1. Seven matings in which there were sperm survival times of 66–76 hr. in a mixed group of pony mares resulted in seven pregnancies. Of six matings with an interval of 90–100 hr., five proved pregnant. One mare, mated with an interval of 126–138 hr., also became pregnant.

2. Where pregnancy urine extract is injected to bring about ovulation, the injection-ovulation interval can be accurately forecast at 40–48 hr. If the interval is longer the follicle was not sufficiently advanced to warrant injection, if shorter the follicle would have ovulated naturally in the same time.