New Zealand Journal of
Agricultural Research abstracts
The influence of replacement
policies on stability of production in a simulated cow-calf farm system
A. J. Romera*
S. T. Morris†
J. Hodgson
W. D. Stirling
College of Sciences
Massey University
Private Bag 11 222
Palmerston North, New Zealand
S. J. R. Woodward
Woodward Research Limited
P.O. Box 21 160
Hamilton, New Zealand
*Present
address: INTA, CC 276 (7620) Balcarce, Argentina.
†Author
for correspondence.
Present
address: Institute of Veterinary, Animal and Biomedical Sciences,
Massey University, Private Bag 11 222, Palmerston North, New
Zealand. s.t.morris@massey.ac.nz
Abstract This
paper explores the dynamic consequences of different replacement
policies on the production outcomes of pastoral cow-calf systems using
a simulation model of a cow-calf farm at the INTA-Balcarce Research
Station, Argentina. The model is dynamic, mechanistic, climate driven,
and implements management strategies with flexible rules. Three
replacement policies were analysed: a) enough replacement heifers were
retained each year to achieve a target number of cows; b) a constant
number of replacements was retained each year; and c) no limit was
imposed on the number of replacements, but the number of age-culled
cows was restricted. These policies were repeated (replicated) 50
times, using first an average climatic year from the Balcarce region
and then a random sequence of 50 years drawn from the same dataset. The
differences in performance indicators between the average values for
the different replacement policies were small (1–5%), although
statistically significant. The differences in standard deviation (SD)
were greater, with Policy C being the most stable as indicated by the
reduced standard deviation in animals and liveweight sold by 7 and 12%,
respectively, in comparison with Policy A. Policy B produced
more variable results (5 and 9%, greater SD in liveweight and animals
sold, than Policy A, respectively). The differentiation between
strategies was shown to be dependent on the environmental variability
being simulated, due to complex interactions between the environment
and the management strategy, specifically being exaggerated when
environmental variability was artificially reduced by using average
weather.
Keywords cow-calf
system; replacement policy; system-generated variability
A04013; Received 8 December
2004; accepted 8 December 2005; Online publication date 28 February
2006
New Zealand Journal of
Agricultural Research, 2006, Vol. 49:
35–44
0028–8233/06/4901–0035 © The Royal Society of New Zealand 2006
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