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Biology of Reproduction, Vol 12, 423-430, Copyright © 1975 by Society for the Study of Reproduction

Uterine Contractions in the Estrous Ewe

H. W. HAWK 1

1 Reproduction Laboratory, Animal Physiology and Genetics Institute, U.S.D.A., Agricultural Research Center Beltsville, Maryland 20705


One hundred fifty-three ewes were laparotomized, and their uteri were exteriorized and observed for 10 min for origin and direction of individual uterine contractions. The number of contractions generally averaged between four and seven per minute. At 5 h after the beginning of estrus, 67 percent of the uterine contractions originated near the body of the uterus and moved anteriorly. At 26 h (late estrus). 35 percent of the contractions originated near the uterine body and 42 percent originated near the tubo-uterine junctions. At 48 h (after the end of estrus), 75 percent of the contractions originated at the tubo-uterine junctions and moved toward the cervix.

The administration of either 6, 30 or 150 µg of estradiol 17-beta between 20 and 40 h after the beginning of estrus prevented the change in direction of contractions. Removing the ovaries during estrus did not prevent the change.

When the ovaries were removed from ewes during the luteal phase of the estrous cycle, the administration of either estradiol or estradiol plus progesterone had, in 48 h, initiated uterine contractions that were typical of early estrus.

The data suggest that endogenous estrogen initiates the type of uterine motility seen during early estrus, and that declining estrogen secretion is responsible for the change in direction of contractions during estrus.

 Accepted on November 14, 1974






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Copyright © 1975 by the Society for the Study of Reproduction.