Cow-calf Production Systems Research Articles

Análise da sensibilidade da metodologia dos centros de custos mediante a introdução de tecnologias em um sistema de produção de cria

Um modelo de simulação bioeconômico foi desenvolvido em um sistema de produção tradicional em pecuária de cria (SPT) para a aplicação da metodologia dos centros de custos com o objetivo de avaliar sua sensibilidade mediante a introdução de tecnologias de desmame precoce em vacas primíparas (SDP), campo melhorado para vacas primíparas e metade do lote das vacas secundíparas (SCM) e suplementação protéica para novilhas de reposição (SSP) destinadas a aumentar a taxa de prenhez neste sistema (SPT). As informações do desempenho biológico foram obtidas por meio de revisão bibliográfica sobre os indicadores de produção e os dados econômicos e de custos foram obtidos a partir de valores de mercado. As entradas do modelo foram: estrutura do rebanho; custos de produção; e tecnologias de produção. As saídas do modelo foram: custo operacional (CO); custo de desembolso (CD); custo de produção por centro (CPC); custo unitário por bezerro (CUB); custo por quilo desmamado (C/kg); custo anual por vaca (CAV); ponto de equilíbrio financeiro (PEF), margem operacional (MO), taxa de prenhez (TP), taxa de desmame (TD), produtividade/vaca (Pr), número de bezerros desmamados (NBD), ponto de equilíbrio em bezerros (PEB) e produção total em quilos (PT). A utilização da metodologia dos centros de custos se mostrou sensível ao identificar variações nos indicadores técnicos e econômicos e nos custos de cada centro produtivo. A introdução do SDP, SCM e SSP melhorou os indicadores técnicos e a margem operacional e, ao mesmo tempo, apresentou relação direta com as variações nos centros de custo, comprovando a sensibilidade da metodologia de custeio em relação ao impacto no SPT.

Adaptive management of stocking rates to reduce effects of drought on cow-calf production systems in semi-arid rangelands

We used simple ecological sustainability simulator (SESS) [Díaz-Solís, 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. Agric. Syst. 76, 655–680. <http://dx.doi.org/10.1016/j.agsy.2005.07.008>], modified to represent each of five management strategies (sets of decision rules) for adjusting stocking rates, to identify strategies that could reduce effects of drought on cow-calf production systems in semi-arid rangelands. We parameterized the model to represent a region of extensive cow-calf production in the northeastern portion of the Mexican state of Coahuila, and evaluated animal performance (animal body condition, cow mortality, and calf production) and range condition resulting from each strategy under random precipitation conditions typical of the region. To evaluate the validity of the randomly generated precipitation, we conducted the simulations under an historical (1950–1994) precipitation regime. The five management strategies included one with no adjustments to stocking rate (CONTROL, most common current practice), one with stocking rate adjustment rules based on changes in animal body condition (BCS), and three with different stocking rate adjustment rules based on various comparisons of recent-year precipitation with long-term mean precipitation during the growing season (March–November) (REPLA, PPT 1Y, PPT 2Y). Each strategy was evaluated at each of three initial base-level stock cow stocking rates (125, 250 and 500 AUY · 5000 ha −1). Stocking rate adjustments consisted of partial or total de-stocking, with the re-establishment, or not, of the initial number of stock cows before the beginning of the subsequent breeding season. Results of 45-year simulations under both random and historical precipitation suggest CONTROL and PPT 2Y (based on comparison of current year and previous year precipitation with the long-term mean) strategies, combined with the high base-level stocking rate, are the worst and best, respectively. Under the historical precipitation regime, in the last period of time simulated (1980–1994) these two strategies resulted, respectively, in poor (0.5) versus good range condition (1.0), animal body condition scores of 2.6 versus 5.2, annual cow mortalities of 76 versus 5%, and calf production rates of 0.9 versus 10.6 kg ha −1 year −1 at weaning. The PPT 1Y strategy (based on comparison of current year precipitation with the long-term mean) produced results fairly similar to PPT 2Y, with BCS and REPLA strategies producing results intermediate between CONTROL and PPT 2Y. Our results suggest it is advantageous to adjust stocking rates based on precipitation during the current growing season since it improves cattle production without damaging range condition. Considering the practical feasibility of the strategies, we recommend the PPT 1Y strategy because it maintains range condition at moderate stocking rates, results in good animal performance and does not require total de-stocking of the ranch. The simple method we developed to stochastically generate monthly precipitation produces a time series of precipitation values that were representative of general historical precipitation patterns and provided realistic levels of uncertainty in simulated forage production to evaluate alternative management strategies.

Breeding objectives for Angus and Charolais specialized sire lines for use in the emerging sector of South African beef production

Breeding indigenous cows to terminal sires may facilitate production of calves in the emerging sector that better meet commercial feedlot requirements. Thus, the objective of this research was to develop breeding objectives for Angus and Charolais terminal sires to be used in breeding Afrikaner, Bonsmara, and Nguni cows. An aggregated simulation model that is reliant on user inputs for the phenotypic characterization of the germplasm and economic characterization of the production environment was developed. Relative economic values were calculated by approximating partial derivatives of simulated profit with respect to economically relevant traits. Correlations among the breeding objectives calculated from simulations of Angus and Charolais bulls bred to Afrikaner, Bonsmara and Nguni cows were consistently > 0.9. Thus, an average index could be used for all six scenarios with little loss of selection efficiency. On average, relative emphasis given to breeding values for survival, direct weaning weight, postweaning daily gain, postweaning daily feed intake, dressing percent, and fat depth were 31.1, 31.0, 17.3, 1.4, 19.1, 0.2%, respectively. These breeding objectives may be viewed as an appropriate step in the evolution of multi-trait selection to facilitate poverty alleviation among cattle producers in the emerging sector through wealth creation resulting from their production of calves for industrial feeding. Keywords: Beef cattle, genetic evaluation, selection strategy, crossbreeding, cow-calf production system South African Journal of Animal Science Vol. 37 (1) 2007: pp. 1-10

Melhoria organizacional na produção de bezerros de corte a partir dos centros de custos

O objetivo neste trabalho foi evidenciar a importância do custo de produção na pecuária de cria, descrevendo uma metodologia padronizada que consiga mensurar o custo de produção de bezerros de corte e, simultaneamente, validar o método em um sistema de produção. Dentro deste contexto, neste trabalho discute-se, inicialmente, a relevância da implantação da metodologia dos centros de custos como suporte à tomada de decisão, devido à necessidade de uma análise segmentada dos processos em sistemas de produção pecuários especializados na cria. As etapas para implantação deste método são descritas. Um sistema de produção, característico da Região Sul do Brasil, foi definido a partir de indicadores técnicos relatados em revisões bibliográficas. Foi simulada a aplicação desta metodologia no sistema em questão, no qual se visualizaram os custos de produção dos diferentes centros produtivos: touros, vacas de cria, recria das novilhas e desmame dos bezerros, possibilitando compreender o impacto de determinados processos e/ou tecnologias no sistema. Conseqüentemente, calcular o custo de produção de bezerros de corte a partir da utilização da metodologia dos centros de custos, mostrou-se factível de utilização em sistemas de produção baseados em pecuária de cria.

Preweaning Performance of Calves from Bonsmara, Brangus, Charolais, Gelbvieh, Hereford, and Romosinuano Sires Bred to Brangus Cows Managed on Native Rangeland or Improved Forages ,

AbstractPreweaning data on 511 spring-born calves from 187 Brangus cows and 129 Bonsmara, Brangus, Charolais, Gelbvieh, Hereford, and Romosinuano sires were measured over a 4-yr period to determine sire breed, sex, and age of dam differences under 2 preweaning forage environments: 1) native tallgrass rangeland (native) or 2) improved warm-season forages (improved). Sire breed differences in birth weight varied across forage (P < 0.05) with Romosinuano-sired calves on improved forages ranked intermediate in birth weight compared with other sire breeds but lightest on native forages. Calves from Charolais and Gelbvieh tended to be heavier at 205 d of age than calves from other sire breeds on improved forages (P < 0.05, except Gelbvieh vs. Hereford, P < 0.12) whereas on native forages, Bonsmara-, Charolais-, and Gelbvieh-sired calves were similar but were heavier than Brangus- and Romosi-nuano-sired calves (P < 0.10). Steer calves were heavier than heifer calves on improved forages (P < 0.01) but not on native forages. Sire breed differences were not significant on improved forages for weaning condition score. On native forage, weaning condition scores were greater for calves sired by Bonsmara and Hereford (P < 0.05) compared with Brangus-, Charolais-, and Gelbvieh-sired calves, and Charolais-sired calves were lesser than other sire breeds (P < 0.05). These results provide evidence of nonadditive associations between preweaning forage systems, sire breed of calves, age of dam, and sex of calf in preweaning traits. Consideration should be given to appropriate combinations of these effects in development of efficient cow-calf production systems.

Livestock Management During Drought in the Northern Great Plains. II. Evaluation of Alternative Strategies for Cow-Calf Enterprises

<h2>ABSTRACT</h2> The objective of this study was to evaluate alternative drought management strategies for their effects on beef cowcalf enterprise profitability based on early detection of drought. A bioeconomic model was parameterized to represent a range-based cow-calf production system in the Northern Great Plains. The base management system was characterized by inputs required to maintain herd size of approximately 511 cows during an average climatic year with a fixed forage base. Treatments were factorially arranged where management (early vs. normal), intensity of drought (moderate, 20% reduction in available forage vs. severe, 40% reduction in available forage), and forage quality [average CP (%), ME (Mcal/kg), and NDF (%) vs. drought-affected values] were evaluated for effects on system performance. Early management (EM) included detecting drought by July 15 and weaning calves at 90 d. Normal management (NM) responded to drought by providing nutritional supplements as needed to maintain animal performance. A second bioeconomic computer model was used to simulate drylot performance for early-weaned calves. Treatments were evaluated based on their effects on ranch gross margins (RGM; gross revenue – variable costs). For EM, RGM was calculated with and without the drylot component. During drought, RGM was reduced compared with the base system: EM at 26 and 57% and NM at 33 and 72% for moderate and severe drought, respectively. For all levels of drought and forage quality, EM had equal or higher RGM than NM. Directly feeding EM calves was generally more efficient than feeding NM cows to produce milk to maintain calf performance.

Beef cow–calf production system integrated with sugarcane production: Simulation model development and application in Japan

The objective of this study was to develop a simulation model for the integration of a beef cow–calf production system and sugarcane production system on Tanegashima Island. A survey was carried out to characterize and identify the role of sugarcane as an alternative feed resource and determine the different interactions within the system. The model was divided into two sub-systems; beef cow–calf and sugarcane and manure production sub-systems. The model is able to simulate the total requirement for energy and protein, and subsequent losses of nitrogen via faeces and urine, throughout the reproductive cycle of a mature cow and the growing stages of her calf. It also estimates the area under sugarcane cultivation for feed and the area on which manure can be applied to complement inorganic fertilizer. A linear programming (LP) approach was used to formulate the least-cost diet and a system simulation method was used to calculate the nitrogen (N) excretion for a cow and her post-weaning calf in the different physiological stages. The model was used to evaluate two scenarios (integrated and specialized scenarios) using production conditions on Tanegashima Island. In the integrated scenario, sugarcane tops were the principal roughage source and organic (manure) was used to complement inorganic fertilizer. In the specialized scenario, Italian ryegrass was the principal feed source and manure was not used. These two scenarios were compared based on the respective feed and fertilizer costs, and the difference between the two scenarios was evaluated as the merit of integration. Sensitivity analyses were also performed to determine the effects of changes in nutritional and management conditions, animal genotype parameters and manure variables on economic variables. The results showed that feed and fertilizer costs were lower in the integrated than in the specialized scenario. Economic variables were sensitive to changes in feeding strategies, especially the metabolizability of feed, days of availability of sugarcane tops, mature liveweight, and manure variables. Utilization of sugarcane tops and manure is economically feasible under the conditions on Tanegashima Island. It is proposed that the developed model is capable of evaluating the biological and economic interaction of beef cow–calf production and sugarcane production systems.

Growth rate, body composition, and meat tenderness in early vs. traditionally weaned beef calves1,2

One hundred forty spring-born Angus x Gelbvieh and purebred Angus steers were selected for study as early weaned (EW; average age at weaning = 90 +/- 30 d) or traditionally weaned (TW; average age at weaning = 174 +/- 37 d) steers that were non-implanted or implanted (Synovex-S, Fort Dodge Animal Health, Overland Park, KS). Initially, steers were sorted by age, sire, and farm, and then allotted randomly in a 2 x 2 factorial arrangement of treatments of EW implanted (EWI), EW nonimplanted (EWN), TW implanted (TWI), or TW nonimplanted (TWN). Ultrasound measurements (US) of LM area (LMA), 12th rib fat thickness (US-BF), and marbling (US-M) were collected every 28 d during the time that steers were on feed. At 202 d of age, EW calves had larger US-LMA, US-BF, and BW than TW calves (37.9 vs. 32.3 cm2, 0.38 vs. 0.26 cm, and 271.6 vs. 218.9 kg, respectively; P < 0.001). At slaughter, EW calves had heavier HCW (290.4 vs. 279.7 kg, respectively; P < 0.05) and greater USDA marbling scores (51.25 vs. 46.26, respectively; P < 0.05) than TW calves; more EW steers graded USDA Choice or greater (P = 0.05). However, no differences were detected in BW (P = 0.15), LMA (P = 0.39), BF (P = 0.45), or liver abscess scores (P = 0.41). Twenty-four implanted steers were selected from the original group of 140 and sorted into two slaughter groups of 12. Twelve implanted steers from each weaning group, matched in slaughter BW but differing in age, were subsampled at slaughter to assess the effect of weaning age and chronological age on muscle tenderness. Younger animals had lower Warner-Bratzler shear force values (P < 0.001) than older calves after 14 d of postmortem aging; however, no differences were found in tenderness after 21 d of aging. Furthermore, there was greater variance (P < 0.001) in Warner-Bratzler shear force values among younger, EW steers vs. older, TW steers. These data provide evidence that early weaning of beef calves may be used as a tool to more effectively manage the cow-calf production system without compromising the quality of the offspring.

Valores econômicos para habilidade de permanência e probabilidade de prenhez aos 14 meses em bovinos de corte

Estimaram-se os valores econômicos para as características reprodutivas de probabilidade de prenhez aos 14 meses (PP14) e habilidade de permanência (HP). Foram simulados dados de uma propriedade pecuária de corte, especializada na fase de cria para aplicação de modelagem bioeconômica. A PP14 foi avaliada considerando taxas percentuais crescentes de prenhez de novilhas aos 14 meses de idade, e a HP foi avaliada a partir da diminuição da taxa de descarte de vacas. O valor econômico da PP14 foi estimado em R$695,97 por unidade percentual de prenhez de novilhas aos 14 meses, avaliada para o sistema produtivo, enquanto o valor econômico da HP variou em função do custo de compra da novilha de reposição. Os valores, avaliados por unidade percentual de diminuição na taxa de descarte de vacas, foram de R$-2.140,00, R$-140,00 e R$2.860,00 para o custo de compra da novilha de R$500,00, R$700,00 e R$1.000,00, respectivamente. Os valores econômicos negativos para HP indicaram que o valor de descarte da vaca superou o custo de compra da novilha. Quanto maior for o valor investido na reposição de novilhas maior será a importância econômica do HP.

Comparative economics of Holstein/Gir F 1 dairy female production and conventional beef cattle suckler herds – A simulation study

Three cow–calf production systems were compared using simulation: N (straightbred Nelore), AN (Nelore cows producing Angus by Nelore calves) and HG (Gir cows producing Holstein by Gir calves). All three systems produced their own straightbred replacement females. Male calves were sold at weaning and female calves in excess of those required to keep the herd size constant were sold at one year of age. In the base situation, F 1 HG females were priced at twice as much as the price per kg of the beef male calves, according to present market values. Typical 1000 ha beef cattle farms were simulated for each system, based on Brachiaria brizantha pastures managed according to recommended practices. Herd dynamics were controlled by reproduction and survival. Literature figures on monthly pasture nutrient production, live weights and milk yield were used to estimate nutrient requirements to match stocking rate to nutrient availability in each system. For calving rate set to 0.8 in all three systems, the total numbers of cows for the N, AN and HG systems were, respectively, 803, 795 and 885 and the total live weight sold annually was 129,070, 133,120 and 127,680 kg. The annual economic return on investment was 5.21%, 5.81% and 10.84%, respectively, for the N, AN and HG systems. Reducing the relative price of the HG heifers diminished the economic superiority of this system over N and AN. The difference was zero when the price of HG heifers was reduced to approximately 1.2 times the beef calf price. This also happened when the calving rate of the Gir cows was set to 0.6 keeping N cows at 0.8 or higher.

Main sources of the economic efficiency of beef cattle production systems

The economic efficiency of several beef production systems on pasture was investigated under different marketing strategies. All calculations were carried out with the computer program ECOWEIGHT. None of the considered production systems was profitable without government subsidies for the assumed economic input values. The subsidies granted when satisfying a set of conditions served for balancing the economic loss in systems selling all surplus weaned calves outside. A profitability of 10 to 25% was reached for this marketing strategy in dependence on the production system. When integrating feedlot, only the purebred system with mating female replacement at an early age (about 15 months) and selling breeding bulls showed profitability, but at a low level (5%). All other systems produced at a loss even when government subsidies were included. A detailed analysis showed a high variability of the profit and profitability of cow-calf production systems in dependence on breeding and marketing strategies and on the level of the biological and economic input parameters. When considering biological performance, reproduction of females was shown to be the main source of economic efficiency in herds producing calves for sale. When applying feedlot, the daily gain in fattening was even more important. Beef prices seem to be the most important economic factor influencing the profitability of all systems (prices for slaughtered animals in the variant with integrated feedlot, prices for calves in the variant with selling of weaned surplus progeny). &amp;nbsp;

A model for simulating rule-based management of cow–calf systems

Pastoral livestock farms are complex and dynamic systems, and are subject to many forms of external disturbance. Management strategies can be aimed to minimize system variations in order to control the system and to achieve specific goals. A research simulation model was developed to study the long term dynamics of complete cow–calf production systems for the Salado Region of Argentina. In the model, the operation of the farm is simulated by decision rules entered by the user. The purpose of the model is to assist in the design and evaluation of pastoral beef breeding systems. This paper discusses the model design in detail and an example is then given in which different strategies of hay use during the winter are compared. The results of the simulations were reasonable, indicating the advantages of using hay in reducing the variability of system productivity, but the different patterns of hay use did not show any impact on the long run performance. The design principles used give considerable flexibility, so the model can be used to simulate and study management combinations available to the farmers.

Effects of breeding date, weaning date, and grazing season length on profitability of cow-calf production systems in southeastern Montana.

Production data from 11 southeastern Montana ranches were used to parameterize a bio-economic computer model of cow/calf range production. Effects of changes in breeding date, weaning date, and range removal date on system performance for a ranch with a fixed forage resource base (3,060 animal unit months of range forage and 744 t of hay) were simulated. Input costs were locally established in 1994. Cattle prices were determined by week from 13-yr averages. For the base scenario, breeding season was 66 d with breeding starting on June 9. Weaning, range removal, and calf sales occurred on November 3. Cows were fed stored forages from November 3 until turnout to grazing (May 1). Five replications were simulated for combinations of breeding, weaning, and range removal dates in a factorial design. Each factor was deviated from the base scenario by +/- 14 and 28 d. Production efficiency was measured by break-even steer price. Gross margin (gross revenue - variable costs) was used as a measure of profitability. Increasing calf age (and weight) at sale time, by decreasing breeding date and(or) increasing weaning date, improved ranch efficiency and profitability. Increasing range removal date improved system performance even though extending the grazing season led to decreased herd size. Compared to the base system, the best system increased gross margin by approximately 17%. Responses for gross margin reflect the dynamics of herd size, purchased feed expense, and production efficiency. Results suggest that for range-based cow-calf enterprises in the northern Great Plains, production efficiency and profitability may be improved by increasing calf weaning age and extending the grazing season, even if herd size must be reduced.

Elk Management Strategies and Profitability of Beef Cattle Ranches

Computer simulation was used to determine the effects of wild elk (Cervus elaphus) on available forage, cattle herd size, and ranch gross margin in southwestern Montana beef cow-calf production systems. Data collected from 5 southwestern Montana ranches were used to develop input parameters for bio-economic models of elk forage harvest and beef production. Input parameters described ranch resources, animal inventories, and animal management. Cattle herd size ranged from 241 to 1147 head. Elk numbers varied by season within ranch and ranged from 49 to 421 head. Ranches were simulated as currently managed with elk present and with 10, 20, 30, and 100% of the elk removed. Simulated management scenarios were replicated 10 times. Data from each ranch were analyzed by one-way analysis of variance. Cattle herd size, gross margin, and available forage significantly (P < 0.05) increased when all elk were removed; however, the magnitude of these effects differed among ranches. Removal of all elk permitted cattle herd size to increase from 7 to 32% across ranches. Annual costs of elk on the 5 ranches (i.e., increase in gross margin from elk removal) ranged from $5,949 to $21,152. On an AUM basis, elk costs ranged from $8.55 to $14.51. Three management alternatives were evaluated for their potential to recover elk costs: Montana's Block Management Program, coordinated exchange of forage use, and leasing of hunting access. For each ranch, at least one of these management strategies could recover all estimated costs of providing elk habitat. Elk can significantly reduce profits for cow-calf ranches in southwestern Montana. Elk impacts on beef enterprise profits are closely associated with efficiency of resource use by cattie-i.e., ranches with lower unit costs of production lose more gross margin by providing forage for elk compared to ranches with higher production costs. DOI:10.2458/azu_jrm_v55i2_torstenson

Elk management strategies and profitability of beef cattle ranches

Computer simulation was used to determine the effects of wild elk (Cervus elaphus) on available forage, cattle herd size, and ranch gross margin in southwestern Montana beef cow-calf production systems. Data collected from 5 southwestern Montana ranches were used to develop input parameters for bio-economic models of elk forage harvest and beef production. Input parameters described ranch resources, animal inventories, and animal management. Cattle herd size ranged from 241 to 1147 head. Elk numbers varied by season within ranch and ranged from 49 to 421 head. Ranches were simulated as currently managed with elk present and with 10, 20, 30, and 100% of the elk removed. Simulated management scenarios were replicated 10 times. Data from each ranch were analyzed by one-way analysis of variance. Cattle herd size, gross margin, and available forage significantly (P &lt; 0.05) increased when all elk were removed; however, the magnitude of these effects differed among ranches. Removal of all elk permitted cattle herd size to increase from 7 to 32% across ranches. Annual costs of elk on the 5 ranches (i.e., increase in gross margin from elk removal) ranged from 5,949 to 21,152. On an AUM basis, elk costs ranged from 8.55 to 14.51. Three management alternatives were evaluated for their potential to recover elk costs: Montana's Block Management Program, coordinated exchange of forage use, and leasing of hunting access. For each ranch, at least one of these management strategies could recover all estimated costs of providing elk habitat. Elk can significantly reduce profits for cow-calf ranches in southwestern Montana. Elk impacts on beef enterprise profits are closely associated with efficiency of resource use by cattie-i.e., ranches with lower unit costs of production lose more gross margin by providing forage for elk compared to ranches with higher production costs.

A simple ecological sustainability simulator (SESS) for stocking rate management on semi-arid grazinglands

We constructed a simple simulation model (SESS) of the dynamics of forage growth and standing crop and cattle production to evaluate the ecological sustainability of management alternatives for extensive cow-calf production systems in northeastern México and south Texas. Equations were written to estimate annual net primary production based on range condition, annual precipitation, and soil characteristics typical of the region. Simulations were conducted for annual precipitation levels of 300, 500, and 700 mm to estimate total and green standing crop dynamics, cattle grazing efficiency, and range condition trend for different stocking rates. The model-estimated stocking rates to achieve stable or slight improvement of range condition for the three precipitation levels were close to 58, 15, and 6 ha per animal-unit-year (AUY), respectively. With the model parameterized for precipitation and soil characteristics combined with the stocking rates recommended by COTECOCA (1979. Coahuila. Tipos de vegetación, sitos de productividad forrajera y coeficientes de agostadero. Secretaria de Recursos Hidráulicos. Comisión Técnico Consultiva para la Determinación Regional de los Coeficientes de Agostadero. México), we conducted 20-year simulations for three groups of range sites of Coahuila, México (annual precipitation: 1: 270 mm, 2: 351 mm and 3: 467 mm). The trends of body condition score and range condition for years 5, 10, 15, and 20 were similar within each of the three groups. The stocking rates recommended by COTECOCA were too high for sustainability on range site groups with 270 and 351 mm annual precipitation. The simulated probabilities for pregnancy rates at different stocking rates for the three groups indicated that the stocking rates recommended by COTECOCA were too high to achieve pregnancy rates ⩾80% in 8 out of 10 years with no supplement in the form of hay or concentrated feeds. Model simulations suggested that, in the absence of supplemental feed, ecological sustainability and acceptable livestock production could be achieved simultaneously at light stocking rates.

Simulation of cow-calf production systems in a range environment: I. Model development.

A mathematical computer model of beef cattle production systems was developed at Montana State University. The objective of this report was to describe the rationale and procedures used to simulate animal and system performance. The model was designed to simulate the dynamic relationships among cattle genotype, physiological state, forage quality, and management in range environments. Forage intake, energy and protein metabolism, growth, reproduction, lactation, and changes in chemical body composition are simulated for individual animals over complete life cycles. Expenses driven by animal performance, management decisions, and land resources are tabulated. Several biological and economic measures of system performance can be computed, including ratios of inputs (e.g., DM, CP, ME, dollars) to outputs (e.g., weight, lean), break even prices, and annual gross margin per cow or ranch. Primary uses of the model include the evaluation of system responses to changes in breeding strategies and management in range production/marketing systems.

Simulation of cow-calf production systems in a range environment: II. Model evaluation.

Development of a general beef cattle simulation model was described in a companion paper. The objectives of this research were to demonstrate and evaluate the model's performance. Four experiments were conducted to demonstrate 1) life-cycle weight and body condition changes for different genotypes raised in a northern range environment; 2) responses in forage intake and weight to changes in forage quality, protein supplementation, and cow physiological state; 3) responses in reproduction, weight, body condition, and calf growth to differences in pre- and postpartum nutrition; and 4) differences in enterprise efficiency and profit for different genotypes and mating systems. Results indicated that the model performs acceptably for the types of situations for which it was designed and highlighted areas of animal science where more information is needed in order to better understand and manipulate beef cattle systems. Computer simulation models are useful tools to facilitate the integration of scientific concepts and to help scientists, teachers, and producers better understand the complex production systems that they study and manage. In addition to addressing enterprise-level problems that are beyond the scope of traditional experimentation, modeling and simulation help identify research needs and foster exchange among disciplines.

A Simulation Study on the Effects of Cow Size and Milk Production on Bioeconomic Efficiency of Range Beef Cattle

Pang, H., Makarechian, M.H. and Basarab, J.A. 1999. A simulation study on the effects of cow size and milk production on bioeconomic efficiency of range beef cattle. J. Appl. Anim. Res., 16: 119–128. A dynamic simulation model, Alberta Beef Production Simulation System (ABPSS) was used to evaluate the effects of cow size (mature cow weights of 450, 550 and 650 kg), milk production (peak milk yields of 5.4, 8.2 and 10.9 kg d−1), calf market price (low, medium and high) and their interactions on bioeconomic efficiency of cow-calf production systems. The model is composed of four main submodels: Herd Inventory, Nutrient Requirements, Forage Production and Economics. Bioeconomic efficiency was defined as the difference between total cost and total return. The results of simulations indicated that dry matter intake (DMI) and total cost per cow increased with increasing cow size. At a. constant weaning age of 200 days, medium size cows had the maximum bioeconomic efficiency at the low price level, while large size cows had the highest bioeconomic efficiency at the high price level. The results indicate that there are significant interactions between cow size and market price for bioeconomic efficiency. At a constant weaning age (200 d), calf forage DMI decreased with higher milk production, but calf milk DMI, cow DMI and total cost per cow increased with higher milk production. The high milk producing cows had the highest bioeconomic efficiency because of heavier calves at weaning, regardless of price level and the cow size.

Estimation of Net Present Value of Beef Females of Various Ages and the Economic Sensitivity of Net Present Value to Changes in Production

The objective of this study was to economically evaluate the value of future production and the economic sensitivity to changes in production throughout the life of the beef female in a cow-calf production system. Production and cost data were obtained from an existing ranching operation during the 1996 production year. A Net Present Value (NPV) analysis was used to determine the value of future production. Present values for 1-, 2-, 3-, 4-, 5-, 6-, and 7-yr-old beef cows were $786, $1027, $1146, $1210, $1171, $1088, and $1068, respectively, with the highest residual value occurring in 4-yr-old cows. The economic sensitivity of NPV to changes in production was measured in the yearling and bred heifer analysis. This was obtained by estimating the change in NPV resulting from a 1% change in a production parameter. The change in the NPV is called a shadow price and represents the breakeven cost of changing the production parameter. The shadow prices for the yearling analysis were: $4.30 for yearling pregnancy (YP); $2.68, 2-yr-old pregnancy (2P); $3.55, spring cull sales in 2-yr-old heifers (2SC); $2.79, calf death loss in 2-yr-old dams (2CD); and $2.50, weaning weight in 2-yr-old dams (2WW). Shadow prices in the bred heifer analysis were: $5.67 (2P); $6.51 (2SC); $3.75 (2CD) and $3.36 (2WW).