Oxytocin release and its relationship to dihydro-15-keto PGF2alpha and arginine vasopressin release during parturition and to suckling in postpartum mares.

Pituitary blood was collected from the intercavernal sinus in five mares before and during parturition, and in nine mares immediately after parturition to investigate oxytocin patterns during parturition and early lactation, and to determine the relationship between oxytocin, prostaglandin and arginine vasopressin during parturition. In four mares in which sample collection began at least 6 h before rupture of the chorioallantois, a significant increase (P < 0.05) in PGF(2alpha) concentration was detected before a significant increase in oxytocin concentration. Cross-correlation analysis of log-transformed oxytocin and PGF(2alpha) concentrations revealed a significant correlation (P < 0.05) at a 6 min lag period, indicating that in the 2 h before delivery of the foal, an increase in prostaglandin was followed 6 min later by an increase in oxytocin. A significant effect of suckling on oxytocin release by the mare was detected in only two of nine mares, when oxytocin concentrations were evaluated 0-3 min after suckling. When foals were prevented from sucking for 1 h, by being either muzzled (n = 2) or separated from the mare (n = 2), there was no significant association between resumption of suckling and oxytocin release by the mare. The results of these studies show that: (i) oxytocin secretion from the maternal posterior pituitary gland begins before, or in association with, the onset of the second stage of labour, and that prostaglandin increases in the peripheral circulation before oxytocin release; and (ii) suckling is not significantly related to oxytocin release in mares.

Associations among prostaglandin F2alpha, plasma zinc, copper and iron concentrations and fetal loss in cows and mares.

The objective of this study was to test the hypothesis that PGF2alpha is associated with abortion and changes in plasma Zn, Cu, and Fe concentrations in cows and mares in their first trimester of pregnancy. Eleven pregnant cows were infused with endotoxin (n = 5) or endotoxin plus an inhibitor of cycloxygenase, flunixin meglumine (n = 6). Blood was collected over a 5-d period. Additionally, 4 mares were treated every 24 h with cloprostenol sodium and blood was collected hourly until abortion. Plasma Zn, Cu, and Fe were determined. Three of five cows treated with endotoxin aborted, but none of the six cows treated with endotoxin and flunixin meglumine aborted. Aborting cows had lower plasma Zn (P = 0.048) over the 5-d study period compared with the nonaborting cows. The changes in Zn corresponded to release of PGF2alpha. All 4 mares aborted and plasma Zn concentrations were lower (P = 0.008) and Cu/Zn was higher (P = 0.02) 12 h after cloprostenol treatment. Plasma Zn may be a useful biomarker for risk of spontaneous abortion, and the decline in plasma Zn may be caused by PGF2alpha.

Diagnostic testing for pituitary pars intermedia dysfunction in horses.

Pituitary pars intermedia dysfunction is a slowly progressive disorder that afflicts most breeds of horses. Because it shares features with human Cushing disease, it has been referred to as equine Cushing disease. A variety of tests of pituitary-adrenocortical function were performed on horses with evidence of pituitary pars intermediate dysfunction, and results were compared with those in healthy control horses. Diurnal variations in plasma cortisol concentration were not statistically different between control horses and those with pituitary pars intermedia dysfunction. An ACTH stimulation (1 U of natural ACTH gel/kg of body weight, IM) test or a combined dexamethasone suppression test (10 mg, IM) and ACTH stimulation (100 mg of synthetic ACTH, IV) test also failed to distinguish horses with pituitary pars intermedia dysfunction from control horses. A significant (P < 0.001) dose-related suppression of cortisol concentration in response to increasing doses (5, 10, 20, and 40 micrograms/kg) of dexamethasone was observed in control horses but not in those with pituitary pars intermedia dysfunction. On the basis of plasma cortisol concentration, the dexamethasone suppression test, using 40 micrograms/kg, whether initiated at 5 PM with sample collection at 15 (8 AM) and 19 (12 PM) hours after dexamethasone administration, or initiated at 12 AM with sample collection at 8 (8 AM), 12 (12 PM), 16 (4 PM), 20 (8 PM), and 24 (12 AM) hours after dexamethasone administration, reliably distinguished between control horses and those with pituitary pars intermedia dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian and endocrine patterns associated with reproductive abnormalities in llamas and alpacas.

Ovarian activity was characterized in llamas and alpacas with hypoplastic ovaries, cystic follicles, or ovulatory failure. Ovarian follicular activity was determined by transrectal ultrasonography and urinary estrone sulfate analysis; pituitary response was determined by measurement of plasma concentrations of luteinizing hormone. Llamas and alpacas with hypoplastic ovaries had follicles < or = 6 mm (minimal ovulatory size, 7 mm). Cystic follicles, defined as > 12 mm, were maintained for a mean of 9 days. Follicular activity in the ovary contralateral to the cystic follicle tended to be suppressed while the cystic follicle was present. Ovarian response to copulation in females with cystic follicles varied according to the stage of the cystic follicle. Animals with ovulatory failure did not release adequate luteinizing hormone after copulation, even though they had mature and normal follicles (8 to 12 mm). The cystic follicle syndrome appears to be temporary, whereas the syndromes involving hypoplastic ovaries and ovulatory failure may permanently affect fertility.

Biology of ovarian cycles, pregnancy and pseudopregnancy in the domestic cat.

Puberty in the female cat occurs between the ages of 8 and 10 months. Cats are seasonally polyoestrous, reflex ovulators. The oestrous cycle can occur as often as every 2-3 weeks. Ovulation usually occurs 24-36 h after copulation, and implantation occurs 12-13 days after copulation. The duration of gestation in the cat is 64-67 days (average 66 days). The corpora lutea secrete increasing amounts of progesterone, starting 1-2 days after ovulation. If implantation occurs, progesterone concentrations continue to increase throughout days 25-30, then slowly decline throughout the rest of pregnancy. In the absence of pregnancy, the corpora lutea reach their peak progestational activity within 10-15 days and then decline, with basal progesterone values being noted by days 30-35. Relaxin is produced by the fetoplacental unit beginning at about day 20 of gestation and continuing throughout the rest of pregnancy. Prolactin production increases from about day 35. Like those of prostaglandin F2 alpha, concentrations of prolactin plateau at about day 50 and increase abruptly just before delivery.

Pregnancy failure in cats associated with long-term dietary taurine insufficiency.

The effect of long-term dietary taurine insufficiency on reproductive function was studied in adult female domestic cats (n = 11). Cats were time-mated during taurine-deficient (6 months) and refed (6 months) states, and the outcome of ovulatory cycles and breeding was analysed. Serum progesterone and relaxin concentrations were evaluated in order to characterize pregnancies, including those resulting in resorption of fetuses, and pseudopregnancies. Increased resorption of fetuses, reduced litter size, and increased incidence of stillborn kittens was observed in queens while on taurine-deficient diets, as well as after refeeding of a taurine-enriched diet. Overall, 30% of the ovulatory cycles resulted in the delivery of kittens, with mean live and stillborn litter sizes of 2.2 +/- 0.4 and 0.8 +/- 0.4 kittens (mean +/- SEM), respectively. The remaining ovulatory cycles resulted either in pregnancies in which fetuses were resorbed (38%), or in pseudopregnancies (32%). Ovulatory cycles resulting in resorbed fetuses were characterized by the appearance of relaxin on day 20 of gestation, but with a subsequent decrease to non-pregnant concentrations by day 25 of gestation. These results suggest that reproductive failure in domestic cats exposed to long-term nutritional taurine deficiency is associated with a postovulatory defect manifest within the first 10 days after implantation, and that this defect is not reversible upon refeeding of a taurine-enriched diet for 6 months.

Pituitary response to repeated copulation and/or gonadotropin-releasing hormone administration in llamas and alpacas.

The response of the pituitary gland and ovary to repeated copulatory periods and/or gonadotropin-releasing hormone (GnRH, i.v. 1000 micrograms) administration was determined in llamas and alpacas. Eighty adult females (41 llamas and 39 alpacas with ovulatory follicles) were divided into three general groups for each species as follows: copulation (one or two copulations at either 6- or 24-h intervals) GnRH treatment (one or two treatments at either 6- or 24-h intervals), and combined treatment (copulation followed by GnRH treatment, or GnRH followed by copulation at either 6- or 24-h intervals). An additional control (nontreated) group was composed of 4 llamas and 4 alpacas. The first copulation or treatment with GnRH provoked LH release sufficient to cause ovulation in most of the females (alpacas, 89%; llamas, 92%); urinary pregnanediol glucuronide values, used to verify ovulation, were significantly elevated 48 h after copulation and/or GnRH treatment. A second stimulus, copulation or GnRH, provoked no LH response with concentrations similar to those in nontreated controls and in females not ovulating. Llamas and alpacas thus were refractory to a second copulatory or GnRH stimulus with regard to LH release for up to 24 h following an initial ovulatory release of LH.

Ram influence on ovarian and sexual activity in anestrous ewes: effects of isolation of ewes from rams before joining and date of ram introduction.

A 2-yr experiment was conducted to determine whether isolation of ewes from rams is necessary to achieve a high response to the ram effect and whether ewes respond as well in May as in June. The experiment was conducted at two locations, with the same four treatments at each location. The four treatments differed with respect to ewe proximity to rams before mating (isolated vs adjacent) and date of joining with novel breeding rams (May 15 vs June 15). The proximity treatment at one location was changed in the 2nd yr; teaser rams were joined with the ewes instead of being adjacent to them. Overall, 86% of the eligible ewes were judged to have responded to the ram effect. A period of isolation before mating did not increase response compared with ewes that remained adjacent to, or in contact with, rams (86 vs 85%). Response was greater (P less than .05) in June and in the 2nd yr (P = .05). A physiological response, different from that generally described, was identified. Ewes ovulated approximately 8 d (8.0 +/- .19 d) after joining with breeding rams. The subsequent ovulation, accompanied by estrus, occurred approximately 15 d later (15.3 +/- .29 d). Eighty-five percent (87/102) of the ewes sampled responded in this manner. However, 82% (31/38) of a sample of these ewes had at least one morphologically normal corpus luteum when examined by laparoscopy 4 d after joining. It seems that these corpora lutea were not completely functional with respect to progesterone production. The ram effect can be achieved without prior isolation of ewes from rams.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of ovarian follicle size on pituitary and ovarian responses to copulation in domesticated South American camelids.

The relation of ovarian follicle size to pituitary and ovarian responses to copulation was studied in domesticated South American camelids (llamas and alpacas). Females from each species were divided into four groups according to follicle size: small (4-5 mm), growing (6-7 mm), mature (8-12 mm), and regressing (10-7 mm). The pituitary response to copulation was determined by analysis of LH and FSH concentrations in plasma. The ovarian response to copulation was determined by ultrasonography and by analysis of estrone sulfate (follicular status) and pregnanediol glucuronide (luteal status) concentrations in urine. Females with small follicles (4-5 mm) released less LH after copulation than did those with larger follicles, and ovulation was not induced. Females with growing and mature follicles (7-12 mm) released LH in response to copulation that was adequate to induce ovulation and to initiate normal luteal activity. While copulation-induced LH release in females with regressing follicles was similar to that released in animals with growing and mature follicles, regressing follicles were luteinized instead of being ovulated. The luteal structure formed as a result of luteinization of follicles had a short life span, i.e., 5.1 days. Copulation-induced LH release was significantly higher in llamas vs. alpacas in animals with mature or regressing follicles, but not in those with small or growing follicles. Urinary estrone sulfate and pregnanediol glucuronide concentrations correlated positively with the presence of follicles and corpora lutea, respectively.

Urinary steroids in the periparturient and postpartum periods through early pregnancy in llamas.

Urinary steroids were determined daily in the periparturient and postpartum periods, including early pregnancy, in the female llama. Estrone sulfate (E(1)S) and pregnanediol glucuronide (PdG) concentrations were determined by enzyme immunoassay with values corrected for variations in urine concentration by creatinine. Estrone sulfate concentrations, elevated during the last 20 days of gestation through 12 hours before parturition, were declining at the time of delivery. Pregnanediol glucuronide concentrations followed a pattern similar to that of estrone sulfate except that values began to decrease 5 days before parturition. Values for both E(1)S and PdG were basal by 24 hours after delivery. The first significant elevation of estrone sulfate, indicative of initial follicle development, was observed 5 days after parturition. Pregnanediol glucuronide concentrations were low during the postpartum period until 4 to 5 days after breeding. The PdG values rose steadily following copulatory-induced ovulation, which was initiated at about 2 weeks postpartum; values continued to increase through the first 15 days of pregnancy.

Role of eicosanoids in abortion and its prevention by treatment with flunixin meglumine in cows during the first trimester of pregnancy.

Intravenous infusion of E. coli endotoxin at a rate of 4.16 ng/kg/min over 6 hr (total dose 1.5 micrograms/kg) in 5 cows in the first trimester of gestation induced abortion between 60 and 72 hr in three cows. Plasma PGF2 alpha levels in the aborting cows increased significantly to 289% of the zero time control (ZTC) at 1 hr and remained elevated for 9 hr. The PGF2 alpha level remained unaffected in the non-aborting cows except at 2 hr. The plasma TxB2 levels were increased by 6 to 18 fold for 6 hr in both the aborting and non-aborting cows relative to their ZTC controls. The 6-keto-PGF1 alpha levels were significantly increased to 2 to 3 fold only in the aborting cows. Plasma cortisol levels were increased maximally to 1,500% of ZTC at 5 hr in the aborting cows. Thereafter, the levels gradually declined but remained significantly elevated for 24 hr. The increases in the cortisol levels in the non-aborting cows were only 280% of ZTC at 5 hr and returned to ZTC value by 12 hr. Plasma progesterone levels in the aborting cows remained unaffected until 12 hr followed by a progressive decline through 18 hr to extremely low levels at 3, 4, and 5 days. Endotoxin-infusion caused hyperglycemia in both aborting and non-aborting cows and lactic acidemia in the aborting cows. Treatment with two doses of flunixin meglumine (FM, 1.1 mg/kg), an inhibitor of cyclooxygenase, 1 hr prior to endotoxin infusion and then 13 hr later, completely prevented the endotoxin-induced abortion and increases in the plasma PGF2 alpha, TxB2 and 6-keto-PGF1 alpha concentrations. The PGE level remained unaffected. Although FM treatment failed to abolish endotoxin-induced increases in the plasma cortisol and lactic acid levels, it effectively prevented marked decreases in the progesterone and increases in the glucose concentrations. It was concluded that the use of FM offers therapeutic promise in preventing bovine abortion caused by endotoxin resulting from bacterial infection during the 1st trimester of gestation.

Relationship of serum estradiol and progesterone concentrations to the excretion profiles of their major urinary metabolites as measured by enzyme immunoassay and radioimmunoassay.

Paired daily blood and urine samples were collected from 10 apparently healthy premenopausal women to compare the hormone profiles of estradiol (E2) and progesterone in serum with those of estrone conjugates (E1Conj) and pregnanediol-3-glucuronide (PdG) in urine. Serum hormones were measured by radioimmunoassay (RIA) kits, whereas the urinary steroid metabolites were assessed by both RIA and enzyme immunoassay (EIA). RIA and EIA values for urinary E1Conj and PdG were not different, and both methods produced urinary profiles that paralleled the profile of the parent steroid in serum. However, the simplicity, flexibility, and economy of EIA will make this method more widely applicable. Mean E1Conj values lagged behind concentrations of serum E2 by one day or less, whereas daily urinary PdG profiles lagged behind serum progesterone by one to two days. Mean urinary profiles of E1Conj were similar whether or not creatinine was used to adjust for urine volume; however, creatinine indexing was beneficial when urinary profiles in individual cycles were compared with changes of serum E2.

Urinary and plasma estrogen conjugates, estradiol and estrone concentrations in nonpregnant and early pregnant mares.

A direct radioimmunoassay for estrogen conjugates (EC) was applied to paired blood and urine samples collected from 20 mares and compared against estrone (E(1)) and estradiol-17beta (E(2)) to monitor changes in estrogen production during ovulatory cycles and early pregnancy. Blood samples were taken daily from five mares through two consecutive ovulations and from six mares at 6-h intervals starting 48 hours prior to ovulation and continuing after ovulation had occurred. Blood samples were also collected daily or three times per week from conception until Day 60 of pregnancy in nine pregnant mares. The mean urinary EC, plasma EC and plasma E(2) dynamics were parallel in nonpregnant mares, with a 3-fold increase in mean urinary EC concentrations from baseline to the ovulatory peak, a 1.8-fold increase in mean plasma EC concentrations and a 1.4-fold increase in mean plasma E(2) concentrations. In early pregnancy, a two-fold increase in mean plasma E(1) and EC concentrations occurred in concert with a five-fold rise in mean urinary EC concentrations, whereas plasma E(2) did not change. Following hydrolysis and chromatographic separation, E(1) and E(2) were identified as the hydrolytic products in the urine of nonpregnant and pregnant mares; however, an unidentified estrogen was the major hydrolytic product in nonpregnant mares and pregnant mares prior to Day 38 of pregnancy. The increased resolution of the EC profiles compared with the profiles of other estrogen components indicates that the determination of EC in urine or plasma provides a useful alternative method for monitoring reproductive events in mares.

Effects of flunixin meglumine on endotoxin-induced prostaglandin F2 alpha secretion during early pregnancy in mares.

The role of prostaglandin F2 alpha (PGF2 alpha) in embryonic loss following induced endotoxemia was studied in mares that were 21 to 44 days pregnant. Thirteen pregnant mares were treated with a nonsteroidal anti-inflammatory drug, flunixin meglumine, to inhibit the synthesis of PGF2 alpha caused by Salmonella typhimurium endotoxin given IV. Flunixin meglumine was administered either before injection of the endotoxin (group 1, -10 min; n = 7), or after endotoxin injection into the mares (group 2, 1 hour, n = 3; group 3, 2 hours, n = 3); 12 pregnant mares (group 4) were given only S typhimurium endotoxin. In group 4, the secretion of PGF2 alpha, as determined by plasma 15-keto-13,14-dihydro-PGF2 alpha concentrations, was biphasic, initially peaking at 30 minutes followed by a second, larger peak approximately 105 minutes after the endotoxin was given IV. When flunixin meglumine was administered at -10 minutes, synthesis of PGF2 alpha was inhibited for several hours, after administration of flunixin meglumine at 1 hour, the second secretory surge of PGF2 alpha was blocked, and administration of the drug at 2 hours did not substantially modify the secretion of PGF2 alpha. Plasma progesterone concentrations were unchanged after endotoxin injections were given in group 1. In group 2, progesterone values decreased less than 2 ng/ml and remained low for several days. In group 3 and group 4, progesterone concentrations decreased to values less than 0.5 ng/ml by 48 hours after endotoxin injections were given.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of progesterone deficiency as a cause of fetal death in mares with experimentally induced endotoxemia.

The role of decreased luteal activity in embryonic loss after induced endotoxemia was studied in mares 21 to 35 days pregnant. Fourteen pregnant mares were treated daily with 44 mg of altrenogest to compensate for the loss of endogenous progesterone secretion caused by prostaglandin F2 alpha (PGF2 alpha) synthesis and release following intravenous administration of Salmonella typhimurium endotoxin. Altrenogest was administered daily from the day of endotoxin injection until day 40 of gestation (group 1; n = 7), until day 70 (group 2; n = 5), or until day 50 (group 3; n = 2). In all mares, secretion of PGF2 alpha, as determined by the plasma 15-keto-13,14-dihydro-PGF2 alpha concentrations, followed a biphasic pattern, with an initial peak at 30 minutes followed by a second, larger peak at 105 minutes after endotoxin injection. Plasma progesterone concentrations decreased in all mares to values less than 1 ng/ml within 24 hours after endotoxin injection. In group 1, progesterone concentrations for all mares were less than 1 ng/ml until the final day of altrenogest treatment. In 6 of 7 mares in group 1, the fetuses died within 4 days after the end of treatment, with progesterone concentrations less than 1 ng/ml at that time. In the mare that remained pregnant after the end of treatment, plasma progesterone concentration was 1.6 ng/ml on day 41 and increased to 4.4 ng/ml on day 44. In group 2, all mares remained pregnant, even though plasma progesterone concentrations were less than 1 ng/ml in 4 of 5 mares from the day after endotoxin injection until after the end of altrenogest treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Follicular and endocrine responses of anoestrous mares to administration of native GnRH or a GnRH agonist.

Thirty-seven seasonally anoestrous mares were divided into treatment and control groups and given 10 micrograms of native GnRH (GnRH) per hour using a peristaltic pump, or 10 micrograms GnRH agonist (GnRHa) twice daily, beginning on either 13 January, 13 February or 14 March. Treatment with GnRH was equally effective in inducing ovulation in January (4/5), February (4/5) and March (3/4). GnRHa treatment was more effective in inducing ovulation in February (4/5) and March (4/4) than in January (2/8). Peak luteinizing hormone (LH) concentrations in mares induced to ovulate with GnRH (7.4 +/- 1.5 ng/ml) were significantly higher than LH concentrations in mares induced to ovulate with GnRHa (1.8 +/- 0.2 ng/ml). Urinary oestrogen conjugate concentrations increased parallel to increases in follicular diameter during treatment. Ovulations induced by GnRH or GnRHa were followed by a normal luteal phase. All mares induced to ovulate in January and February returned to anoestrous following withdrawal of GnRH support. The results suggest that the efficacy of GnRHa in the induction of ovulation in anoestrous mares is influenced by season, whereas the efficacy of pulsatile GnRH administration is not affected by season.

An oestrogen conjugate enzyme immunoassay for monitoring pregnancy in the mare: limitations of the assay between days 40 and 70 of gestation.

A direct enzyme immunoassay was developed to measure conjugated oestrogens in the plasma of pregnant mares. The antibody was produced in rabbits using oestrone-3-glucuronide (E1G) conjugated to bovine serum albumin. The enzyme conjugate was E1G conjugated to horseradish peroxidase. A sharp increase in plasma E1G concentrations occurred between Days 35 and 40 of gestation. Values declined slightly to Day 45, remained relatively constant to around Day 70 and rose sharply thereafter. Fetal death before Day 35 had no effect on plasma concentrations of E1G. Fetal death after Day 35 in conjunction with endotoxin-induced regression of the corpus luteum (CL) resulted in a decrease in plasma E1G levels to non-pregnant values within 3-4 days. Endotoxaemia without fetal death between Days 35 and 70 resulted in marked, but transient, decreases in plasma E1G concentrations. Fetal death without CL regression after Day 35 did not produce an immediate decline in plasma E1G concentrations and existing levels were maintained for 10-14 days. These findings indicate that between Days 35 and 70 of pregnancy, plasma E1G concentrations are not directly correlated with fetal viability; they appear to reflect increased oestrogen secretion by the CL under the influence of chorionic gonadotropin. After Day 70, E1G concentrations begin to reflect directly the production of oestrogen by the developing feto-placental unit.

The corpus luteum: source of oestrogen during early pregnancy in the mare.

Thirty pregnant mares were assigned to 3 groups: Group 1 (n = 10) mares served as controls; Group 2 (n = 10) mares were treated with altrenogest (44 mg/day) from Day 16 to 80 and Group 3 (n = 10) mares were treated with a luteolytic dose of PGF2 alpha on Day 16 followed by altrenogest (44 mg/day) until Day 80. Concentrations of progesterone and chorionic gonadotrophin (CG) in plasma and oestrogen conjugate (OC) in urine were determined between Days 16 and 80 of gestation. In Group 3, complete luteolysis occurred in all 10 mares following administration of PGF2 alpha. Six of the 10 mares did not have an active CL from Day 16 until after Day 60 of pregnancy (Group 3a); the remaining 4 mares developed a new CL on Days 32, 40, 43 and 49 of pregnancy (Group 3b). In Groups 1 and 2, an increase in oestrogen secretion was observed between (Group 3b). In Groups 1 and 2, an increase in oestrogen secretion was observed between Days 35 and 40. In Group 3a, OC concentrations in the absence of an active CL were significantly lower than in Groups 1 and 2, and oestrogen secretion did not increase between Days 20 and 50. In Group 3b, OC concentrations remained low in the absence of an active CL. After the onset of CG secretion, OC concentrations increased to values similar to Groups 1 and 2 in conjunction with the development of a new CL. The results of this experiment demonstrate that the increase in oestrogen secretion observed between Days 35 and 50 of pregnancy requires the presence of an active CL.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian follicular dynamics in the llama.

Ovarian follicular dynamics were determined in adult llamas by ultrasonography and palpation per rectum and hormone analysis (estradiol-17 beta and estrogen conjugates) of plasma and urine. The relationship of gonadotropin secretion to follicular development was determined by the analysis of plasma FSH and LH concentrations. Progesterone analysis of plasma was used to verify or deny the presence of CL. Final follicular development (from 3 mm) averaged 4.8 days, while the duration of the mature follicle (8-12 mm) averaged 5.0 days; regression of the follicle occurred over about 4 days. The development of a subsequent dominant follicle usually began within 2-3 days after onset of regression of the dominant follicle. While several follicles were present at the time of the demise of the dominant follicle, only one follicle continued to develop. The interval between ovarian follicle waves averaged 11.1 days. Dominant follicle activity alternated between ovaries in 81% of the cycles. The occurrence of dominant follicles was evenly distributed between ovaries. While plasma estradiol and estrogen conjugate concentrations were positively associated (p less than 0.05) with follicular activity, urinary estrogen conjugate concentrations best reflected ovarian follicular dynamics (p less than 0.001). Daily FSH concentrations in plasma were not correlated with follicular activity. LH concentrations in plasma were low in all animals throughout the study, indicating estrogen from developing ovarian follicles does not induce the release of LH. Progesterone values were low during the study, indicating that the llama does not spontaneously ovulate, at least under the conditions of this study. In summary, llamas have overlapping ovarian follicle waves that occur at about 11-day intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

Source of oestrogen in early pregnancy in the mare.

Oestrogen secretion was determined by oestrogen conjugate (EC) analysis of urine in three groups of pregnant mares: Group I (N = 6), animals ovariectomized on Day 18-19 of gestation with pregnancy maintained by daily administration of an oral progestagen, altrenogest; Group II (N = 9), untreated, pregnant mares; Group III (N = 5) intact, pregnant mares treated daily with altrenogest. The mean EC concentrations in the ovariectomized mares in Group I increased in a constant linear manner from 17 ng/mg Cr on Day 20 to 291 ng/mg Cr on Day 70, with no apparent surge in oestrogen secretion around Day 39. Mean EC concentrations on Days 33, 39 and 44 were respectively 41, 48, and 73 ng/mg Cr. In the intact mares in Groups II and III (shown in parentheses), the mean urinary EC concentrations were 201 (171) ng/mg Cr between Days 20 and 33 of gestation, increased rapidly from 172 (77) ng/mg Cr on Day 33 to a peak of 1066 (895) ng/mg Cr on Day 39, followed by a decline to 637 (719) ng/mg Cr on Day 44. After Day 44, EC concentrations continued to increase in a linear manner to 1191 (842) ng/mg Cr on Day 70. The mean EC concentrations between Days 20 and 70 in Group I were significantly (P less than 0.05) lower than in mares in Groups II and III. EC concentrations in Group III mares were significantly lower (P less than 0.05) than in Group II mares between Days 28 and 34.(ABSTRACT TRUNCATED AT 250 WORDS)