship such that stocked walleyes generally survived at lower rates in large lakes than in small lakes, which may be due to a greater diversity of predators in larger lakes. Based on our analysis, we recommend stocking small fingerling walleyes at a rate of 75 fish/ha in northern Wisconsin lakes.

Effects of stocking and nitrogen fertilization rates on steers grazing dallisgrass-dominated pasture1

To compare the performance of steer calves managed under different stocking rates (SR; 3.7, 6.2, 8.6, and 11.1 steers/ha for 140 d; chi(I1)) and N fertilization rates (112, 224, and 336 kg of N/ha; chi(I2)) in May 1996, 1997, and 1998, 72 steer calves (BW = 231 +/- 2.5 kg) were assigned randomly to one of 12 0.81-ha dallisgrass (51%)/common bermudagrass (32%) pastures. One-third of the fertilizer was applied in the form of ammonium nitrate in May, June, and August to achieve the prescribed totals. Treatments were separated using a polynomial regression equation: gammai = beta0 + beta1chi(I1) + beta2chi(I2) + beta(11)chi2(I1) + beta(12)chi2(I2) + beta(12)chi(i1)chi(i2) + epsilonI, with years as replicates. Within the range of the data, ADG and BW gain per steer were greatest at a stocking rate of 3.7 steers/ha and 336 kg/ha of N. Body weight gain per hectare peaked at 701 kg when cattle were stocked at 8.9 steers/ha and the pasture was fertilized with 336 kg/ha of N. The least cost of production was at a stocking rate of 3.7 steers/ha, with 112 kg/ha of fertilizer N applied, and the greatest cost of production was at a stocking rate of 11.1 steers/ha with 336 kg/ha of fertilizer N applied. Fertilization at 336 kg/ha of N produced the most profitable stocking rate at 7.3 steers/ha and returned 355.64 dollars. The optimal stocking rate for net return was 79, 81, and 82% of that for maximum BW gain per hectare for 112, 224, and 336 kg/ha of N, respectively. Under the assumptions made in the financial analysis, these data show that the economically optimal carrying capacity of similar pastures can be increased with N fertilizer up to at least 336 kg/ha annually.

Use of irrigated pastures in semi-arid grazinglands: A dynamic model for stocking rate decisions

We present a simple simulation model as an aid to conventional expensive field experimentation and as a decision support system tool for animal production in irrigated pastures within semi-arid grazinglands. We also demonstrate and discuss the integration of results from conventional field experiments within the context of simulation models. We first develop a spreadsheet to estimate animal production under different stocking rates and pasture characteristics, and then incorporate functions from the spreadsheet and from the literature into a dynamic simulation model. The spreadsheet, which is programmed in EXCEL, is a static, deterministic series of calculations that estimates weight gain of grazing animals under different stocking rates and pasture conditions based on decision rules and functions reported by NRC and MAFF. The simulation model, which is programmed in STELLA ® Research 6.0 for use on a personal computer, is dynamic and stochastic. Simulation results were close to observed values for northern Mexico with regard to annual yield of dry standing crop (21,434 vs. 23,637 kg ha −1), dry matter digestibility (67–78% vs. 70–74%), and optimum stocking rate as live weight (892–2567 vs. 2250 kg ha −1). Simulation results indicated the highest optimum stocking rate was 2567 ± 62 kg ha −1 in July and the lowest was 892 ± 106 kg ha −1 in January. The highest daily gain per head was 1.144 ± 0.006 kg in February and the lowest was 0.480 ± 0.052 kg in July. Daily forage allowance for the optimum stocking rate varied during the year from 4.05 ± 0.053 in July to 4.84 ± 0.008% of live weight in January. Producers should maintain a herd size that allows maintenance of the optimum stocking rate during months of low growth and, during months of high growth, should graze only the area required to cover the recommended forage allowance, and cut the rest of the forage.

Thirteen-year growth of jarrah (Eucalyptus marginata) on rehabilitated bauxite mines in south-western Australia

Summary Alcoa's objective is to restore its bauxite mines in south-western Australia to a productive self-sustaining jarrah forest. This paper describes the growth and form of 13-y-old jarrah (Eucalyptus marginata) trees established from seed and planted seedlings, and subject to various fertiliser, understorey seed and spacing treatments. Seeded jarrah had a mean establishment density of 2662 stems ha−1 and a density of 2300 stems ha−1 after 13 y, a survival rate of 86%. Sixty-two per cent of the seeded trees developed into saplings (> 1.5 m tall). The saplings had a mean height of 9.0 m and dbhob of 14.4 cm after 13 y. The mean density of potential sawlogs (trees with a single stem to at least 2 m) was 1297 stems ha−1 after 13 y. The presence of tall native legumes (acacias) decreased the percentage of trees that became saplings from 72% to 53%. When N fertiliser was not provided the legumes had a suppressive effect on the basal area and bole volume of potential sawlogs, reducing them to 60% and 57%, respectively, of the values without legumes. Planted jarrah trees had a mean survival rate over all treatments of 84% after 13 y. Closer tree spacing (particularly 1 m × 1 m) resulted in significantly lower survival (77%) than the wider spacings. Inclusion of tall native legumes with closer tree spacing reduced survival even more (69% at 1 m × 1 m). The mean sapling height across all planted treatments was 9.1 m. The mean dbhob was 15.2 cm with 67% becoming saplings. Closer tree spacing had the strongest effect in significantly reducing all of these parameters. Tall native legumes reduced the dbhob of the jarrah trees and reduced the overall mean height of all jarrah by limiting the proportion of jarrah that became saplings. Absence of added N fertiliser also significantly reduced these measures. Basal areas were similar in rehabilitated and unmined forest after 13 y. Mean annual growth increments (1.52 m2 ha−1 seeded, 2.72 m2 ha−1 planted) were similar to those reported for similar aged regrowth forest (2.62 m2 ha−1) and higher than older thinned (0.45 m2 ha−1) or unthinned (0.19 m2 ha−1) unmined forest. Basal area increments were higher from 8–13 y than 0–8 y, indicating that growth rates were not slowing down over this period. The optimum stocking rate for jarrah in rehabilitated bauxite mines will be a balance between growth rate, tree form, other environmental factors and cost considerations. The current rehabilitation prescription aims to establish 1300 stems ha−1 of ‘total eucalypts’ by broadcast seeding (jarrah and marri — Corymbia calophylla). This study indicates that an initial stocking of 1300 stems ha−1 is optimum and meets Alcoa's mine rehabilitation completion criterion of providing at least 300 potential sawlogs ha−1 at 15 y of age.

Carbon sequestration in dryland ecosystems.

Drylands occupy 6.15 billion hectares (Bha) or 47.2% of the world's land area. Of this, 3.5 to 4.0 Bha (57%-65%) are either desertified or prone to desertification. Despite the low soil organic carbon (SOC) concentration, total SOC pool of soils of the drylands is 241 Pg (1 Pg = petagram = 10(15)g = 1 billion metric ton) or 15.5% of the world's total of 1550 Pg to 1-meter depth. Desertification has caused historic C loss of 20 to 30 Pg. Assuming that two-thirds of the historic loss can be resequestered, the total potential of SOC sequestration is 12 to 20 Pg C over a 50-year period. Land use and management practices to sequester SOC include afforestation with appropriate species, soil management on cropland, pasture management on grazing land, and restoration of degraded soils and ecosystems through afforestation and conversion to other restorative land uses. Tree species suitable for afforestation in dryland ecosystems include Mesquite, Acacia, Neem and others. Recommended soil management practices include application of biosolids (e.g., manure, sludge), which enhance activity of soil macrofauna (e.g., termites), use of vegetative mulches, water harvesting, and judicious irrigation systems. Recommended practices of managing grazing lands include controlled grazing at an optimal stocking rate, fire management, and growing improved species. The estimated potential of SOC sequestration is about 1 Pg C/y for the world and 50 Tg C/y for the U.S. This potential of dryland soils is relevant to both the Kyoto Protocol under UNFCCC and the U.S. Farm Bill 2002.

Pasture Forages, Supplementation Rate, and Stocking Rate Effects on Dairy Cow Performance

Objectives were to evaluate effects of forage species, stocking rate, and supplementation rate on performance and physiology of grazing lactating Holstein cows under intensive rotational stocking management during summer. Eight treatments were arranged in a 2×2×2 factorial design. Animals (n=62) grazed pastures of Tifton 85 bermudagrass or Florigraze rhizoma peanut, a tropical legume. Low and high stocking rates were 7.5 and 10.0 cows/ha for bermudagrass and 5.0 and 7.5 cows/ha for rhizoma peanut. Within each forage-stocking rate combination, cows were fed supplement at 0.33 or 0.5kg of supplement (as-fed basis)/kg daily milk production. Cows grazing rhizoma peanut pastures produced more milk (16.9 vs. 15.4kg/d) but had higher rectal temperatures (39.4 vs. 39.1°C). Milk production per cow was improved at the higher stocking rate for bermudagrass but was reduced at the higher stocking rate for peanuts. Increasing supplementation rate boosted plasma glucose, milk production, and milk protein percent. Increased supplementation rate had a greater positive impact on milk production of cows grazing bermudagrass compared to rhizoma peanut (21.9 vs. 10.6% increase) due to a lower substitution of grain for forage intake. Organic matter intakes of forage, supplement, and total diet were greatest by cows grazing rhizoma peanut pastures and averaged 12.4, 6.1, and 18.5kg/d compared to 9.2, 5.4, and 14.6kg/d for cows grazing bermudagrass. Despite lower individual feed intake and performance, production per unit land area was 29% greater (112 vs. 90kg of milk/ha per d) for cows grazing bermudagrass due to the greater stocking rate possible with that forage. Only cows supplemented at the high rate and kept at the high stocking rate on bermudagrass maintained body weight. Cows on other treatments lost body weight. Tifton 85 bermudagrass appears to be an excellent summer forage for dairy cows grazing in the southeastern U.S. given its nutritive value characteristics and high yields. Optimum stocking rate may be as high as 10 cows/ha during times of peak growth of forage for low-to-moderately producing cows fed supplement. Furthermore, the positive milk production response to additional supplement when cows grazed Tifton 85 pastures (0.8kg/kg of supplement), indicates the value of providing supplement to cows grazing this moderate quality forage.

Stocking Rate and Cow-Calf Production on Sand Sagebrush Rangeland

Stocking rate is generally considered to be the most important management factor in sustainable grazing of Great Plains grasslands over management periods of 10 to 20 years or longer. Most studies to determine optimum stocking rates have compared only 2 or 3 discrete stocking rates. Our objective was to determine cow, calf, and economic performance on sand sagebrush (Artemisia filifolia Torr.) rangeland as a continuous function of stocking rate. Replicated stocking rates of 0.11, 0.15, and 0.22 head ha-1 were studied over an 8-year period. Cow weight declined as stocking rate increased in drought years but was not affected by stocking rate in wetter years. Weaning percentage was not affected by stocking rate but variation within treatment groups was high. Calf birth weight and weaning weight both declined as stocking rate increased. Comparing 0.11 and 0.22 head ha-1, calf production cow-1 declined from 206 to 144 kg cow-1 as stocking rate increased but calf production ha-1 increased from 22.6 to 31.7 kg calf ha-1. Net returns were maximized at $7.87 ha-1 year-1 at a stocking rate of 0.172 head ha-1, well within the range of experimental treatments. Net returns were within 5% of maximum between stocking rates of 0.156 and 0.183 head ha-1. The variability of all responses increased as stocking rate increased. Simulation indicated that improved livestock prices and increased animal productivity shifted the economic optimum stocking rate to higher levels, which would put more pressure on the conservation ethic of land managers. DOI:10.2458/azu_jrm_v55i6_gillen

Influence of Grazing Lease Terms on Economic Optimal Stocking Rates

The terms of grazing lease contracts potentially influence a tenant's incentive to preserve the vegetation resource. Annual stocking rate decisions dictate the degree of overgrazing, which can be cumulative over long periods of time. The objective of this study was to identify the impact the tenant's lease length and lease type has on profit maximizing stocking rates. A multi-period nonlinear programming model was developed to identify economically optimal stocking rates each year over a 24-year period. The model was solved under 1-, 4-, 8-, and 12-year leases on a and basis. The relative importance of each lease alternative and other input values in explaining the tenant's optimal stocking rate was ranked based on standardized ordinary least squares coefficient estimates. Lease length and lease type had a minor impact on optimal stocking rates relative to non-lease factors such as livestock prices and production costs. Holding lease length constant, per ha leases generated a 2% higher average stocking rate than per head leases. Optimal stocking rates were inversely related to the length of the lease. Twelve-year leases generated 18 and 13% lower optimal stocking rates than the 1-year per ha and per head leases, respectively. The optimal stocking rate difference between an 8-year and a 12-year lease was negligible, suggesting the 8-year lease would provide a similar incentive to protect vegetation as a lease with a longer planning horizon. DOI:10.2458/azu_jrm_v55i5_may

A landscape‐scale model for optimal management of sheep grazingin the Magellanic steppe

Abstract. Effective management of rangelands requires the development of landscape‐scale models for predicting spatial and temporal variability of forage. In the Magellanic tussock steppes, as in other cold‐temperate regions, grazing capacity is dependent on the winter season. To develop a management tool for the region, we analysed links between winter forage availability, weather, stocking rate and vegetation structure. We studied four paddocks over five years with a range of stocking rates from 0 to 1.53 sheep.ha‐1. We sampled forb and non‐tussock graminoid biomass, vegetation structure and faecal pellet abundance at the end of each summer. Daily temperature and rainfall data were also recorded. A regression model explained the amount of winter forage as a positive function of graminoid cover, spring minimum temperature, annual precipitation and a negative function of dwarf shrub canopy, bare soil and stocking rate (R2= 0.59). Interactions of structural variables with precipitation and stocking rate were detected, indicating strong fluctuations of forage availability in lawn communities dominated by short graminoids. The most probable causes of this response would be higher utilisation and lack of canopy structure. Our results illustrate how maps of vegetation structure, obtainable from satellite images, with weather and stocking rate data could be used for predicting optimal stocking rates in large, heterogeneous sheep paddocks.ed.

Influence of grazing lease terms on economic optimal stocking rates

The terms of grazing lease contracts potentially influence a tenant's incentive to preserve the vegetation resource. Annual stocking rate decisions dictate the degree of overgrazing, which can be cumulative over long periods of time. The objective of this study was to identify the impact the tenant's lease length and lease type has on profit maximizing stocking rates. A multi-period nonlinear programming model was developed to identify economically optimal stocking rates each year over a 24-year period. The model was solved under 1-, 4-, 8-, and 12-year leases on a "per ha" and "per head" basis. The relative importance of each lease alternative and other input values in explaining the tenant's optimal stocking rate was ranked based on standardized ordinary least squares coefficient estimates. Lease length and lease type had a minor impact on optimal stocking rates relative to non-lease factors such as livestock prices and production costs. Holding lease length constant, per ha leases generated a 2% higher average stocking rate than per head leases. Optimal stocking rates were inversely related to the length of the lease. Twelve-year leases generated 18 and 13% lower optimal stocking rates than the 1-year per ha and per head leases, respectively. The optimal stocking rate difference between an 8-year and a 12-year lease was negligible, suggesting the 8-year lease would provide a similar incentive to protect vegetation as a lease with a longer planning horizon.

Stocking rate and cow-calf production on sand sagebrush rangeland

Stocking rate is generally considered to be the most important management factor in sustainable grazing of Great Plains grasslands over management periods of 10 to 20 years or longer. Most studies to determine optimum stocking rates have compared only 2 or 3 discrete stocking rates. Our objective was to determine cow, calf, and economic performance on sand sagebrush (Artemisia filifolia Torr.) rangeland as a continuous function of stocking rate. Replicated stocking rates of 0.11, 0.15, and 0.22 head ha-1 were studied over an 8-year period. Cow weight declined as stocking rate increased in drought years but was not affected by stocking rate in wetter years. Weaning percentage was not affected by stocking rate but variation within treatment groups was high. Calf birth weight and weaning weight both declined as stocking rate increased. Comparing 0.11 and 0.22 head ha-1, calf production cow-1 declined from 206 to 144 kg cow-1 as stocking rate increased but calf production ha-1 increased from 22.6 to 31.7 kg calf ha-1. Net returns were maximized at 7.87 ha-1 year-1 at a stocking rate of 0.172 head ha-1, well within the range of experimental treatments. Net returns were within 5% of maximum between stocking rates of 0.156 and 0.183 head ha-1. The variability of all responses increased as stocking rate increased. Simulation indicated that improved livestock prices and increased animal productivity shifted the economic optimum stocking rate to higher levels, which would put more pressure on the conservation ethic of land managers.