Simulation: An aid to decisions on superphosphate use for beef production

A model of a steer beef production system, developed for a Mediterranean environment in Argentina, was evaluated for a similar environment in Australia. After testing against experimental data, the model was used to examine the effects of a range of pasture growth responses to a current application of superphosphate in an average and a poor season, and for different combinations of stocking rates, beef prices and dates of sale.Gross margins were small at low stocking rate, irrespective of the level of pasture response to fertiliser. In an average season, higher stocking rates were profitable, particularly if prices were high and large responses possible. In a poor season, however, these same stocking rates gave negative gross margins although large responses did reduce the size of the loss. The adverse effects of a poor season were least at lower stocking rates or if steers were sold earlier at the end of spring rather than in late summer.It is suggested that, where data on the growth response of pasture to fertiliser in a given farm situation are provided, this simple model can provide an early assessment of subsequent fertiliser strategy in that situation.     

Beef production systems and sales strategies in an extensive ranching region in South Africa

Rainfall variability and stocking rate in extensive ranching regions in the Northwestern Transvaal, South Africa, can have substantial influence on feed availability per animal and thus on beef production. A simulation model was developed to compare the degree of variability of revenues from four beef production systems, ranging from inflexible weaner marketing to marketing of 3-year-old oxen. Regression equations relating stocking rate and rainfall to calving percentage and weaning mass, and actual rainfall data over a period of 54 years were used in the analysis. Results indicated a lower mean revenue with a low income variation for the more intensive weaner system as compared to the more flexible 26–28-months and 39–42-months oxen production systems. Thus, in this area, characterised by low and rather variable rainfall, superior economic results can be obtained by choosing flexible production systems and marketing strategies.     

Deferred grazing of Mediterranean annual pasture for increased winter sheep production

Deferred grazing of Mediterranean annual pasture involves the removal of sheep while the pasture re-establishes following the break of season, to allow a more rapid development of leaf area—and hence growth rate—of pasture during the ensuing winter months. Reported animal production responses to this practice have been variable, therefore a published mathematical model of a deferred grazing system was used to explore some of the reasons underlying this variation.Computer simulation was used to predict the effects of stocking rate, length of deferment and initial plant density. The results suggest that the response to deferment is markedly dependent on all three factors. The combinations of stocking rate and length of deferment maximising the response to deferred grazing were found to vary widely, depending on intial plant density and the economic weighting given to the value of liveweight produced. It was concluded that future experimentation needs to critically examine the interaction between these three factors if profitable response situations are to be defined more accurately.     

Application of a simple ecological sustainability simulator (SESS) as a management tool in the semi-arid rangelands of northeastern Mexico

We use a simple ecological sustainability simulator (SESS) [Diaz-Solis, H., Kothmann, M.M., Hamilton, W.T., Grant, W.E., 2003. A simple ecological sustainability simulator (SESS) for stocking rate management on semi-arid grazinglands, 76, 655] for rangelands with mean annual precipitation of 500 mm to evaluate tendencies in range productivity and cattle production under four management options: (1) supplemental feeding, (2) short-term reduction of stocking rate, (3) early weaning, and (4) adjustment of breeding seasons. We have made five modifications to SESS for the present paper. (1) Cattle mortality now occurs each month as a function of body condition. (2) Cows that are not pregnant 2 months after the end of the breeding season are sold. (3) Forage intake is calculated separately for each cohort of cows. (4) Cows that have been sold or have died are replaced just before the beginning of each breeding season (except for the short-term reduction of stocking rate strategy). (5) The calculation of stocking rate now includes cows, bulls, nursing calves, weaned heifers less than 20 months of age, and pre-reproductive heifers aged 20 months or older.Simulation results suggest the four management options might be ranked from best to worst, in terms of increasing cattle production while maintaining range productivity, as: (1) short-term reduction of stocking rate, (2) adjustment of breeding seasons, (3) early weaning, and (4) supplementation. Short-term reduction of high stocking rates reduces the deterioration of range productivity because of the reduction in the number of stock. Adjustment of breeding seasons such that periods of highest energy requirements of cows and calves coincide with periods of highest forage production increases percentage pregnancy. Early weaning of calves improves the body condition of cows and increases annual production of weaned calves, but does not reduce the stocking rate and thus does not improve range productivity. Supplemental feeding, and other management practices that artificially sustain herbivores, break the negative feedback that promotes good range productivity and maintains long-term system stability. In general, strategies to increase cattle production in semi-arid rangelands should be based on the improvement of natural forage production.     

Evaluation of strategies for tracking climatic variation in semi-arid grazing systems

Ways of ‘tracking’ environmental fluctuations could be of value in limiting drought-induced mortality and increasing output. We examined a range of tracking policies, designed to tackle climatic variation, using a simulation model of a semi-arid grazing system. These compared annual sales designed to limit stocking rate, pre-emptive sales triggered by insufficient rainfall, and variable sales and stocking rate regimes determined by the current season's rainfall. Although the flexible stocking strategies did reduce mortality losses, compared with fixed stocking, they did not increase average annual sales. The main reasons for this are that major losses of stock are associated less with 1-year than with 2-year droughts, which are difficult to track, and that destocking can be really effective only if the productive potential of the herd can be re-established more rapidly than is possible from depleted herd resources. Tracking policies did have a considerable advantage in terms of reduced inter-annual variability of sales, which would be of economic benefit to the commercial livestock sector. For subsistence pastoralists, the traditional policies of maintaining the maximum number of breeding stock, and of hoping that most of them will survive drought, may be as close as ‘opportunistic’ management can get to dealing with drought.     

Using simulation to assess the risks and returns from pasture improvement for beef production in agriculturally underdeveloped regions

Improved pasture technology for beef production provides the potential for significant increases in food production in many agriculturally underdeveloped regions of the world. However, if extension officers and farmers are to accept new pasture technology they must be convinced that it is superior to the traditional system, not only in terms of expected return but also in terms of its relative riskiness.This paper describes a simulation model developed to assess the risks and returns from establishing improved pasture in an extensive beef breeding enterprise. Particular attention has been given to modelling the effect of stocking rate policy as this is a major management factor that will affect both the returns and risks associated with pasture improvement.Use of the model is illustrated for an enterprise in northeastern New South Wales, Australia, where much of the beef industry has been tradionally based on poor native pastures.     

Unravelling the rationale of `overgrazing' and stocking rates in the beef production systems of Central Brazil using a bi-criteria compromise programming model

In Central Brazil, the long-term sustainability of beef cattle systems is under threat over vast tracts of farming areas, as more than half of the 50 million hectares of sown pastures are suffering from degradation. Overgrazing practised to maintain high stocking rates is regarded as one of the main causes. High stocking rates are deliberate and crucial decisions taken by the farmers, which appear paradoxical, even irrational given the state of knowledge regarding the consequences of overgrazing. The phenomenon however appears inextricably linked with the objectives that farmers hold. In this research those objectives were elicited first and from their ranking two, `asset value of cattle (representing cattle ownership)' and `present value of economic returns', were chosen to develop an original bi-criteria Compromise Programming model to test various hypotheses postulated to explain the overgrazing behaviour. As part of the model a pasture productivity index is derived to estimate the pasture recovery cost. Different scenarios based on farmers' attitudes towards overgrazing, pasture costs and capital availability were analysed. The results of the model runs show that benefits from holding more cattle can outweigh the increased pasture recovery and maintenance costs. This result undermines the hypothesis that farmers practise overgrazing because they are unaware or uncaring about overgrazing costs. An appropriate approach to the problem of pasture degradation requires information on the economics, and its interplay with farmers' objectives, for a wide range of pasture recovery and maintenance methods. Seen within the context of farmers' objectives, some level of overgrazing appears rational. Advocacy of the simple `no overgrazing' rule is an insufficient strategy to maintain the long-term sustainability of the beef production systems in Central Brazil.     

A predictive model for beef cattle growth and carcass composition

Due to public concerns over food quality and animal welfare, beef producers are under increasing pressure to produce a high-quality product while still maintaining economic efficiency. Hence the need for a model for the accurate prediction of growth and carcass composition of beef cattle that is flexible enough to deal with the wide range of breeds of cattle and feeding regimes, either silage only or supplemented with concentrates, encountered on UK farms. This paper describes a model that has been developed based on a substantial database of experimental observations from a series of trials carried out by the Department of Agriculture for Northern Ireland. If animal and feed costs are provided, the model can provide information on the most economic level of concentrate feeding to achieve the animal growth and quality of carcass composition required.     

Pasture and forage crop systems for non-irrigated dairy farms in southern Australia: 3. Estimated economic value of additional home-grown feed

Dairy systems in southern Australia rely on grazed feed from pasture to supply between 50% and 70% of total herd feed requirements on an annual basis. However, the dominant pasture type in the region, which is based on perennial ryegrass (Lolium perenne), commonly results in feed deficits in summer which must be filled with supplements purchased off-farm, and feed surpluses in spring which must be conserved. Both of these strictures impose costs on farm businesses. It is likely, therefore, that additional grazeable feed available to dairy herds in southern Australia may have different economic value when interactions between season, stocking rate, calving date, and locality are taken into account. The analysis reported in this paper aimed to estimate, using the farm systems simulation model UDDER, the effect of these interactions on the efficiency with which extra feed can be converted to extra milk production, and therefore the possible gross economic value of the additional feed.‘Base’ farm simulations for ‘average’ and ‘top 10%’ farms (ranked according to farm profitability) in two localities (Terang: average annual rainfall 796 mm, 8 month growing season; and Ellinbank: average annual rainfall 1085 mm, 9-10 month growing season) were created to mimic the physical production and profitability of these farms as seen in regional farm benchmark datasets. These simulations were then altered to add the equivalent of 10% of the total annual herbage accumulation used in the Base simulation either on a pro-rata basis all year round, or in autumn only, in winter only, in spring only, or in summer only. The additional feed amounted to 620 and 780 kg DM/ha for Terang average and top 10% farms respectively, and 735 and 905 kg DM/ha for Ellinbank average and top 10% farms respectively. The management policies used in the Base simulations were then adjusted to harvest as much of the extra feed as possible, either by direct grazing or through silage conservation, while keeping the key system state indicators of cow condition score and average farm pasture cover within the limits known to result in long-term sustainable production.The efficiency with which extra feed was utilised was greatest in summer in all scenarios (80-100% of the extra feed supplied was harvested, all by direct grazing). This translated into consistently high gross economic returns of between $0.26 and $0.34 per kg DM of extra feed added to the model. Utilisation efficiency was lower in all other seasons and/or required marked increases in silage conservation, both of which resulted in lower gross economic returns per kg DM of additional feed. The impact of interactions between locality, season, stocking rate (higher in top 10% farm simulations than average farm simulations) and calving date (earlier at Terang than at Ellinbank) were clearly captured in the model. These interactions have very large effects on the profitability of growing extra feed at different times of the year. Agronomic research for the southern Australia dairy industry should focus on low-cost ways for supplying additional grazeable feed in summer, since current forage species options for this time of year are limited.     

A mathematical model of the United States beef production system

Dynamic linear programming was used to model the US beef production system, to determine the cattle cycle effects on feeder cattle supplies and to select feeding options that would maximise USDA choice and prime quality grade beef production. The model represented the US as a five-region beef production system with inter-regional transportation of offspring for feeding purposes. Cow weights, offspring weaning weights and feed efficiency were different for each region, but the feeding activities were the same in each region except for region two. In region two the feeding of grain to steer and heifer offspring was not an industry practice. Dynamic properties of the model were achieved through constraints that transferred animals from year zero (initial condition) to year five using calving, cow culling, replacement heifer and death loss rates as controlling parameters. The results of model exercises that used historical parameter values indicate that there will be a significant decrease in the supply of beef at all grade levels over the next five years. They also suggest that it is more economically efficient to feed calves from the southeastern and northern parts of the USA if they are transported to the southwestern region.     

Stability,resilience and sustainability in pasture-based grazing systems

In this paper we employ a simple dynamic simulation model to illustrate and extend the pasture envelope concept as an approach to characterising the stability, resilience and sustainability of pasture-based beef grazing enterprises. The pasture envelope is a form of phase diagram in which the trajectories over time of key biophysical variables such as pasture biomass and composition are graphed against critical thresholds established on the basis of pasture growth rates and livestock growth requirements. We extend the concept to incorporate key financial variables such as cash flow and critical financial thresholds. The model simulates a steer fattening enterprise based on a phalaris and sub-clover pasture in the Northern Tablelands of New South Wales, Australia. The model incorporates pasture growth and senescence for the two pasture species with competition between the species for soil nutrients and light, preferential grazing of the two species by the livestock with livestock growth based on pasture consumption. The model incorporates a variety of decision rules for rotating livestock among multiple paddocks. The model did not simulate changes in soil nutrients. Scaling the seasonal growth pattern of the pasture species captured the influence of rainfall and temperature on pasture growth.Two sets of simulations were run to illustrate the use of the pasture envelope concept to explore the economic and biological stability and resilience of the pasture system. The first set was designed to explore the financial and biological stability of the enterprise and involved simulating the impact of different stocking rates and rotation period on pasture production and composition, and cash flow. The second set of simulations was designed more to explore the resilience of the enterprise and involved introducing shocks to the enterprise in the form of `droughts' of varying strengths. This was achieved by, for example, reducing the maximum growth rate for both pasture species by 50% but maintaining the same seasonal pattern in the maximum growth rates of each species. The first simulation showed that at low stocking rates the enterprise was biologically stable, but cash flow was also low. Increasing stocking rates increased the cash flow, but also reduced the biological stability of the pasture until at very high stocking rates the pasture system collapsed. Changing the rotation period also affected the stability of the enterprise. In situations where the rotation period was very long, greater than 120 days (or 20 days/paddock), the biological system became unsustainable due to detrimental changes in pasture composition. The enterprise was somewhat resilient to drought at stocking rates less than 1 steer/ha. At stocking rates of 1 steer/ha, the enterprise was economically and biologically unsustainable in moderate or severe droughts. At a stocking rate of 1.25 steers/ha, the enterprise was unsustainable for droughts of any severity.     

Modelling dairy cattle feeding in the South-East region of Brazil

Computer modelling techniques were applied to study the structure of traditional dairy farms in the South-East region of Brazil and to help define research priorities and policies. Animal feeding is considered the principal factor affecting dairy cattle performance in the study. Knowledge of animal nutrition and feed supply from Brazilian and other literature was synthesized in two mathematical models. One model deals with the optimization of resources used in supplementary feeding for dairy cows under grazing; the other predicts dairy cow performance under a range of feeding conditions imposed by changes in the level of supplementation, stocking rate and calving date. Both models are empirical in nature. The modelling approach shows itself to be a useful means of defining research priorities and making recommendations on practical aspects of dairy cow feeding and management.     

Simulation of beef cattle production systems in the Llanos of Colombia: Part 2—Results of the modelling

Verifications and validations were conducted of a simulation model of beef cattle production on tropical ranges of the Colombian Llanos. Liveweight changes were simulated for individual cows sampled at random, for cow herds alternately grazing native savanna and molasses grass (Melinis minutiflora) and for steers grazing native savanna. Correlation coefficients between observed and simulated liveweight change were high. Simulations of the calving rates of cow herds from two experiments at Carimagua Research Station were also conducted and there was reasonably good agreement between observed and simulated data. Shortcomings of the model included an inability to simulate the heavy weight losses of grazing animals on molasses grass during the dry season and under-estimates of calving rates for the most productive herds. An experiment was conducted with the validated model from which it was concluded that grazing molasses grass and weaning of calves at 84 days of age would do little to increase calving rate.     

Energy minimised v. cost minimised alternatives for the US beef production system

A model of the US beef production system has been utilised to project tradeoffs between minimised cost of feeding and minimised fossil energy use to produce amounts of beef similar to 1976 consumption. Cost minimisation approaches the present actual beef production system, but suggests increases in bull feeding and the use of silage and grass finishing of cattle. Energy minimisation indicated energy savings could exceed the equivalent of 240 million barrels of crude oil/year. If energy costs increased three times the 1979 levels, energy and cost minimised solutions appear equivalent.USDA ‘Choice’ grade has been a cost effective strategy, even without consideration of price differentials for the higher quality beef. However, maintenance of current levels of ‘Choice’ beef production does not appear optimal from an energy efficiency standpoint. The model results for energy minimisation suggest an increase in grass finishing and feeding of large bulls, rather than steers, practices which could further reduce fossil fuel inputs, but would result in less ‘Choice’ quality meat. Each increase in energy efficiency in the beef system (other than simple elimination of waste) may be anticipated to have a cost penalty over current practice, given constant or moderately increasing energy costs.However, if energy prices were to reach three times their present level, the model suggests that national cost minimisation would require more energy efficient production systems, and the production of the higher quality beef grades would increase in relative expense. The beef industry does not, at present, minimise energy input because energy's apparent real cost has been low compared with other inputs.     

Lamb production: A case study of experimentation and simulation

Empirical relationships derived from field experiments were combined to form the basis of a model of a lamb production system. The model was then used to examine the effects of a management strategy which field results had indicated would benefit lamb production.This strategy reduced the area of pasture grazed until the end of mating with the aims of restricting ewe liveweights at mating and increasing pasture availability during pregnancy to ensure liveweight gains. The effects on gross margins were calculated for different combinations of environment, stocking rate and meat prices.This feeding restriction increased gross margins considerably if there was a marked trough in winter feed supplies, or if prices were low. In general, their effects were small relative to the influence of stocking rate.It is suggested that the contrast between large management effects found by experiment and relatively small effects predicted by the model is due to differences in constraints imposed by research workers and producers.     

基于高光谱技术的牛肉含水率无损检测

牛肉含水率的高低不仅直接影响牛肉品质,而且会对消费者造成经济损失。为此,通过实验探究了采用高光谱图像技术对牛肉含水率进行检测的可行性,为检测牛肉品质提供依据。采用82个牛肉后腿样本作为实验材料,按5×4×1cm的规格通过国际烘干法测量其真实含水量,并采集它们的光谱图像;获取样本的光谱信息后,通过ENVI及Mat Lab软件获取感兴趣区域。同时,利用不同的预处理方法,分别建立BP神经网络和偏最小二乘校正模型,通过比对两种模型结果,偏最小二乘校正模型能够更有效预测牛肉含水率,校正集相关系数为0.91,校正标准差为0.121,预测集的相关系数为0.89,预测标准差为0.118。研究结果证实,利用高光谱图像技术可以快速无损检测牛肉含水率。     

Kleingrass growth and utilization by growing steers

A model of kleingrass (Panicum coloratum L.) growth and utilization by steers is presented. The model included stochastic inputs of climatological characteristics, water retention at different soil depths, rainfall runoff, potential evapotranspiration, forage growth, forage intake and steer performance. The model was used in a 2 × 3 × 4 factorial experiment where the factors were energy systems (ARC, 1965 versus NRC, 1976), stocking rates (2·47 head per hectare, 4·32 head per hectare and 6·18 head per hectare), and four management options. Individual steer weights by months were not significantly affected by the use of either energy system. Steer weights at the end of the grazing season were affected (F = 0·06) by energy system, the NRC system predicting 7·2 kg per head more liveweight gain than the ARC system. The light stocking rate had greater (P = 0·01?0·13) daily gains over months than the heavier stocking rates. The heavy stocking rate resulted, however, in greater (P < 0·05) production per hectare per year than the lighter stocking rates. Season-long production per hectare favored (P < 0·1) management options that removed steers immediately after forage was consumed rather than anticipating rainfall and new forage growth. The light stocking rate had the least mean seasonal production per hectare (P < 0.·05) but also had the least year-to-year variability. The heavy stocking rater yielded the greater (P < 0·05) mean seasonal production per hectare but the year-to-year variation was much greater. It was emphasized that the use of such probabilities of production could aid the grazier in making stocking rate and related decisions.     

Exploring the link between farmers' objectives and the phenomenon of pasture degradation in the beef production systems of Central Brazil

In Central Brazil, half the area under sown pasture suffers from the phenomenon of pasture degradation; overgrazing is believed to be the main cause. Farmers' objectives and their links to the practice of overgrazing have been explored to obtain a better understanding of the decisions related to the setting of the stocking rate. A survey of beef cattle farmers was carried out, preceded by an exploratory poll of experts on such production systems. The method of paired comparisons was used for eliciting and analysing farmers' objectives. ‘Intergenerational transfer’ and ‘cattle ownership’ are the most dominant objectives. Because cattle ownership is implicitly included in the assets involved in intergenerational transfer, possessing cattle assumes an outstanding importance in the hierarchy of farmers' objectives. These findings elucidate the paradox of overgrazing and provide a basis for treating the perception on the influence of objectives on the degradation phenomenon from being a conjecture to that of an empirically valid hypothesis. They also suggest the need for incorporating the objective ‘maximise the number of cattle owned’ in the analysis and modelling of stocking rate decisions.     

Ruminant feeding systems in West Java,Indonesia

Data collected from 350 ruminant rearers are presented in relation to four altitude strate in West Java. In each stratum and sample village, further selection of rearers was made on the basis of main land-use type and livestock species reared. The study was conducted in the dry season of 1982.Sixteen existing systems of feeding ruminants were identified. These comprised different combinations of hand feeding, full grazing, tethering and free range grazing practices. Further simplification resulted in four main systems—full grazing, full hand feeding, mainly grazing and mainly hand feeding.Characteristics and prevalence of these feeding systems are described and related to altitudinal strata and seasons.Hand feeding was the most common system above 100 m in altitude and was especially prevalent in the wet season. However, below 100 m (where 50% of livestock units are located) combinations (mainly grazing) were most common in the wet season and grazing was predominant in the dry season.This study is intended to provide a sound background for planning research on feeding, and for village livestock development in West Java.