Beukes P C, Palliser C C, Macdonald K A, Lancaster J A S, Levy G, Thorrold B S, Wastney M E
DairyNZ Ltd., Private Bag 3221, Hamilton 3240, New Zealand.
J Dairy Sci. 2008 Jun;91(6):2353-60. doi: 10.3168/jds.2007-0728.
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.
在新西兰的温带气候条件下，动物可以全年在户外放牧。牧场会补充保存饲料，其数量由季节性牧草生长情况、畜群的遗传特性以及载畜率决定。影响生产的因素众多，利用田间试验来探索所有农场系统选项既不切实际又成本高昂。已开发出一种原地放牧牧场系统模型，以提供一个用于开发和测试新型农场系统的工具；例如，不同水平的外购补充饲料和不同水平的氮肥施用，以维持可持续性、环境完整性和盈利能力。它由一个软件框架组成，该框架每天将气候信息与用于牧草生长和动物新陈代谢的动态、机理成分模型以及管理政策相联系。一个独特之处在于，这些成分模型是由其他团队开发并以其原始软件语言保留下来的。本研究的目的是将这个称为全农场模型（WFM）的模型与一项为期3年的农场试验进行比较，在该试验中专门收集了用于评估WFM的数据。第一年的数据用于开发WFM，第二年和第三年的数据用于评估该模型。该模型预测的年度牧草产量、季末奶牛体重、奶牛体况评分以及整个季节的牧草覆盖情况，相对预测误差<20%。尽管年度和月度牧草及补充饲料摄入量的预测精度尚可，但牛奶产量和乳固体（脂肪 + 蛋白质）被高估了约30%，这表明乳腺中饲料向脂肪、蛋白质和乳糖的代谢转化需要优化。由于饲料生长和摄入量的预测是可接受的，因此可以使用WFM进行经济预测，并对牛奶产量进行调整，以测试不同的管理政策、气候变化或使用遗传改良的动物、牧草或作物。
