Optimum Replacement Policies for the Control of Subclinical Mastitis due to S.aureus in Dairy Cows

A dynamic program was used to establish the optimum replacement policy for dairy herds, taking into account subclinical mastitis caused by the bacteria Staphylococcus aureus. This particular pathogen is resistant to normal drug therapies and therefore culling is the major method of control. Methods are described to account for output losses due to yield loss and a reduction in milk price caused by extra somatic cells secreted into the milk by infected cows. Extra culling was justified in both infected and control herds in order to reduce the level of infection in the herd. The method described allows replacement policy to be treated as control expenditure rather than an output loss in the economic analysis of farm animal disease. This approach will become even more important as consumers demand an alternative to the prophylactic use of antibiotics in agriculture without compromising food quality and safety.     

DYNAMIC FARM—LEVEL PLANNING MODEL FOR BEEF FEEDLOT PRODUCTION AND MARKETING

The study is aimed at formulating and empirically applying a dynamic farm-level model for the planning of optimal beef feedlot production and marketing strategies. A dynamic programming (DP) model is used to calculate the optimal feeding schedule (i.e. liveweight gain sequence), market liveweight and stock replacement for a single bull calf over a one-year planning period, taking into account seasonal fluctuations of planning parameters such as beef prices, feeding costs, nutritional requirements, and stock replacement costs and obtainability. The DP model includes a linear programming (LP) subroutine for calculating least-cost feed rations. The planning model is empirically applied using data and assumptions representative offeedlots in the Coastal Plain region of Israel where most feedlot production and marketing decisions are made by ‘rule-of-thumb’ using set liveweight gain sequences, market standards and stock replacement decisions. The empirical findings indicate that the profitability of feedlot production and marketing could be increased by an average of 10% over that obtained from ‘rule-of-thumb’ decision rules.     

A stochastic dynamic programming framework for weed control decision making: an application to Avena fatua L.

This paper develops a stochastic multi-period decision model to analyse a continuous wheat cropping system infested by wild oats (Avena fatua L.), in southern Australia. The multi-period solutions is obtained by employing a dynamic programming model in conjunction with a bioeconomic simulation model. An empirically estimated dose response function is used to derive the optimal herbicide rate. Uncertainties due to environmental effects on the performance of herbicide and crop yields are modelled and optimal decision rules derived. The results indicate that substantial economic gains can be realised if herbicide dose decisions are taken by considering future profit effects of current decisions, as opposed to the more common approach of only considering the current-period effect.     

Faustmann vs. real options theory – An experimental investigation of foresters’ harvesting decisions

Among the most complex decisions in forestry is the decision of when to harvest a stand. Many investment theories have been established and adjusted to maximize profit, yet limited knowledge is available regarding the predictive power of theories. Understanding foresters’ harvesting behavior, however, is important for forest management and policy support. Thus, the question arises as to what extent risky harvesting decisions comply with economic theories. Therefore, we conduct an incentive-based economic experiment with 107 forestry decision makers in order to analyze this research question. This approach is well-established in the field of behavioral economics since it has the advantage of analyzing certain economic parameters isolated from further aspects of the decision situation. We use the Faustmann–Pressler–Ohlin theorem and a real options approach as normative benchmarks. The present study provides evidence that none of the examined theories fully comply with the observed behavior. However, the harvesting behavior coincides significantly more with the real options theory than with the Faustmann–Pressler–Ohlin theorem. It can thus be stated that a higher degree of education leads to decisions that are more in accordance with the real options theory.     

Optimal pest control in greenhouse production of ornamental crops

In this study, we develop a conceptual bioeconomic model of floriculture production with aesthetic benefits, wherein optimal decision rules depend on an intertemporal economic objective to maximize profits subject to economic and biological processes. Necessary conditions of the model identify optimal trajectories (e.g., simultaneous, single, or cycling controls) that define decision rules and economic thresholds for profit maximizing growers producing crops with aesthetic attributes. The necessary conditions also highlight intertemporal trade‐offs between aesthetic benefits and expected future net benefits of arthropod stocks, which have important policy implications. The model is applied to the greenhouse production system of ivy geranium.     

Longevity and Genetic Improvement Issues in Replacing Dairy Cows

The objective of this research is to identify optimal economic replacement strategies for dairy cows within the framework of genetic improvement and to compare these strategies with those followed by Alberta dairy farmers. Production records from four commercial dairy herds are used to model the optimum replacement policy within a wealth-maximizing objective, allowing comparison of predicted results with observed practice in the industry. Unplanned replacement, due to biologial failure of cows, is included in the model as a finite Markov process. The economically optimal replacement time is found to occur at the end of the sixth lactation, with only minor penalties for suboptimality. Planned replacement after the sixth lactation requires culling approximately one quarter of the herd annually, and results in an average herd age of 5.77 years. Since the band of economically reasonable replacement policies extends from the third to the tenth lactation, the average herd age ranges from 4.48 years and 7.02 years. The observed average age of Alberta milking herds of 4. 78 years lies in the lower part of this predicted range. While one can conclude that the model leads to an optimum that is consistent with the observed behavior of Alberta dairy farmers, one must temper this conclusion with the caution that additional research, especially regarding the technical lactation curve, is indicated L'objet de la présente recherche était de dégager des stratégies de remplacement economiquement opti-males pour les vaches laitières, compte tenu des exigences de l'amelioration génétique, et de comparer ces stratégies avec celles qu'utilisent les producteurs laitiers de I 'Alberta. On a utilisé les relevés de production de quatre exploitations laitières commercials pour modéliser les stratégies de remplacement optimales dans un objectif de maximisation des revenus. Le modèle permet également de comparer les résultats prédits avec ceux observés sur le terrain. Les remplacements non prévus, à cause de défauts biologiques des vaches, étaient inclus dans le modèle comme processus de Markov fini. L'époque de remplacement économiquement optimale s'est révélée être le fin de la sixième lactation, avec seulement de légères pertes de rentabilité pour les situations suboptimales. Le remplacement planifié après la sixième lactation exigeait la mise à la réforme d'environ un quart du troupeau chaque année et donnait pour le troupeau un age moyen de 5,77 ans. Comme l'écart des possibilités de remplacement économiquement plausibles va de la troisième à la dixieme lactation, l'âge moyen des troupeaux se situe entre 4,48 et 7,02 ans. L'âge moyen réel des troupeaux laitiers de l'Alberta (4,78 ans) se situe dans le bas de eel écart de prédiction. Tout en reconnaissant que le modèle conduit à un optimum cohérent avec le comportentent réel des producteurs laitiers de l'Alberta, il reste qu'on a besoin de plus de recherche dans ce domaine, en particulier en ce qui concerne la courbe de lactation technique     

THE ECONOMIC ADVANTAGE OF LONGEVITY IN THE DAIRY COW

An adaptive stochastic dynamic programming model is described which solves the optimum replacement decision problem for the dairy cow under physical and financial assumptions currently typical for the UK. By expressing the expected net present value of the replacement heifer as an annuity equivalent under various assumptions with and without enforced (involuntary) culling an estimate of the value of longevity was obtained and an assessment made of its sensitivity to key assumptions. Increased longevity added about $20 per extra lactation per year on to the investment potential of the replacement dairy heifer under the assumptions made. This figure is sensitive to replacement cost, but could be used to provide economic values for longevity as part of an economic breeding objective for dairy cattle in the UK.     

LABOUR ON THE FAMILY FARM: A THEORY AND SOME POLICY IMPLICATIONS

This paper seeks to examine the labour-input decisions on family farms at a theoretical level and to demonstrate some policy implications of this theory. Where the family has the opportunity to work on the land, utility maximisation, rather than profit maximisation, would seem to be a more appropriate criterion for decision-making. Accordingly, the decision-making process is analysed under this alternative assumption. We then consider some of the policy implications of this model. In particular, we consider the effects of policies on the labour-inputs since the optimal allocation of labour is at the heart of most agricultural policies.     

A STOCHASTIC MODEL FOR THE OPTIMAL REPLACEMENT OF RUBBER TREES

Recognizing the lack of realism in optimal replacement analyses that assume constant prices and yield patterns over time, a stochastic model appropriate to rubber production is developed. Data drawn from Peninsular Malaysia are used to implement the model. The results suggest that efforts should be directed towards establishing bench mark maximum annuities as guides to more economic replanting decisions rather than emphasizing earlier replanting per se. The significance of price stabilization policies also becomes evident.     

RESPONSES TO RISK IN WEED CONTROL DECISIONS UNDER EXPECTED PROFIT MAXIMISATION

Risk is an important characteristic of decisions about weed control in crops. In this paper it is shown that risk can affect weed control decisions even if the objective of the decision maker is to maximise expected profits: that is, even if the decision maker is ‘risk-neutral’ in the usual economic sense. This is shown for two decision frameworks: the optimal rate approach and the economic threshold approach. Empirical results are presented for control of ryegrass in wheat in Western Australia. It is found that, in general, risk reduces the optimal level of herbicide use under expected profit maximisation. Although individual sources of risk have a small impact on the optimal decision rules, combinations of uncertain variables can have a relatively large effect.     

SIMULTANEITY IN THE UK DAIRY SECTOR*

Because of the high degree of interdependence in the livestock sector, the endogenous variables of econometric models should be simultaneously determined. This paper describes the specification, estimation and evaluation of a model of the UK dairy sector in which the herd size, number of culls, replacement heifer price and milk price are determined simultaneously. The major policy conclusion that emerges from the model is that any attempt to increase the price of milk received by farmers via a structural change in the policy rule used to fix the price will be offset by over 50% as a result of increases in the supply of milk.     

Effects of EU dairy policy reform for Dutch dairy farming: a primal approach using GMM estimation

This paper estimates a production function for milk using ageneralised method of moments estimator to avoid the endogeneityproblem. Using the first-order conditions for profit maximisation,the economic effects for individual Dutch dairy farms of the2003 EU dairy policy reform are analysed. With an expected milkprice decrease of 21 per cent, profit decreases on average by22 per cent. EU direct payments compensate for roughly 53 percent of this fall in profit. The profit reduction means that69 per cent of all small farms have negative income from farming,compared with 15 per cent in the initial situation.     

Cost‐Effective Control Strategies for Johne's Disease in Dairy Herds

Johne's disease (JD), or paratuberculosis, is an incurable and infectious disease of ruminants, caused by infection with Mycobacterium avium ssp. paratuberculosis (MAP), and costing an estimated CAD$15 million in Canada and US$200–$250 million in the United States. This study examines the economic and epidemiological consequences of various MAP control options in the context of controlling JD in dairy herds. A discrete optimal control model is developed utilizing the disease‐specific animal compartment model and maximizing the net present value of a dairy operation. The results identify the optimal control option together with the associated herd dynamics and optimal culling rates of cows in different infection states. The results show that comprehensive, effective, and profitable JD control programs can be developed for dairy farms.     

Means-end chain analysis explains soil fertility management decisions by peri-urban vegetable growers in Kenya

Past studies of the use of soil fertility management strategies by farmers usually model input use decisions based on the neoclassical utility/profit maximization principle in which farmers use soil fertility management inputs primarily to increase revenues and profits. However, there is, to date, no study that explains exactly how this decision-making process occurs and the role which personal values play in driving the choice of soil fertility management inputs. This article systematically maps the relationship between choice of soil fertility management strategy (attributes), its outcomes (consequences) and the personal values that motivate the choice. It specifically uses the means-end chain approach to construct hierarchical value maps that relate the attributes to consequences, and ultimately to the personal values. The study finds that the use of soil fertility management strategies by peri-urban fresh vegetable growers is driven by five personal values, namely happiness, comfortable life, independence, good/healthy life and achievement of life goals. It also finds that while farmers seek to increase profit (hence incomes), profit maximization is not the end driver of the use of soil fertility management inputs. It concludes that a lot more goes into farmers’ decision-making process relating to the use of soil fertility management practices than can be explained by the neoclassical profit/utility maximization principle. The study discusses the policy implications of these findings.     

非粮化对粮食绿色全要素生产率的门槛效应研究

[目的]非粮化关乎国家粮食安全,研究非粮化对粮食绿色全要素生产率的门槛效应,有利于正确认识非粮化,也为制定差异化农业绿色发展政策提供理论依据。[方法]文章以2008—2018年我国26个省（市、自治区）为样本,在运用SBM-GML模型测算粮食绿色全要素生产率的基础上,结合面板门槛模型和耦合协调度模型,探究了非粮化与粮食绿色全要素生产率之间存在的非线性关系。[结果]（1）样本期内所考察地区的粮食绿色全要素生产率均实现破“1”增长,且相较于粮食主产区、产销平衡区以及全国平均值而言,粮食主销区的粮食绿色全要素生产率增长更为显著。（2）非粮化对粮食绿色全要素生产率的影响,确存在以种粮利润为门槛变量的单一门槛效应,其门槛值为7.638,且两者之间的负向关系在跨过门槛值之后将显著大幅提升。（3）分区域来看,各区域非粮化与种粮利润之间耦合协调度的变动趋势,与其粮食绿色全要素生产率的变动趋势基本一致。[结论]采取差异化的非粮化控制措施,可以最大程度上提升粮食绿色全要素生产率。低门槛地区可建立非粮化预警机制,而高门槛地区则应采取严格控制措施,但都须将种粮利润协同保护作为重要工具手段。     

Economic Replacement of a Heterogeneous Herd

A model was developed to determine the optimal slaughter weights of pigs with heterogeneous growth raised in a 1,000 head barn and marketed in truckload groups. Under commonly used revenue schemes, which include discounts for weight and leanness, the optimal strategy was to market one or two truckloads of the heaviest animals, to wait several days, and then to market the rest of the herd. This multiple marketing strategy allows the producer to avoid some sort losses for heavy animals, but only modestly extends the grow/finish period, reflecting the dominance of the opportunity cost of facilities in the herd replacement decision.     

Optimal vessel size and output in the Australian northern prawn fishery: a restricted profit function approach*

Individual transferable quotas (ITQs) are to be introduced into Australia’s Northern Prawn fishery in the near future. Total allowable catches (TACs) are to be set with the objective of maximising economic efficiency in the fishery. Under ITQs, vessel owners have the ability to adjust their fishing activities to maximise profits and changes in fleet structure resulting from management changes need to be considered when determining TACs. A restricted profit function for the fishery was estimated to determine the optimal vessel characteristics and output levels as a guide to how the fleet may adjust under an ITQ system. Vessels were found to be currently close to their optimal size given average historic prices and current stock conditions. However, higher tiger prawn stocks are expected to result in the average size of vessels increasing, with rising fuel prices also likely to result in capital being substituted for fishing days. Optimal average vessel‐level catches of the main species are lower than current average vessel catches for a wide range of input and output prices. These changes in vessel characteristics and behaviour need to be incorporated in the derivation of the optimal TACs if economic efficiency objectives are to be achieved.     

Rainfall or price variability: what determines rangeland management decisions? A simulation-optimization approach to South African savannas

Savannas cover the greater part of Africa and Australia and almost half of South America and contribute to the livelihoods of more than 350 million people. With the intensification of land use during the second half of the 20th century, savannas have become increasingly degraded through bush encroachment as a consequence of increased grazing pressure. Research on rangeland dynamics, however, provides contradicting answers with regard to the causes and possible remedies of bush encroachment. In this article we present results from an application of a simulation-optimization model to the case of extensive rangeland management in South Africa. Our model differs from previous approaches in that it explicitly accounts for the influence of stochastic prices and rainfall on economically optimal management decisions. By showing the implications of neglecting price variation and stochasticity in rangeland models we provide new insights with regard to the determinants of bush encroachment and rangeland managers' economic return. We demonstrate that, in the case of South Africa, optimal rangeland management is likely to lead to bush encroachment that eventually makes livestock holding unprofitable. Yet, we identify the costs of fire management to be a limiting factor for managers to counteract bush encroachment and explore the impact of policy measures to reduce fire control costs on the ecological and economic sustainability of livestock holding.     

矿业权评估的若干理论和方法问题

应尽快对矿业权评估价值给出一个明确的经济内涵.矿业权评估价值不能包含矿产资源所有权人的收益.矿业权评估价值的经济内涵是:"矿业权合理勘查投资+矿业权合理勘查投资的平均收益+矿业权人应分享的矿产开发超额利润余额.目前<准则>DCF法存在的主要缺陷是,转让者获得全部超额利润余额,而受让者则与该超额利润余额无缘,这不公平.建议修改<准则>DCF法,将矿业权评估价值中的超额利润余额按转让者与受让者的投资比例分配.成本途径法基本不可行.对预查、普查探矿权的评估,推荐采用可比销售法.     

Policy drivers of farm succession and inheritance

Farm succession and inheritance is increasingly considered a complex phenomenon which not only affects core dimensions of farm family life but also the agricultural sector more widely. Intergenerational farm transfer in particular is increasingly viewed as fundamental to the sustainability and development of global agriculture. In the majority of EU countries, the average age of farmers is increasing, while the number of farmers under 40 years of age is decreasing. There is growing concern that this demographic trend may have negative impacts on the agricultural industry because it is younger and not older farmers who are associated with more efficient and effective production practices. The question of what motivates decisions to transfer farms is a complex one, and research to date has not apparently enlightened agricultural policy to the extent that current trends towards an ageing farm population are being managed. This research aims to investigate economic and financial aspects of the policy drivers of farm succession and inheritance in Ireland to understand what it is about the policy environment that is failing to stimulate higher levels of farm transfer. It draws on the Teagasc National Farm Survey data which provides Irish data to the Farm Accountancy Data Network in the European Commission. A hypothetical microsimulation model is used to investigate economic factors of farm transfers, with scenarios created to test these factors and their impacts on the transfer process. The Net Present Value (NPV) of income streams for farmers and their successors are calculated to assess which scenarios have the highest/lowest financial effects. The findings illustrate a range of possible scenarios for farm succession/inheritance, with some results indicating that under current policy retaining a farm until death may be more economically beneficial to a farmer than transferring land before death.