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.
Evaluation of the potential effects of embryo transfer on milk production on commercial dairy herds: The development of a markov chain model
Abstract The actual or potential availability of new breeding technologies is likely to have far reaching effects on the national bovine herd at the enterprise, farm, regional and national levels. A Markov chain model has been developed to determine the effects of such technologies over a 15-year period. A strategy of using either embryo transfer (ET) followed by two artificial inseminations (AI) or (for animals already derived from ET in an earlier generation) three passes of AI, results in a 55 state model. Typical conception rates, herd structure, milk yield and culling rates are used to model such a strategy and average milk yield increases from 5551 l/annum in year 1 to 6348 l/annum in year 15. The rate of increase is faster in the earlier years at 51 l/annum than in the final years 45 l/annum as initially more animals are bred to ET than AI. Increasing the conception rates to ET increases the milk yields in the early stages, but by year 15 the benefits are minimal. However, varying the genetic lift obtained from the ET has a greater and longer lasting effect on milk yields; increasing the lift from 10% to 15% which increases final milk yield to 6594 l/annum and a 5% lift reduces the final milk yield to 6102 l/annum. The model described is highly flexible and can be adapted easily to consider alternative breeding strategies including twinning and sexing and performance parameters other than milk yield.
The chromosomes of Chrysanthemum,
NEW varieties of the garden chrysanthemum arise primarily from seed. They are propagated vegetatively and many give rise to bud sports in sequence and in parallel to give whole families of varieties. The original sports would naturally be chimras and it is not surprising therefore that they often revert to the previous type. Whereas some varieties sport continually from the time of their origin, others remain stable for many years. Those considered in this account do, mostly, sport freely. Since varieties may remain stable for a considerable number of years and then suddenly sport it is probable that all varieties possess the ability to sport. The origin of bud sports is unpredictable. Some confusion in naming has arisen as the same or similar sports have occurred and been propagated in different places under different names. Consequently there are, for example, several forms similar to, but not identical with, the original Favourite Supreme raised by Messrs A. G. Vinten. It might well be that each individual variety would be better termed a sub-family to include all its minor variants. The different Chrysanthemum sports are described in scattered numbers of the R.H.S. Journal—more particularly, for the Favourite family, in Vol. 63, 1938, pp. 139-141. The object of this study is to discover the cause of sporting.