Effect of frequency of pasture measurement on estimation of pasture growth rates: field observations and predictions of a whole farm model

Prewer, W.E.; Lile, J.A.; Macdonald, Kevin; K, Bright; Palliser, C.C.; Lancaster, J.A.S.; Wastney, Meryl E.

doi:10.33584/jnzg.2002.64.2480

Cited by 2 publications

(1 citation statement)

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“…Some of the difference between the predicted and observed PGR may relate to the frequency of measurement because observed values were made weekly, whereas in the model it was assessed by averaging the growth rate in all paddocks daily. The frequency of measurement affects the estimate of PGR (Prewer et al, 2002). Alternatively, the model may have allocated the feed more efficiently (e.g., Journal of Dairy Science Vol.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of a Whole-Farm Model for Pasture-Based Dairy Systems

Beukes

Palliser

Macdonald

et al. 2008

Journal of Dairy Science

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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.

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Section: Discussionmentioning

confidence: 99%