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.
Experimental Study for a Double-Glazed Forced-Flow Solar Collector/Regenerator
Experimental study of a double-glazed forced-convection solar collector/regenerator for absorption solar cooling is presented. The south facing experimental solar collector/regenerator with 10 deg slope is located at Kaohsiung, Taiwan at 120{degree}19minutesE longitude and 22{degree}34minutesN latitude. The size of the collector is 1 m wide and 7 m long with an effective regeneration area of 0.9 m by 6 m. Previous study for single-glazed forced-convection solar collector/regenerator operated at the same location has shown to have a best day-average efficiency of 17%. In order to raise the system performance, a double-glazed collector/regenerator is constructed such that air can be preheated in the upper channel flow. The preheated air is then conducted into the lower channel where it contacts with the film flow of solar heated lithium-chloride solution and regenerates the solution by carrying out the evaporated water vapor. The preheated air has lower relative humidity but the same humidity ratio since it is sensibly heated. Therefore, the regeneration driving potential is increased. The present study shows that the best day-average efficiency can reach 20% which increases the feasibility of the open-cycle absorption solar cooling system. Effects of controlling parameters on the collector/regenerator performance are studied, and heat and mass transfer correlationsmore » are also presented for design purposes.« less