The application of modern breeding technologies to the practical breeding of horses has accelerated worldwide over the past two decades in all breeds and types of horses except the Thoroughbred. Artificial insemination (AI) with fresh extended semen is used routinely on most stud farms with considerable improvements in efficiency, fertility, disease control and management costs. The ability of cooled semen to retain high fertility for 24-48 hours enables its widescale shipment within and between countries by modern transport methods. Even the use of deep frozen semen is increasing rapidly, in conjunction with a single fixed–time insemination in relation to gonadotrophininduced ovulation. The wide scale use of the ultrasound scanner to monitor follicular development and ovulation has markedly improved diagnosis of the optimum insemination time, with consequent improvements in conception rates. However, repeated scanning examinations at intervals of only 4-6 hours in order to carry out insemination of frozen-thawed semen after, rather than before, ovulation is illogical and inefficient.