Although the reason for the controversial and inconsistent effects of exogenous hormones administered at time of breeding to aid sperm transport are uncertain, it is possible that results could be affected by the hormone and dosage and the method and timing of administration. It is also possible that effective sperm transport depends upon precise regulation of the direction, strength,duration and frequency of contractions as regulated by certain levels of estrogen, prostaglandins, and oxytocin which may be difficult to mimic consistently with administration of a single hormone.