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The effect of endometrial biopsy on ovulatory interval in mares
THE EFFECT OF ENDOMETRIAL
BIOPSY ON OWLATORY
INTERVAL
IN MARES
R.O. Gilbert' Department of Theriogenology Faculty of Veterinary Science, University of Pretoria Private Bag X04, Onderstepoort, 0110 South Africa. Received
for publication: APTiT 13, 1989 Accepted: June 21, 1989 ABSTRACT
Luteolysis with subsequent shortening of diestrus has been reported to follow equine endometrial biopsy performed early in the lute.al phase of the estrous cycle, but a comprehensive study of the effect of endometrial biopsy on cycle length at different times of the cycle has not been reported. In this study, endometrial biopsies were obtained from four different pony mares on each of Days 0, 4, 8, 12, 16 and 20 after ovulation as determined by serial palpation per rectum. Compared with control cycles in the same mares, the ovulatory interval was shortened in mares from which biopsies were obtained on Days 4 and 8, it was lengthened in from which samples were taken on Days 16 and 20 and it remained unchanged by biopsies performed on Days 0 and 12. Although the changes were less consistent and smaller than those observed in cows, our findings are similar to those reported for effects of endometrial manipulation or uterine infusion on the estrous cycle of cows. Key words:
endometrial
biopsy,
estrous cycle, mare
INTRODUCTION Endonetrial biopsy specimens are frequently obtained as part of the reproductive evaluation of the mare. Luteolysis has been reported to follow the biopsy procedure if it is performed early in diestrus (1,2). The effect of endometrial biopsy later in the estrous cycle has not been reported in mares. In another study, intrauterine infusion of saline solutions between Days 4 and I after ovulation shortened the ovulatory interval in most mares (3). Intrauterine infusion on Days 1 to 13 after the onset of behavioral diestrus was reported by Arthur (4) who found no effect on cycle length in one mare infused on Day 1 and another mare infused on Day Acknowledgments: Ms. Deborah van Zyl and Ms. Ester Botha provided their technical assistance. Ms. Valerie Killeen, Mr. Samuel Mathaung and Mr. Jameson Khosa were responsible for the care of the This project was supported by a grant from the University ponies. of Pretoria. 'Present address: Department of Clinical Sciences, New York State College of Veterinary Medicine, Cornell University, Ithaca, NY 14853-6401.
SEF’TEMBER 1989 VOL. 32 NO. 3
451
THERIOGENOLOGY
12. Mares infused between Days 2 and 9 showed shorter cycles than expected. A single mare infused on Day 13 after the onset of diestrus had a longer than expected diestrous period and ovulatory interval. It was the aim of this study to establish the effect, if any, of obtaining endometrial biopsies at various stages of the estrous cycle on ovulatory interval in mares. MATERIALS
AND METHODS
Twenty-four pony mares, of mixed Welsh and Nooitgedacht Pony breeding, were available for this trial. They ranged in age from 3 to 14 yr, and were all healthy and in good condition. All were either maiden mares or had normal reproductive histories. All the mares had a normal endometrial histology and were placed in endometrial Category I according to the criteria of Kenney (5). The trial took place during the natural breeding season of the southern hemisphere. During this time the mares had ad libitum access to teff (Eraorostis teff) hay. The mares were teased daily by exposure to a vigorous stallion over a teasing bar. During periods of estrous behavior, daily The day of rectal examination of the ovaries was performed. was recorded as the first day on which a corpus ovulation hemorrhagicum was palpable, and was defined as Day 0 of the estrous cycle. randomly In the second experimental mares were cycle, allocated to have endometrial biopsy specimens obtained on Day 0, 4, 8, 12, 16 or 20 of the cycle (four different mares per biopsy day). A Yeoman biopsy punch was used to obtain biopsies from the A single dorsal aspect of the base of the right uterine horn. operator was responsible for obtaining all specimens. Biopsy cycle length was compared with a control cycle length in the same mares using Wilcoxin's signed-rank test for paired samples (6). For purposes of analysis, the effect of biopsy early in the cycle (Day 4 or 8) or late in the cycle (Day 16 or 20) was examined. RESULTS The mean ovulatory interval for the control cycle of all mares was 20.96 2 2.3 d. The details of control and biopsy cycle lengths appear in Table 1. Biopsy on Day 0 or 12 of the estrous cycle did not affect Biopsy on Day 4 shortened the cycle length by more than 1 d. ovulatory interval by 1 to 6 d, and on Day 8 by 0 to 9 d compared with the previous cycle of the same mare. Of the mares from which endometrial biopsy specimens were obtained on Day 16, one had a slightly shortened cycle (2 d), but the ovulatory interval of the other mares was increased by 1 to 5 d. Three mares from which samples had been taken on Day 20 had increased ovulatory intervals (1 to 5 d). The other mare in this group had ovulated during the
452
SEPTEMBER 1989 VOL. 32 NO. 3
THERIOGENOLOGY
12 h preceding the biopsy. It was concluded that biopsy on Day 4 or 8 of the cycle produced a shortening of the ovulatory interval (P =: 0.016) and that a biopsy performed later in the cycle (Day 16 to increase or 20) tended ovulatory interval (P < 0.10). Endometrial biopsy on Day 0 or 12 post ovulation had no effect on ovulatory interval (P > 0.10) Table
1.
The effect of endometrial biopsy at various stages of the estrous cycle on ovulatory interval in mares.
Day of Biopsy
0
4
8
12
16
20
Ovulatory interval (Control cycle)
20.0 k1.4
21.3 +2.9
21.0 +3.5
20.5 +1.8
21.7 51.7
20.8 +0.4
Ovulatory interval (Bicpsy cycle)
20.0 +1.0
18.0 53.4
18.3 22.1
20.5 +1.7
23.3 +2.3
22.6 42.2
Biopsy cycle > 1 d shorter than control
O/4
3/4
3/4
O/4
O/4
O/4
Biopsy cycle > 1 d longer than control
O/4
O/4
O/4
O/4
3/4
214
DISCUSSION The results of this trial indicate a significant reduction in ovulatory interval in mares from which endometrial biopsy samples were obtained on Day 4 or 8 after ovulation. No change was associated with biopsy specimens obtained on Day 0 or 12. A biopsy obtained on Day 16 or 20 increased the ovulatory interval. (One mare scheduled for biopsy on Day 20 after a previous ovulation ovulated on the day of the biopsy.) These results are compatible with previously reported work. In one study (1) premature luteolysis with shortening of diestrus occurred after endometrial biopsy of mares 4 d after ovulation. The length of diestrus was not altered by taking endometrial biopsy specimens during estrus. The authors do not report whether the latter biopsy specimens were obtained before or after ovulation. Arthur (4) reported cycles of normal length (21-d ovulatory interval) in one mare receiving an intrauterine infusion on the first day of diestrus and of another mare treated on the twelfth day of diestrus. Ovulatory interval was shortened (13 to 19 d) in 15 mares treated between Days 2 and 9 of diestrus. A single mare treated on Day 13 of diestrus had a 23-d ovulatory interval. No mares were treated after Day 13 of diestrus. Likewise, Hurtgen and Ganjam (2) reported consistent shortening of the estrous cycle following endometrial biopsy on Day 4. Neely et al (3) also examined the effect of intrauterine saline infusion 4 to 7 d after ovulation and recorded shorter than normal cycles in 13 of 18
SEPTIEMBER 1989 VOL. 32 NO. 3
453
THERIOGENOLOGY
mares. The mechanism involved was reported to be premature luteolysis brought about by endometrial manipulation (1,3). There is a paucity of reports of endometrial biopsy (or intrauterine infusion) later than 12 d after ovulation in mares. Similar interventions in cows are known to be associated with lengthened ovulatory intervals (7), corresponding with our findings. The proposed mechanism of lengthening the bovine estrous cycle associated with intrauterine infusion in the second half of the luteal phase of the cycle is the postponement of luteolysis (7). This seems unlikely to be the mechanism in mares, since most mares in the Days 16 and 20 groups had already undergone luteolysis and were showing estrous behavior at the time that the biopsies were obtained. A more direct effect on folliculoqenesis or ovulation seems probable. Although the effects of endometrial manipulation on the equine estrous cycle seem to be smaller and less consistent than those reported for cows, it is important for clinicians to understand the effects of so common a procedure as endometrial biopsy on the estrous cycle of the animals they treat. Further investigation of these effects is also likely to enhance our understanding of utero-ovarian communication in folliculoqenesis and ovulation. REFERENCES 1.
Baker, C.B., Newton, D.I., Mather, E.C. and Oxender, W.D. Luteolysis in mares after endometrial biopsy. Am. J. Vet. Res. 42:1816-1818 (1981).
2.
Hurtqen, J.P. and Ganjam, V.K. The effect of intrauterine and cervical manipulation on oestrous cycle and hormone profiles. J. Reprod. Fertil. 27 (Suppl.):191-197 (1979).
3.
Neely, D.P., Hughes, J.P., Stabenfeldt, G.H. and Evans, J.W. The influence of intrauterine saline infusion on luteal function and cyclical activity in the mare. J. Reprod. Fertil. 22 (Suppl.) =:235-239 (1975).
4.
Arthur, G.H. Influence of intrauterine saline infusion upon the oestrous cycle of the mare. J. Reprod. Fertil. 23 (Suppl.):231-234 (1975).
5.
Cyclic and pathologic changes of Kenney, R.M. endometrium as detected by biopsy, with a note embryonic death. J. Am. Vet. Med. Assoc. m:241-262
6.
Snedecor, G.W. and Cochran, W.G. Statistical Methods. State University Press, Ames, IA, 1980, pp. 141-143.
7.
Seguin, B. Altering estrous cycles in cows by intrauterine infusion. D.A. In: Morrow, Therapy in (ed.) Current Therioqenoloqy. W.B. Saunders Company, Philadelphia, 1980, pp. 177-180.
454
SEPTEMBER 1989 VOL. 32 NO. 3
the mare on early (1978). Iowa
BIOPSY ON OWLATORY
INTERVAL
IN MARES
R.O. Gilbert' Department of Theriogenology Faculty of Veterinary Science, University of Pretoria Private Bag X04, Onderstepoort, 0110 South Africa. Received
for publication: APTiT 13, 1989 Accepted: June 21, 1989 ABSTRACT
Luteolysis with subsequent shortening of diestrus has been reported to follow equine endometrial biopsy performed early in the lute.al phase of the estrous cycle, but a comprehensive study of the effect of endometrial biopsy on cycle length at different times of the cycle has not been reported. In this study, endometrial biopsies were obtained from four different pony mares on each of Days 0, 4, 8, 12, 16 and 20 after ovulation as determined by serial palpation per rectum. Compared with control cycles in the same mares, the ovulatory interval was shortened in mares from which biopsies were obtained on Days 4 and 8, it was lengthened in from which samples were taken on Days 16 and 20 and it remained unchanged by biopsies performed on Days 0 and 12. Although the changes were less consistent and smaller than those observed in cows, our findings are similar to those reported for effects of endometrial manipulation or uterine infusion on the estrous cycle of cows. Key words:
endometrial
biopsy,
estrous cycle, mare
INTRODUCTION Endonetrial biopsy specimens are frequently obtained as part of the reproductive evaluation of the mare. Luteolysis has been reported to follow the biopsy procedure if it is performed early in diestrus (1,2). The effect of endometrial biopsy later in the estrous cycle has not been reported in mares. In another study, intrauterine infusion of saline solutions between Days 4 and I after ovulation shortened the ovulatory interval in most mares (3). Intrauterine infusion on Days 1 to 13 after the onset of behavioral diestrus was reported by Arthur (4) who found no effect on cycle length in one mare infused on Day 1 and another mare infused on Day Acknowledgments: Ms. Deborah van Zyl and Ms. Ester Botha provided their technical assistance. Ms. Valerie Killeen, Mr. Samuel Mathaung and Mr. Jameson Khosa were responsible for the care of the This project was supported by a grant from the University ponies. of Pretoria. 'Present address: Department of Clinical Sciences, New York State College of Veterinary Medicine, Cornell University, Ithaca, NY 14853-6401.
SEF’TEMBER 1989 VOL. 32 NO. 3
451
THERIOGENOLOGY
12. Mares infused between Days 2 and 9 showed shorter cycles than expected. A single mare infused on Day 13 after the onset of diestrus had a longer than expected diestrous period and ovulatory interval. It was the aim of this study to establish the effect, if any, of obtaining endometrial biopsies at various stages of the estrous cycle on ovulatory interval in mares. MATERIALS
AND METHODS
Twenty-four pony mares, of mixed Welsh and Nooitgedacht Pony breeding, were available for this trial. They ranged in age from 3 to 14 yr, and were all healthy and in good condition. All were either maiden mares or had normal reproductive histories. All the mares had a normal endometrial histology and were placed in endometrial Category I according to the criteria of Kenney (5). The trial took place during the natural breeding season of the southern hemisphere. During this time the mares had ad libitum access to teff (Eraorostis teff) hay. The mares were teased daily by exposure to a vigorous stallion over a teasing bar. During periods of estrous behavior, daily The day of rectal examination of the ovaries was performed. was recorded as the first day on which a corpus ovulation hemorrhagicum was palpable, and was defined as Day 0 of the estrous cycle. randomly In the second experimental mares were cycle, allocated to have endometrial biopsy specimens obtained on Day 0, 4, 8, 12, 16 or 20 of the cycle (four different mares per biopsy day). A Yeoman biopsy punch was used to obtain biopsies from the A single dorsal aspect of the base of the right uterine horn. operator was responsible for obtaining all specimens. Biopsy cycle length was compared with a control cycle length in the same mares using Wilcoxin's signed-rank test for paired samples (6). For purposes of analysis, the effect of biopsy early in the cycle (Day 4 or 8) or late in the cycle (Day 16 or 20) was examined. RESULTS The mean ovulatory interval for the control cycle of all mares was 20.96 2 2.3 d. The details of control and biopsy cycle lengths appear in Table 1. Biopsy on Day 0 or 12 of the estrous cycle did not affect Biopsy on Day 4 shortened the cycle length by more than 1 d. ovulatory interval by 1 to 6 d, and on Day 8 by 0 to 9 d compared with the previous cycle of the same mare. Of the mares from which endometrial biopsy specimens were obtained on Day 16, one had a slightly shortened cycle (2 d), but the ovulatory interval of the other mares was increased by 1 to 5 d. Three mares from which samples had been taken on Day 20 had increased ovulatory intervals (1 to 5 d). The other mare in this group had ovulated during the
452
SEPTEMBER 1989 VOL. 32 NO. 3
THERIOGENOLOGY
12 h preceding the biopsy. It was concluded that biopsy on Day 4 or 8 of the cycle produced a shortening of the ovulatory interval (P =: 0.016) and that a biopsy performed later in the cycle (Day 16 to increase or 20) tended ovulatory interval (P < 0.10). Endometrial biopsy on Day 0 or 12 post ovulation had no effect on ovulatory interval (P > 0.10) Table
1.
The effect of endometrial biopsy at various stages of the estrous cycle on ovulatory interval in mares.
Day of Biopsy
0
4
8
12
16
20
Ovulatory interval (Control cycle)
20.0 k1.4
21.3 +2.9
21.0 +3.5
20.5 +1.8
21.7 51.7
20.8 +0.4
Ovulatory interval (Bicpsy cycle)
20.0 +1.0
18.0 53.4
18.3 22.1
20.5 +1.7
23.3 +2.3
22.6 42.2
Biopsy cycle > 1 d shorter than control
O/4
3/4
3/4
O/4
O/4
O/4
Biopsy cycle > 1 d longer than control
O/4
O/4
O/4
O/4
3/4
214
DISCUSSION The results of this trial indicate a significant reduction in ovulatory interval in mares from which endometrial biopsy samples were obtained on Day 4 or 8 after ovulation. No change was associated with biopsy specimens obtained on Day 0 or 12. A biopsy obtained on Day 16 or 20 increased the ovulatory interval. (One mare scheduled for biopsy on Day 20 after a previous ovulation ovulated on the day of the biopsy.) These results are compatible with previously reported work. In one study (1) premature luteolysis with shortening of diestrus occurred after endometrial biopsy of mares 4 d after ovulation. The length of diestrus was not altered by taking endometrial biopsy specimens during estrus. The authors do not report whether the latter biopsy specimens were obtained before or after ovulation. Arthur (4) reported cycles of normal length (21-d ovulatory interval) in one mare receiving an intrauterine infusion on the first day of diestrus and of another mare treated on the twelfth day of diestrus. Ovulatory interval was shortened (13 to 19 d) in 15 mares treated between Days 2 and 9 of diestrus. A single mare treated on Day 13 of diestrus had a 23-d ovulatory interval. No mares were treated after Day 13 of diestrus. Likewise, Hurtgen and Ganjam (2) reported consistent shortening of the estrous cycle following endometrial biopsy on Day 4. Neely et al (3) also examined the effect of intrauterine saline infusion 4 to 7 d after ovulation and recorded shorter than normal cycles in 13 of 18
SEPTIEMBER 1989 VOL. 32 NO. 3
453
THERIOGENOLOGY
mares. The mechanism involved was reported to be premature luteolysis brought about by endometrial manipulation (1,3). There is a paucity of reports of endometrial biopsy (or intrauterine infusion) later than 12 d after ovulation in mares. Similar interventions in cows are known to be associated with lengthened ovulatory intervals (7), corresponding with our findings. The proposed mechanism of lengthening the bovine estrous cycle associated with intrauterine infusion in the second half of the luteal phase of the cycle is the postponement of luteolysis (7). This seems unlikely to be the mechanism in mares, since most mares in the Days 16 and 20 groups had already undergone luteolysis and were showing estrous behavior at the time that the biopsies were obtained. A more direct effect on folliculoqenesis or ovulation seems probable. Although the effects of endometrial manipulation on the equine estrous cycle seem to be smaller and less consistent than those reported for cows, it is important for clinicians to understand the effects of so common a procedure as endometrial biopsy on the estrous cycle of the animals they treat. Further investigation of these effects is also likely to enhance our understanding of utero-ovarian communication in folliculoqenesis and ovulation. REFERENCES 1.
Baker, C.B., Newton, D.I., Mather, E.C. and Oxender, W.D. Luteolysis in mares after endometrial biopsy. Am. J. Vet. Res. 42:1816-1818 (1981).
2.
Hurtqen, J.P. and Ganjam, V.K. The effect of intrauterine and cervical manipulation on oestrous cycle and hormone profiles. J. Reprod. Fertil. 27 (Suppl.):191-197 (1979).
3.
Neely, D.P., Hughes, J.P., Stabenfeldt, G.H. and Evans, J.W. The influence of intrauterine saline infusion on luteal function and cyclical activity in the mare. J. Reprod. Fertil. 22 (Suppl.) =:235-239 (1975).
4.
Arthur, G.H. Influence of intrauterine saline infusion upon the oestrous cycle of the mare. J. Reprod. Fertil. 23 (Suppl.):231-234 (1975).
5.
Cyclic and pathologic changes of Kenney, R.M. endometrium as detected by biopsy, with a note embryonic death. J. Am. Vet. Med. Assoc. m:241-262
6.
Snedecor, G.W. and Cochran, W.G. Statistical Methods. State University Press, Ames, IA, 1980, pp. 141-143.
7.
Seguin, B. Altering estrous cycles in cows by intrauterine infusion. D.A. In: Morrow, Therapy in (ed.) Current Therioqenoloqy. W.B. Saunders Company, Philadelphia, 1980, pp. 177-180.
454
SEPTEMBER 1989 VOL. 32 NO. 3
the mare on early (1978). Iowa