Modelling dairy cattle feeding in the South-East region of Brazil

Computer modelling techniques were applied to study the structure of traditional dairy farms in the South-East region of Brazil and to help define research priorities and policies. Animal feeding is considered the principal factor affecting dairy cattle performance in the study. Knowledge of animal nutrition and feed supply from Brazilian and other literature was synthesized in two mathematical models. One model deals with the optimization of resources used in supplementary feeding for dairy cows under grazing; the other predicts dairy cow performance under a range of feeding conditions imposed by changes in the level of supplementation, stocking rate and calving date. Both models are empirical in nature. The modelling approach shows itself to be a useful means of defining research priorities and making recommendations on practical aspects of dairy cow feeding and management.     

A dairy herd cash flow model

A model that estimates milk production, revenue from milk sales and concentrate requirements for a diary herd is described. The model is designed for a programmable calculator for use by staff of the Agricultural Development and Advisory Service in their consultancy work on farms.     

Modelling the determinants of grassland stocking rates on dairy farms in England and Wales

An attempt has been made to provide a quantitative model of grassland management on a dairy farm which could be used for predictive purposes to establish appropriate stocking rates in relation to the resources available and the consequences of changing the level of resources used. The model takes into account the effect of rainfall, the available water capacity of the soil, soil drainage and fertiliser usage on grass production and the calving pattern, milk yield and availability of other feeds in determining grass requirements. Allowance is made for the fact that the response to unpredictable variation in grass production may be to under-stock. There was reasonably good agreement between predicted and actual stocking rates for a group of 33 dairy farms, but the predictions were too variable for acceptance of the model as a reliable aid in management planning on individual farms. Nonetheless, the model showed sufficient promise to suggest that it may be feasible to make predictions for individual farms in the future if a clearer understanding of a number of aspects of grassland management can be obtained: most notably, how farmers respond to risk, how managerial ability and financial constraints affect stocking intensity and how farmers integrate, in practice, grazing and conservation.     

Financial implications of recent declines in reproduction and survival of Holstein-Friesian cows in spring-calving Irish dairy herds

Milk production and reproductive performance were monitored in 14 spring calving dairy herds in the south of Ireland between 1990 and 2003. In these herds, the average pedigree index for milk yield increased by 25 kg per year from 1990 to 2001, while the average proportion of Holstein-Friesian genes in the cows increased from 8% in 1990 to 63% in 2001. Over this period, milk production per cow increased by 54 kg/year, while replacement rate increased from 16% in 1990 to 27% in 2003. To evaluate the farm-level financial implications of associated changes in calving pattern, milk production and replacement rate, data from the 14 spring-calving herds were included in the Moorepark Dairy System Model for each of the 14 years. Two milk production scenarios were investigated, which included EU milk quota applied at farm level (S1) and no milk quota (S2). The influence of variation in milk price, cull cow value, replacement heifer cost and replacement rate were modelled using stochastic budgeting. In S1 there was a significant linear increase (P < 0.05) in margin per cow (€10.8), margin per kg of milk produced (0.13 cent) and net farm profit (€546) over the 14-year period. Similarly in S2 there was a significant linear increase in margin/cow (€11.3), margin/kg (0.14 cent) and farm profit (€1089) over the 14-year period. However, the analysis showed that if reproductive performance, calving spread and replacement rate could have been maintained at 1990 levels for each of the 14 years then the increase per cow, per kg of milk and farm profit per year would have been €22.1, 0.31 cent and €1341 for S1, and €22.8, 0.32 cent and €2183 for S2, respectively. Stochastic analysis showed that farm profit was most sensitive to changes in milk price, followed by replacement rate.     

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.     

Development and evaluation of a pastoral simulation model that predicts dairy cattle performance based on animal genotype and environmental sensitivity information

A dairy cattle simulation model for pastoral systems that considers how dairy cow genotypes respond to different environments is described. The dairy cow is represented by five modules for maintenance, pregnancy, growth, body energy reserves and lactation with the influence of environmental factors on processes included within each module. Feed intake is predicted based on the requirements for maintenance, growth and pregnancy, and the dairy cow’s potential for yields of milk, fat and protein and body fat change in a given environment. The effects of various temporary environmental factors such as cow body condition score, climate, feed quality and the stage of pregnancy are all considered when predicting yields of milk, fat and protein, energy and dry matter intake. The model was evaluated using information from a prior experimental study with 1990s Holstein-Friesian dairy cattle of North American/European or New Zealand origin managed in a pasture-based system in early to peak lactation. The model was able to predict, to a high degree of accuracy, mean values for yields of milk, fat and protein, and concentrations of fat and protein. However for individual cows, feed intake and live weight change were less reliably predicted. The major source of error was a lack of simulated variation, rather than any systematic bias. The major advance of the model is its ability to predict performance from genetic and environmental sensitivity information for particular breeds, and its ability to predict feed intake and yields of milk, fat and protein concurrently.     

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.     

Computer simulation of monitoring herd productivity under extensive conditions: Sampling error of herd size and offtake rate

Monitoring extensive pastorialist herds was simulated using a personal computer program designed to yield balance sheets for numbers and annual rates of births, mortalities, cullings and herd growth, as well as for herd structure in successive periods of weeks or months. Instead of calving rate, the program used frequency distributions of first parturition age and parturition interval, together with sterility rates, to generate individual reproduction. It took 15 years for herd size to become free from carry-over effects due to inherent herd history. Offtake rate seemed to be a convenient statistic for measuring productivity under the conditions of stable environment and herd policy. It was not auto-correlated and its sampling error followed binomial expectation. The standard error of annual offtake rate was large and, even with monitoring periods of as much as two years, some herds were three or four times as productive as others. A menu-driven program that can handle different animal species and various herd development policies without prior modification can be useful for testing hypotheses which would otherwise be difficult to treat mathematically. Practical monitoring schemes should maintain corresponding packages for routine purposes.     

Modelling the Drying Kinetics of Maize in a Microwave Environment

Microwave drying of grains is fundamentally different from either convection or conduction drying. Drying of cereal grains appears to proceed mainly in the period when the drying rate is decreasing (in the falling rate period), a characteristic of internally controlled diffusion. However, the analytical solution to Fick's second law of diffusion for a homogeneous, isotropic sphere with constant initial and boundary conditions does not adequately describe the drying behaviour. In an attempt to overcome this problem, the moisture ratio was written in terms of the surface moisture content rather than the equilibrium value. The associated surface drying coefficient, as determined by an iterative technique, was found to be expressible as a linear function of the initial free moisture content of the grain. The resulting empirical model better described the observed drying kinetics. This approach also resulted in good fits to independent data from experiments on convective drying of rough rice, microwave drying of wheat and combined microwave-fluidized bed drying of wheat.     

Modelling worker physical health and societal sustainability at farm level: An application to conventional and organic dairy farming

Farm-level modelling can be used to determine how farming systems and individual farm-management measures influence different sustainability indicators. Until now however, worker physical health and societal sustainability have been lacking in farm models. For this paper, we first selected attributes of physical health (working conditions) and societal sustainability (food safety, animal welfare and health, and landscape quality). Second, possible sustainability indicators for these attributes were identified, and those selected were included in an existing dairy farm LP-model that was subsequently used to analyse possible differences in societal sustainability within and between a conventional and organic dairy farming system. Results for physical health and societal sustainability were similar for conventional and organic dairy farming systems in the basis situation, as well as in the situation where additional management measures were applied to improve societal sustainability, but improved animal welfare did result in the organic system due to prescribed grazing, and due to assumed summer feeding in the conventional system. Results show that additional management measures considerably improved societal sustainability of the conventional as well as the organic system. LP-modelling appeared to be a suitable method for comparing farming systems and determining the effect of management measures on physical health and societal sustainability. The level of societal sustainability is determined mainly by applied management measures, and is related to the particular farming system in only a very limited way. This implies that societal sustainability is mainly dependent on the cost-effectiveness of management measures and on the attitude of the dairy farmer.     

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.     

Modelling and measuring evapotranspiration in a daily drip irrigated cotton field

Summary An eddy correlation system (ECS) was used to estimate evapotranspiration (E) in a daily drip irrigated cotton field. Cotton yield, water use, and their ratio (Water use efficiency; WUE) were compared in four irrigation treatments. Three treatments were irrigated at levels of 85, 100, and 115% of E, while the fourth was irrigated according to grower's usual practice. E data were used to verify a one dimensional numerical model which simulates, in real time, the different energy fluxes existing in the soil-plant-atmosphere system. The model requires input of vegetation parameters (leaf area index, photometric properties, shading factor, root density distribution), soil parameters texture, hydraulic and photo-metric properties, temporal micrometeorological data (solar radiation, wind speed, air temperature and humidity) measured above the field, and irrigation quantities. The verification study was carried out during a cotton growing season in Hula Valley, Northern Israel. Results show that E rates are strongly affected by the intensity and arrival time of the inland penetrating Mediterranean sea breeze. WUE in the treatment which was irrigated according to the ECS was highest. Accurate estimations were also made by the model.     

Modelling weekly rainfall data for crop planning in a sub-humid climate of India

In this study, two and three-parameter probability distributions have been compared to identify the most appropriate distribution to describe the weekly rainfall data in a sub-humid climate of India. The “best” distribution among different data sets has been identified using probability plot and Anderson–Darling (AD) test for goodness-of-fit, along with the appropriateness of estimated percentiles. One single probability distribution has not been found appropriate to represent all the data sets though Weibull distribution has been found promising for most of the data sets. Gamma probability distribution, which is generally employed for describing weekly rainfall data, was found to grossly approximate the underlying process. Likelihood ratio (LR) test revealed that three-parameter distributions did not significantly improve the fit over two-parameter distributions within the same family. The developed models for different data sets have been employed for computing minimum assured amount of rainfall at different probability levels. Minimum assured rainfall at 40% probability level was found to be in close agreement with the long-term average weekly rainfall data as depicted by L2 and Chebycheff norms. The effect of departure from minimum assured rainfall at 70% probability level on yield of rainfed maize in the region has also been studied using the available experimental data collected from three different field experiments. The effect of intervening drought was found to be most serious in reducing the crop yield by 37–58% as compared to other scenarios representing rainfall amount and its distribution under a sub-humid climate.     

Modelling of river flushing and water quality in a tributary constrained by barrages

In developing countries, natural river regimes are increasingly undergone human modifications. All these constraints strongly affect the river systems. However, study on minor tributary of modified river is few. Thus the interest of this paper is to explore a tributary due to extensively regulated flow regime of mainstem river constrained by two barrages. The mainstem and tributary are deteriorating in its water quality due to the existing estuarial barrage impoundment. However by inserting another barrage in the middle stretch, modelling efforts have shown that the fluvial quality in the tributary improves compared to the former conditions. This has indicated that barrage operations are offering chances of improving a constrained tributary in terms of flow, flushing capability and water quality.     

An economic evaluation of breeding systems with selection and crossing of large white and landrace pigs in a closed herd

Computer models of a number of systems for combining the Large White and Landrace pig breeds were developed. These systems were: 1, firstcross; 2, backcross; 3, rotational cross and 4, synthetic. The models incorporated both selection and heterosis. The monetary gains from running these systems for a period of 10 years were estimated as deviations from returns from a Large White control herd.In the absence of selection, heterosis alone gave gains of A$183, $430, $271 and $164 per sow place for systems 1, 2, 3 and 4. Values were increased markedly by selection. Using typical values for the cost and accuracy of selection and optimum structures of the systems, monetary gains were increased with selection to A$1245, $1492, $1258 and $1311 for systems 1, 2, 3 and 4. Sensitivity analyses revealed wide confidence limits for these gains.In all but the largest herds (> 500 sows), the real value of the complex systems (e.g. backcross) is likely to be diminished relative to the simpler systems (e.g. synthetic) because management costs are expected to be higher and optimum herd structures cannot be attained.     

A dynamic model for the simulation of cattle herd production systems: 2-An investigation of various factors influencing the voluntary intake of dry matter and the use of the model in their validation

Various published systems for the prediction of dry matter (DM) intake are discussed, with special emphasis on their relationship to DM digestibility. Suggestions are made for the modification of the Conrad (1966) equations and their adaptation to different types of cattle and environment.The equations were included in a dynamic simulation model to test their accuracy in predicting weight changes in growing steers under grazing conditions in Botswana and the UK. It was found that predicted weights were generally within 0.4–1.5% of measured weights and that fluctuations in the predicted liveweight curves closely followed the pattern of the observed ones, showing that the equations can provide a sound basis for the prediction of DM intake in agricultural practice in general and in livestock simulation models in particular.     

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.     

Mesophilic anaerobic digestion of high solids cattle waste in a packed bed digester

A mixture of manure and straw (26·3% total solids) obtained from the overwintering of dairy cattle was anaerobically digested in a 10 litre packed bed reactor, through which liquor (which provided the inoculum) was continuously recycled. The system was operated as a batch process (Digester A) for retention times of 40 and 70 days. A mean gas yield of 0·215 m³/kg VS added was obtained with a mean gas composition of 62·6% methane, together with a mean volatile solids reduction of 31% and cellulose reduction of 57%. To improve the efficiency of the process, a digester containing fresh solid material (C) was linked in series with a digester (B) which had operated for 40 days by recycling liquor between digesters B and C. This resulted in a gas yield of 0·264 m³/kg VS added in digester B, an increase of 18·6% in gas yield compared to digester A over the same period. The gas production in digester C was comparable to a batch digestion operating over the same period of time.     

The performance and economics of a dairy refrigeration heat recovery unit

The results of a series of experiments on a refrigeration heat recovery unit designed to provide 300 1 of 60°C water from a 2·25 kW refrigeration system cooling 21001 of milk per day are presented. The unit was inserted between the compressor and condenser of the refrigeration plant and tested with two condenser systems (air and water), four condenser pressures (6·5 bar, 7·5 bar, 10 bar and 12 bar), two milk inlet temperatures (23°C and 18°C), and two milk final temperatures (4°C and 7°C). In addition, tests on receiver pressure and suction superheat were performed to determine their effect on the overall system performance.Increasing condenser pressure caused the gross heat recovery to rise from 15·1 MJ (4·2 kWh) d⁻¹ m⁻³ to 29·2 MJ (8·1 kWh) d⁻¹ m⁻³ of milk for the water cooled system, while water outlet temperatures rose from 45°C to 64°C. The corresponding ranges for the air cooled condenser were 13·7 MJ (3·8 kWh) d⁻¹ m⁻³ to 23·8 MJ (6·6 kWh) d⁻¹ m⁻³, and 38°C to 55°C. Changing milk inlet and final temperatures gave a proportional change in cooling times and total heat recovery, but had no effect on C.O.P. or heat recovery rates. Suction superheating increased the total heat recovery by approximately 3·2 MJ (0·9 kWh) d⁻¹ m⁻³, and water outlet temperatures by 5°C. Although increasing condenser pressure resulted in an increase in gross heat recovery, these gains were offset by the additional compressor power required. The net heat recovery varied between 13·7 MJ (3·8 kWh) d⁻¹ m⁻³ at 6·5 bar, to 19·1 MJ (5·3 kWh) d⁻¹ m⁻³ at 12 bar for the water cooled system. For the air cooled condenser system the net heat recovery remained fairly constant at approximately 11·5 MJ (3·2 kWh) d⁻¹ m⁻³.Based on these figures, the annual savings have been calculated under various conditions. At 10 cents per kWh, the heat recovery unit used in a system with a water cooled condenser operating at 12 bar, with suction superheat, on a farm producing 2100 1 per day, could save $NZ453 per annum. For a 210 cow dairy farm, such a system would cost around $NZ5000 (including the cost of the water cooled condenser), making the installation marginally uneconomic. However, heat recovery systems on larger farms are likely to be more attractive financially, because the increase in return is not matched by a similar increase in cost. The optimum operating conditions may vary if the electricity tariffs are altered. Methods of increasing the net heat recovery are considered and other techniques for reducing hot water power consumption are discussed.     

Modelling the dynamics of sheep flocks in Egypt

A structured multi-period Goal Programming model for the determination of the optimal age structure of a flock of sheep given a set of sheep breeder goals is used to evaluate three sheep breeding flock cases in Egypt. The cases are: flocks with a fixed size over an arbitrary period of 5 years, flocks with a growing size over the same period and flocks with a fixed size and stable age structure over time. The breeder's goals considered are the total increase of kilograms weaned and the total wool produced by the flock, the decrease of the average flock age and the flock initial purchase cost.The model was applied on the local Rahmany Egyptian sheep. Results for the three considered cases are presented and discussed.