Polyspermic fertilization in pigs during the luteal phase of the estrous cycle.

Abstract

AbstractMammalian eggs ovulated during the luteal phase of the estrous cycle or after progesterone injections rarely become fertilized, but the reasons for this low incidence of fertilization are not clear. Mature gilts were injected subcutaneously with 1,500 i.u. pregnant mare's serum gonadotrophin on Day 5 (second day of estrus designated as Day 1), followed by 500 i.u. human chorionic gonadotrophin intramuscularly on Day 9; ovulation occurred 40 to 42 hours later. Eggs recovered from the oviducts of slaughtered animals at specific intervals after ovulation were fixed, stained, and examined by phase‐contrast microscopy.None of the injected animals showed estrous symptoms. Of 165 eggs examined on Days 11 or 12 from 14 noninseminated animals, 160 (96.9%) were secondary oocytes and five (3.1%) were primary oocytes. Eggs penetrated by spermatozoa were recovered from 14 of 26 animals inseminated 4 to 18 hours before ovulation with 120 ml of fresh, undiluted semen; spermatozoa were recovered from the oviducts of a further three animals. Fifty‐one (31.9%) of 160 penetrated eggs from these 14 animals were normally fertilized, three eggs (1.9%) were fragmenting, nine (5.6%) were primary oocytes, and 97 (60.6%) were polyspermic. The polyspermic eggs contained varying numbers of accessory male pronuclei (2‐7) as well as from 2 to > 50 swollen and unswollen sperm heads. The high incidence of polyspermic eggs found during the luteal phase was considered to be due to an effect of the oviducal environment under the influence of ovarian progesterone on the mechanism controlling the block to polyspermy.