RESUMEN
Nitrogen loads to several New Zealand lakes are dominated by nonpoint runoff from pastoral farmland which adversely affects lake water quality. A 'cap and trade' scheme is being considered to help meet targets set for nitrogen loads to Lake Rotorua, and a numerical model, NTRADER, has been developed to simulate and compare alternative schemes. NTRADER models both the geophysics of nitrogen generation and transport, including groundwater lag times, and the economics of 'cap and trade' schemes. It integrates the output from several existing models, including a farm-scale nitrogen leaching and abatement model, a farm-scale management economic model, and a catchment-scale nitrogen transport model. This paper details modeling methods and compares possible trading program design features for the Lake Rotorua catchment. Model simulations demonstrate how a cap and trade program could be used to effectively achieve challenging environmental goals in the targeted catchment. However, results also show that, due to complex hydrogeology, satisfactory environmental outcomes may be not achieved unless groundwater lag times are incorporated into the regulatory scheme. One way to do this, as demonstrated here, would be to explicitly include lag times in the cap and trade program. The utility of the model is further demonstrated by quantifying relative differences in abatement costs across potential regulatory schemes.
Asunto(s)
Lagos/química , Modelos Teóricos , Nitrógeno/análisis , Contaminantes Químicos del Agua/análisis , Agua Subterránea/química , Nueva Zelanda , Nitrógeno/química , Contaminantes Químicos del Agua/químicaRESUMEN
The model of R. L. Baldwin predicts various aspects of digestion and metabolism in the cow including nutrient partitioning between milk and body stores. However, prediction bias has been observed for body weight (BW) and body condition score (BCS) when diets of differing energy density are simulated over long periods. Originally, the model overpredicted BW loss in early lactation and gain in late lactation. This bias was reversed and limited to early lactation when a better representation of milk synthesis capacity was introduced into the model. It was hypothesized that a better representation of the effects of energy status on anabolic and catabolic hormones and a more complete representation of metabolic demands and growth associated with pregnancy would help in improving predictions of body tissue mobilization in early lactation. Providing independent glucose reference points and independent sensitivity scalars for the 3 hormones driven by glucose concentrations improved overall model precision. These improvements were primarily realized through reductions in prediction errors for blood glucose concentrations and BCS. In both cases, slope bias associated with the predictions was reduced, indicating that the changes in representation were beneficial although BCS bias was not completely removed. Milk component yields were predicted with slightly greater mean and slope bias. The addition of enhanced pregnancy calculations did not provide apparent additional benefit relative to model prediction errors. However, the data used for the assessments did not include observations from the last 60 d of gestation, where BW gain and metabolic demand associated with pregnancy would be expected to be greater. Improvements in BCS were not observed when the revised model was tested using an independent data set. Predictions of blood fatty acids, the rate of BCS and BW loss, and milk fat yields in early lactation were still inappropriate and require further work. The results could be caused by inaccurate early lactation intakes, the aggregated representation of blood fatty acids, or an inadequate representation of peripheral insulin resistance during early lactation.
Asunto(s)
Fenómenos Fisiológicos Nutricionales de los Animales/fisiología , Bovinos/metabolismo , Digestión , Hormonas/fisiología , Lactancia , Modelos Biológicos , Animales , Glucemia/metabolismo , Composición Corporal , Peso Corporal , Dieta , Ingestión de Energía , Metabolismo Energético , Femenino , Glucosa/metabolismo , Leche/química , EmbarazoRESUMEN
In the temperate climate of New Zealand, animals can be grazed outdoors all year round. The pasture is supplemented with conserved feed, with the amount being determined by seasonal pasture growth, genetics of the herd, and stocking rate. The large number of factors that affect production makes it impractical and expensive to use field trials to explore all the farm system options. A model of an in situ-grazed pasture system has been developed to provide a tool for developing and testing novel farm systems; for example, different levels of bought-in supplements and different levels of nitrogen fertilizer application, to maintain sustainability or environmental integrity and profitability. It consists of a software framework that links climate information, on a daily basis, with dynamic, mechanistic component-models for pasture growth and animal metabolism, as well as management policies. A unique feature is that the component models were developed and published by other groups, and are retained in their original software language. The aim of this study was to compare the model, called the whole-farm model (WFM) with a farm trial that was conducted over 3 yr and in which data were collected specifically for evaluating the WFM. Data were used from the first year to develop the WFM and data from the second and third year to evaluate the model. The model predicted annual pasture production, end-of-season cow liveweight, cow body condition score, and pasture cover across season with relative prediction error <20%. Milk yield and milksolids (fat + protein) were overpredicted by approximately 30% even though both annual and monthly pasture and supplement intake were predicted with acceptable accuracy, suggesting that the metabolic conversion of feed to fat, protein, and lactose in the mammary gland needs to be refined. Because feed growth and intake predictions were acceptable, economic predictions can be made using the WFM, with an adjustment for milk yield, to test different management policies, alterations in climate, or the use of genetically improved animals, pastures, or crops.
Asunto(s)
Fenómenos Fisiológicos Nutricionales de los Animales/fisiología , Bovinos/fisiología , Industria Lechera/métodos , Lactancia/fisiología , Modelos Biológicos , Poaceae , Reproducción/fisiología , Alimentación Animal , Animales , Bovinos/genética , Bovinos/crecimiento & desarrollo , Bovinos/metabolismo , Simulación por Computador , Femenino , Lactancia/genética , Leche/metabolismo , Nueva Zelanda , Valor Predictivo de las Pruebas , Reproducción/genética , Estaciones del AñoRESUMEN
The Molly model predicts various aspects of digestion and metabolism in the cow, including nutrient partitioning between milk and body stores. It has been observed previously that the model underpredicts milk component yield responses to nutrition and consequently overpredicts body energy store responses. In Molly, mammary enzyme activity is represented as an aggregate of mammary cell numbers and activity per cell with minimal endocrine regulation. Work by others suggests that mammary cells can cycle between active and quiescent states in response to various stimuli. Simple models of milk production have demonstrated the utility of this representation when using the model to simulate variable milking and nutrient restriction. It was hypothesized that replacing the current representation of mammary cells and enzyme activity in Molly with a representation of active and quiescent cells and improving the representation of endocrine control of cell activity would improve predictions of milk component yield. The static representation of cell numbers was replaced with a representation of cell growth during gestation and early lactation periods and first-order cell death. Enzyme capacity for fat and protein synthesis was assumed to be proportional to cell numbers. Enzyme capacity for lactose synthesis was represented with the same equation form as for cell numbers. Data used for parameter estimation were collected as part of an extended lactation trial. Cows with North American or New Zealand genotypes were fed 0, 3, or 6 kg of concentrate dry matter daily during a 600-d lactation. The original model had root mean square prediction errors of 17.7, 22.3, and 19.8% for lactose, protein, and fat yield, respectively, as compared with values of 8.3, 9.4, and 11.7% for the revised model, respectively. The original model predicted body weight with an error of 19.7% vs. 5.7% for the revised model. Based on these observations, it was concluded that representing mammary synthetic capacity as a function of active cell numbers and revisions to endocrine control of cell activity was meritorious.
Asunto(s)
Bovinos/fisiología , Lactancia/fisiología , Glándulas Mamarias Animales/citología , Glándulas Mamarias Animales/enzimología , Modelos Biológicos , Animales , Constitución Corporal/fisiología , Peso Corporal/fisiología , Simulación por Computador , Industria Lechera , Grasas/análisis , Femenino , Genotipo , Lactosa/análisis , Leche/química , Proteínas de la Leche/análisis , Factores de TiempoRESUMEN
Methods based on the use of hydropathy scales have been used widely to ascertain the secondary structures of proteins. However, over 100 such scales have been reported in the literature, and which of these is the most successful in terms of the prediction rate of the correct structure is not clear. This article, therefore, reports a comprehensive analysis of the relative success of hydropathy scales to locate beta-strands on the surfaces of proteins. The technique we used is based on the technique proposed by Fraser and Parry, but it includes a modification that allows a higher rate of successful prediction and a lower rate of overprediction. We used as a basis for assessing the predictions a database of sequence-unique structures that we previously established. Proteins 2001;42:243-255.
Asunto(s)
Estructura Secundaria de Proteína , Proteínas/química , Algoritmos , Biología Computacional/métodosRESUMEN
From a representative set of monomeric globular proteins with known three-dimensional structures, beta-strands with lengths > or = 5 amino acids have been identified and catalogued. By ascertaining the accessible surface areas of the constituent residues in these strands, and by checking whether the exposed/buried pattern is 80% or more similar to that in an idealized surface strand, a subset of structures can be delineated in which the beta-strands are all sited on the surface of the protein. The corresponding sequence data show that about 50% of the residues are apolar (Val, Ile, Leu, Phe, Tyr, Ala) and that the common occurrence of valine (14.3%), isoleucine (9.6%), and threonine (8.1%) is a characteristic feature. The frequencies of occurrence of those amino acids in the strands that face the aqueous environment and the interior have also been determined separately and show that most surface strands have a substructure of the form (apolar-X)(n), where X is approximately equally divided between apolar, charged, and hydrophilic residues. Using the frequency data thus obtained, allied with an algorithm to delineate potential surface beta-strands from characteristic hydropathy profiles, it is now possible to search through the sequences of proteins with unknown tertiary structures and make realistic predictions of the presence of this element of structure on the protein surface. In addition, new data are presented on the distribution of the various types of residues on the surface of proteins and in their interior. Significant differences were observed, not all of which have been identified previously. Furthermore, the distribution of the types of residue in a surface beta-strand was compared to that corresponding to the surfaces of all of the proteins in our database. Again, very characteristic differences were observed. These are helpful in recognizing the presence of surface beta-strands.