An evaluation of the Stockpol(TM) model
R.W. Webby, D.G., McCall, V.J. Blanchard
AgResearch, Whatawhata Research Centre, Private Bag 3089,
Hamilton, New Zealand
Proceedings of the New Zealand Society of Animal Production. 1995,
55: 145-159
The Stockpol model was designed for decision support on New
Zealand sheep and beef cattle farms. It indicates the biological
feasibility of a livestock system and provides the opportunity for users
to test alternative livestock policies. An evaluation of the Stockpol
model was made using 44 data sets from farmlet trials at Gore,
Ballantrae, and Whatawhata Research Centres and data from Massey
University's Riverside farmin the Waiarapa. These data covered a range
of sheep and beef finishing systems. The main test compared the measured
pasture growth rate with that required by Stockpol to predict the
monthly pasture cover recorded in the data. Measured and required
pasture growth rates differed significantly (<0.01) in July, August and
September. The model was conservative and required an average of 5.1
kgDM/ha/day more growth over these months than was measured. In other
months the differences were small and non significant. When animal
demand was adjusted to mimic pasture cover, adjustments of minus 22%
from July to September were required. Overall it was considered tha
Stockpol can be used with confidence for analysing options for farmer
decision making. Areas for further improvement of Stockpol have been
defined as the pasture growth model in early spring. Aspects of the
animal demand in early spring also need to be tested more vigorously.
The evaluation emphasised the importance of consistent input data for
use in models. For example, the pasture measurement technique was
different at each of the four sites studied. This may explain some of
the variation between predicted and measured data.
Keywords: NZSAPAB;
decision support; livestock policy; feed supply; pasture cover; feed
demand
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Last Updated 25-01-1997
