CONTEXT: Cow-calf and fattening grazing systems in the tropical, well-drained savanna ecosystem of the Eastern Plains in the Colombian Orinoco River Basin are being intensified to enhance technical efficiency. These systems, often starting from degraded pastures, present significant challenges for both researchers and producers in analyzing and predicting their transformation. OBJECTIVE: This study aimed to develop a model capable of simulating the multifaceted interaction between land use, beef herd management, animal productivity, enteric methane (CH4) emissions, and carbon footprint (CF) at the system level. The model should assist in making informed decisions towards sustainable beef farming systems that improve resource management. METHODS: The model compared three alternative regional scenarios (SCEs) using conceptual medium-sized 400ha farms. Scenario (SCE) 0 starts with degraded Urochloa humidicola pastures, followed by low-intensity rejuvenation to support a cow-calf system. SCE 1 follows a similar path but introduces, in later stages, 100 ha of moderately well-managed, better-quality U. brizantha pastures to further develop the cow-calf system. SCE 2 begins as SCE 1 but later transitions into a full-cycle beef production system. In all cases, the systems are conservatively managed to ensure sustainable production. RESULTS AND CONCLUSIONS: The outputs of the modelled SCEs reveal and quantify the complex interplay of numerous system feedbacks, determining system outputs and identifying quantitative variables that significantly influence system behaviors. Culling rates of cows and the fattening of feeder cattle are decisive events that modify the dynamics of the beef herds over time, impacting production and greenhouse gas emission outputs. Under conservative management, all three SCEs resulted in significant increases in production ha -1 and animal units -1 (AU; 450 kg), although the magnitude and temporal development of these increases varied among SCEs. These increases were accompanied by higher enteric CH4 emissions ha -1. However, emissions substantially decreased AU -1 and kg -1 liveweight sold, reducing CFs. This highlights the potential of well-managed Neotropical beef cattle grazing systems (NBCGS) to balance productive gains with environmental sustainability, offering actionable strategies to enhance NBCGS management. SIGNIFICANCE: This study underscores the importance of evaluating Neotropical beef cattle grazing systems (NBCGS) across various temporal and spatial dimensions and considering technical decisions. Simulation modelling constitutes a powerful tool for assessing system dynamics that are otherwise difficult to design and subject to long-term field research. This approach enables a deeper understanding of the trade-offs and interactions within NBCGS, facilitating more informed and sustainable decision-making.

Long-term reproductive performance of beef breeding herds grazing sown pastures in the neotropical savanna environment of Eastern Colombia (Llanos) is not well documented, while the lifelong reproductive consequences of raising replacement heifers subject to different growth regimes is also intriguing. The study aimed to assess the effects of liveweight (LW), age, and their interaction on conception probabilities of Bos indicus replacement females by analyzing two seven- and eight-years lasting experiments that used commercial Brahman heifers subject initially to different growth rates on Urochloa humidicola pastures. The experiments included two periods, namely the growth period from weaning until 270 kg LW during which heifers were subjected to three stocking rates to attain different rates of gain, and the subsequent reproduction phase subject to common grazing for all growth treatments. The conception data fitted well logistic regressions in which LW and age were the predictor variables during the first two conceptions but the relationship disappeared in subsequent conceptions. Prediction equations compared well with extensive data from northern Australia that showed similar trends. Liveweight of adult cows only increased consistently during pregnancy, but following weaning their LWs returned to the initial low LWs attained at conception. Over the length of the experiments, weaning rates as percentages of calves born were 88% for the two treatments with higher LW gains during the growth period, and 81% for the lowest gaining treatment. Calving intervals were 19-20 months across treatments. It is suggested that the data and equations provided can guide decision making in extensive breeding herds.

An exploratory study was conducted to analyze combinations of variables that define typological groups that condition the abandonment/continuity of sheep farming in the semi-arid region of Chile. Three typological groups were identified. Group I is made up of middle-aged farmers with the largest flocks. Group II has typical farms from an arid zone, own by elderly male farmers. Group III is located in areas near urban centers and has a greater presence of women farmers. The study allowed to identify the variables that influence the continuity of sheep farmers and to determine strategies that avoid/delay the abandonment of the activity.

Dairy production systems are heterogeneous as they are influenced by farm location and structure, markets, environmental conditions, and the producers' preferences and peculiarities. A typology of the existing dairy systems in Chile was developed with the objective of identifying homogenous groups that would allow for the characterization of adaptation strategies to changing environmental, social, technological, political and economic variables. Multivariate analyses were performed on data from official surveys carried out in 2009, 2011, 2013, and 2015. Six groups (I-VI) were identified representing 26.9%, 21.5%, 21.6%, 14.6%, 6.8% and 8.6% of the population surveyed. Group I was the largest, and it included non-specialized commercial dairies. Group II clustered semi-extensive, medium to large dairies that rely mostly on high yielding improved pastures. Group III included small, semi-extensive commercial farms that make a more intense use of pastoral resources, such as sown pastures and improved native grasslands. Groups IV, V, and VI corresponded to specialized dairies, highly market-oriented, that use annual forages to supplement intensively managed and planned pastures, but that differ in size and some management strategies. The observed temporal changes and adaptations over time were closely linked to farm size, intensity in the use of various technologies, the number and the breed of the dairy cows, and the presence of other agricultural activities in the property. The effect of variable prices of milk and system inputs differed by group. Given the social and economic importance of dairies throughout Central and Southern Chile, a number of interventions are proposed, including technical modifications, extension initiatives, and changes in policies.

The savannas of eastern Colombia located in the Orinoco river basin represent 18% of the Latin American neotropical savannas, and those areas that are tillable and closer to markets are subject to considerable anthropic pressure in the quest for intensification. Historically, and even today, beef cattle production constitutes the main land use, and much of it is subjected to extensive management. This paper describes for the first time, the use of cattle grazing experiments to assess methane (CH4) emissions from neotropical savanna-based beef breeding systems, and with the support of published research conducted next to them, estimates of the carbon (C) footprint in carbon dioxide equivalents (CO2-eq) for the whole system. Over 5 years and covering complete reproductive cycles, a conventional weaning (CW) herd system was compared to an early weaning (EW) herd system, that represented a modest degree of more intensive savanna management. Differences were found between the two management practices in total CH4 emissions, emission intensities [kg CH4 kg(-1) calf born and kg CH4 kg(-1) liveweight gain (LWG)] and emission efficiencies (kg CO2-eq kg(-1) calf born and kg CH4 kg(-1) LWG), that mostly associated with the different lactation lengths. When both herd systems were carried over until calves, later yearlings, reached to 25 months of age, the differences in favor of EW breeding herd system were diminished. The calculated C footprint in (CO2-eq) of both management practices was near neutral subjected to a number of assumptions and the use of limited published information on savanna C stocks and CH4 and nitrous oxide (N2O) emissions from soil, and it is posited that both herd systems were nearly in equilibrium. The available data and results show the need for further information on the neotropical savanna C stocks and C sequestration potential of soils of the Orinoco river basin. More reliable datasets regarding below-ground C inputs and CH4 and N2O emissions from soil are needed to provide a useful basal benchmark for, and approach to, future analyses of environmental impact of more intensive beef herd systems in the region.

The present study used surveys of the cattle sector over the period of 2009–2015 to develop a typology of cattle farms to evaluate their evolution over time and to identify variables that may be associated with systems’ adaptive changes and continuance. Four groups of farms were defined using multivariate analyses as follows: Group I are small calf-cow operations using non-specialized beef breeds; Group II is similar to Group I but employs specialized beef breeds; Group III is dedicated to finishing cattle, and Group IV are larger farms (>1000 animals) with a complete cycle of breeding and fattening. In general, beef cattle production in the temperate—Mediterranean Southern Zone of Chile is declining in response to the opening up of the economy that allows for ample imports, the high opportunity cost of land, and recurrent droughts associated with climate change. Current policies and regulations have modified farms’ businesses models depending on their ease of access to markets, farm size and financial capacity. The defined groups require different development paths and strategies. Sustainable intensification is an alternative strategy for farms in Group I and II, particularly if they were to contract the finishing stage of their cattle with Group III farms. In contrast, it is suggested that Group IV farms concentrate on pastoral production using low external inputs to enhance the production of “natural” beef for high-value niche markets, with positive externalities.

Cow–calf operations constitute the main land-use system in the 18 million ha of well drained tropical savannas of Colombia located in the Orinoco basin. There, numerous sex and age animal categories are present, ranging from suckling calves to old cull cows and steers, which in variable proportions are stocked at one animal unit (AU)/5–10 ha, depending on the ranch and distance from markets. In parallel, early-on farm observations showed that when sown pastures are introduced, graziers recur to opportunistic partial fattening of cull animals for a rapid economic return. The paper reports animal weight gains of cull cows, old steers, and young heifers and yearlings over seven consecutive years grazing on a low fertiliser-input well managed Andropogon gayanus-based pasture and four contemporary years on Brachiaria humidicola. The first 2 years involved three stocking rates (SR; 1.38, 1.85 and 2.32 animal units/ha), whereas a single SR of 1.33 animal units/ha was used for the remainder. A large database that included chemical, and in vitro and in vivo digestibility, values for all forages involved, was used as an input to a mathematical model to estimate methane (CH4) emissions. Estimations were compared with weight-based predictions derived from chamber measurements recorded recently in tropical Australia. Faecal mineral concentration varied little (not significantly) among SR and animal categories. Weight gains of old steers were 4–24% larger than those of cull cows, which, in turn, were larger than those of young steers and heifers (P < 0.01). Excepting one year, the performance of cull cows and old steers did not differ between pastures, confirming earlier on-ranch observations of reasonable weight gains of adult cattle on both pastures. The predicted carcass composition of cull cows and old steers did not differ between pastures either. Over the length of the experiment, cull cows emitted significantly less CH4 than did old steers (129 vs 141 g/day) on A. gayanus, while emissions on B. humidicola amounted to 128 and 137 g/day respectively. Despite between-year differences in animal performance, they are indicative of well managed pasture sustainability. They also show some of the trade-offs involved in the use of contrasting animal categories and pastures in terms of weight performance and predicted carcass composition and CH4 production. The authors expect that the present results will contribute to a rational, science-based discussion of the role of beef systems vis-à-vis environment in a region with limited production alternatives.

The Eastern Plains of Colombia (“Llanos”) are made up of acid soils with low nutrient concentrations covered by tropical savannas, but they constitute a very important land resource for the country. The Llanos have traditionally supported extensive beef cattle production systems but are increasingly in demand for food, feed and oil production. The establishment of improved tropical pastures is a continuing trend as a means of intensifying beef production. Published data and the authors’ own on-farm databases were collated and analyzed to estimate commercial cattle weight gains. A total of 198 records representing pastures directly drilled into native savanna and pastures undersown with rain-fed upland rice and maize were available for the 1979‒2016 period, and were compared with savanna-based beef production. Records were available for sown paddocks 1‒15 years in age that were managed solely by ranchers or by consensus between ranchers and researchers. Performance was not affected by who made the management decisions. Pastures sown in association with maize largely out-yielded all others, but observations on these paddocks were restricted to only 3 years and there was a steep fall in production with age. Differences between conventionally established and rice-associated pastures decreased rapidly over time, and production from these pastures did not differ over the longer term. Pasture age and stocking rate during the rainy season were the major factors influencing output from all systems. Overall, adjusted, long-term weight gains per year ranged between 11 and 386 kg/ha for savanna and maize undersown pastures. The data suggest a need to document long-term planned, regular, crop-pasture rotations, but none was available. The analyses provide valuable, long-term estimates of realized beef production under commercial conditions that should assist in decision-making by graziers and policy makers.

Extensive, rangeland-based beef production systems that predominate in the neotropical savannas of northern South America are low input-low output beef breeding systems, and their intensification faces major hurdles due to their location, soil, water and topographic constraints. Intensification requires the introduction of improved pastures strategically managed to complement the native savannas, to improve production and to allow opportunities for a wider range of associated ecosystem services. This study assessed the feasibility of early weaning of beef calves onto small areas of sown pastures to aid system intensification. Weaning calves at 90 days of age and grazing on Andropgon gayanus, A. gayanus-Pueraria phaseoloides, A. gayanus-Centrosema acutifolium and Brachiaria humidicola-Arachis pintoi sown tropical pastures stocked at 6 animals/ha was compared with conventional weaning on native savanna over 4 consecutive years. The reproductive performance of their Brahman (Bos indicus) and crossbred [Brahman x San Martinero (native; B. taurus)] dams grazing savanna (0.2 cows/ha) was monitored in comparison with control cow-calf systems, where calves were weaned onto savanna between 240 and 270 days of age. Post-weaning weight gains of early weaned calves on sown pasture (0.1‒0.2 kg/d) were much lower than those of unweaned animals on savanna (0.31‒0.35 kg/d), but compensatory gains realized after the end of the weaning experiments allowed early weaned calves to reach weights similar to those of control animals 400 days after the end of the pasture phase. As expected, early weaned cows achieved higher live weights and had shorter inter-calving intervals than their counterparts. Trade-offs between performance of calves and of cows are discussed, but it is suggested that the strategic use of small areas of sown pastures for early weaned calves may productively complement large areas of native savannas. It is hypothesized that the improved quality, frequency and intensity of management required by these intensified systems may place a burden on these low-input primary enterprises, which may also challenge the productive and environmental adaptive capacity of primary resource users.Keywords: Cattle, extensive systems, intensification, rangelands, sustainability, tropical pastures.

Grassland based sheep production systems in the semi-arid to sub-humid Central region of Chile are expected to improve technical and economic efficiency, while at the same time decreasing emissions of greenhouse gases (GHG). An existing empirical, stochastic simulation model of grazing sheep production was modified to allow for a cradle-to-farm-gate quantification of GHG under a large number of scenarios. The model includes pasture availability and utilization, supplementation of sheep, milk and lamb production, and carbon sequestration by forages and soils among others. Simulated scenarios included factorial combinations of a range of farm types previously typified and a range of sheep management practices, and their interaction with dry, average, or rainy years that affected grass growth. The carbon footprint (CF) was calculated for 20 runs of each case. Numerous interactions between animal outputs, forage availability and CF, as well as trade-offs, were found. Rainfall patterns had a significant effect on range and sown pastures yields when other factors were kept constant. A decrease of 32% in average rainfall for a dry year resulted in a reduction of forage production of 13%, whereas a rainy year with rainfall 36% higher than average, increased it by 12%, Forage yields had a significant effect on CF. Three different farm types showed CF of 7.4 to 13.3CO2-eq·kg−1LW−1. Farms that used higher inputs had higher forage production and lower CF, which decreased further if soil C sequestration is accounted for. Large farms that had lower stocking rates than the rest, and that used Merino sheep with high reproductive rates, had lower CF than the smaller farms that make a more intense land use. Reproductive rates had a large and significant effect on CF as they determine the number of ewes required to maintain constant production and overall flock composition. The average CF for lamb production across all scenarios was 14.8kgCO2-eq·kgLW−1, and decreased by 2kg CO2-eq·kgLW−1 when carbon sequestration was accounted for. The simulated systems were stable in years with average rainfall, but their sustainability seems fragile if faced with a sequence of dry years. It is concluded that the abundant interactions between the rainfall pattern and management variables would be difficult to study in field experiments, and that simulation modelling is a powerful tool to assess the consequences of numerous climate and production scenarios.

Los sistemas de producción de carne bovina en una de las principales zonas ganaderas del Sur de Chile son identificados y caracterizados tomando como base de agrupación las combinaciones de aprovechamientos de especies vegetales. El objetivo del trabajo fue identificar, caracterizar y describir la evolución de sistemas de producción bovinos de carne en la región de la Araucanía y determinar su relación con la utilización de instrumentos de fomento agropecuario tanto públicos como privados. Datos obtenidos desde dos Censos agropecuarios (INE 1997, 2007) se utilizaron como variables de caracterización, permitiendo junto con la diferenciación de grupos, identificar relaciones de dependencia entre grupo, tamaño de hato, aspectos sociales y programas de fomento agropecuario. Los aprovechamientos con mayor presencia correspondieron a praderas naturales, praderas mejoradas, forrajeras perennes, especies forestales, cereales y forrajeras anuales. Tres combinaciones de aprovechamientos fueron seleccionadas por representar al total de explotaciones de la región. Se observaron diferencias significativas en variables cuantitativas y cualitativas entre grupos y años evaluados (P≤0.01).

Central Chile has a semi-arid, Mediterranean-type climate, characterized by mild temperatures and irregular and unreliable winter rainfall. Meat sheep production managed in extensive systems is an important agricultural activity of the area. A dynamic, stochastic, simulation sheep model was developed with the objective of assessing the water footprint of extensive lamb production in relation to factorial combinations of annual rainfall, stocking rate, and rate of supplementation of ewes and lambs. The simulation model includes two sub models that estimate grass and lamb growth respectively. The model allows estimation of the water footprint of sheep production, its partitioning into green-blue-grey water, and of tradeoffs in physical outputs. Dry (424mm) and very dry (380mm) years occurred in 40% of cases reported for the 1972–2014 period. Green, blue and grey water footprints were significantly affected by the variables studied. The lowest water footprint was found in average years (702mm; 5369L·kg of LW−1 sold) and increased to 7741L·kg of LW−1 sold in dry years when ewes were supplemented with grain. Numerous significant interactions between yearly rainfall and feeding strategies were found that are indicative of the management challenges faced by the system. The simulation model proved to be a powerful tool to examine a variety of climatic and production scenarios in order to infer possible future trends in response to climate change and production strategies.

Stocking rate is the relationship between number of animals and the area of the grazing management unit. This chapter focuses on the C4 grass regions of the several continents that have major grassland zones and the types of grazing systems that have evolved. The grasses of southern Africa are well classified for the purpose of assessing range condition. Both wild game animals and domestic livestock are critically important animal resources in many African countries. Native and sown grasslands constitute the major land use system in tropical South America, where there is a 4: 1 ratio of grazinglands to cropland. Tropical South America is the center of origin of numerous herbaceous legumes and many were selected, bred, and adopted in Australia. In many parts of the tropics, grazing systems, as such, are not well developed because of social and economic aspects associated with small land holdings and limited capacity for livestock.

To evaluate increased levels of dehydrated olive cake (DOC) in lambs ration on main carcass traits, 40 Suffolk Down male lambs (75.8 ± 7.4 days of age, 24.5 ± 3.1 kg live weight) were randomly assigned to one of five treatment groups. Four experimental isoenergetic and isoproteic diets were used with different levels of DOC: 0, 16, 32 and 48%, and an un-weaned group were kept with their mothers on grazing. Lambs had 8 days of adaptation to the diets, which were gradually introduced along with good quality alfalfa hay. During 47 days of the experiment, the lambs were confined in individual pens (1.4 m 2 ) and subsequently slaughtered at 123 ± 7 days with an average live weight of 32.56 ± 2.62 kg. The live weight at slaughter (LWS), hot carcass weight, cold carcass weight, commercial yield (CY), real dressing percentage (RDP), body components weight (blood, hide, head, legs, full and empty digestive tract, and viscera), rib eye area (REA), back fat thickness (BFT), renal pelvic fat weight, and commercial cutting yield (CCY) were recorded. Additionally, the tissue composition and its ratios were calculated from the shoulder and leg. The carcass traits, CY, RDP, and REA decreased and BFT increased with increasing amounts of DOC in the diet (P≤0.05). No significant differences (P>0.05) in CCY, tissue composition and ratios among the tissues of the shoulder and leg joints were detected. The addition of DOC to the diet did not affect the quality of the lamb carcass. Se evaluo la inclusion de alperujo deshidratado de oliva (ADO) en la racion de corderos sobre las principales caracteristicas de la canal, utilizando 40 corderos Suffolk Down (75,8 ± 7,4 dias de edad, 24,5 ± 3,1 kg peso vivo). ADO se incluyo en cuatro dietas: Dieta control con 0% ADO (DC), DC con 16, 32 y 48% ADO, mas un grupo a pastoreo que se mantuvo con sus madres. Durante el ensayo (47 dias), los corderos se mantuvieron en corrales individuales (1,4 m 2 ). Los corderos fueron sacrificados a los 123 ± 7 dias, y peso vivo promedio de 32,56 ± 2,62 kg. Al sacrificio se registro: peso vivo, peso de la canal caliente, peso de la canal fria, rendimiento comercial (RC), rendimiento verdadero de la canal (RV), peso de los componentes del cuerpo (sangre, piel, cabeza, piernas, el tracto digestivo lleno y vacio, y visceras), area del ojo del lomo (AOL), espesor de grasa dorsal (EGD), peso de grasa peri-renal y rendimiento de corte comercial (RCC). Adicionalmente, en espaldilla (E) y pierna (P) se estudiaron los componentes del tejido (CT) y sus proporciones (PT). El incremento de ADO en la dieta causo una disminucion de RC, RV y AOL y un aumento de EGD (P 0,05) en RCC, ni en CT y PT de H y P. La adicion de ADO a dietas de corderos, en los niveles utilizados en este trabajo, no afecto la calidad de la canal de cordero.

The dynamics of sheep systems the Mediterranean region have been influenced by reforms coming from the Common Agricultural Policy, and the general economic evolution of markets. The aim of this study was the analysis of the structural changes that occurred between 1999 and 2009, and the identification of future implications for the sheep systems in Andalusia region, Spain. Analysis of the structural changes allowed the generation of strategic information, identified trends that should suggest new rural policies and changes that are likely to have social and environmental impacts, and lastly, prioritize future research. The application of multivariate methodology allowed clustering the farm population into four groups. The typology of these systems was determined by variables related to the sheep subsystem, by the set of agricultural activities, and by changes in swine husbandry, within a context of changes in land tenure and the drive for agricultural intensification. Major modifications of extant systems included a 42% reduction in the number of farms, a decrease in sheep numbers, replacement of native rangelands with improved pastures, olive trees and orchards, a reduction of traditional extensive pastoral activities, and increases in hog production in Dehesa grasslands. Given the historical economic and social importance of the sheep-cereal system, the observed substantial modifications of land use suggest a need to assess their consequences in terms of social and environmental impacts, as well as their implications for climate change.

SUMMARYA mechanistic model (COWPOLL) was used to estimate enteric methane (CH4) emissions from beef production systems in Chile. The results expressed as a proportion of gross energy intake (GEI) were compared with enteric fermentation data reported in the last Chilean greenhouse gases inventory, which utilized an earlier the Intergovernmental Panel on Climate Change Tier 2 approach. The simulation analysis was based on information from feedstuffs, dry matter intake (DMI), body weight (BW) and average daily gain (ADG) of steers raised and finished at two research facilities located in Central and Southern Chile, as well as three simulated scenarios for grass-based finishing systems in Southern Chile. Data for feedlot production systems in the central region were assessed by considering steers fed a forage : concentrate ratio of 23 : 77 using maize silage and wheat straw as roughage sources during the stages of backgrounding and fattening. Average DMI were 7·3±0·62 and 9·2±0·55 kg/day per steer for backgrounding and fattening, respectively, whereas ADG were 1·1±0·22 and 1·3±0·37 kg/day for backgrounding and fattening. For the Southern Chilean fattening production systems, the forage : concentrate ratio was 56 : 44 with ryegrass pasture as the sole forage source. In this case, average DMI was 9·97±0·51 and ADG was 1·1±0·24 kg/day per steer. Two of the grass-based scenarios used the same initial BW information as that used for the Central and Southern Chilean systems, but feedlot diets were replaced by ryegrass pasture. The third grass-based scenario used an initial BW of 390 kg. In all the grass-based scenarios an ADG of 0·90 kg/day, with maximum DMI estimated as a proportion of BW (0·01 of NDF, kg/kg BW), was assumed. The results of the simulation analysis showed that emission factors (Ym; fraction of GEI) ranged from 0·062 to 0·079 of GEI. Smaller values were associated with finishing systems that included a lower proportion of forage in the diet due to higher propionate production, which serves as a sink for hydrogen in the rumen. Cattle finished in feedlot systems had an average of 0·062 of GEI lost as CH4, whereas grass-based cattle had losses of 0·079 of GEI. Enteric CH4 emissions for the systems using grass-based and concentrate diets were 261 and 159 g/kg weight gain, respectively. The Chilean CH4 inventory employs a fixed Ym of 0·060 to estimate enteric fermentation for all cattle. This value is lower than the average Ym obtained in the current simulation analysis (0·071 of GEI), which results in underestimation of enteric CH4 emissions from beef cattle. However, these results need to be checked against field measurements of CH4 emissions. Implementation of mechanistic models in the preparation of national greenhouse gas inventories is feasible if appropriate information is provided, allowing dietary characteristics and regional particularities to be taken into consideration.

A sheep farm typology was developed to describe the evolution of sheep farming between the censuses of 1997 and 2007 in the semiarid zone of Central Chile. The typology yielded three groups (I–III) that accounted for 81, 17 and 2.5% of the farms respectively, differing in farm size and in the ratio of sheep to cattle and other agricultural activities. Sheep represented 80–86% of the livestock units in small farms, as opposed to 53% in the larger, more diversified, ranches. Farm-based technical and economic parameters were not available. Stochastic mathematical simulation of bioeconomic performance for prototype farms representative of each of the three groups showed differences accounted for by farm size, farm diversification and animal breed. Large between-farms within group variation in performance suggest the existence of room for incorporation of technology. Smaller flock sizes in I and II were associated with larger production costs and less income per lamb and per kg live weight. Larger farms carrying Merino produced more lambs per ewe and had lower unitary costs. Unaccounted for costs of family labor in the smaller farms, together with some evidence of their gradual decapitalization, explain the continued existence of the small sheep farm sector. Implications for the future development of these farms are discussed.