A network model that determines the optimal path of breed-crossing decisions to maximize net returns☆
Abstract A model for finding the sequence of breed-crossing decisions that maximizes the expected discounted net returns over a given number of generations is presented. The method is based on network analysis. The assumptions are that there is an initial breed of females, and that all females, in a generation will be mated to one of a given number of alternative breeds. The optimal path of breed-crossing decisions depends on the revenues expected from additive direct effects, maternal effects. breed-specific individual and maternal heterosis effects, and the cost associated with choosing a particular breed of sires. A simple numerical example is presented.
Indicators and framework for analysing the technical and economic performance of irrigation systems at farm level
In North African countries, irrigation considerably increases production. Given the run‐down condition of irrigation equipment, the rehabilitation and modernization of irrigation schemes is a topical question. In addition, some irrigation projects are currently being implemented thus requiring investments, and judicious decisions have to be taken. At the same time farms in North Africa are increasingly confronted with environmental constraints and held accountable for environmental practices. This article proposes an approach to simultaneously take into account the technical, agricultural, economic and environmental objectives at the farm level, considered to be a relevant decision unit. Such indicators enable pertinent comparisons of different water management strategies in private, public and mixed systems. A method is proposed for the calculation of performance indicators from the plot to the farm level. The indicators enable the performance of irrigated systems to be compared in terms of both effectiveness and efficiency. A graphic representation of the indicators enables the synthetic analysis of the results for a given farm thereby making it possible to highlight the weakness of the production system. The method is applied to two farms in the Gharb area in Morocco and two farms in the Mitidja plain in Algeria. Copyright © 2009 John Wiley & Sons, Ltd.
Levels of investment in testing the genetic improvement of livestock
Abstract The general form of the response curve for benefits (discounted returns—costs) expected from different levels of investment in testing and selection has been studied. While costs tend to increase linearly with the level of testing, returns increase log-linearly. Thus there is an optimum level of testing to obtain maximum benefits. However, the response curve has a broad flat top, so a wide range of testing levels are only marginally sub-optimal. At low levels of testing the benefit/cost ratios are high, so the level can be chosen to make livestock improvement competitive with other investment opportunities. In practice, reproductive rate sets upper limits on the rate of genetic change possible. This, and an acceptance of a higher rate of inbreeding, may allow small breeding enterprises to make almost as much genetic improvement as large breeding programmes. Excessive testing, and duplication of selection effort, may be wasteful, while diversification to alternatives as an insurance may be worthwhile.