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.     

Modeling the relationship between reproductive performance and net-revenue in dairy herds

A dynamic stochastic simulation model to study the relationship between reproductive performance and net-revenue in dairy herds is described. Herds included cows, heifers and calves described by individual characteristics and state variables. The latter were updated using time steps of one week in conjunction with calculations of milk revenue, sales revenue, feed costs, breeding costs, additional costs and net-revenue. Discrete events at the animal level, e.g. involuntary culling, estrous detection and conception were triggered stochastically. Voluntary culling was modeled using the future profitability of cows and potential replacements as determined by dynamic programming. Management and production system were defined by decision variables, e.g. estrous detection rate (EDRT), impregnation factor (IF) and rebreeding policy (RBP). Increases in net-revenue (NR) due to a 1% improvement in EDRT ranged from Cdn. $−2·9 at an EDRT of 75% to Cdn. $22·5 at an EDRT of 35% and were influenced by RBP. Hence, highest increase in NR due to improvement of EDRT can be expected at low reproductive efficiency.     

Replacement policy in dairy herds on farms where heifers compete with cows for grassland: Part 2-Experimentation

Replacement policy is not easy to determine on dairy farms where heifers compete with cows for grassland. Using a computer simulation model of this farm situation, two factorial experiments were conducted to evaluate quantitatively the effect of different replacement rates on profitability and herd improvement.The variables changed in herds of average health and very good health were replacement rate (0·14, 0·22, 0·30), age at first calving (36, 24 months), calving index (13, 12 months) and AI sire merit (standard, premium). Initially, the experimental herd had average health, a replacement rate of 0·22, a calving index of 13 months, calved its heifers at 36 months and had been using standard bulls for many years.After 15 years, the increase in the level of a sinking fund when the age at first calving was reduced was between three and five times greater than when premium bulls were used, calving index was reduced or herd health was improved. There was a major interaction between replacement rate and age at first calving.Yield per cow was significantly reduced (P≤0·001) by reducing the age at first calving and significantly increased when premium bulls (P≤0·001) were used or when herd health was improved (P≤0·05).Some treatments were not tested as expected due to the restraining effect of a 13-month calving interval on the availability of cows for breeding pure in a seasonally calving herd.     

Replacement policy in dairy herds on farms where heifers compete with cows for grassland—Part 3: A revised hypothesis

A preliminary investigation of replacement policy on dairy farms where heifers compete with cows for grassland suggested that profitability falls as replacement rate increases, because the number of cows able to be milked and the maturity of the herd override the gains in milk yield per cow due to genetic improvement by culling for insufficient yield and by the greater use of a sire of high genetic merit.This hypothesis was inadequate to cover all the situations investigated in two factorial experiments involving changes in herd health status, replacement rate, age at first calving, calving index and the merit of AI sires used in the herd from an initial state for these variables of 0·22, 36 months, 13 months and Standard, respectively.Overall, these was a clear indication that the major influence on profitability was the number of cows in the herd. An increase in replacement rate was not always associated with a fall in profitability, nor was an improvement in yield per cow always associated with a rise in profitability relative to the performance of a control herd after 15 simulated years.The manipulation of replacement rate and age at first calving to achieve an increase in the number of cows in the herd was not necessarily incompatible with a desire for herd improvement either phenotypically (yield per cow) or genetically (herd and heifer genotype), particularly if premium bulls were used.     

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.     

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.     

Simulated comparisons of breeding plans for beef production: Part 3—systems for producing feeder-calves involving intensive culling and additional breeds of sire

A dynamic model of a beef-cow herd producing feeder-calves was used to evaluate nine mating plans and an intensive culling policy in combination with management options of producing replacement heifers or purchasing them. The nine mating plans were: straightbred Angus, two-breed static crosses using Angus dams mated to Hereford, Charolais, Simmental, Jersey, Limousin and South Devon sires, a Hereford-Angus criss-cross and a three-breed static cross using Charolais sires mated to Hereford-Angus dams. All of these crosses were simulated under a culling policy of culling a cow as soon as she failed to produce a calf.Kilogrammes of calf weaned per cow was the criterion of herd productivity. The Hereford-Angus criss-cross and the Charolais Hereford-Angus three-breed static cross were the most productive crosses. The high productivity of the three-breed cross was due to the heavy calves weaned and the high productivity of the criss-cross was due to a high ranking for the number of calves weaned per cow bred.The intensity of culling which was practised on the cow herd had diverse effects on herd productivity. The heavy culling option increased the proportion of cows in the herd of three years of age or less by 72·6 to 86·4%, resulted in a higher incidence of calving difficulty and decreased the number of calves produced per cow by up to 17·5%. Structure and productivity were altered the most by a change in culling policy when large breeds of sire were used in the mating plans.     

A preliminary model to investigate culling and replacement policy in dairy herds

Replacement policy in dairy herds is not easy to determine when heifers are both home-reared and compete for land with the cows. The difficulty lies in evaluating quantitatively the advantages and disadvantages of low and high replacement rates. A computer simulation model was developed to examine the effects of different replacement rates on genetic improvement in yield per cow, milk output and farm profit at two levels of culling for reasons other than insufficient yield.The working hypothesis suggested by the results is that profitability falls as replacement rate increases because the number of cows able to be milked and the maturity of the herd over-ride the gains in milk yield per cow due to genetic improvement by yield culling and the greater use of a sire of high genetic merit.     

Dairy farm nutrient management model. 1. Model description and validation

Intensive dairy farming results in significant phosphorus (P) emission to the environment. Field data indicates that farm-gate P surplus is highly positive in Finland and strategies to mitigate the surplus are needed. The objectives of this study were to build a P cycle model for dairy farms (1) and to validate the model with independent field data (2). The dairy farm nutrient management model (“Lypsikki”) described in this paper includes three sub-models: (1) soil and crop, (2) dairy herd and (3) manure management. The model is based on empirical regression equations allowing estimations of crop and milk yields in response to increased fertilisation and nutrient supply, respectively. In addition, the model includes a dynamic simulation model of the dairy herd structure and calculation of the farm-gate nutrient surplus. The model was validated with independent annual (average for 1-4 years) farm-gate P surplus data from 21 dairy farms. Model simulations were conducted using two levels of soil productivity, mean (M) and low (L). The model validation indicated a strong relationships between model-predicted and observed farm-gate P surplus: (M: R² = 0.77 and L: R² = 0.80). The line bias between the model-predicted and observed data was negligible and insignificant (P > 0.6) suggesting a robustness of the model. The mean biases were relatively high and significant (M: 4.7 and L: 1.8 kg/ha, P < 0.001), but evidently related to overestimation of crop yields that has to be taken into account when using the model on a single farm. The prediction error of the model (observed minus predicted P surplus) was significantly correlated to the difference between simulated and observed P import in feeds (M: R² = 0.55 and L: R² = 0.51). This suggests either that all the dairy farms did not fully exploit the possibilities in the crop production or that all the model assumptions are not correct. The effects of purchased feed and fertiliser P and exported milk P (per cow or cropping area) on farm-gate P surplus were of the same magnitude in both observed and simulated data. This implies that the model developed can be used as a management decision tool to find strategies to mitigate P surplus on dairy farms.     

Relating long-term rainfall variability to cattle population dynamics in communal rangelands and a government ranch in southern Ethiopia

This study reconstructed 21 years of household cattle population data in key resource (tula wells) and non-key resource (pond-water) rangelands in southern Ethiopia, as well as 15 years of government cattle breed conservation ranch data, to analyze the relationship between long-term rainfall and cattle population dynamics. For the key-and-non-key resource rangelands, we assessed the reproductive life of cows and the number of calves. For both the communal and ranch systems, we analyzed impacts of multiple droughts on calving rates and herd die-offs. Relationships between pre-drought and post-drought cattle populations were used to evaluate evidence of density-dependence. Breeding females in the key resource tula well rangelands had a longer reproductive life than in the pond-water rangelands, and they produced more calves per reproductive life. Average calving rates were 55% for the communal and 52% for the ranch. Greater reductions in calving rates during droughts implied reduced herd growth potential. Breeding females and immature animals were influenced to a much greater degree by inter-annual rainfall variability than were mature males. The data showed a downward spiral for the total cattle holdings over a 21-year period, with a decline of 54%. The evidence of density-dependence was relatively important at the local land use level as compared with the regional level. Cattle population below carrying capacity under ranch management did not reduce herd die-offs, suggesting that rainfall variability, not density, had greater influence on cattle population dynamics. Long-term trends of cattle populations in the communal and ranch systems synchronized with mean deviations of rainfall. Our results indicate that rainfall variability under the different management systems strongly influenced the dynamics of cattle population, calving rates and mortality. The claim that ranching could be a superior model for range management in Borana over the communal system was not confirmed. The decline in cattle population in southern Ethiopia indicates a need for improved drought management policy. The evidence that droughts were more harmful to breeding females and immature animals than to mature males suggested that drought management needs to focus on herd recruitment potential. For the herders in southern Ethiopia, drought management involved herd mobility and accumulation of herds during periods of favourable rainfall. In the future, the importance of government ranch could be in breed conservation for the maintenance of the Borana cattle breed through distribution of bulls during the drought recovery phase.     

A pasture growth model for use in a whole-farm dairy production model

A generalised climate driven pasture growth model is described and evaluated by comparison to field observation. The model describes dry matter production and green-dead tissue flow dynamics for grazed temperate swards, especially perennial ryegrass (Lolium perenne). The model includes a unique feature to account for light interception by non photosynthetic tissue. Extrapolation across environments occurs by the interaction of climate variables with three parameters that tune the model to a site. These parameters reflect the influence of soil fertility and sward species composition on production patterns. They are: (1) the efficiency of radiant energy use for photosynthesis, (2) the timing of reproductive development and (3) the relative efficiency of radiant energy use in vegetative compared to reproductive swards. Initial parameter settings were derived from data from a sheep grazing experiment in New Zealand. In this paper the ability to describe pasture production under dairy grazing at a different site is confirmed. When the three available parameters were calibrated for the dairy site, all but two of the 42 seasonal estimates of pasture production were within the 95% confidence interval for mean measured production. The model is being used as a component of a whole-farm dairy production model.     

Simulated comparisons of breeding plans for beef production—Part 2: Hereford,angus and Charolais sires bred to Hereford,Angus and Hereford-Angus dams to produce feeder calves

Breeding plans using Hereford, Angus and Charolais sires mated to Hereford, Angus and Hereford-Angus dams were simulated. All breeding plans were considered in combination with a culling policy of culling a cow only if she failed to produce a calf for two consecutive years. The criterion of productivity was kilogrammes of calf produced per cow bred. Productivity of a herd was influenced by the age structure of the herd, since cow fertility, cow and calf mortality and preweaning growth of the calf were determined by the age of the cow, as well as by the genotypes of the cow and calf.For herds with purchased replacement heifers, the three-breed static crosses using Charolais sires were the most productive. The Hereford-Angus criss-cross ranked second, followed by the two-breed static crosses. The two-breed static crosses using Hereford or Angus sires were more productive than the two-breed crosses using Charolais sires. The straightbreds were the least productive. For herds producing their own replacement heifers, producing the replacements from the younger cows increased the kilogrammes of calf produced per cow bred by 2·7% in the Charolais-Angus static cross and 2·8% in the Charolais-Hereford cross.     

Profit in a pig herd from performance testing and selection of breeding stock. The effect of variation in the accuracy and cost of testing

Computer modelling was used to compare a variety of performance testing and selection programmes whose objective was to increase the monetary value of pigs as determined by their rate and efficiency of growth and the leanness of their carcases.Factors varied over feasible ranges were the cost and accuracy of performance testing, the culling rates of breeding stock and the degree of subdivision of the herd into a nucleus supplying breeder replacements for the whole herd and a production unit producing slaughter stock.Net returns per sow, evaluated over 10 years of selection, increased, by 120 times, the standard deviation (sd) of the breeding objective for each improvement of 0·1 in the correlation between the selection criterion and the breeding objective (test accuracy).A unit of the cost of testing each pig equalled 0·4 sd of the breeding objective and net returns in the unsubdivided herd declined by 0·6 for each unit increase in cost. Herd subdivision increased net returns by reducing the number of pigs tested—and hence the cost of testing. The optimum ratios of production unit to breeding nucleus sizes which maximised net returns were found. When herds were subdivided in an optimum way, the decline in net returns with increasing testing costs was reduced sixfold.Returns were highest when boars were worked for only one breeding cycle (approximately 6 months) in both the nucleus and the production unit. Depending on the accuracy and cost of testing, maximum net returns occurred when nucleus sows were culled after one or two farrowings. Sows in the production unit were an optimum combination of culled ‘old’ sows and selected ‘young’ gilts from the nucleus. There were a number of other replacement schemes which were almost equally profitable.     

Simulation of artificial neural network model for trunk sap flow of Pyrus pyrifolia and its comparison with multiple-linear regression

Trunk sap flow of tree is an important index in the irrigation decision of orchard. On the basis of the measured sap flow (SF) of pear tree (Pyrus pyrifolia) in the field, the multiple-linear regression for simulating the SF was obtained after analyzing the relationships between the SF and its affecting factors in this study and an artificial neural network (ANN) technique was applied to construct a nonlinear mapping to simulate the SF, then the simulated SF by two models was, respectively, compared to the measured value. Results showed that trunk SF had significant relationship with the vapour pressure deficit (VPD) in the single-variable analysis method but with soil volumetric water content (θ) using the ANN models with default of different variables. The correlation coefficient (R²), mean relative error (MRE) and root mean square error (RMSE) between the measured and simulated sap flows by the ANN model developed by taking VPD, solar radiation (S_r), air temperature (T), wind speed (W_s), θ, leaf area index (LAI) as the input variables were 0.953, 10.0% and 5.33 L d⁻¹, respectively, and the simulation precision of ANN model was superior to that of multiple-linear regression due to its better performance for the nonlinear relationship between trunk SF and its affecting factors, thus ANN model can simulate trunk sap flow and then may help the efficient water management of orchard.     

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.     

基于Web的奶牛场管理信息系统

介绍基于JSP+SPrvlet+Javabean模式开发的、适合中型奶牛场使用的奶牛场管理信息系统,分为牛群管理、产乳管理、牛群繁殖、统计与分析、养牛场管理及系统管理功能6个方面,可以对奶牛及奶牛场各种技术数据进行分析与综合整理,是一种实用、经济和操作简便的奶牛场信息资料管理系统.     

Implications of on-farm segregation for valuable milk characteristics

Milk composition varies between herds and cows within herds, enabling its segregation on farm, rather than during processing, for the manufacture of specific dairy products. Benefits may include increased product yields, reduced processing costs and greater suitability of differentiated milk for the production of high value niche market products. However, costs are also likely to be greater. An integrated spreadsheet model was developed to determine the break-even premium required for a farmer with a seasonal calving herd to be economically no worse off producing segregated than conventional milk. The model incorporated breeding (quantitative and qualitative traits), cow requirements and feeding, transport, and economic sub-models. Cows were segregated within herd and milk composition was altered over time by genetic selection. Four quantitative trait (“white” milk colour) scenarios and two qualitative trait (BB β-lactoglobulin milk) scenarios were considered.The model suggested that “white” milkfat would need to earn 38.4% more at the farm gate than conventional milkfat for the two systems to break even. “White” milk cows produced less than their status quo counterparts due to the reduced selection pressure on production milk traits and this had a considerable impact on the premium, as did the low initial volumes of white milkfat. The difference in production between the B β-lactoglobulin cows and their status quo counterparts was less than for selection on white milkfat only. The high risk to farmers of discontinuing a differentiated milk policy could be moderated by changing the structure of premium payments over time. Hence, processing companies and farmers will need to work together to facilitate the uptake of milk segregation. This research model could be applied by dairy companies and farmers considering milk segregation policies.     

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.     

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).     

Stochastic simulation of mountain beef cattle systems

A stochastic model for simulating mountain beef cattle systems was described and validated using real data. The model was able to properly simulate complex batches of animals with different initial characteristics and so obtain results about the mean and variance of animal productive and reproductive outputs. Model was used to simulate four feeding strategies during winter period in the conditions of autumn calving in the Spanish Pyrenees. The simulated strategies were CONTROL: 100% of recommendations for the mean animal; LOW1: as 24% restriction from the amount of energy provided to CONTROL, applied only during lactation; LOW2: the same of LOW1, but was applied only the last two thirds of lactation; LOW3: 16% restriction from CONTROL applied at late gestation and first third of lactation. Simulated results showed that restrictions around 25% of the total winter energy requirements of beef cows in housing conditions are possible and sustainable. The best option taking into account reproductive performance and outputs variability seems to be a continuous restriction during all lactation (strategy LOW1). On the other hand, an extensification policy implying extended grazing till mid or late December with housing afterwards (strategy LOW3), is also possible and will have no negative consequences on calf growth (only viability of young calves being outdoors in autumn should be evaluated), but can affect the PPA of cows and so the herd reproductive performance could be compromised in the long term.