Alternative management strategies and drafting policies for irrigated Canterbury sheep farms

Abstract

The purpose of this investigation was to study the economic implications to producers of altering the offtake pattern of lambs on irrigated farms. To permit such a study, a detailed analysis of both management and drafting strategies in the system under analysis, was required. This was necessary because of the complexity of the lamb production system and also because it allowed an assessment and comparison to be made between traditional (dryland) practices and alternative production practices under irrigation.

A simulation model incorporating biological, physical and economic components of the lamb production system on an irrigated farm was constructed and was then used to experiment with alternative management and drafting strategies. These strategies were tested on a few different , ‘farms’ that is, the growth rates of the ‘model’ lamb to which all simulated lambs relate, were varied between ‘farms’. By this method, some allowance was able to be made for the different abilities of farmers in practise, to manage both stock and feed successfully.

Feed supply and demand were best equated when lambing percentage was highest and stocking rates lowest. Returns could be improved upon if the lambs grew at a rate that allowed as many as possible to be drafted as PH’s by early March. Although high lambing percentages do not necessarily equate with high growth rates, this situation was improved by a delay in the mean drafting date which allowed more of the multiple birth lambs to benefit from compensatory growth.

The choice of an optimum management or drafting strategy ultimately depends on each decision maker’s attitude to risk, and, in practise, the decision maker must assess the stocking rate and performance level at which he is most confident.

In conclusion, while, irrigation increases feed supply, higher stocking rates and the rearing of replacements allow little scope to change lamb offtake times although a slight delay appears justified to permit a greater number of lambs to achieve the benchmark grade weight.