Follicle Development during Luteal Phase and Altrenogest Treatment in Pigs

Synchronization of the oestrous cycle of gilts using altrenogest treatment has been found to increase ovulation rate. The current experiment investigated if the increase in ovulation rate after altrenogest treatment is related to increased follicle size at the end of altrenogest treatment compared with late luteal phase follicles. Crossbred gilts (n = 15) received altrenogest during 18 days [20 mg Regumate (Janssen Animal Health, Beerse, Belgium)], starting 5-7 days after onset of first oestrus. Control gilts (n = 15) did not receive altrenogest. At days 10-12 of the oestrous cycle [i.e. in the presence of corpora lutea (CL)], average follicle development was 2.51 +/- 0.20 mm (assessed with ultrasound) in altrenogest-treated gilts and 2.58 +/- 0.16 mm in control gilts (p > 0.10). During the last days of altrenogest treatment (i.e. when CL had gone into regression), average follicle size had increased to 3.01 +/- 0.31 mm (p < 0.05). Subsequent ovulation rate was 16.6 +/- 1.7 in altrenogest treated gilts and 15.1 +/- 1.2 in control gilts (p < 0.05). Altrenogest treatment resulted in increased follicle size after regression of the CL, showing that suppression of follicle growth by altrenogest alone is less severe than suppression by endogenous progesterone (either with or without altrenogest). Altrenogest treatment also resulted in a higher ovulation rate. However, it is unclear if the increased follicle size and higher ovulation rate after altrenogest treatment are causally related, as the relation between the two on an animal level was not significant.     

Efficacy of altrenogest administration to postpone ovulation and subsequent fertility in mares

A recent report suggested administration of altrenogest during the follicular phase could postpone ovulation. Based on these results, two questions were generated. We first hypothesized that by initiating a altrenogest treatment earlier in the estrous cycle, a greater and/or more consistent delay in ovulation would result. Second, we hypothesized that exposure to elevated progestin concentrations might alter viability of the ovulatory follicle and oocyte. The focus of the first experiment was to determine if initiation of altrenogest treatment at different stages of the estrous cycle would yield a more predictable time to ovulation, whereas the second experiment was designed to determine whether mares receiving altrenogest during estrus had compromised fertility. In the first experiment thirty mares of mixed light breed, ranging in age from 5-15 years, were randomly assigned to one of three groups. The two treated groups received altrenogest (0.088 mg/kg of body weight) for two days once a follicle of 30 or 35 mm in diameter was detected. Control mares were not treated. Mares treated with altrenogest whether initiated at the detection of a 30 or 35 mm follicle demonstrated similar (P>.05) day to ovulation interval when adjusted to 35 mm (5.4 and 5.6 days, respectively). Both treated groups demonstrated a delayed interval (P<.05) when compared to control (3.9 days). Thirty-six mares of similar breed and age, were randomly assigned to two groups for use in the second experiment. All mares were monitored daily via transrectal ultrasonography from the time a 35 mm or greater follicle was detected until ovulation. Treated mares received daily doses of altrenogest (0.088 mg/kg of body weight) for two days once a follicle of 35 mm or greater was detected. Control mares received no treatment. Fertility data were collected from mares inseminated every other day with 500 million motile spermatozoa from one of two stallions with proven fertility. Pregnancy data were collected via transrectal ultrasonography at days 12, 14 and 16 post-ovulation. Ovulation data were collected from 27 control cycles and 26 treated cycles. Contrary to previous reports and Experiment 1, no difference (P=0.35) was noted between groups with respect to days to ovulation. Control mares averaged 4.14 days and treated mares averaged 4.7 days to ovulation from initial detection of a 35 mm follicle. Fertility data were also similar (P=0.8) between control and treated mares (66.6% and 61.5% per cycle, respectively). Interestingly, a greater number (P=0.017) of treated cycles (5/26) resulted in follicular regression than did control cycles (0/27). While these data suggest that this dosage of altrenogest may not postpone ovulation, it did appear related to increased incidence of follicular regression. Fertility was unaffected, however, in those mares that ovulated. Further studies are needed in which initiation at different stages of estrus and different doses of altrenogest are used.     

Evaluation of Injectable Sustained Release Progestin Formulations for Suppression of Estrus and Ovulation in Mares

Thirty-one mares were used in an experiment to evaluate the effectiveness of three sustained-release injectable formulations of altrenogest and one formulation of medroxyprogesterone acetate (MPA) for long-term suppression of estrus and ovulation. Luteolysis was induced by injection of prostaglandin-F_2α (Lutalyse) on day 0 (6th day after the previous ovulation) and was immediately followed by treatment with 1) no injection (controls; n = 7), 2) 1.5 mL of an altrenogest solution in sustained-release vehicle (LA 150, 1.5 mL; 225 mg altrenogest; n = 6), 3) 3 mL (450 mg altrenogest) of the same solution (n = 6), 4) 500 mg altrenogest in lactide-glycolide microparticles suspended in 7-mL vehicle (MP 500; n = 6), or 5) 1.0 g MPA as a 5-mL suspension. Mares were checked for estrus daily, and their ovaries scanned every other day until a 25-mm or greater follicle was detected, after which they were scanned daily. Control mares returned to estrus an average of 3.9 days after Lutalyse administration; all the single-injection altrenogest formulations increased (P < .05) the days to return to estrus, with the greatest increase occurring in mares receiving MP 500. Return to estrus was not affected by MPA treatment. Time of ovulation was determined by serial ultrasound scans and confirmed by daily plasma luteinizing hormone (LH) and progesterone concentrations. Control mares ovulated an average of 8.8 days after Lutalyse administration. Treatment with 1.5 or 3 mL of LA 150 increased (P < .05) the mean days to ovulation to 16.5 and 21.2 days, respectively; MP 500 increased (P < .05) the days to ovulation to 33.5 days. Administration of MPA did not affect (P > .1) days to ovulation relative to control mares. The MP 500 treatment provided long-term suppression of estrus and ovulation and could prove useful for that purpose. Treatment with the LA 150 solutions provided shorter-term suppression, and a relatively tight grouping of the individual mares around the mean days to ovulation; these one-shot formulations could be useful for synchronizing ovulation in cyclic mares and inducing normal estrous cyclicity in vernal transitional mares exhibiting erratic, anovulatory estrous periods.     

Efficacy of short-term administration of altrenogest to postpone ovulation in mares

Estrogen from a growing follicle stimulates the preovulatory surge of luteinizing hormone (LH) while progesterone (P) is known to suppress LH. The possibility exists that administration of P, in the presence of an ovulatory follicle, would sufficiently suppress LH and, therefore, delay ovulation. The objective of this research was to elucidate the potential for oral administration of altrenogest (17-Allyl-17β-hydroxyestra-4,9,11-trien-3-one) to postpone ovulation of a preovulatory follicle (35 mm) for approximately two days. Fourteen light-horse mares, ranging in age from two to 19 years, were randomly assigned to one of three treatments (A-.044 mg/kg BW altrenogest for two days; B-.088 mg/kg BW altrenogest for two days; and C- no altrenogest). Mares began treatment when a 35-mm or greater follicle was observed via real-time transrectal ultrasonography. Both number of days until ovulation and follicular maintenance differed between treated and control mares. Number of days until ovulation was increased (P<.05) for mares in treatment A when compared with the control mares. Follicular diameter maintenance, a measurement of follicular diameter throughout treatment, also increased (P<.05) for mares in treatment A when compared with the control mares. Mean LH concentration was not different between mares treated with altrenogest at either treatment dose when compared with the control mares. Pregnancy rates and embryonic vesicle size change were also measured to determine potential effects of altrenogest administration. No differences (P>.05) were found in either characteristic.Short-term administration of altrenogest increased the number of days to ovulation. Further study is warranted to prove conclusively that altrenogest increases follicular maintenance, alters the preovulatory LH surge, and has no detrimental effects upon reproductive efficiency.     

Efficacy of Medroxyprogesterone Acetate in Suppression of Estrus in Cycling Mares

The effects of compounded medroxyprogesterone acetate (MPA) on follicular activity and estrous behavior were evaluated. Eighteen cycling mares were assigned to one of three treatment groups. Mares in the MPA group (n = 6) were injected intramuscularly with 1,600 mg MPA (week 1), then 400 mg weekly for the next 5 weeks. Saline mares (n = 6) were injected intramuscularly weekly for 6 weeks. Altrenogest mares (n = 6) received 10 mL orally daily for 7 weeks. Mares were teased daily for 60 days and categorized as displaying estrous, diestrous, or neutral behavior. Transrectal ultrasound examinations were performed three times weekly, or daily when a 30-mm follicle was identified, until ovulation. Blood samples were harvested weekly for analysis of progesterone concentration and daily from days 14 to 23 for analysis of luteinizing hormone (LH) concentration. Mares treated with saline or MPA showed normal intervals of diestrus and estrus during the study. All altrenogest mares showed behavioral diestrus during treatment. All mares in the saline and MPA groups showed normal follicular development and ovulations. No altrenogest mares ovulated during treatment; four mares returned to estrus and resumed normal follicular development after treatment ceased. Progesterone analyses agreed with transrectal ultrasonographic ovarian activity for all mares. LH levels were lower for altrenogest-treated mares compared with MPA-treated and saline-treated mares during the treatment period. In conclusion, compounded MPA at dose rates and intervals used in this study was not effective in suppression of estrus, follicular development, or LH secretion in mares.     

Effects of a synthetic progestogen, altrenogest, on oestrus synchronisation and fertility in miniature pigs

Groups of six, six and eight miniature gilts, respectively, received 5, 10 or 15 mg/day of altrenogest for 18 days, and the numbers of corpora lutea and residual follicles were counted approximately 14 days after the treatment by an exploratory laparotomy. They were compared with the numbers in a control group of eight gilts which were examined six to eight days after oestrus. The interval between the last dose of altrenogest and the onset of oestrus increased with the dose of altrenogest, and was significantly longer after the treatments with 10 or 15 mg/day than after 5 mg/day (P < 0.01). Significantly more corpora lutea were observed in the gilts receiving 5 or 10 mg/day of altrenogest than in the control gilts (P < 0.1). Groups of six, seven and six miniature gilts that had respectively received 5, 10 or 15 mg/day of altrenogest were artificially inseminated; four, six and five of the gilts in these groups farrowed, and their mean (sd) litter sizes were 5.5 (2.4), 6.8 (1.2) and 5.0 (2.3), respectively. All six of a group of control gilts farrowed and their mean litter size was 5.8 (1.2).     

Effects of a gonadotropin-releasing hormone antagonist and altrenogest on luteinizing hormone concentration and ovulation in the mare

The objective of Experiment 1 was to determine a dose and frequency of gonadotropin-releasing hormone (GnRH) antagonist administration to effectively suppress serum luteinizing hormone (LH) concentration and to delay ovulation when administered to mares. The objectives of Experiment 2 were 1) to determine the effects of subcutaneous or intravenous administration of a GnRH antagonist or oral altrenogest on serum LH concentration in the estrual mare; and 2) to determine the effectiveness of human chorionic gonadotropin (hCG) in inducing ovulation in mares with suppressed LH concentrations. In Experiment 1, mares (N = 20) were randomly assigned and treated with either 5% mannitol (control, single subcutaneous injection, 1 mL, at time 0; n = 5); low-dose GnRH antagonist (single subcutaneous injection, 0.01 mg/kg, at time 0; n = 5); frequent low-dose GnRH antagonist (subcutaneous injections, 0.01 mg/kg, at 0, 6, 18, and 24 hours; n = 5); or high-dose GnRH antagonist (single subcutaneous injection, 0.04 mg/kg, at time 0; n = 5). Both the frequent low-dose and high-dose GnRH antagonist treatments resulted in significantly lower LH concentrations compared with controls at 90, 102, and 114 hours after treatment (P < .05). In Experiment 2, mares (N = 38) were randomly assigned and treated with subcutaneous sterile saline (control), altrenogest (oral), subcutaneous GnRH antagonist, or intravenous GnRH antagonist. LH concentration for the altrenogest group was lower than the control group at 3, 4, 18, and 30 hours after treatment (P < .05). LH concentration for both the subcutaneous and intravenous GnRH antagonist groups were lower compared with the control group at several time points (P < .05). Based on these data, dose but not frequency of administration of a GnRH antagonist lowered LH concentration in the estrous mare but did not delay ovulation. In addition, serum LH concentrations can be lowered and ovulation effectively postponed in mares treated with altrenogest followed by administration of hCG. This indicates that serum LH concentrations can be lowered and ovulation effectively postponed in mares treated with altrenogest followed by administration of hCG.     

Effect of deslorelin acetate on gonadotropin secretion and ovarian follicle development in cycling mares

OBJECTIVE: To evaluate gonadotropin secretion and ovarian function after administration of deslorelin acetate to induce ovulation in mares. DESIGN: Randomized controlled trial. ANIMALS: 16 healthy mares with normal estrous cycles. PROCEDURE: 8 control mares were allowed to ovulate spontaneously, whereas 8 study mares received deslorelin to induce ovulation when an ovarian follicle > 35 mm in diameter was detected. Follicle development and serum concentrations of gonadotropins were monitored daily during 1 estrous cycle. Pituitary responsiveness to administration of gonadotropin-releasing hormone (GnRH) was evaluated 10 days after initial ovulation. RESULTS: Interovulatory intervals of mares treated with deslorelin (mean +/- SD, 25.6 +/- 2.6 days) were longer than those of control mares (22.9 +/- 1.8 days). Diameter of the largest follicle was significantly smaller during 2 days of the diestrous period after ovulation in deslorelin-treated mares than in control mares. Concentrations of follicle-stimulating hormone (FSH) were lower in deslorelin-treated mares on days 5 through 14 than in control mares. Concentrations of luteinizing hormone were not different between groups during most of the cycle. Gonadotropin release in response to administration of GnRH was lower in mares treated with deslorelin acetate than in control mares. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of deslorelin was associated with reduction in circulating concentrations of FSH and gonadotropin response to administration of GnRH during the estrous cycle. Low concentration of FSH in treated mares may lead to delayed follicular development and an increased interovulatory interval.     

The probable identification of monozygous twin embryos in mares

Observations based upon ultrasonic examination in early pregnancy of over 6000 brood mares between 1988 and 1995 identified 956 sets of multiple pregnancies. Ovaries of all mares were examined during estrus and up to four days after ovulation, and again at early (13 to 17 days) and later pregnancy diagnoses. By detailed recording of all identifiable follicles and corpora lutea, it was concluded that 18 twin and seven triplet pregnancies resulted from only single and double ovulations, respectively. The apparent incidence of monozygous twin embryos was at least 2.6%.     

Uterine clearance mechanisms during the early postovulatory period in mares

Uterine response to inoculation with Streptococcus zooepidemicus organisms, 51Cr-labeled 15-microns microspheres, and charcoal was evaluated in 9 mares (4 resistant and 5 susceptible to endometritis) to determine mechanical and cellular clearance rates during the early postovulatory period. Mares were inoculated at estrus prior to ovulation during estrous cycles 1, 3, and 5. Uterine swab specimens for aerobic and anaerobic bacteriologic culture and serum for progesterone determination were obtained on postovulation day 3 during estrous cycle 1, on the day of ovulation during estrous cycle 3, and on postovulation day 5 during estrous cycle 5. Immediately thereafter, the uterus was irrigated with 50 ml of sterile physiologic saline solution containing tracer amounts of 125I-labeled human serum albumin. Streptococcus zooepidemicus was isolated from 10 of 15 (67%) uterine specimens collected from susceptible mares and incubated aerobically. Escherichia coli also was isolated from 2 of the 10 specimens incubated aerobically. Anaerobic bacteriologic culture of specimens from all mares yielded no growth. Chromium-labeled microspheres were recovered twice from 2 susceptible mares, on day 0 and day 5. Charcoal was retained in 5 specimens collected from 3 susceptible mares. Bacteriologic culture of specimens from resistant mares did not yield growth. On day 0, chromium-labeled microspheres and charcoal were recovered once from 1 resistant mare. Mares susceptible to endometritis accumulated more fluid within the uterine lumen after ovulation than did resistant mares (mean +/- SEM, 52.73 +/- 15.22 ml and 7.41 +/- 1.96 ml, respectively; P less than 0.01). From this study, it appeared that uterine cellular and bactericidal mechanisms are dysfunctional during the early postovulatory period. However, there appeared to be no disruption of the mechanisms responsible for mechanical clearance of materials inoculated in the uterus.     

Luteotropic influence of the ovine uterus.

Preliminary observations indicated that the ovine uterus might play a contributing role in the development of the corpus luteum. In order to better define this putative relationship, we monitored luteal function in mature ewes that were hysterectomized or sham-operated at different intervals following induction of ovulation. Corpora lutea formed following hysterectomy carried out immediately after ovulation were subnormal. Circulatory concentrations of progesterone in these animals began to ascend normally, but then achieved a plateau level less than that of control animals. This was attributed to reduced size of the luteal gland, and not to anomalies per unit tissue in morphology or content of progesterone. Luteal activity was not altered in ewes hysterectomized later in the estrous cycle (Day 5). However, when such a luteal phase was terminated by exogenous luteolysin, corpora lutea formed subsequently were defective. It appears that the ovine uterus produces a hormonal factor during metestrus that augments the growth potential of the corpus luteum.     

Effect of Chronic Administration of Oxytocin on Corpus Luteum Function in Cycling Mares

The objective of this study was to determine if intramuscular administration of 60 units of oxytocin once daily for 29 days, regardless of when treatment was initiated during the estrous cycle (i.e., without monitoring estrous behavior and/or detecting ovulation), would induce prolonged corpus luteum (CL) function in cycling mares. Mares were randomly assigned to two groups: (1) saline-treated control (n = 7) and (2) oxytocin-treated (n = 9) subjects. Control mares received 3 cc of saline, and oxytocin-treated mares received 60 units (3 cc) of oxytocin intramuscularly for 29 consecutive days. Treatment was initiated in all mares on the same day (day 1), independent of the day of the cycle. Jugular blood samples for determination of progesterone concentration were collected three times weekly (M, W, and F) for 21 days before treatment was initiated to confirm that all mares had a luteal phase of normal duration immediately before treatment. Beginning on the first day of treatment, blood samples were collected daily for eight days and then three times weekly through day 80. Mares were considered to have prolonged CL function if serum progesterone remained >1.0 ng/mL continuously for at least 25 days after the end of the treatment period. The proportion of mares with prolonged CL function was higher in the oxytocin-treated group than in the saline-treated group (7/9 vs. 1/7, respectively; P < .05). Three of the seven oxytocin-treated mares that developed prolonged CL function initially underwent luteolysis within 4–7 days of the start of oxytocin treatment and then developed prolonged CL function after the subsequent ovulation during the treatment period. In the other four oxytocin-treated mares that developed prolonged CL function, progesterone remained >1.0 ng/mL throughout the treatment period and into the post-treatment period. All mares with prolonged CL function maintained elevated progesterone concentrations through at least day 55 of the study. In conclusion, intramuscular administration of 60 units of oxytocin for 29 consecutive days effectively prolonged CL function in mares, regardless of when treatment was initiated during the estrous cycle. Importantly, this represents a protocol for using oxytocin treatment to prolong CL function that does not require detection of estrous behavior or day of ovulation.     

Corpus Luteum Vascularization and Progesterone Production in Autumn and Winter Cycles of the Mare: Relationship Between Ultrasonographic Characteristics of Corpora Lutea and Plasma Progesterone Concentration in the Last Cycles Before Anestrus

In 20 estrus cycles of 15 mares, Color Doppler ultrasound of corpora lutea and plasma progesterone concentration (P4) was analyzed on days 6, 10, 14, 16, and 18 after ovulation. Progesterone concentration was positively correlated with corpora lutea cross-sectional area (CSA), vascularized area (VA), and index of vascularization (IV = VA/CSA) (P < .0001). Cross-sectional area, VA, and IV in corpora lutea of mares with P4 < 1 ng/mL were significantly lower than in corpora lutea of mares with P4 > 1 ng/mL. Mares with CSA < 3,473 pixels, VA < 25.5 pixels, and IV < 7.6% were prone to express P4 < 1 ng/mL 25.4, 7.9, and 7.6 times more than mares with higher values, respectively. Corpus luteums analyzed parameters differed significantly between last cycles (LCs) of the breeding season and previous cycles until day 14 after ovulation (P < .05). No significant differences were found in P4 between LCs and previous ones.     

Flushing and altrenogest affect litter traits in gilts

Gilts (n = 267) were allotted to flushing (1.55 kg/d additional grain sorghum), altrenogest (15 mg.gilt-1.d-1) and control treatments in a 2 x 2 factorial arrangement. Altrenogest was fed for 14 d. Flushing began on d 9 of the altrenogest treatment and continued until first observed estrus; 209 gilts (78%) were detected in estrus. The interval from the last day of altrenogest feeding to estrus was shorter (P less than .05) with the altrenogest + flushing treatment (6.6 +/- .2 d) than with flushing alone (7.6 + .3 d). Ovulation rates (no. of corpora lutea) were higher (P less than .05) in all flushed gilts (14.5 +/- .4 vs 13.4 +/- .4), whether or not they received altrenogest. Flushing also increased the total number of pigs farrowed (.9 pigs/litter; P = .06) and total litter weight (1.43 kg/litter; P = .01), independent of altrenogest treatment. Number of pigs born alive and weight of live pigs were higher for gilts treated with altrenogest + flushing and inseminated at their pubertal estrus than for gilts in all other treatment combinations. In contrast, gilts receiving only altrenogest had greater live litter weight and more live pigs born when inseminated at a postpubertal estrus than when inseminated at pubertal estrus. We conclude that flushing increased litter size and litter weight, particularly for gilts that were inseminated at their pubertal estrus. Increased litter size resulted from increased ovulation rates, which, in nonflushed gilts, limited litter size at first farrowing.     

Relationship between pharmacological induction of estrous and/or ovulation and twin pregnancy in the Thoroughbred mares

The aim of this study was to evaluate the possible relationship of pharmacological induction of estrous and/or ovulation with the occurrence of twin pregnancies in Thoroughbred mares. Out of 680 mares, 356 received one of the following treatments during the estrous cycle in which they became pregnant: injection of 0.5mg of cloprostenol at the ultrasonographic detection of a CL (n=86); injection of 5000 IU human chorionic gonadotropin (hCG) immediately before mating (n=221); injection of 0.5mg of cloprostenol at the ultrasonographic detection of a CL plus injection of 5000 IU hCG immediately before mating on cloprostenol-induced estrous (n=49). The other 324 mares, not treated for induction of estrous or ovulation in the estrous cycle resulting in pregnancy, were used as control group. The occurrence of twin and single pregnancies in treated and control mares underlines that the percentage of twin pregnancy in treated mares (16.6%) was statistically significantly higher (P<0.0001; odds ratio, OR=2.87) than the percentage of twinning in the control group (6.5%). Comparison of the occurrence of twins between treatments revealed a statistically significant difference between mares treated with hCG alone compared to animals given prostaglandin F2alpha (PGF2alpha) plus hCG. The results show a statistically significant difference for each treatment compared to controls, with the least difference (P<0.05; OR=2.18) for the comparison between hCG treatment group and controls, a significance of P<0.01; OR=3.05 for the comparison between PGF2alpha treatment and controls, and a highly statistically significant difference (P<0.0001; OR=6.37) for the comparison between PGF2alpha plus hCG-treated animals and controls.     

Effect of transportation on the estrous cycle and concentrations of hormones in mares

Effect of transportation on estrous behavior, duration of the estrous cycle, ovulation, pregnancy rates and concentrations of serum cortisol, plasma ascorbic acid (AA), LH, estradiol and progesterone in mares was investigated. Fifteen mares were transported for 792 km (12 h) during the preovulatory stage of estrus. Transported mares were bled immediately before transport (baseline), at midtrip and 0, 12, 24, 48 and 72 h post-transport and twice daily from d 1 before transport to d 1 (estrogen) or 3 (LH) post-ovulation. Blood samples also were taken for progesterone on d 0, 2, 6, 10, 15, 16, 17, 18, 19 and 20 post-ovulation. Nontransported control mares (n = 15) were bled on the same schedule as transported mares. There was no difference (P greater than .05) in number of mares ovulating, estrous behavior, duration of the estrous cycle or pregnancy rate between groups. Cortisol in transported mares increased to concentrations greater (P less than .05) than those in control mares at midtrip and 0 h post-transport. Concentrations of AA in transported mares also increased (P less than .05) at midtrip, then decreased (P less than .05) below baseline at 24 h post-transport. Concentrations of LH and estradiol increased (P less than .05) above baseline throughout the blood-sampling period. Increases apparently were due to preovulatory surges of these hormones. Increase in LH concentrations in transported mares, however, was greater (P less than .05) than that in control mares at 0 h post-transport.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased ovulation rate of adult ewes treated with anti-bovine LH antiserum during the normal breeding season

Adult Suffolk ewes (n = 14) were treated on d 10 of the estrous cycle with anti-bovine luteinizing hormone (LH) antiserum. Control ewes (n = 10) were treated with normal horse serum. Estrous behavior and the number of corpora lutea and ovarian follicles were examined at the subsequent estrous cycle. Daily plasma concentrations of progesterone (P4), follicle stimulating hormone (FSH) and estradiol were determined before and after treatment. Ewes treated with antiserum had a higher (P less than .05) ovulation rate (2.7 +/- .2) than did controls (2.1 +/- .1). No differences were found in the numbers of large (greater than 5 mm) or small (less than 5 mm) follicles between treatment groups. Estrus was delayed (P less than .025) approximately .6 d/in ewes treated with antisera. Immunoreactive FSH increased (P less than .05) within 1 d after treatment and remained higher than the controls for 5 d. Peak estradiol concentrations occurred on d 17 for treated ewes compared with peak concentrations on d 15 or 16 for control ewes. The P4 concentrations were generally less (P less than .025) in treated ewes throughout the luteal phase of the treatment cycle. These data demonstrate that ovulation rate is increased in ewes treated with LH antiserum. The marked increase in plasma FSH suggests a possible mechanism whereby ovulation rate is enhanced.     

Clinical experience with deslorelin (ovuplantTM) in a kentucky thoroughbred broodmare practice (1999)

Palpation records of 155 Throughbred broodmares maintained on one of seven farms (3–80 mares per farm) that were administered deslorelin on one or more estrous cycles (204 treated cycles) during the 1999 breeding season were retrospectively examined. Some deslorelin-treated mares were also treated with hCG (2500 units intravenously), or had no ovulation-inducing drugs administered, during different estrous cycles of the same season. Most mares were treated with an ovulation- inducing drug after returning to their resident farm following breeding and were subsequently examined by transrectal ultrasonography daily until ovulation was confirmed, and again 13–14 and 15–16 days after ovulation for determination of pregnancy status.Per-cycle pregnancy rate for all 155 mares bred was 53%, and for all deslorelin breeding was 57%. Per-cycle pregnancy rates for mares ovulating 0–1 days, 1–2 days, and 2–3 days after treatment with deslorelin did not differ (P>0.05). Forty-six mares received more than one treatment during the breeding season, yielding 115 breedings (estrous cycles) for comparison of pregnancy rates among treatment. Per-cycle pregnancy rates for these mares did not differ among treatments (P>0.10).No differences due to treatment were detected in mean interval to ovulation (P>0.10). Mean interovulatory interval was longer for deslorelin-treated mares than for untreated or hCG treated mares (P>0.01). Eighty percent (80%) of deslorelin-treated mares had interovulatory intervals of 18–25 days, and 19% had interovulatory intervals>25 days. Ninety-seven percent (97%) of untreated or hCG-treated mares had interovulatory interovulatory intervals>25 days. More deslorelin-treated mares had extended (>25 days) interovulatory intervals than hCG- or nontreated-mares (P>0.05). In this group of Thoroughbred mares, it appeared that season (month) and management (farm) factors had only minor effects on the incidence of extended interovulatory intervals following use of deslorelin.     

Reproductive response of mares after treatment with progestogens with and without the additional of estradiol

A study involving 60 light-horse mares was conducted both to evaluate the response of mares to injectable progester- one or altrenogest and to determine ifestradiol in combination with either progestogen provided any added benefit. Treatments were initiated at either early estrus, late estrus, early diestrus, mid-diestrus or late diestrus in order to assess the effect of stage of cycle at onset of treatment. Within each of these stages of the cycle, mares were randomly assigned to 1 of 4 treatments: 150 mg progesterone injected i.m. (P); 150 mg progesterone + 10 mg estradio11713 injected i.m. (P+); .044 mg altrenogest per kg body weight orally (A); and .044 mg per kg body weight orally plus 10 mg estradiol 1713 i.m. (A+). All treatments were given daily for 7 days with 10 mg PGFaCt given on day 7 to all mares. The number of mares ovulating by day 14 after treatment (N=15/group) was 13, 7,11 and 8 forA, A+, P and P+, respectively. The response of mares to progesterone and altrenogest was similar. Fewer (Pì0.05) mares given combined steroid treatments ovulated within 14 days (15 of 30) than those given progestogen treatments. Stage of cycle had no affect (Pì0.05) on response of mares ovulating within 14 days or after 14 days of treatment. Mares that ovulated within 14 days of treatment had larger foUieles after progestogen treatment than those not ovulating by 14 days.