American Journal of Primatology Supplement 151-55 (1982)

Ovulation Time: A Factor in Ape Fertility Assessment CHARLES E. GRAHAM Primate Research Institute, New Mexico State University, Hollomun AFB

In chimpanzees, ovulation time can be estimated in relation to the time of sexual swelling regression, itself a periovulatory parameter. Correlations of steroid hormone and gonadotropin levels, endometrial morphology, basal tem- perature, and ovarian morphology consistently suggest a close temporal cor- relation between ovulation and the last days of maximal sexual swelling.

In the gorilla, LH elevations occur during the one to four days of labial swelling, suggesting that ovulation is restricted to this easily detectable phase of the menstrual cycle.

The menstrual cycle of the orang-utan lacks an externally visible periovu- latory indicator, such as the sexual swelling, for correlation with ovulation time. Possibly a sharply defined period of female sexual proceptivity could provide a usable periovulatory criterion applicable to captive orang-utans.

Key words: ape, ovulation, gonadotropin, steroid hormone, endometrium, breeding

INTRODUCTION

In planning breeding programs for great apes, knowledge of ovulation time in relation to detectable reference parameters is extremely helpful. Such information is especially useful if restricted mating periods are to be used to permit one male to serve several females, as is frequently the practice with chimpanzees (Pan troglodytes). It is also relevant to strategies that restrict mating exposure in order to conserve semen or optimize copulatory patterns in the orang-utan (Pongopygmaeus) or the gorilla (Gorilla gorilla). Lastly, confidence in the time of ovulation is important when assessing male fertility in terms of conception rate. This paper reviews the current state of knowledge on ovulation time, particularly in relation to genital swelling.

CHIMPANZEE

Sexual Swelling and Steroid Hormones

The sexual swelling of the female chimpanzee is a conspicuous, hairless, unpigmented perivaginal area. The swelling develops during the follicular phase under the influence of follicular estrogen secretion, and regresses early in the luteal phase due to withdrawal

Received March 16, 1981; accepted April 17, 1981.

Address reprint requests to Charles E. Graham, PhD, Division of Reproductive Biology, Primate Research Institute, New Mexico State University, P.O. Box 1027, Holloman AFB, NM 88330.

0275-2565/8210051-0051$02.00 0 1982 Alan R. Liss, Inc.

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of estrogen and secretion of progesterone (which has an inhibitory effect on estrogen- induced swelling). These relationships are supported by assays of urinary ovarian steroid levels during a total of 11 menstrual cycles [Graham et al, 1972; Graham, in press; McArthur et al, in press] and circulating gonadotropin and steroid levels in nine cycles studied by Reyes et al, 119751 and in 16 cycles studied by Graham & Gosselin [unpublished]. All these studies showed a correlation between rising estrogen levels and increasing sexual swelling during the follicular phase; after the ovulatory gonad- otropin surge, sexual swelling regression was correlated with increasing progestin levels and decreasing estrogen levels. Confirmation came from hormone-replacement studies in ovariectomized chimpanzees [Graham et al, 19721. These relationships imply that ovulation is correlated in time with sexual swelling regression.

Endometrium Secretory transformation of the endometrium is a progesterone-dependent event that

occurs in women approximately 40 hours after ovulation [Delaforge et al, 19701. In a study of 34 endometrial biopsies of chimpanzees, it was found that secretory changes first occurred on the first day of swelling regression, and all biopsies were secretory on the second day of regression [Graham, 19731. If the human hormonal temporal rela- tionships may be extrapolated to the chimpanzee, this would place ovulation during the last two days of maximal swelling.

Basal Body Temperature

In women, increasing estrogen levels in the follicular phase are associated with a fall in basal body temperature that is reversed by progesterone secretion. The temperature nadir is closely associated in time with ovulation [Morris et al, 19761. Using a remote temperature telemetry system, temperature nadirs in chimpanzees

were detected in nine of 11 cycles studied, and these occurred on the last two days of maximal swelling [Graham et al, 19771.

Luteinizing Hormone (LH) Ovulation is triggered by a surge of luteinizing hormone that, in women, typically

peaks in the circulation 12-24 hours earlier [Yussman & Taymor, 19701. In 300 random morning plasma samples obtained under Ketamine anesthesia during the menstrual cycle of chimpanzees, a pronounced peak of LH (determined by radioimmunoassay) occurred on the last two days of maximal sexual swelling [Graham, 19811. Sequential serum samples in 16 menstrual cycles of nine adult chimpanzees trained

to submit for alert venipuncture were subjected to LH determinations by radioimmu- noassay [Graham & Gosselin, unpublished]. The study also included cycles from one chimpanzee sampled under anesthesia. (One additional cycle is not included because no LH peak was seen.) Eight of 16 LH peaks occurred on day - 2 when the last day of maximal swelling is designated day 0. The exact distribution of LH peaks is shown in Table I. The maximal incidence of serum LH peaks occurred approximately one day earlier in this study than might have been predicted on the basis of the studies pre- viously cited. This may be explained on the basis that in earlier studies performed at Yerkes Primate Center regression of the sexual swelling was determined by palpation. The study of LH peaks in alert subjects, however, was performed at the author’s current location, where regression is diagnosed on the basis of visual evaluation. This technique typically yields a later indication of swelling regression. The latter method is expected to detect regression about one day later than the first. An earlier study in alert chim-

Owlation Time in Apes 53

TABLE I. Cycle Day of LH Peaks in Daily Determinations in Chimpanzees

-6 - 5 - 4 - 3 - 2 - 1 0 + 1 + 2

Serum" 0 1 3 1 8 3 0 0 0 Urineb 0 0 0 1 0 1 1 5" 0

"Graham and Gosselin [unpublished findings]. bMcArthur et a1 [in press]. 'Because of uncertainty about the exact day of regression, one peak could be interpreted as occurring either on day + 1 or day +2.

panzees failed to yield any consistent correlation of plasma LH peak with sexual swell- ing regression [Reyes et al, 19751.

We have also studied by radioimmunoassay the correlation of urinary LH peaks with sexual swelling regression in nine menstrual cycles of three chimpanzees [McArthur et al, in press]. These data, included in Table I, indicate that most frequently urinary LH peaks occurred on the first day of sexual swelling regression. It is important to note that urinary LH excretion peaks may be delayed at least 12-24 hours past the serum peak [Gould & Faulkner, in press]. The incidence of immunoreactive LH in the urine detectable with the nonhuman

primate pregnancy test provides a valuable indication of ovulation time lGould & Faulkner, in press], The pregnancy test cross-reacts sufficiently well with the urinary LH to detect the ovulatory peak, although not the basal levels. In interpreting the data, it is important to remember that, with this method, LH may be detectable on one to four days of the cycle but that this qualitative test cannot differentiate the LH peak day. The results of 36 cycles (58 positive tests) suggest a Gaussian distribution with a mode on approximately the last day of maximum swelling. These LH data indicate ovulation usually occurrs on the last two days of maximal sexual swelling.

Laparoscopy

While laparoscopy can provide direct evidence of the condition of the ovary, it is difficult to estimate the interval to ovulation on the basis of the appearance of a follicle or corpus luteum, because of the lack of objective criteria. However, an analysis of the presence or absence of a follicle or a corpus luteum in relation to a periovulatory event can provide a useful indicator. Graham [19731 has noted a trend toward unovulated follicles before swelling regression and ovulated follicles afterwards. Gould & Faulkner [in press] found that in ten of ten instances in which the ovaries were examined 14 to 18 hours after the first day on which LH could be detected in the urine with the nonhuman primate pregnancy test, only follicles were found. Conversely in 17 instances examined 22 and 28 hours after first detection of LH, only ruptured follicles were seen. Thus, the first appearance of LH in the urine is probably followed by ovulation 18-22 hours later. Thus, these endoscopies bear out the close correlation between days of LH detection in urine and swelling regression previously proposed, although the data are not adequate for a more precise correlation.

Incidence of Timed Matings Reevaluating early data from Yerkes and his colleagues on timed matings, Martin

[1981] has tabulated the known single-day matings resulting in conception. When these

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data are related to the last day of maximal swelling (day 01, the results show a wider spread (from day - 5 to day 0) than might have been expected on the basis of the data discussed above. However, it is important to realize that while the physiological data suggest that ovulation most often occurs on the last two days of maximal swelling, the same data also indicate that ovulation sometimes occurs earlier. We do not know the longevity of chimpanzee sperm in the genital tract, but if it is substantial, estimating the time of ovulation on the basis of single-day matings could be hazardous. Further- more, it should be noted that the series of timed matings is very small. Therefore, these timed matings may not provide reliable data on ovulation time in chimpanzees.

GORILLA

The gorilla develops an unobtrusive labial swelling that normally remains at maxi- mum size for only one to four days [Nadler et al, 19791. In one study of serum gonad- otropins during four menstrual cycles, the LH peak in each case occurred on the second day of maximal labial tumescence. In another series of cycles [Nadler, Collins, and Blank, in preparation] slightly greater variation in the timing of the LH peak was observed, although it always occurred during the restricted period of maximal labial swelling. Two of the cycles studied were accompanied by endometrial biopsies on the first and second days of labial regression [Graham, 19811. The first of these showed a mixed proliferativelsecretory pattern and the second an early secretory pattern. These combined data strongly suggest that ovulation occurs toward the end of the one- to four-day period of maximum labial swelling.

ORANG-UTAN

Preliminary studies on the orang-utan are inadequate to establish the time of ovu- lation in relation to any parameter. Slow progress is due in part to the absence of any externally visible change such as a sexual swelling. Study of urinary steroids by Collins et a1 119751 did not provide correlations precise enough for ovulation prediction. Nadler and Graham [unpublished data1 have assembled some data on the length of the inter- menstrual interval, based on use of a test for occult menstrual blood in urine (Hemastix, Ames, Iowa). Sixty percent of cycles were 25-27 days long (n = 23). The ovulatory LH peak was detected by Nadler [unpublished data] in 12 cycles using the nonhuman primate pregnancy test, and the luteal duration so defined by the interval between the urinary LH peak and menses was less than 11 days in 85% of cycles. These data only provide a starting point for future studies aimed at establishing the

periovulatory temporal correlates of the orang-utan. Recent laboratory studies point toward the possibility of a restricted period of sexual proceptivity under conditions when the female controls access to the male [Nadler, in press]. If confirmed, this ob- servation could provide the basis for a readily observed periovulatory criterion that could easily be correlated with the occurrence in the urine of LH detectable with the nonhuman primate pregnancy test.

CONCLUSIONS

1. There are adequate data to state the time of ovulation in the chimpanzee in relation to sexual swelling regression with considerable confidence. Ovulation most often occurs on the last two days of maximal sexual swelling.

Ovulation Time in Apes 55

2. Although the data in the gorilla are much more limited, they strongly point to an association between ovulation and the short period of maximal labial tumescence.

3. The time of ovulation in the orang-utan cannot yet be defined in terms of a midcycle event. However, data indicating that the menstrual cycle length is usually 25-27 days suggest that it will be possible in the future to define the interval between prior menses and ovulation with a moderate degree of reliability.

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Delaforge, J.P.; Thomas, K.; Ferin, J. Time re- lationships between LH discharge and endom- etrial morphology and histochemistry in the woman. ACTA EUROPEA FERTILITATIS 2:141-166, 1970.

Gould, K.G.; and Faulkner, J.R. Development, validation and application of a rapid method for detection of ovulation in great apes and the human. FERTILITY AND STERILITY (1981).

Graham, C.E. Chimpanzee endometrium and sexual swelling during menstrual cycle or hormone administration. FOLIA PRIMATO- LOGIA 19:458-468, 1973.

Graham, C.E. Menstrual cycle of the great apes, in REPRODUCTIVE BIOLOGY OF THE GREAT APES: COMPARATIVE AND BIOMEDICAL PERSPECTIVES. C.E. Gra- ham, ed. New York, Academic Press, 1981.

Graham, C.E.; Collins, D.C.; Robinson, H.; Preedy, J.R.K. Urinary levels of estrogens and pregnanediol and plasma levels of progester- one during the menstrual cycle of the chim- panzee: relationship to the sexual swelling ENDOCRINOLOGY 91:13-24, 1972.

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Morris, N.M.; Underwood, L.E.; Easterling, W. Temporal relationship between basal body temperature nadir and luteinizing hormone surge in normal women. FERTILITY AND STERILITY 27:780-783, 1976.

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Reyes, F.I.; Winter, J.S.D.; Faiman, C.; Hobson, W.C. Serial serum levels of gonadotropins, prolactin and sex steroids in the nonpregnant and pregnant chimpanzee. ENDOCRINOL- OGY 96:1447-1455, 1975.

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