The recovery of spermatozoa from the reproductive tract of the spayed ewe treated with progesterone and oestrogen.

were administered 48 hr after four progesterone regimens (0, 5, 10 and 20 mg/day for 12 days). Each ewe was inseminated 24 hr later with 0\m=.\15ml undiluted semen (\m=ge\500\m=x\106 spermatozoa). After a further 24 hr, the ewes were slaughtered and the vagina, cervix, uterus and Fallopian tubes were flushed for spermatozoa. The population of spermatozoa in the cervix was highly dependent upon oestrogen (P<0\m=.\001)and appeared to be related to dose (P=0\m=.\1).There was no significant mean effect of progesterone but there was a significant interaction with oestrogen (P<0\m=.\05).High numbers of spermatozoa were associated with high doses of oestrogen and of progesterone. The numbers of spermatozoa in the vagina were not related to oestrogen and there was no relationship with the numbers in the cervix (r = \m=-\0\m=.\011). Penetration and maintenance of a cervical population of spermatozoa was related to the level ofoestrogen and full expression required adequate progesterone influence preceding that of oestrogen.