EVALUATION OF THE POTENTIAL EFFECTS OF EMBRYO-TRANSFER ON MILK-PRODUCTION ON COMMERCIAL DAIRY HERDS - THE DEVELOPMENT OF A MARKOV-CHAIN MODEL

The actual or potential availability of new breeding technologies is l ikely to have far reaching effects on the national bovine herd at the enterprise, farm, regional and national levels. A Markov chain model h as been developed to determine the effects of such technologies over a 15-year period. A strategy of using either, embryo transfer (ET) foll owed by two artificial inseminations (AI) or (for animals already deri ved 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 y ield 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 tha n 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 y ields in the early stages, but by year 15 the benefits are minimal. Ho wever, 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 re duces the final milk yield to 6102 l/annum. The model described is hig hly flexible and can be adapted easily to consider alternative breedin g strategies including twinning and sexing and performance parameters other than milk yield.