Estrus estrous cycle

Age, gender, and strain differences affect elevated-plus maze (EPM) performance. Young females generally spend less time on the open arms than males, although this varies with the estrous cycle. Pro-estrus rodents spend significantly more time on open arms than di-estrus females (or male mice) (9). 

Abnormal findings for estrous animals include persistent estrus, prolonged diestrus, or anestrus (May and Finch 1988). To characterize the estrous cycle in appropriate experimental animals, studies can use vaginal cytology or other cyclic signs in animals that menstruate,... 

In animals with estrous cycles, the onset of puberty is marked by vaginal opening. Reproductive senescence may manifest as persistent vaginal estrus followed by anestrus. A change in the age at puberty or reproductive senescence is sufficient to characterize reproductive toxicity, although it is desirable to have supporting data that explain the mechanism of toxicity. 

During the estrous cycle (and especially during estrus) mares sometimes exhibit undesirable behavioral or physical problems that may interfere with performance. These problems include difficulties in training or riding, back or hindquarter pain and aggressive behavior. A wide variety of treatments have been employed with variable efficacy (Jorgensen et al 1996). 

Vaginal cytology of female rats provided with drinking water containing selenate or selenite indicated that the rats spent more time in diestrus and less time in proestrus and estrus than the controls (NTP 1994). This effect occurred following treatment with 0.31 mg selenium/kg/day as selenate or 0.86 mg selenium/kg/day as selenite. The animals in these studies were not mated, so it is not known if the effects on the estrous cycle had any effect on fertility. Effects on the estrous cycle were not observed in mice treated with selenate or selenite in the drinking water at doses up to 7.17 mg selenium/kg/day for selenate, or at doses up to 3.83 selenium/kg/day for selenite (NTP 1994). 

The hormonal control of the estrous cycle and ovulation is similar in eutherian and marsupial mammals (Sutherland et al., 1980). However, in marsupials, gestation is always shorter than the estroUs cycle and pregnancy does not interrupt the cyclic recurrence of estrus (Sharman, 1970). Spontaneous ovulation appears to be the rule in marsupials and the estrous cycle of polyestrous species is approximately one month in length (Tyndale-Biscoe, 1973). The effects of social factors on reproduction in female marsupials have not heretofore been examined systematically, in part because it has been difficult to maintain and breed... 

Estrus, ovulation and mating were expected to occur in a random pattern over the 32 days ("ideal" estrous cycle length) following the familiarization period. Since the gestation period is approximately 15 days in gray opossums, and there was a two day familiarization period, births were expected to occur uniformly over the 17-49 days following pairing, A chi-square test for uniform occurrence of births between days 17 and 49 was therefore conducted. 

Much of our work is focused on the elucidation of the semiochemistry involved in the response of Asian bull elephants to urine of cows in estrus. The number of flehmen responses exhibited by a bull as the result of contact with female urine begins to increase about six weeks prior to ovulation (Hess et al., 1983), probably an indication that the stage of the estrous cycle and the impending receptivity of the female are being revealed to the males via specific chemical components of urine. We have exploited this dependable chemosensory response to develop a unique bioassay to guide chemical fractionation toward isolation and characterization of the responsible substance or substances. The bioassay developed has proved reliable in over 5000 double blind tests using three bulls during a period of four years. 

For determination of the estrous cycle, vaginal smears were collected 54-60 days postpartum. Smears were fixed in acetone for 10 min at room temperature and then subjected to H E staining. The estrous cycle averages 4 to 5 days. The estrus phase may last from 9 to 15 hours. The exfoliated cytology is characterized by marked squamification and comification of the cells and the disappearance of leukocytes. During the latter part of estrus, these cells appear to... 

The understanding of the estrous cycle and the effects of various hormone treatments on follicular dynamics leads to the development of protocols that efficiently handle the estrous cycle and ovulation [16]. These protocols involve the use of hormones that mimic the physiological release during the estrous cycle, allowing estrus synchronization [16]. Hence, hormone therapy for synchronization of estrus and ovulation is the key tool for responding to the need for more and better calves per year. 

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