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H. W. HAWK and B. S. COOPER

Summary.

Nine parous ewes were used in each of seven ovarian states or hormone treatment groups : oestrus, the luteal phase of the oestrous cycle, an ovariectomized untreated group, and four groups of ovariectomized ewes treated with oestradiol or combinations of oestradiol and progesterone. Each uterine horn was ligated at either end and 0·07 ml of fresh ram semen, containing an average of 199 × 106 sperm cells, was deposited in the uterine lumen. The horns were flushed 5 hr later and intact sperm cells and tailless sperm heads were counted in the flushings.

As compared with the results from ovariectomized control ewes, either oestradiol administered to ovariectomized ewes or the ovarian hormones of ewes in natural oestrus increased both the breakage and the disappearance of sperm cells. Exogenous progesterone or the ovarian hormones of luteal phase ewes both decreased the breakage and disappearance of sperm cells, and the administration of progesterone before or at the same time as oestradiol tended to decrease sperm cell breakage.

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A. S. McNEILLY, K. J. COOPER and D. B. CRIGHTON

Dietary restriction in the rat has been shown to affect the oestrous cycle, increasing the length of the di-oestrous period and producing a reduction in the cellular content of the vaginal smear (Mulinos & Pomerantz, 1940). Cooper & Haynes (1967) demonstrated that the introduction of a male to the cage of a female rat subjected to dietary restriction resulted in a shortening of the cycle regardless of the stage at which the male was introduced. In those animals which failed to mate at the first oestrus after introduction of the male (detected by the vaginal smear technique), the subsequent cycle again appeared to be of shorter duration than those before the introduction of the male, indicating that the female continued to respond to the presence of the male. The present