Corpus luteum function and embryonic mortality in buffaloes treated with a GnRH agonist, hCG and progesterone

The effect of treatment with a GnRH agonist, hCG or progesterone (P(4)) on corpus luteum function and embryonic mortality was investigated in buffaloes inseminated during mid-winter. Italian Mediterranean buffaloes (n=309) were synchronized using the Ovsynch with timed-AI program and mated by AI at 16 h (Day 0) and 40 h after the second injection of GnRH. On Day 5, buffaloes were randomly assigned to four groups: Control (no treatment, n=69), GnRH agonist (buserelin acetate, 12.6 microg, n=73), hCG (1500 IU, n=75) and P(4) (PRID without E(2) for 10 days, n=77). Progesterone (pg/ml) was determined in milk whey on Days 5, 10, 15 and 20 and pregnancy diagnosis was undertaken on Day 26 by ultrasound and Day 40 by rectal palpation. Treatment with buserelin and hCG increased (p<0.05) P(4) on Day 15 compared with controls (456+/-27, 451+/-24 and 346+/-28 pg/ml, respectively). Buffaloes treated with a PRID had intermediate P(4) concentrations (380+/-23 pg/ml). Embryonic mortality between Days 26 and 40 (22.9%) and pregnancies at Day 40 (48.9%) did not differ between treatments. A higher (p<0.01) P(4) concentration was found on Day 20 in pregnant animals compared with non-pregnant and embryonic mortality buffaloes, which did not differ. In summary, buserelin and hCG increased P(4) concentrations on Day 15 but this was not associated with a reduced incidence of embryonic mortality in buffaloes during mid-winter.     

Endometrial histology and post-partum mares treated with progesterone and synthetic GnRH (AY-24,031).

Foal heat was significantly delayed in 15 Thoroughbred and Quarter-horse mares by 200 mg progesterone in oil from Days 5--14 post partum. Nine of these mares subsequently received daily i.v. injections of 2 mg of a synthetic GnRH preparation (AY-24,031) from Day 2 of the progesterone-delayed oestrus but this treatment did not significantly shorten oestrus or hasten ovulation. Uterine biopsies taken on Day 15 post partum from all the mares showed a mixed endometrial morphology having both oestrous and dioestrous characteristics. There was an increased proliferation of endometrial glands in these animals at the time of ovulation compared to control mares having a normal foal heat.     

Controlling interrelationships of progesterone/LH and estradiol/LH in mares

The interrelationships of progesterone, estradiol, and LH were studied in mares (n=9), beginning at the first ovulation (Day 0) of an interovulatory interval. An increase in mean progesterone concentrations began on Day 0 and reached maximum on Day 6, with luteolysis beginning on Day 14. A common progesterone threshold concentration of about 2 ng/ml for a negative effect on LH occurred at the beginning and end of the luteal phase. Progesterone and LH concentrations decreased at a similar rate from Day 6 until the onset of luteolysis on Day 14, consistent with a decreasing positive effect of LH on progesterone. Concentrations of LH during the increase in the ovulatory surge consisted of two linear regression segments involving a rate of 0.4 ng/ml/day for Days 14-22 and 1.8 ng/ml/day for Day 22 to 1 day after the second ovulation. The end of the first segment and beginning of the second segment was 2 days before ovulation and was the day the ovulatory estradiol surge was at a peak.     

FSH and LH concentrations in periparturient mares.

The influence of the ovaries and presence of a foal on periparturient concentrations of FSH and LH were studied in 19 Pony mares. In intact and ovariectomized mares, mean concentrations of FSH fluctuated between 1.1and 9.9 ng/ml on Days -14 to-1 before parturition (Day 0). A surge of FSH occurred in all mares in association with parturition. From Days 1 to 10, the high levels of FSH gradually decreased in the intact group to the minimal concentrations that occur during oestrus, but remained elevated in the ovariectomized mares. There were no significant pre-partum changes in LH in either type of mare. Post-partum changes in LH concentrations increased at a similar rate in ovariectomized and intact mares. The presence of a foal significantly lengthened the interval to first oestrus, depressed LH levels on Days 6--10 and decreased the FSH concentrations as averaged over the 10 days before the first ovulation after parturition.     

Ovarian follicles, ovulations and progesterone concentrations in aged versus young mares

The objectives of this study were: 1) to document age-related ovulation failure in mares and 2) to contrast the number of ovarian follicles, occurrence of ovulations, and postovulatory concentrations of progesterone in aged versus young mares. In Experiment 1, 4 of 10 aged (25- to 33-years-old) mares were anovulatory between July 1 and September 1, 1989. In Experiment 2, two of 25 aged (20- to 30-years-old) and none of 21 young (3- to 12-years-old) mares were anovulatory between February 1 and June 30, 1990. The average (+/- SEM) day of the first ovulation was later (P<0.05) for aged versus young mares (May 9 +/- 7.1 vs April 25 +/- 7.4 days, respectively). There tended (P<0.10) to be fewer 11- to 20-mm ovarian follicles in aged versus young mares (2.8 +/- 0.2 vs 5.3 +/- 0.1, respectively), but there was no difference (P>0.10) in the total number of ovarian follicles in aged versus young mares (21.0 +/- 0.3 vs 26.1 +/- 0.2, respectively) during the pooled periovulatory period of the first and second (single) ovulations. The number of ovulatory cycles during the study period was less (P=0.01) for aged versus young mares (2.2 +/- 0.3 vs 3.2 +/- 0.3). Plasma progesterone concentrations on Days 10 and 15 of the first ovulatory cycle were higher (P<0.05) in aged versus young mares.     

Delayed treatment with GnRH agonist, hCG and progesterone and reduced embryonic mortality in buffaloes

The present study examined the effect of delayed treatment with tropic hormones and progesterone (P₄) on embryonic mortality in buffaloes. Buffaloes with a conceptus on Day 25 after AI were assigned to the following treatments: Control (n = 41), i.m. physiological saline; GnRH agonist (n = 36), i.m. 12 μg buserelin acetate; hCG (n = 33), i.m. 1500 IU hCG; P₄ (n = 38), i.m. 341 mg P₄ every 4 days on three occasions. Control buffaloes had an embryonic mortality of 41.4% (17/41) between Days 25 and 45, and this was reduced (P < 0.01) by treatment with GnRH agonist (11.1%, 4/36), hCG (9.0%, 3/33) and P₄ (13.1%, 5/38). On Day 45, buffaloes treated with hCG and which ovulated had greater (P < 0.05) concentrations of P₄ in whey (453 ± 41 pg/ml) than buffaloes in the same treatment that did not ovulate (297 ± 32 pg/ml). A similar but non-significant trend was observed for buffaloes treated with GnRH agonist. It was concluded from the findings that the treatment of buffaloes on Day 25 after AI with tropic hormones or P₄ is beneficial to processes associated with embryonic implantation.     

Pregnancy patterns during the early fetal period in high producing dairy cows treated with GnRH or progesterone

In order to explore pregnancy patterns in high producing dairy cows treated with GnRH or progesterone at pregnancy diagnosis (Days 28-34), two consecutive experiments were designed. In Experiment 1, cows bearing a single embryo were randomly assigned to a PRID (n = 40; cows fitted with a progesterone releasing intra-vaginal device for 28 days), GnRH (n = 40; cows receiving GnRH) or Control (n = 26; untreated cows) group. PRID treatment led to a rise in plasma progesterone concentrations in the 7 days following the onset of treatment compared to the other two groups. In Experiment 2, in which we also examined twin pregnancies, animals were randomly assigned to PRID (n = 312) or GnRH (n = 294) treatment groups. Treatments were the same as described for Experiment 1. Logistic regression procedures revealed that in cows with a single corpus luteum, the probability of pregnancy loss between the first (Days 28-34) and second (Days 65-62) pregnancy diagnosis decreased by a factor of 0.51 in the PRID group compared to the GnRH group. However, in cows with two or more corpora lutea, PRID treatment increased the likelihood of pregnancy loss by a factor of three, compared to GnRH treatment. In cows carrying twins, the conceptus reduction rate was higher (P = 0.02) for the GnRH (36%) than for the PRID (16.4%) group. Formation of a new corpus luteum was recorded in 17.7% of cows in the GnRH group. Our results indicate that compared to GnRH treatment, progesterone treatment given at pregnancy diagnosis in high producing dairy cows, reduced by a factor of 0.51 and increased by a factor of 3 the probability of pregnancy loss in cows with a single or with two or more corpora lutea, respectively, and reduced the conceptus reduction rate in cows carrying twins. The practical implications of our findings are that in herds with a high incidence of early fetal loss of a non-infectious nature, treatment at the time of pregnancy diagnosis with PRID in cows with one corpus luteum and with GnRH in cows with two or more corpora lutea should offer considerable benefits.     

Embryonic loss in mares: Pregnancy rate, length of interovulatory intervals, and progesterone concentrations associated with loss during days 11 to 15

Pregnancy rates, length of interovulatory intervals, and progesterone concentrations were examined in mares which had ultrasonically detected collections of fluid in the uterine lumen and in mares which lost the embryonic vesicle during Days 11 to 15 and did not become pseudopregnant. In mares with embryonic loss, the loss rate for mares with re-established pregnancies (9 18 ) was greater (P<0.05) than the loss rate for all pregnancies (38 154 ), indicating repeatability. Pregnancy rates were higher (P<0.01) in controls (100 177 ) than in mares with intrauterine fluid collections (2 34 ) or mares with embryonic loss (10 33 ), excluding the pregnancy associated with embryonic loss. The mean length (days) of the interovulatory interval was reduced (P<0.05) in mares with intrauterine fluid collections (20.4 +/-0.9) and in mares with embryonic loss both for the intervals in which loss occurred (19.6 +/-0.7) and for intervals in which pregnancy was not detected (21.0 +/-1.0; controls, 23.5 +/-0.6). Mean progesterone concentration (ng/ml) on Day 7 was lower (P<0.05) in mares with intrauterine fluid collections (8.8 +/-1.8) and in mares with embryonic loss (12.1 +/-1.1) than in pregnant controls (17.2 +/-0.9) and nonpregnant controls (17.5 +/-0.1). The embryonic loss seemed attributable to uterine-induced luteolysis in association with uterine inflammation, but the possibility of involvement of a primary luteal inadequacy or other factors in at least some of the mares was not eliminated.     

Effects of ovarian input on GnRH and LH secretion immediately postovulation in pony mares

The potential involvement of ovarian factors in regulating GnRH and LH postovulation was studied in ovarian intact (Group 1; n=3) and ovariectomized (OVX; Group 2; n=3) mares (OVX within 12 hr of ovulation). Blood samples were collected every 10 min for 6 hr from jugular vein (JV) and intercavernous sinus (ICS) during estrus and on Day 8 postovulation for LH and GnRH analysis. Additionally, JV samples were collected twice daily (12-hr intervals) for 30 days for LH and progesterone (P4) analysis. A significant treatment x day effect (P<0.0001) describes declining plasma LH concentrations in intact mares, and regression analysis indicated that response curves were not parallel (P<0.001). Plasma LH concentrations remained elevated in OVX mares. LH increased further in OVX mares by Day 8 post-OVX (P<0.06), reflecting the increased (P<0.07) LH episode amplitude. GnRH decreased from estrus to Day 8 in both groups reflecting an effect of sampling period (P<0.03). GnRH episode amplitude declined (P<0.08) from estrus (62.8+/-3.1 pg/mL) to Day 8 (46.3+/-3.1 pg/mL) in OVX mares, but not in control mares (intact estrus, 36.5+/-6.4; intact Day 8, 37.5+/-7.3; OVX estrus, 62.8+/-3.1; OVX Day 8, 46.3+/-3.1 pg/mL). In conclusion, we propose that postovulatory LH decline requires ovarian feedback in mares, and that OVX alters GnRH secretory dynamics such that LH concentrations does not decline postovulation and, in fact, is further elevated with time after OVX.     

Follicular development and plasma concentrations of LH and prolactin in anestrous female dogs treated with the dopamine agonist cabergoline

The effect of a daily administration of a dopamine agonist (cabergoline, 5 microg/kg) for 4 weeks, starting about 95 days after the end of estrus on follicular development and its relationship with LH and prolactin secretion has been investigated in two groups of anestrous bitches (Beagles and Greyhounds). Pro-estrus was detected in 80% (8/10) of beagles and 50% (3/6) of treated greyhounds. The mean inter-estrus interval of treated animals was 132+/-5.0 and 169+/-7.0 days for beagles and greyhounds, respectively, and in both this differed significantly from the cycle preceding treatment (192+/-9.0 and 198+/-12.0 days) and from that in untreated bitches (194+/-11.0 and 196+/-11.0 days for beagles and greyhounds, respectively (all comparisons at P<0.001). The interval from the beginning of treatment to pro-estrus in responding animals was 13.3+/-1.90 days in beagles and 20.3+/-1.70 days in greyhounds. Cabergoline increased (P<0.001) the length of pro-estrus (10.6+/-0.50 and 11.7+/-0.50 days) in the treated estrus cycle compared to the previous estrus cycle (8.4+/-0.30 and 8.8+/-0.40 days for in beagles and greyhound, respectively). Ovarian enlargement and follicle development was detected by ultrasound in 90% of treated beagles and in 83% of greyhound between the second and third weeks of treatment, but only 80% of beagles and 66% of treated greyhound displayed pro-estrus and estrus. In the treated bitches, mean plasma LH increased (P<0.001) before pro-estrus. There was high variability in mean plasma prolactin levels between animals. These data indicate that the administration of the dopamine agonist cabergoline to anestrous bitches increases mean LH plasma levels and induces follicular development shortly before pro-estrus but this activity is not always followed by pro-estrus and estrus. Finally, prolactin per se does not have a prominent role in the control of folliculogenesis in the bitch.     

Pregnancy rates and sexual behavior under pasture breeding conditions in mares

Pony mares (n=480) and 16 stallions were assigned to four herds of 60 mares and one stallion (large herds) and to 12 herds of 20 mares and one stallion (small herds). The stallions remained with the herds continuously for all of the large herds and seven of the small herds. In the five remaining small herds the stallion was put into a herd for three hours every two days for 12 observation periods. Pregnancy rates and day of ovulation were estimated by size of embryonal enlargements. Mean pregnancy rates of 51% and 54% were obtained in the small herds and 42% in the large herds during a 48-day period (equivalent to two estrous cycles). Pregnancy rates for herds with the stallion present continuously were higher (P<0.01) for the small herds than for the large herds for days 1-24 (42% versus 19%). There was no effect of herd size on number of mares becoming pregnant per herd on days 1-24, but more mares (P<0.01) became pregnant during days 25-48 in the large herds (13.2 mares per herd versus 1.8). In the herds in which the stallion was present intermittently, the number of times that the stallion rebred the same mare when more than one mare was in estrus was greater (P<0.01) than what would be expected to occur by chance (observed, 21%; expected, 11%). Repeated breeding of the same mare seemed related to the availability or activity of the mare, since such mares more frequently followed and positioned themselves in the vicinity of the stallion. Most of the interferences by a mare which involved keeping the stallion and another mare apart were directed at the mare, whereas most of the interferences during mounting were directed at the stallion (P<0.01). Mares were more likely (P<0.01) to interfere when in estrus than when in nonestrus. When interfering mares were in nonestrus, their hostility was usually directed at the stallion (92%), whereas when in estrus their interference was more frequently directed at a mare (73%, P<0.01).     

GnRH treatment at artificial insemination in beef cattle fails to increase plasma progesterone concentrations or pregnancy rates

Treatment with GnRH at the onset of standing estrus increased pregnancy percentages and circulating concentrations of progesterone in repeat breeder dairy cows. The objective of this study was to determine the effect of treatment with GnRH at AI on concentrations of progesterone and conception rates in beef cattle that exhibited estrus. Two hundred ninety-three heifers at four locations were synchronized with the Select Synch plus CIDR protocol (given GnRH and a CIDR was placed into the vagina, and 7 d later, given PGF_2α and CIDR removed; n = 253) or the 14-19 melengestrol acetate (MGA) protocol (MGA fed at 0.5 mg/head/d for 14 d, with PGF_2α 19 d after MGA withdrawal n = 40) and AI was done after detection of estrus. At Location 1, blood samples were collected on Day 2, 4, 6, 10, 15, and 18 after AI (Day 0 = AI). Two hundred and fifty postpartum cows at two locations were synchronized with the Select Synch plus CIDR protocol, and AI was performed after detection of estrus. At AI, cattle were alternately assigned to one of two treatments: (1) treatment with GnRH (100 μg) at AI (n = 127 heifers and n = 108 cows); or (2) non-treated control (n = 120 heifers and n = 119 cows). Concentrations of progesterone tended to be greater in control heifers compared to GnRH-treated heifers on Days 6 (P = 0.08), 10 (P = 0.07), and 15 (P = 0.11). Overall conception rates were 68% and 66% for GnRH treated and control, respectively, and were not different between treatments (P = 0.72). In summary, treatment with GnRH at time of AI had no influence on conception rates in cattle that had exhibited estrus.     

Characterization of plasma progesterone concentrations for two distinct luteal morphologies in mares

Plasma progesterone concentrations in mares were determined in two experiments during the time that the luteal glands were detectable by transrectal ultrasonography. In both experiments, corpora lutea were classified into two tupes of morphologies based on their ultrasonic appearance: centrally nonechogenic luteal glands (fluid-filled) and uniformly echogenic luteal glands (non-fluid-filled). In Experiment 1, daily blood samples were taken from horse mares during August through October and May through July. There were no significant effects of season or luteal morphology on progesterone concentration. There was a significant main effect of day, but no day-by-season or day-by-morphology interactions. Progesterone increased significantly between Days 1 and 3 (mean progesterone concentration, 2.5 vs 5.2 ng/ml, respectively), between Days 3 and 4 (5.2 vs 7.8 ng/ml), and between Days 4 and 5 (7.8 vs 11.0 ng/ml). Progesterone did not decrease significantly until between Days 11 and 15 (11.6 and 6.1 ng/ml). Subsequent decreases occurred between Days 15 and 16 (6.1 vs 3.9 ng/ml), and Days 16 and 17 (3.9 vs 2.5 ng/ml). In Experiment 2, blood samples were obtained from pony mares at 1 2 - h intervals for 3 h before and 2 h after the defined onset of luteal development (end of evacuation of the ovulatory follicle). Additional blood samples were taken at 5, 8 and 12 h after the onset of luteal development, and thereafter at 12-h intervals for 5d. There were no significant differences between centrally nonechogenic luteal glands (n = 7) and uniformly echogenic luteal glands (n = 5) during the first 5 d of luteal development. There was no time-by-morphology interaction, but there was a significant time effect. The first significant increase in progesterone concentration occurred between Hours 12 and 24 (0.5 vs 1.1 ng/ml). Additional increases were detected between Hours 24 and 36 (1.1 vs 2.6 ng/ml), Hours 36 and 48 (2.6 vs 4.3 ng/ml), Hours 48 and 60 (4.3 vs 6.1 ng/ml), Hours 60 and 72 (6.1 vs 9.4 ng/ml), and Hours 72 and 96 (9.4 vs 13.8 ng/ml). The hypothesis was supported that fluid-filled corpora lutea do not differ from non-fluid-filled corpora lutea with regard to progesterone production.     

Effects of age and altrenogest treatment on conceptus development and secretion of LH, progesterone and eCG in early-pregnant mares

The treatment of early pregnant mares with a history of repeated early embryonic loss with the progestin altrenogest has become routine; however no controlled studies on the efficiency of altrenogest to prevent embryonic losses are available so far. In the present study, we have investigated effects of altrenogest treatment in mares on conceptus development and the secretion of LH, progesterone, and eCG until day 100 of pregnancy. In addition, differences related to age of mares were assessed. Mares were treated with altrenogest (0.044 mg/kg per os once daily) or sunflower oil (10 ml per os once daily) from day 6 to day 100 after ovulation. Blood samples for analysis of LH, progesterone, and eCG were collected. The size of the embryonic vesicle and embryo/fetus was determined by ultrasound. No difference in the per cycle pregnancy rate between altrenogest-treated (75%) and sunflower oil-treated mares (74%) was detected (n.s.). A significant effect of age but not of altrenogest treatment on mean diameter of the embryonic vesicle was found between days 12 and 22 of pregnancy (e.g. day 15: control, 4-8 years: 22.9 ± 1.0 mm, >8 years: 22.0 ± 1.7 mm, altrenogest, 4-8 years: 26.1 ± 2.0 mm, >8 years: 20.4 ± 1.0 mm, P < 0.05). A significant effect of age and treatment on size of the embryo proper between days 30 and 45 was detected (P < 0.05). In the control group but not in the altrenogest group, size of the embryo proper respective fetus was negatively correlated with age of the mares (day 30: r = −0.834, P < 0.05; day 35: r = −0.506, P < 0.05). Plasma concentrations of LH and progesterone were neither effected by age nor by treatment of mares, but significant effects of age and altrenogest treatment on eCG concentrations between days 40 and 130 were detected (P < 0.05). The present study demonstrates for the first time a positive influence of altrenogest-treatment on a retarded development of the embryo respective fetus around the beginning of placentation in mares older than 8 years.     

Regulation of LH beta subunit mRNA in immature female rats during GnRH agonist treatment

In order to determine the changes in the expression of LH beta messenger ribonucleic acid (mRNA) during GnRH agonist (GnRHa) treatment (0.94 mg/28 days), the concentration of the mRNA of LH beta was assessed together with the serum LH concentration, pituitary LH content and LH response to GnRH at various times during long-acting GnRHa treatment in immature female rats. The serum LH concentration was increased at hour 1, gradually decreased starting at approximately hour 3 and had returned to the control level on day 28. Pituitary LH began to decrease at hour 3. The concentrations of LH beta mRNA were not significantly different from those in the control group from hour 1 to hour 18, but were lower from day 3 to day 28. Serum LH response to native GnRH (1 micrograms) began to be inhibited on day 7. These results indicate that the short term treatment with GnRHa stimulates the release of preformed LH rather than synthesis of LH beta mRNA and that the long term treatment inhibited the expression of LH beta mRNA in a time dependent manner.     

The effect of exogenous progesterone on plasma LH and milk progesterone concentrations in multiple-suckling post-partum cows

Fourteen Friesian cows each suckling four calves were treated for a 7-day period (a) between days 20–40 post partum with progesterone-releasing intravaginal devices (PRID) containing 2% progesterone (Group 1; n = 5), (b) between days 51–264 post partum with PRIDS containing 2% progesterone (Group 2; n = 6) and (c) between days 29–214 days post partum with PRIDS containing 0% progesterone (Group 3; n = 3). Mean plasma LH concentrations decreased during PRID treatment in Group 2 cows only and pre-ovulatory LH surges were observed in $\text{5}\text{6}$ of these cows between 38 and 84 h after coil removal. All Group 2 cows underwent at least one ovarian cycle following PRID removal. No pre-ovulatory LH surges were observed in either Group 1 or Group 3 cows and only one cow (Group 3) underwent an ovarian cycle after treatment. It is suggested that there is an increase in pituitary responsiveness to the feedback effects of progesterone during the post-partum period.     

Time-course relationships between serum LH, serum progesterone and urinary preganediol concentrations in normal women

A specific and sensitive gas chromatographic method was used to investigate the concentration of pregnanediol glucuronide in urine in relation to the time of ovulation. Serum LH and progesterone concentrations in the same subjects were used as evidence for the occurrence of ovulation. The urinary concentration of pregnanediol glucuronide in 24-hour collections and in overnight specimens increased 2-fold or more from the day of the midcycle LH peak to the time of predicted ovulation (24-48 hour after the LH peak) in parallel with the rise in serum progesterone concentration.     

Effect of exogenous progesterone on pregnancy rates after surgical embryo transfer in mares

A completely randomized experimental design was used to investigate the effect of supplemental progesterone on pregnancy rates of recipient mares. Every other recipient mare received daily 200 mg progesterone in oil beginning the day of surgical embryo transfer and lasting until either Day 120 of pregnancy or until pregnancy failure was confirmed by ultrasound. Progesterone supplementation did not affect pregnancy rate (P > 0.05). Overall, embryos that did not result in pregnancy were of greater mean diameter than embryos that resulted in pregnancy (P < 0.05). Pregnancy rates tended (P < 0.1) to be greater in recipients that were detected to be ovulating the same day or prior to that of the donor and that had been supplemented with progesterone (75 %) as opposed to untreated control mares of the same synchrony group (40 %). Progesterone supplementation did not affect the incidence of embryonic loss; however, there was a slightly higher loss of pregnancies between Day 15 and 30 in treated versus untreated recipients. There was no effect (P > 0.05) of treatment on pregnancy rate for embryos recovered from fertile versus subfertile donor mares. However, overall, there tended (P < 0.1) to be fewer pregnancies with embryos recovered from subfertile (50 %) as compared to fertile donors (75 %). It was concluded that supplemental progesterone at the dosage and frequency described was not beneficial in improving pregnancy rates in cyclic recipient mares after surgical embryo transfer.     

Role of luteinizing hormone in follicle deviation based on manipulating progesterone concentrations in mares

The effects of several doses of progesterone on FSH and LH concentrations were used to study the role of the gonadotropins on deviation in growth rates of the two largest follicles during the establishment of follicle dominance. Progesterone was given to pony mares at a daily dose rate of 0 mg (controls), 30 mg (low dose), 100 mg (intermediate dose), and 300 mg (high dose). All follicles > or = 6 mm were ablated at Day 10 (Day 0 = ovulation) to initiate a new follicular wave; prostaglandin F(2alpha) was given to induce luteolysis, and progesterone was given from Days 10 to 24. The low dose did not significantly alter any of the ovarian or gonadotropin end points. The high dose reduced (P < 0.05) the ablation-induced FSH concentrations on Day 11. Maximum diameter of the largest follicle (17.2 +/- 0.6 mm) and the second-largest follicle (15.5 +/- 0.9 mm) in the high-dose group was less (P < 0.04) than the diameter of the second-largest follicle in the controls (20.0 +/- 1.0 mm) at the beginning of deviation (Day 16.7 +/- 0.4). Thus, the growth of the two largest follicles was reduced by the high dose, presumably through depression of FSH, so that the follicles did not attain a diameter characteristic of deviation in the controls. The intermediate dose did not affect FSH concentrations. However, the LH concentrations increased in the control, low, and intermediate groups, but then decreased (P < 0.05) in the intermediate group to pretreatment levels. The LH decrease in the intermediate group occurred 2 days before deviation in the controls. The maximum diameter of the largest follicle was less (P < 0.0001) in the intermediate group (27.3 +/- 1.8 mm) than in the controls (38.9 +/- 1.5 mm), but the maximum diameter of the second-largest follicle was not different between the two groups (19.0 +/- 1.1 vs. 20.3 +/- 1.0 mm). Thus, the onset of deviation, as assessed by the second-largest follicle, was not delayed by the decrease in LH. Diameter of the largest follicle by Day 18 in the intermediate group (23.1 +/- 1.6 mm) was less (P < 0.05) than in the controls (28.0 +/- 1.0 mm). These results suggest that circulating LH was not involved in the initiation of dominance (inhibition of other follicles by the largest follicle) but was required for the continued growth of the largest follicle after or concurrently with its initial expression of dominance.