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At least 25% of lambs born in Australia die before marking. Research across southern Australia has demonstrated that reducing mob size at lambing by 100 ewes will, on average, increase the survival of single-born lambs by 0.8% and twin-born lambs by 2.2%. In this paper we assessed the economic value of lambing ewes in smaller mobs to improve lamb survival. The analysis considered scenarios for Merino and non-Merino flocks where producers subdivided lambing paddocks using temporary or permanent fencing, or where ewes were reallocated within existing paddocks based on ewe pregnancy status. Optimum mob sizes were most sensitive to the type of fencing used for subdivision, whether ewes were single- or twin-bearing, whether the effect of paddock size on potential stocking rate was included and the target return on investment. Breed, ewe stocking rate, scanning percentage and lamb price also impacted optimum mob size but had a smaller effect. The optimum mob size for twin-bearing Merino and non-Merino ewes was between 34% and 60% that of single-bearing ewes and this was similar for scenarios where paddocks were subdivided or ewes were reallocated within existing paddocks. Permanent subdivision of paddocks also presents an opportunity to increase stocking rate by capitalising on the benefits of improved pasture utilisation in smaller paddocks. The relationship between paddock size and pasture utilisation is not well quantified but it has an important effect on optimum mob and paddock size. The value of reallocating ewes within existing paddocks was greatest at a scanning percentage of 150% as this presents the greatest opportunity to alter mob sizes for single- and twin-bearing ewes. The economic return from adjusting the relative mob size of twin-bearing ewes from 100% to 50% that of single-bearing ewes was up to $0.27/Merino ewe/yr and $0.44/non-Merino ewe/yr with lamb at $6/kg carcass weight. Overall, these analyses demonstrate that reducing mob size at lambing can be a profitable strategy for improving lamb survival depending on the current size of lambing mobs. However, it is difficult to provide generic recommendations to producers for the optimum mob size of ewes and value of paddock subdivision because these are dependent on enterprise-specific factors.

Volatility of markets and climate are driving exporting dairy industries to increase milk production from pasture. However, some regions are not able to grow due to economic, social and environmental constraints. The objective of this study was to analyse at the farm system level the opportunities and challenges for the growth of pasture-based dairy production in Uruguay. A national database of 256 dairy farms was used to compare four groups of Uruguayan farms selected according to the total milk production growth rate from 2013 to 2017. Their productivity (milk production per hectare) and profit was compared by fitting mixed models. Complementarily, the International Farm Comparison Network database was used to compare biophysical and economic indicators of typical farm systems of Argentina, Australia, Ireland, Holland, New Zealand, United States and Uruguay from 2013 to 2017. The growing groups of farms (medium and high growth; >5% per year) showed more productivity due to their higher stocking rate and achieved a higher margin over feed cost and a lower feeding cost per L of milk than the shrinking groups (medium and high decrease

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.

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.

This paper presents a series of Monte Carlo computer experiments designed to determine the effect of irrigation, stocking rate and lamb drafting weight on the profitability and productivity of a sheep grazing enterprise. The experiments were performed on a hypothetical farm in the Canterbury Plains of New Zealand. Pasture growth parameters were estimated based on a 21-year series of monthly measurements and were used to introduce production risk into the model. The paper demonstrates that, independently of the risk atittude of the producer, it is important to account for the stochastic nature of the environment in an agricultural management model.

A six year on-station research project used a model-farm approach to study the benefits of improved crop-livestock integration, achieved through the introduction of leguminous forage species into crop rotations. Previous papers reported the conceptual framework, methods and experimental results. A model farm with integrated crop-sheep enterprises had twice the output of metabolizable energy and a higher stocking rate compared to a model farm with traditional rotations. A linear programming model suggested that integration improved farm profits and stocking rates, but improving the nutritional regime of ewes reduced farm profits. The model-farm approach allows close supervision of animals but otherwise had several weaknesses, in particular the difficulty of mimicking the real farm environment on a research station. If the weaknesses are corrected, the approach could be applied with substantial benefits in national programs that have under-utilized land, animal and staffing resources.

The first paper in this series described the development of procedures for predicting the effect of management changes on wool growth rate and fleece characteristics. A model of a self-replacing flock of Merino ewes was modified to provide weekly predictions of wool growth rate, fibre diameter, staple length and staple strength. This paper presents the results of a comparison of biological predictions of the model with field observations collected under a range of seasonal conditions and stocking rates. The results of the comparisons demonstrated the ability of the model to mimic the seasonal pattern of events and the trends in pasture and sheep performance generated by a wide range of stocking rates. The model successfully predicted the direct effects of stocking rate and changing seasonal conditions, as well as the interactions between them. For most of the fleece data, the model predictions were well within one standard deviation of the field observations. No major biases in the predictions of the model were evident.

A simple mathematical model has been formulated to model a simple rotational grazing system of two fields, where a mob of animals is grazed first in one field, then the other. By using linear functions for the rate of herbage mass accumulation and for the rate of animal herbage intake, this system may be solved explicitly to yield expressions for (1) the total intake per animal over the time period, and (2) the total remaining herbage after grazing. Regarding the swap over time as an optimal control variable, these expressions can be optimized. The results are analysed for various initial conditions, including stocking rate, initial biomass in each field, and field Comparisons are made with continuous grazing. Extensions to the model are discussed.

A simulation model was written to study how sward characteristics affect steer performance and the grazing behavior of steers. This model, called INTERFACE, simulates grazing behaviour as affected by both horizontal and vertical distribution of forage quality throughout simulated swards. Simulated steers grazed small, rectangular pastures containing a tall fescue monoculture. Horizontally, the pasture was divided into 12 equally-sized sites with the water and mineral source both located in one site. Steers randomly selected a site for grazing. Vertically, the sward was divided into five layers, each of which varied in quality, i.e. proportion of cell wall, nitrogen, minerals or lignin. Results of trial simulations indicated that steers spent more time grazing sites near the water source and progressively less as distance from the water source increased. Grazing time increased as the sward became shorter and more inferior in quality. Although this model simulates diet selection simply as a random process, grazing time comparisons with actual grazing data suggest that this assumption may be adequate. This model can be used to test hypotheses about grazing behavior as influenced by forage quality and sward height.

The economic effect of increased stocking rate permitted by the introduction of dry season feedin is evaluated with reference to the growing/fatening system of beef production in the sub-humid tropics. A widely applicable model is derived which requires few input variables, all of which will be easily obtainable in a specific location. The economic break-even point in terms of feeding cost and dry season length can be determined in order to assess the value of local diets or attempt the formulation of new ones. Increae in profitability due to dry season feeding is assessed taking into account increase in stocking rate, seasonal de-stocking practices, length of dry season, growth rates, feed costs and beef price. The model is appropriate for use in developing countries and can be employed manually to determine rapidly those management options worthy of more detailed consideration.

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.

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

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.

The performance of young beef cattle from 6 months to 30 months old grazing on lucerne-based pastures was compared with that on phalaris—subterranean clover pastures at Canberra over four years at 1·5, 2·0 and 2·5 animals ha−1. Three anthelmintic treatments of nil, an autumn drenching and suppressive drenching were compared. The suppressive treatment was not truly effective before spring of the third year when drenching was increased from > three-weekly to ≤ two-weekly. Cattle on lucerne generally performed better than those on phalaris. In the first two years the improved performance seemed to result from the provision of better quality feed in summer. In the other two years the major benefits occurred in spring and were associated with lower losses caused by helminth parasites on cattle grazing lucerne. Gains did not differ between pasture types when internal parasites were effectively suppressed by the ≤ two-weekly treatments. The maximum gross margins on each pasture were obtained at about 2·0 steers ha−1.

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.

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.

The effects of rotational and continuous grazing on long-term steady-state productivity of a continuously growing pasture were examined in a simple mathematical model representing both plant growth and herbivore consumption as functions of green plant biomass. The results showed that moderate rotation, with few subdivisions and short cycles, had only minor effects on productivity, compared with continuous grazing. Intensive rotation (many subdivisions and/or long cycles) resulted in a substantial decrease in long-term productivity in the absence of an ungrazeable plant residual or when the stocking rate was moderate and the initial condition (biomass) of the pasture high. When the stocking rate was high and the initial condition of the pasture poor, but an ungrazeable residual was present, intensive rotation substantially increased the long-term productivity compared with continuous and moderate rotational grazing.

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.

In grassland systems where grazing and conservation areas are separate, the farmer must decide on the N rates to use in the two areas and on the proportion of the total area to devote to conservation. Quantified relationships between N supply and herbage yields, and estimates of DM requirements, were used to determine the optimum split of total area for cutting and grazing and the N rates to be used to maximise stocking rate for a fixed total fertiliser N usage, or to minimise N usage for a fixed stocking rate. Results indicated that the optimum split of area was around 70% grazed, 30% cut for conservation, with higher N rates on the cut area than on the grazed area. The method also allowed estimates to be made of the economic optimum fertiliser N usage and stocking rate.

Previously described forage and beef models were used to investigate the biological productivity of continuous (CG) and rotational grazing (RG) systems on common bermudagrass ( Cynodon dactylon (L.) Pers.) in the southern USA. Simulated factorial experiments allowed examination of the interacting effects of agronomic practices and grazing system variables on cattle (yearling steer) production per area and average daily gains. Cattle production-stocking rate curves were compared to determine (1) the stocking rate (S max ) at which peak cattle production (G max ) occurred and (2) which grazing system class was potentially more productive. Results indicated that RG permitted greater S max , particularly at low fertilization levels. However, the grazing system class which yielded greater G max was a function of the number of paddocks used in the RG system. RG systems with less than 8 paddocks generally produced less beef per area than CG; those with more than 8 paddocks were more productive. High fertilization levels favored RG systems with large numbers of paddocks and rapid rotation. The paddock number effect resulted from increasing production efficiency (ratio of animal production to herbage production) with increasing numbers of paddocks. The exercise corroborated a hypothesized stocking rate by grazing system class interaction but also indicated that biological productivity of grazing systems may be influenced by multiple interacting effects of input variables.