Oviductal vein resection affects pregnancy rates in sheep

Progesterone is delivered locally via the oviductal vein to the cranial uterine horn ipsilateral to the ovary bearing the corpus luteum. Removal of the oviductal vein reduces this local delivery of progesterone. The objective of this experiment was to determine if local delivery of progesterone via the oviductal vein is necessary for embryo survival. Twenty-five nulliparous ewes were bred at estrus to fertile rams. On day 4 following breeding, ewes were randomly assigned to one of two treatment groups: oviductal vein resection (n = 11) or sham operated controls (n = 14). Following midventral laparotomy, the oviductal vein was isolated, ligated and removed. In the sham surgery control ewes, the oviductal vein was isolated, sutures were placed around the vein but were left unsecured. Following surgery, ewes were returned to the flock. Jugular venous blood samples were collected daily for 25 days after surgery and every third day until day 68 post breeding. On day 85 post breeding, ewes were laparotomized again to confirm pregnancy and location of the fetus. Blood samples were analyzed for progesterone via radioimmunoassay. The proportion of ewes pregnant in the oviductal vein resected groups were greater (p less than or equal to .08) than in the control, sham surgery group. Transuterine migration of embryos occurred in 2/4 pregnant, sham operated control ewes whereas migration occurred in 0/8 of the pregnant, oviductal vein resected ewes. Patterns of progesterone secretion differed (p less than or equal to .001) between pregnant and nonpregnant ewes across the entire sampling period. During maternal recognition of pregnancy, days 13 to 21 after breeding, overall mean jugular venous concentrations of progesterone were lower (p less than or equal to .05) in the oviductal vein resected ewes and patterns of secretion tended to differ (p less than or equal to .09) between oviductal vein resected and sham operated control ewes. It is concluded that oviductal vein resection increases pregnancy rates in nulliparous ewes and this may be due to a reduction in the local delivery of an inhibitor of embryo survival, possibly progesterone, or by maintaining the appropriate uterine environment conducive to a successful pregnancy.