Optimal cow replacement on New Zealand seasonal supply dairy farms : a thesis presented in partial fulfilment of the requirements for a Mastrate [sic] degree of Agricultural Science in Animal Science at Massey University
An intraherd best linear unbiased prediction (BLUP) model for
predicting the future milkfat production of individual cows was developed.
A major advantage of the BLUP technique was to enable prediction of the
future milkfat production of freshening heifers, since relationships
between animals were included in the model. These predictions of future
performance were incorporated, along with various costs and revenues Qf
production in New Zealand and calving date, into a model to arrive at an
expected net revenue for each individual cow.
Three models to rank cows on future profitability were developed and
evaluated. Two models utilised dynamic programming procedures. One
model estimated the annualised present value of the net returns of each
cow and her replacement up to a predetermined planning horizon. The
second model used the same criterion, but also a11owed optimal
replacement to occur in future seasons. The third model utilised
replacement model evaluation techniques and estimated the annualised
present value of the net returns based on the remaining economic lifespan
of individual cows.
The models were tested over a large number of different situations.
The effects of changes in the different economic parameters are discussed
and the behaviour of each model is documented. The parameters directly
associated with the cost of replacement had the greatest effect on the
annual present value's (APV) of individual cows. The optimal rankings were
affected by the price of the heifer replacement and the price of
manufacturing beef, whereas milkfat price played an insignificant role.
Varying the price of manufacturing beef and the price of the heifer
replacement simultaneously had only a small effect on the ranking of the
cows. The parameters such as interest rate and planning horizon also
affected the APVs produced by the dynamic models. Increasing the planning
horizon post 10 yeors coused o reduction in the voriotion between the
It was concluded that the dynamic programming model which allowed
optimal replacement in future seasons provided the best system for
ranking cows on expected future income.