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- Title
THE OESTROUS CYCLE OF THE MARE AND ITS UTERINE CONTROL.
- Authors
Hughes, J. P.; Stabenfeldt, G. H.; Evans, J. W.
- Abstract
SUMMARY The reproductive findings from a group of nonpregnant mares were studied. Oestrous cycle length averaged 20.6 days (range 13-34) excluding anoestrous periods, or 25 days (31-141) if included. Average oestrus length was 5.7 days (range 1-24) but from February to May it averaged 7.6 days (range 2-24) and from May to November 4.8 days (range 1-10). Seventy-eight per cent of the mares ovulated within 48 hours prior to the end of oestrus, 10% were out of oestrus before ovulation occurred, while 76% of the ovulations occurred between 4 p.m. and 8 a.m. Follicles averaged 45 mm in size the day of ovulation and multiple ovulations occurred 25.5% of the time. Oestrus without associated ovulation was very uncommon in this group of mares, whereas ovulation without oestrus occurred in 6 of the 11 mares, including one mare who ovulated 32 of 34 times without oestrus. The CL were palpable for an average period of 8.9 days (range 1-18). On occasions, a hematoma formed within the ovulation site, reached a size of 10-12 cm in length and persisted beyond the next ovulation without affecting cycle length. Dioestrus averaged 15.4 days (range 6-25) excluding anoestrus, or 19.5 days (range 6-121) if anoestrus was included. Dioestrous ovulations unaccompanied by signs of oestrus and with the cervix pale, tight, dry and sticky occurred in 10 of the 11 mares. The CL formed following dioestrous ovuations were normal, but did not affect cycle length. A syndrome of spontaneous prolongation of the corpus luteum for 2 to 3 months was observed in 6 of the 11 mares. Oestrus was not manifested during this time, but considerable follicular activity and, in some instances, ovulation was observed. Hysterectomised mares and some mares with pyometra had prolonged CL and follicular activity with a few ovulating similar to mares with spontaneously-prolonged CL. Other mares with pyometra had normal cyclic ovarian activity. Evidence suggests that the endometrium had been destroyed by the infection in the anoestrus mares with pyometra and, thus, was incapable of forming and/or releasing luteolytic factors. Experimental intrauterine inoculation of Streptococcus zooepidemicus during dioestrus reduced oestrous cycle length in 5 of 7 inoculations, whereas inoculations during oestrus failed to alter cycle length.
- Publication
Australian Veterinary Journal, 1977, Vol 53, Issue 9, p415
- ISSN
0005-0423
- Publication type
Article
- DOI
10.1111/j.1751-0813.1977.tb05488.x