A bio-economic modelling project for small-scale milk production systems in South-East Brazil: Part 2—refinement and use of the model to analyse some short- and long-term management strategies

The further development and use of a bio-economic model to simulate small-scale dairy enterprises in South-East Brazil are reported.The account of animal nutrition has been refined to take account of protein requirements in addition to energy balance. A new version has been developed which allows for the inheritance of production traits.The model has been used to analyse the effects of short-term management decisions on feeding strategies and longer term breeding policies for herd development. It has been used, also, to examine the possibilities of culling for reproductive performance and the effects of a range of growth rates of replacement heifers on overall herd performance.     

A model for estimating potential market offtake from subsistence herds

A mathematical model is presented of the regional cattle herd within a subsistence pastoral system, in a semi-arid region, where empirical data on herd production are restricted to a few basic properties under average conditions.The model was developed to estimate the potential market offtake for a region in Kwazulu (Republic of South Africa). Currently, this region is overstocked and low production levels are prevalent.The model was used to simulate various offtake strategies and it was found than an approximate threefold increase in sustainable annual revenue can be achieved while simultaneously reducing grazing pressure.     

A Markov decision sow model representing the productive lifespan of herd sows

A Markov decision sow model has been developed to represent the productive and reproductive lifespan of herd sows. This model precisely describes the herd structure at equilibrium based on actual farm data. Model outputs are the herd structure at equilibrium, and technical and economic indexes. Validation has been performed by comparing observed and simulated outputs from specific farm data. A complementary validation using a statistical χ² test based on Pearson's statistic is proposed to compare herd distributions at equilibrium. The model is intended to be used by farmers and runs on micro computers.     

Simulated comparisons of breeding plans for beef production—Part 1: A dynamic model to evaluate the effect of mating plan on herd age structure and productivity

A computer program to simulate beef production is described. The model is based on the principles of industrial dynamics and constructed in the simulation language DYNAMO. This dynamic model is composed of subroutines that simulate herd structure for a cow herd and a production herd composed of calves from the cow herd. Additional subroutines model pre-weaning and post-weaning growth of the calves.The portion of the model that simulates the herd structure includes ten age classes of cow. The subroutine which models the portion of the herd between 2 and 9 years of age utilises twelve variables to describe the events that occur in the herd during the passage of a year. The age structure of the herd is influenced by the breeding system and the way in which the herd is managed.The production herd is modelled by sequential subroutines. These subroutines follow the number and growth of calves weaned from the cow herd until they are sold at 32, 52, 67 or 85 weeks of age. Mating plans utilising different breeds can be simulated in combination with various management options.     

奶牛发情行为的检测研究

在奶牛养殖中,为增加牛奶产量,使奶牛及时受孕、产犊并提高泌乳期是非常重要的,而要达到上述目的,正确、高效地预测以及检测奶牛的发情期,并适时配种尤为关键。因此,奶牛发情的及时和准确识别则变得举足轻重,在牛群管理中具有重要地位。传统的奶牛发情检测方法愈加不能满足现代化奶牛养殖场的需求,基于微机系统的自动化电子检测技术迫切需要应用到奶牛发情检测中。对奶牛的发情行为的影响因素、传统检测方法以及数字化的检测方法进行了阐述,并对其数字化检测趋势进行了系统深入的探讨。     

Replacement policy in dairy herds on farms where heifers compete with the cows for Grassland—part 1: Model construction and validation

It is difficult to evaluate quantitatively the effect of different replacement rates on dairy farm profitability and dairy herd improvement. Computer simulation models were developed to tackle this problem and to formulate hypotheses that might be useful for research and advisory purposes.A model was constructed and validated against actual average yields of heifers entering the national herd of England and Wales over the period 1962–1976. It was used to generate information on the initial state of herds that could be used in experiments. A second model was adapted from this generation model to handle the replacement situation where heifers are reared on the farm where they are to be used and compete with the cows for grassland.     

A linear programming formulation of the Markovian decision process approach to modelling the dairy replacement problem

In modelling the replacement decision in dairy herd management, the most common approach taken is to use dynamic programming to determine the optimal policy by comparing the future expected profitability of an animal to that of it's potential replacement. It does not, however, take into account the performance of the entire herd or that of all potential replacements, which is particularly important if replacements originate from the same herd. This paper demonstrates how to overcome this inadequacy by formulating the problem as a multi-component Markovian decision process and then solving it as an associated linear programming model. The proposed methodology is illustrated by using a simple, but realistic, example for determining the optimal replacement strategy for a dairy herd over a 10-year planning horizon. The results show that replacements should be bred from heifer cows in order to increase the genetic turnover; however, no more animals than is necessary should be culled to increase this turnover. It is also shown how to include considerations such as problems of milk quota management, and other similar resource allocation decisions into the model. Additional improvements to the model could involve considering culling of animals suffering from disease.     

Simulation of forage harvest and conservation on dairy farms

A computer model was developed to simulate forage systems on dairy farms. The model simulated alfalfa growth, corn silage and corn grain yields, harvest, storage, feeding and ration formulation for a dairy herd. A 26-year series of historical weather data from East Lansing, Michigan, was used to compare management and technological alternatives on the basis of average net return and year-to-year variations. For example, a four-cut alfalfa system was found to be more profitable than a three-cut system 90% of the time. The comparison of a hay system with a silage system was very sensitive to forage intake assumptions; the break-even point shifted from 120 ha to 40 ha when silage intake was increased by 5%. The model can be used to assess the impact of new forage conservation methods under a wide range of climatic and management conditions.     

Probit analysis of livestock producers' demand for private veterinary services in the high potential agricultural areas of Kenya

In this paper, empirical maximum likelihood (ML) and weighted least squares (WLS) estimates of socio-economic factors influencing the demand for private veterinary services in the high potential agricultural areas of Kenya are derived using probit analysis. While ML estimates explain 65 and 56% of the variation in demand for artificial insemination and clinical services, respectively, WLS estimates explain 74 and 72% of the variation after correcting for sample selection bias using the Heckman two-step procedure. Based on the ML and WLS coefficients, herd size, number of breeding cows, farm income, education, knowledge of husbandry practices and time devoted to farm activities are identified as important determinants of demand and are used to construct producer demand profiles. Using the predictive success rate together with information on the profiles, the model correctly classifies the demand for artificial insemination and clinical services to be higher than demand for vaccination and herd health services.     

A dynamic model for the simulation of cattle herd production systems: Part 1—General description and the effects of simulation techniques on model results

A computerised model to describe and predict cattle production for any herd size and time period and for a wide range of environments, was developed from a model published by Sanders & Cartwright (1979a, b).The dynamics of the model are based on the flow of energy from vegetative sources to animal products in a single-animal or cow-calf unit, so that the model is appropriate even for smallholder herds. A separate flow of numbers records the dynamically changing herd size and structure.Reproduction and mortality are linked to the nutritional and physiological status of each individual. Their occurrence is triggered stochastically to preserve the integer quality of the herd. In all other respects the model is deterministic.The simulated herd can be of any number, breed, sex and age composition. Breeds are distinguished by mature size, growth rate and milk production: they can be single, dual and/or triple purpose (dairy and/or beef and/or draught). Feeding management can be grazing, stall-feeding or a combination of the two. Routines are included which can simulate different types of management decisions and their repercussions. Functions for the quantification of the model were selected according to preset guidelines, generally following an investigation of conflicting hypotheses.There are eight different output options (tabular and graphical), representing various levels of model resolution.     

A model to find and test decision rules for turnout date and grazing area allocation for a dairy cow system in spring

Use of grazing is decreasing in dairy cow systems in many European countries. However, pasture has a lower production cost than most conserved forage. Furthermore, agronomic decision rules are available to provide dairy cows with sufficient quality and quantity of dry matter. The decline in use of grazing is partly due to organisational difficulties in planning the grazing period. Land use at the farm level requires that this plan must be made in September, about 6 months before the turnout date. This area planning depends on the decision rule used for the turnout date. So we propose to search for a combination of area planning and turnout decision rules that allows a dairy herd to be fed in the spring by means of grazing without any risk of an interruption in the feeding. For this we propose to use a simulation model combining a grass growth model and a model for scheduling the farmer's decisions. A test of a turnout date rule showed that it is necessary to use an area allocation decision rule that depends on the turnout date rule and not the converse. We therefore proposed another turnout date rule based on the available herbage per ha and we calculated the area to allocate on the basis of this turnout rule.     

Simulation of the intake and partition of nutrients by the dairy cow: Part II— The yield and composition of milk

This paper is the second in a series describing a computer-based simulation model designed for use as a management control aid for the dairy herd and concerned with the intake and partition of nutrients by the cow. Milk production is represented in the model in two parts; the first estimates the potential milk yield for each 24 h simulation interval and the second is concerned with matching the available metabolites to the requirements associated with the potential yield. In each case, a conceptual scheme for inclusion in the model is outlined in relation to the relevant literature and the manner in which these schemes are represented in the model is described.     

Simulated effects of changing strategies on production performance of Gobra Zebu cattle

Analyses of various management strategies available for the production of Gobra Zebu cattle at Dahra Research Station were conducted using a dynamic cattle production simulation model. Growth, milk production, forage and management characteristics collected at the station were the major input data used. Effects of the management strategies on production performances were predicted by examining changes in breeding season, breeding age, weaning age and supplementation regimes on productivity indices. The indices used were efficiency of nutrient utilization (ENU), defined as liveweight sold per 100 kg DM consumed, and cow productivity index (CPI), defined as liveweight sold per cow exposed. When females were exposed to calve first at 3 years of age, the ENU (94·4) and CPI (4·04) were highest for breeding from September to November and lowest (77·93 and 3·43, respectively) for breeding from July to September. Weaning at 7 months of age resulted in the highest ENU and CPI (94·89 and 3·95) while weaning at 5 months generated the lowest ENU and CPI (83·93 and 3·58). Among all feeding alternatives, the highest ENU (105·84) and CPI (4·21) were obtained when the entire cow herd was supplemented from May to July. Supplementation of mature cows only was the most desirable strategy among the selective supplemental feeding practices with regard to cow age classes. Results provided valuable guidelines for selecting management practices likely to increase Gobra Zebu productivity.     

Simulation of production systems in East Africa by use of interfaced forage and cattle models

A forage model and a cattle production model were interfaced and adapted for tropical production conditions in East Africa. The objectives of the modelling were to structure and conceptualise a complex system for better comprehension, thereby determining constraints on a traditional African grazing system. The model was designed to simulate the physical linkages between the scarce resource of forage and the outputs of cattle, meat and milk. The effects of improved management practices were examined for a traditional village livestock grazing system. Verification and validation for the baseline village herd were carried out using several different sources of data. A combination of a restricted breeding season, supplemental feeding during the dry season and a seasonal sales policy resulted in a 40% increase in net revenue to village producers above the baseline for a ten-year period.     

Model of the small scale dairying enterprise: An aid to resource allocation in agricultural development

A model of a smallholder dairying system in the high potential country in Kenya is briefly described. A sensitivity analysis was carried out with the model for two replacement policies and six herd sizes. The ensuing output of mean monthly milk yields and incomes was subjected to an analysis of variance where the major effects of four performance variables were ascertained. Response surfaces were fitted to the data generated from the model and were used to demonstrate that the relative income responses to an improvement in each variable dependend on the initial levels of performance.It is suggested that the technique reported here may be utilised as part of a larger cost-benefit analysis designed to assist in the allocation of resources for research and development aimed at improving the performance of smallholder dairy farmers. In addition, there is a need for greater involvement in extension research, so that the cost of obtaining an improvement at the farm level in a given performance variable can be estimated. Guidance of research and development priorities with respect to the smallholder dairy industry could then proceed in a more rational manner.     

The CAMDAIRY model for formulating and analysing dairy cow rations

The paper describes a package of computer programs known as ‘CAMDAIRY’, which is written for CP/M80 and MS-DOS operating systems. The core program is a bio-mathematical model of a lactating cow, which incorporates functions to predict nutrient requirements, feed intake, substitution effects when feeding concentrates, tissue mobilisation and partition of nutrient utilisation between milk production and growth. Nutrient partitioning is described by a series of asymptotic curves relating energy intake to milk production, such that energy requirements per litre increase progressively with level of milk production. This model is incorporated into an econometric model, ‘Maximum Profit’, which uses linear programming procedures to formulate rations for up to two groups of cows in a herd in a way which maximises income above feed costs, whilst meeting nutrient requirements and satisfying constraints on feed supply and milk production requirements. Other programs in the CAMDAIRY package are ‘Least Cost’, a program which calculates a leastcost ration using fixed energy requirements for milk production, and ‘Analysis’, a program which predicts likely milk production given characteristics of the cows, feed intake and feed composition.     

Simulation of swine herd population dynamics

A discrete stochastic simulation model of swine herd population dynamics is described. The model is homomorphic with the life cycle of hogs. Each animal is individually represented in the model and is tracked throughout its life in the production system. The example production system used was a 100-breeding sow, farrow-to-finish, high-investment, complete confinement system. The model was developed in a specialized discrete simulation language—GPSS. The model provides both the magnitude and the variability of annual production levels, feed consumption and other population statistics. The output of the herd dynamics model was used in a spread-sheet program for economic analysis. This program computes annual revenues, costs and rate of return to capital investment over the 10-year analysis period by using the discounted cash flow method. It provides both the average values and 95% confidence intervals of the annual income and the rate of return. The application of the model for analyzing the interrelationships of biological, physical, economic and management factors is demonstrated. Other applications for system design, management planning, facility scheduling and resource allocation are also described.     

Development of a mathematical model to study the impacts of production and management policies on the herd dynamics and profitability of dairy goats

The reduction in goat milk production and the competitiveness of more profitable activities have increased the adoption of measures to enhance goat milk and meat around the world. A simulation model was built to evaluate the dynamics of a dairy goat herd under different scenarios of production. A System Dynamics approach was used to identify management policies that could affect the behaviour of the herd over 10 years of simulation using data from a dairy goat herd in Brazil. The impact of reproductive and mortality rates, one or two annual reproductive cycles on production, and economic health of dairy goats on changes in the herd dynamics were evaluated. Simulations indicated that small changes in reproduction and mortality rates and milk price can considerably affect the dynamics of the herd as well as the financial health of the production system. The interferences created to visualize the effects were not immediately realized because of intrinsic delays in the system. The comparison of models with one or two breeding seasons indicated that the latter was considerably more profitable and had a faster turnover. It was also found that the two breeding season had a greater capacity to support reduction in milk price that could generate financial instability in the production system. It was concluded that mathematical models can be used to predict impacts in management policies on herd dynamics and sensitivity to support the dairy goat activity showing its viability as an agricultural activity that can contribute to the production and incomes in small farms.     

Modelling the economics of animal health control programs using dynamic programming

A new application of an optimization tool, dynamic programming (DP), is described to model the economics of animal health control programs. To demonstrate the value of this technique, a model is applied to determine optimal net benefits of controlling East Coast fever (ECF) in Malawi Zebu cattle in the Lilongwe plateau. The objective function was the present value of net benefits due to treatment, defined as mortality savings minus treatment costs. Mortality savings were based on decreased mortality from ECF following treatment. Model constraints included herd size, animal (herd) nutritional requirements, and program budget. Treatment options were tank dipping in acaricide, and vaccination. Secondary data from a dipping trial of 1800 Malawi Zebu cattle conducted from 1991 to 1994 were used to determine probabilities of mortality. Total optimal net benefits of long-term treatment (25 years, i = 10%) from vaccination (Malawi Kwacha (MK) 21 069) exceeded benefits for treatment with chlorfenvinphos acaricide (MK15 203).