Uterine contraction patterns and fertility in early postpartum ewes
D.O. Kiesling
*, M.A. Akinbami
1, S. Meredith, J.E. Warren Jr
2 307 Foster Hall, Lincoln University, Jefferson City, MO 65102-0029, USAReceived 26 August 1999; accepted 23 February 2000
Abstract
Three experiments were conducted to determine: (1) the direction of uterine contractions in Days 32 and 52 postpartum ewes (Experiment 1); (2) the effect of PGF2aon direction of uterine contractions (Experiment 2); and (3) the effect of PGF2a
on fertility rates in Day 32 postpartum ewes (Experiment 3). In Experiment 1, non-lambing (>90 days postpartum) and lambing ewes (day of lambingDay 0) received medroxyprogesterone acetate (MAP) vaginal sponges for 8 days and 500 IU of eCG at sponge withdrawal (Days 30 or 50 postpartum). At the time of eCG injection, ewes were divided into the following groups: (1) non-lambing (control;n29); (2) Day 32 postpartum dry (n15) and lactating (n16); and (3) Day 52 postpartum dry (n14) and lactating (n16). At estrus or 60 h post-eCG, the uterus was exteriorized through a mid-ventral incision, and the origin and direction of uterine contractions were recorded for 10 min. In Experiment 2, ewes received MAP sponges on Day 16 postpartum followed by 500 IU of eCG on day of sponge removal (Day 30). At estrus, the ewes were divided into the following treatments: (1) two injections of saline 4 h apart (n10) and (2) 12.5 mg of PGF2afollowed by another 12.5 mg 4 h
later (n7). After the second injection, ewes were laparotomized and uterine contractions were counted. In Experiment 3, estrus was induced in postpartum ewes, and ewes were mated to two rams, then received the same two treatments as described in Experiment 2 (ramsaline;n32 and ramPGF2a;n28). Two days following mating, ewes were laparotomized and the
oviducts ¯ushed for recovery of ova. In Experiment 1, lactational status had no effect, therefore, the data were pooled. Control ewes had a greater percentage (p<0.05) of uterine contractions (69%) moving towards the oviducts than did Day 32 (8%) or Day 52 (43%) ewes. In Experiment 2, PGF2atreatment increased the proportion of contractions (p<0.05) moving toward the
oviducts (controls 16%, PGF2a42%). Number of PGF2a-treated ewes (Experiment 3) with fertilized ova were not signi®cantly
different from the control ewes (5/32 versus 2/28; respectively). In conclusion, it can be said that the direction of uterine contractions moving toward the oviducts increased as the postpartum interval progressed or if they received PGF2ainjection.
PGF2atreatment did not improve fertility rates in Day 32 postpartum ewes.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Fertility rates; PGF2a; Postpartum ewes; Uterine contractions
1. Introduction
In an estrous ewe the majority of uterine contrac-tions originate from the caudal part of the uterine horn and move cranially (Hawk, 1973; Hawk and Echtern-kamp, 1973). This contraction pattern has been asso-ciated with the rapid transport of sperm to the oviducts (Hawk, 1983). It is not known if the direction of uterine contractions are the same in ewes at an induced
*Corresponding author. Tel.:1-573-681-5384;
fax:1-573-681-5548.
E-mail address: kiesling@lincolnu.edu (D.O. Kiesling)
1Present address: Morehouse School of Medicine, Atlanta, GA 30310-1495, USA.
2Present address: West Virginia University, Morgantown, WV, USA.
estrus during the early postpartum period. Ewes bred at an induced estrus 32 days after lambing have poor fertility (10%). Fertility improves as lambing to breed-ing interval increases with an 80% conception rate on Day 52 postpartum (Warren et al., 1989). The low fertility observed in ewes during the early postpartum period has been associated with poor sperm transport (Warren et al., 1989).
In rabbits, prostaglandin F2a, (PGF2a) injected near
the time of insemination increased the sperm numbers in the oviducts of the reproductive tract 2±3 h later (Hawk et al., 1982). In cycling ewes, injections of PGF2aincreased both frequency and strength of
uter-ine contractions as measured by a physiograph (Hawk and Conley, 1985). Edquist et al. (1975) and Gustafs-son (1978) injected PGF2a into ewes at the time of
insemination and found more sperm in the oviducts of treated than of control ewes 16 or 24 h later. Dimov and Georgiev (1977) demonstrated that the addition of PGF2a, and prostaglandin E2 to diluted ram semen
increased fertility by more than 15%.
To achieve two lamb crops in 1 year, acceptable fertility rates must be obtained within 30±35 days after lambing. It appears that sperm transport to the site of fertilization is minimal in 32 days postpartum ewes. Therefore, factors that could in¯uence sperm transport such as direction of uterine contractions and the effect of PGF2aon uterine contractions and fertility need to
be evaluated. The following experiments were designed to: (1) determine the pattern of uterine contractions of Days 32 and 52 postpartum ewes, compared to non-lambing controls; (2) evaluate the effect of PGF2aon direction of uterine contractions in
the postpartum ewe and (3) determine the effect of PGF2aon fertility in Day 32 postpartum ewes bred
during the anestrous and estrous seasons.
2. Materials and methods
2.1. Animals
HampshireSuffolk cross ewes (n202) ranging in age from 2 to 5 years were maintained in a dry lot with access to a barn with an open southern exposure. Ewes were fed a 12% CP corn±soybean meal ration (0.25 kg per ewe per day) plus orchard/grass hay ad libitum. The experiments were conducted in the Midwestern
region of the United States near Jefferson City, MO, located at 388N latitude, 948W longitude and at a geographical altitude of 168 m.
2.2. Experiment 1
Ewes from June and July lambing, and non-lambing ewes (controls; at least 90±120 days from last lamb-ing; n29) were used for the study. Beginning on Days 22 or 42 postpartum (day of lambing0) ewes
received a 40 mg medroxyprogesterone acetate (MAP; Intervet, Holland) impregnated vaginal sponge for 8 days. At sponge removal ewes were injected with 500 IU eCG (Intervet, Holland). Estrus was induced in controls using the same procedure except the time that treatment was initiated was no earlier than 90±120 days postpartum. Ewes were randomly assigned within postpartum days into the following groups: (1) Day 32 postpartum dry (n15) and postpartum lactating (n16) and (2) Day 52 postpartum dry (n14) and postpartum lactating (n16). Postpartum dry ewes either lost their lambs at birth or had their lambs weaned at Day 10 postpartum. Lactating ewes had their lambs with them throughout the experiment. At estrus or 60 h post-eCG (whichever came ®rst), ewes were anesthetized with 20 mg of pentobarbital sodium, placed in dorsal recumbency on a surgical table, and the uterus exteriorized through a mid-ven-tral incision. Uterine contractions were observed using the procedure of Hawk (1975). Three minutes after the uterus was exteriorized, the origin and direction of movement of uterine contractions was recorded during a 10 min interval (by an observer for each horn). Contractions were recorded as originating either in the caudal, middle or cranial one-third of the uterine horn. Direction of contractions was recorded as either moving toward the oviduct, toward the cervix, in both directions, or no movement. The uterus was not moistened during the period of observation to prevent stimulus-induced contractions. Drying of the serosa was not observed.
variance (ANOVA) with three treatments: controls, Day 32 postpartum and Day 52 postpartum ewes. Least square means were performed to determine differences between speci®c treatments (SAS, 1988). Percentage of ewes exhibiting estrus, was determined by chi-square (SAS, 1988).
2.3. Experiment 2
Ewes (n17) which lambed in September and
October each received a vaginal MAP sponge on Day 16 postpartum (day of lambingDay 0) followed by 500 IU of eCG on day of sponge removal (Day 30). At estrus, the ewes were divided into the following treatment groups: (1) controls received two injections of 0.9% saline (2.5 ml each) 4 h apart (n10) and (2) PGF2a-treated ewes (n7) received two injections
(each injection 12.5 mg) of PGF2a4 h apart (Lutalyse,
Pharmacia & UpJohn Co., Kalamazoo, MI, USA). Immediately following the second injection, ewes were laparotomized and uterine contractions were recorded in each horn for a 10 min period as described in Experiment 1. Differences between treatments in direction of uterine contractions were determined in ANOVA (SAS, 1988).
2.4. Experiment 3
Postpartum ewes (n20) which lambed in Septem-ber and OctoSeptem-ber, and postpartum ewes (n40) which lambed in February and March, received a vaginal MAP sponge on Day 16 postpartum (day of lam-bingDay 0) and 750 IU eCG at the time of sponge removal on Day 30 postpartum. Ewes that were 90± 120 days since last lambing (n15, estrous season;
n20, anestrous season) were mated at an induced estrus (received a MAP sponge for 14 days plus 750 IU eCG at sponge removal) and allowed to lamb to determine fertility of rams. Ewes were checked for estrus twice daily with a vasectomized ram. At estrus, postpartum ewes were randomly assigned to two treatment groups: (1) ramsaline, which were mated by two fertile rams during a 10 min period and given an injection of 2.5 ml of 0.9% saline after mating and an additional injection 4 h later (n28) and (2) ramPGF2a-treated ewes, which were mated as
described in Group 1 and given an injection of 12.5 mg of PGF2a immediately after mating and an
additional 12.5 mg injection 4 h later (n32). Two days following estrus, postpartum ewes were lapar-otomized and the oviduct adjacent to the ovary con-taining the corpus luteum was ¯ushed for ova. Ova were evaluated for cleavage under a phase contrast microscope.
The initial design was a 22 factorial arrangement with two treatments (ramsaline and ramPGF2a)
and two seasons (fall and spring). There was no effect of season, therefore, the data were pooled and reana-lyzed as ANOVA with two treatments (ramsaline and ramPGF2a) using the General Linear Models
Procedure of SAS (SAS, 1988).
3. Results
3.1. Experiment 1
Percentage of ewes exhibiting estrus was similar among controls, Days 32 and 52 ewes (69, 55 and 50%), respectively. Mean number of uterine contrac-tions moving toward the oviducts was greater (p<0.05) for the control ewes than the Days 32 or 52 ewes (Table 1). Day 52 ewes had more contractions (p<0.05) moving towards the oviducts than Day 32 ewes. There were more uterine contractions moving towards the cervix of Day 32 ewes than in Day 52 ewes.
For the control ewes, origin of contractions was equally divided among the caudal, middle and cranial portions of the uterine horn (Table 1). The majority (76%) of the uterine contractions originated from the cranial part of the uterus and moved towards the cervix in Day 32 ewes, whereas only 51% of uterine con-tractions originated in the cranial part of the uterus and moved toward the cervix in Day 52 ewes (Table 1).
3.2. Experiment 2
PGF2a-treated ewes had more (p<0.05) contractions
moving towards the oviducts than did the controls (Table 2). The percentage of contractions moving toward the cervix was 58% (p<0.05) for PGF2a-treated
ewes compared to 84% in the controls.
3.3. Experiment 3
The percentage of ewes exhibiting estrus was 100% in all treatment groups. The percentage of ewes
lamb-ing was 66% for controls (90±120 days since last lambing) indicating normal fertility of rams used in this study. PGF2a treatment of Day 32 postpartum
ewes did not improve fertility (Table 3).
4. Discussion
Some reports have suggested that the uterus has completed involution in ewes by 30 days after lambing (a review by Kiracofe, 1980). However, histological evaluation of the luminal contents and endometrium at this time revealed that the number of lymphocytes and plasma cells exceeded those found in control ewes (Akinbami, 1989). The amount of uterine debris and leukocytes decreases as the time from lambing increases, with a corresponding increase in contrac-tions moving from the cervix to the oviducts, and an increase in fertility rate.
Table 1
Direction and origin of uterine contractions (meanS.E.) in postpartum ewesa
Uterine contractions Treatmentb
Control (n29) Day 32 (n31) Day 52 (n30)
Total number of contractions 322 362 353
Directionc
Moving towards oviducts 222 (69%) c 31 (8%) d 152 (43%) e
Moving neither or both ways 21 (6%) 31 (8%) 31 (8%)
Moving towards cervix 81 (25%) c 302 (84%) d 172 (49%) e
Origind
Caudal 122 (38%) c,e 31 (8%) d 101(28%) e
Middle 111 (33%) 61 (16%) 71 (21%)
Cranial 91 (28%) c 272 (76%) d 182 (51%) e
aNumbers in rows with different letters (c, d, e) differ (p<0.05).
bUterine contractions of control ewes originated throughout the uterus and were moving towards the oviducts, whereas, Days 32 and 52 ewes majority of uterine contractions originated in the anterior part of the uterus and moved toward the cervix.
cMean uterine contractionsS.E. per 10 min. Percentages are of the total contractions moving towards or away from oviducts. dPercentages are of the total contractions originating from the caudal, middle or cranial part of the uterus.
Table 2
Effect of PGF2aon uterine contractions in Day 32 postpartum ewes
Treatment N Mean uterine contractionsS.E. per 10 min
Total Moving towards oviductsa Away from oviductsa
Control 10 321 51 (16%) a 271 (84%) a
PGF2a 7 242 102 (42%) b 142 (58%) b
aNumbers in columns with different letters (a, b) differ (p<0.05).
Table 3
Effect of PGF2aon fertility in Day 32 postpartum ewes a
Treatment N Ewes with fertilized ova
Ewes with unfertilized ova
Ramsaline 28 2 (7%) 26 (93%) RamPGF2a 32 5 (16%) 27 (84%)
This is supported by data demonstrating that place-ment of intrauterine devices (IUD) into the uterine horn of estrous ewes causes contraction patterns simi-lar to Day 32 postpartum ewes. This reversal of direction of contractions with IUD resulted in a reduced number of sperm in the oviducts and is associated with loss of fertility (Hawk, 1967, 1969). Once the device is removed, direction of contractions move from the cervix to the oviduct and fertility is restored.
PGF2awas injected in an attempt to change
direc-tion of contracdirec-tions in Day 32 postpartum ewes. Although PGF2a increased the number of uterine
contractions moving towards the oviducts, there was no improvement in fertility. Even with the change in direction of contractions, sperm may not have been transported in large enough numbers to the oviducts for fertilization to take place (Hunter and Nichol, 1983). The effect of changing the direction of uterine contractions on the number of sperm actually reaching the site of fertilization was not determined in the present experiment. It seems unlikely, however, that PGF2asuccessfully increased the number of sperm at
the ampullary-isthmus junction because surgical deposition of semen at this site signi®cantly improved fertility in Day 32 postpartum ewes (Warren et al., 1989). Even if the change in direction of uterine contractions by PGF2aresulted in more sperm moving
towards the site of fertilization, they were probably destroyed in the uterus before reaching the site. This is thought possible because of the higher number of leukocytes found in the Day 32 postpartum uterus (Akinbami, 1989) and leukocytes are one of the two major causes for loss of sperm (Bedford, 1965; Matt-ner, 1968). The adverse uterine environment at this postpartum stage is further illustrated by Akinbami et al. (1996) and Wallace et al. (1989) who demon-strated that embryos migrating into the uterine horn have poor survival rate early postpartum. Future treat-ments to improve fertility may need to be focused more on improving the uterine environment rather than direction of uterine contractions.
5. Conclusion
The high proportion of uterine contractions origi-nating near the oviducts and moving toward the cervix
in Day 32 postpartum ewes could be one cause for the poor fertility in ewes bred during the postpartum period. Although direction of uterine contractions could be reversed with PGF2a injections, there was
no improvement in fertility. Evaluating factors that cause low fertility during the early postpartum period may result in methods to improve fertility at this stage.
Acknowledgements
The authors are grateful to G.A. Dudenhoeffer and Arlene Stewart for their assistance with the handling of ewes. This work has been supported by CSREES project No. MO-X-OP96±416 of the Animal Science Program in Cooperative Research.
References
Akinbami, M., 1989. Maternal factors affecting conception in postpartum ewes. Ph.D. Dissertation, University of Missouri, Columbia.
Akinbami, M.A., Kiesling, D.O., Meredith, S., Warren Jr., J.E., Day, B.N., 1996. Embryonic survival in the uterus of ewes inseminated at the uterotubal junction on day 32 postpartum. Theriogenology 45, 1129±1139.
Bedford, J.M., 1965. Effect of environment on phagocytosis of rabbit spermatozoa. J. Reprod. Fertil. 9, 249±256.
Dimov, V., Georgiev, G., 1977. Ram semen prostaglandin concentration and its effect on fertility. J. Anim. Sci. 44, 1050±1054.
Edquist, S., Einarsson, S., Gustafsson, B., 1975. Effect of prostaglandin F2aon sperm transport in the reproductive tract of the ewe. Acta Vet. Scand. 16, 149±151.
Gustafsson, B.J., 1978. Aspects of fertility with frozen-thawed ram semen. Cryobiology 15, 358.
Hawk, H.W., 1967. Investigations on the anti-fertility effect of intrauterine devices in the ewe. J. Reprod. Fertil. 14, 49±59. Hawk, H.W., 1969. Some effects of intrauterine devices on
reproductive function in the ewe. Fertil. Steril. 20, 1±13. Hawk, H.W., 1973. Uterine motility and sperm transport in the
estrous ewe after prostaglandin-induced regression ofCorpora lutea. J. Anim. Sci. 37, 1380±1385.
Hawk, H.W., 1975. Hormonal control of changes in the direction of uterine contractions in the estrous ewe. Biol. Reprod. 12, 423± 430.
Hawk, H.W., 1983. Sperm survival and transport in the female reproductive tract (cattle, sheep, swine). J. Dairy Sci. 66, 2645± 2660.
Hawk, H.W., Echternkamp, S.E., 1973. Uterine contractions in the ewe during progestagen-regulated oestrus. J. Reprod. Fertil. 34, 347±349.
Hawk, H.W., Cooper, B.S., Conley, H.H., 1982. Effect of acetylcholine, prostaglandin F2a and estradiol on number of sperm in the reproductive tract of inseminated rabbits. J. Anim. Sci. 55, 891±900.
Hunter, R.H.F., Nichol, R., 1983. Transport of spermatozoa in the sheep oviduct: preovulatory sequestering of cells in the caudal isthmus. J. Exp. Zool. 228, 121±128.
Kiracofe, G.H., 1980. Uterine involution: it's role in regulating postpartum intervals. J. Anim. Sci. (Suppl. 2) 16±22.
Mattner, P.E., 1968. The distribution of spermatozoa and leukocytes in the female genital tract of goats and cattle. J. Reprod. Fertil. 17, 253±261.
SAS Institute Inc., 1988. User's Guide: Statistics. SAS Institute Inc., Cary, NC.
Wallace, J.M., Robinson, J.J., Aitken, R.P., 1989. Successful pre-gnancies after transfer of embryos recovered from ewes induced to ovulate 24±29 days postpartum. J. Reprod. Fertil. 86, 627±635. Warren Jr., J.E., Kiesling, D.O., Akinbami, M.A., Price, E.A.,
