The Vaginal Smear of the Ewe.

As an introduction to the study of the physiology of reproduction in sheep we have investigated the vaginal smear of 15 ewes daily for variable periods of time, 6 of them for 11 months. Three of these have been followed through pregnancy and lactation. Data have also been accumulated regarding the lengths of the breeding periods, oestrous cycles and the length of oestrum. Oestrum was first evidenced about the first of September and 6 of the sheep that were maintained went into anoestrum about the first of March, a breeding period of about 6 months. Our data in regard to the length of the cycle confirm that recently given by Allen et al. 1 The length of the cycle is slightly less than 17 days on the average with extremes ranging between 16 and 23 days. There was only one instance which fell outside of the 16-18 day period.

There are well defined changes in the character of the vaginal smear depending upon the time of the oestrous cycle. In general it may be said that these changes are more apparent macroscopically than microscopically. On the first day of heat, and in rare instances on the second, the smear consists of transparent mucus in which one finds floating cell flocculi. The cells present are polymorphonuclear leucocytes, cornified cells, and small epithelial cells. On the second day of oestrum or on the first day of metoestrum the smear becomes dry and has a cheesy appearance. Cornified cells and small epithelial cells are present. Large numbers of leucocytes are usually present for about a day on or between the second to seventh day of metoestrum. Cornified cells are never completely absent and in fact, one often encounters smears which appear similar to early metoestral smears in dioestrum.