Biomedical subjects

D R Bergfelt

Publications and source records attributed to D R Bergfelt.

53 records · Page 3Linked to original sources

PubMed1995

Prostaglandin F2 alpha receptors in the early bovine corpus luteum.

Since the early CL (< or = 4 days after ovulation) does not regress after injection of PGF2 alpha, this study was designed to determine whether number or affinity of PGF2 alpha receptors was lower in the early as compared with the midstage CL. Heifers were randomly assigned to have ovaries removed on Day 2, 4, 6, or 10 (n = 4 heifers per day; Day 0 = day of ovulation). Plasma progesterone concentrations and the weight and size of the CL increased from Day 2 to 6, indicating normal CL development. Plasma membranes from individual CL were evaluated for PGF2 alpha receptor concentration and affinity by Scatchard analysis. CL from each of the 4 days of the estrous cycle were not different with respect to PGF2 alpha receptor concentration (number per microgram of plasma membrane protein) and affinity. To examine tissue specificity, PGF2 alpha binding was evaluated in 12 organs or tissues. High-affinity PGF2 alpha receptors were found in the CL and adrenal medulla but not in granulosa cells or other tissues. In conclusion, a single class of high-affinity PGF2 alpha receptors was present within the bovine CL by 2 days after ovulation; therefore the reported lack of responsiveness to PGF2 alpha in the early CL was not attributable to a deficiency of high-affinity PGF2 alpha receptors.

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PubMed1994

Follicular and FSH responses to parturition during the anovulatory season in mares.

The ovaries of periparturient pony mares (n=9 to 16 parturitions per month for January to April) were scanned ultrasonically on the day of parturition, while those of postpartum and control mares (n=12) were examined at least twice weekly. Four mares had apparent lactational anovulation (incidence, 7%) that corrected spontaneously (1 mare) or within 14 d after the weaning of foals on August 10 (3 mares). All but 2 of the postpartum ovulations occurred after April 29; that is, parturition did not effectively stimulate ovulation in ponies foaling during the anovulatory season. Mean diameter of the largest follicle per month increased (P<0.001) progressively in the controls (means: 11.4, 14.4, 19.0 and 24.5 mm for January to April, respectively). In the parturient mares, the diameter of the largest follicle on day of parturition did not increase over months (range of means: 13.6 to 16.9 mm), indicating that a suppressive effect of pregnancy counteracted the stimulatory effect of season. Within each month of parturition, diameter of the largest follicle increased (P<0.05) between Day 0 (day of parturition) and Day 3 or 7. Blood samples for FSH assay were taken daily for 14 d from 6 mares with parturition in the middle of each month and from 6 controls on the corresponding calendar days. In periparturient mares, a significant increase in mean FSH concentrations occurred for all months of parturition between Day-2 and Day 0, followed by a significant decrease between Day 3 and Day 7. Maximum means for the periparturient FSH profile were temporally related to the beginning of follicular growth. In the controls, FSH concentrations were not affected by month or day, or by their interaction. Within each month, mean FSH concentrations were lower (P<0.05) in the periparturient mares than in the controls (averaged over all months: 3.9+/-0.1 versus 7.9+/-0.3 ng/ml) even though follicular growth was greater following parturition than during the corresponding calendar days in controls.

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PubMed1993

Relationships between FSH surges and follicular waves during the estrous cycle in mares.

Individual follicles >/=15 mm were monitored daily by ultrasonography in 12 mares during the estrous cycle. Follicular waves were designated as major waves (primary and secondary) and minor waves based on maximum diameter of the largest follicle of a wave (major waves, 34 to 47 mm; minor waves, 18 to 25 mm). Dominance of the largest follicle of major waves was indicated by a wide difference (mean, 18 mm) in maximum diameter relative to the second largest follicle. Dominant follicles of primary waves (n=12) emerged (attained 15 mm) at a mean of Day 12 and resulted in the ovulations associated with estrus (ovulation=Day 0). The dominant follicle of a secondary wave (n=1) emerged on Day 2 and subsequently ovulated in synchrony with the dominant follicle of the primary wave, which emerged on Day 9. The largest follicles of minor waves (n=4) emerged at a mean of Day 5, reached a mean maximum diameter 3 days later, and subsequently regressed. There was a significant increase in mean daily FSH concentrations either 6 days (primary wave) or 4 days (minor waves) before the emergence of a wave. Mean concentrations of FSH decreased significantly 2 days after emergence of the primary wave. Divergence between diameter of the dominant and largest subordinate follicle of the primary wave was indicated by a significantly greater mean diameter of the dominant follicle than of the largest subordinate follicle 3 days after wave emergence and by the cessation of growth of the largest subordinate follicle beginning 4 days after the emergence of a wave. Surges of FSH were identified in individual mares by a cycle-detection program; surges occurred every 3 to 7 days. Elevated mean FSH concentrations over the 6 days prior to emergence of the primary wave was attributable to a significantly greater frequency of individual FSH surges before wave emergence than after emergence and to an increase in magnitude of peak concentrations of FSH associated with individual surges.

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PubMed1993

Growth of small follicles and concentrations of FSH during the equine oestrous cycle.

The temporal associations between increases in FSH and growth of small follicles (2-20 mm) were studied during one oestrous cycle (ovulation to ovulation) in 15 horse mares. Follicular diameters were obtained ultrasonically. For each day, follicles were combined for both ovaries, grouped from largest to smallest (excluding dominant follicles), and divided into three to five tiers of six follicles for each mare (for example: tier 1, six largest follicles; tier 2, next six largest follicles). A significant increase in mean diameters followed by a significant decrease was used to define a follicular wave within each of the tiers for each mare. Day of wave emergence was defined by the lowest mean preceding the increase. Follicular waves were detected in all tiers in each mare. The number of detected waves per interovulatory interval was greater (P < 0.05) for tier 5 (2.8 +/- 0.4) than for tier 1 (1.1 +/- 0.1) and tier 2 (1.9 +/- 0.3). A primary follicular wave (wave giving rise to the dominant follicle that ovulated during the subsequent oestrus) was identified in tier 1 in all mares. Composite profiles were constructed by normalizing each tier for each mare to the mean day of emergence of the primary wave for all mares, as detected in tier 1. The composite follicular profiles for the five tiers were approximately parallel; the follicles for tiers 2-5 emerged on the mean day of emergence of the primary wave (6 days after ovulation). The range of follicular means on the common day of wave emergence was 3 mm (tier 5) to 12 mm (tier 1).(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1992

Associations between FSH concentrations and major and minor follicular waves in pregnant mares.

Follicular waves were detected in 19 pregnant mares (Days 11 to 40) by a significant increase followed by a significant decrease in diameters of follicles after removing large (>or=25 mm) follicles from the data sets. The waves were defined as major (largest follicle, >or=35 mm; n=18) or minor (largest follicle, <35 mm; n=17). Six mares (32%) had 2 successive major waves beginning on mean Days 15.2 and 26.8; 6 had a solitary major wave beginning on Days 11 to 20; and 6 had only minor waves occurring at irregular intervals. The mean interval between minor waves (7.8 days) was less (P<0.05) than for major waves (11.7 days). Mean divergence in diameters of the largest and second largest follicles of a wave began 4 days after the detected emergence of consecutive major waves, and was taken as the beginning of the expression of dominance by the largest follicle. The interval from emergence to divergence was several days longer (P<0.05) for solitary major waves than for consecutive waves. Dominance was not detected for the minor waves, using mean diameters of the 2 largest follicles, but was apparent on inspection of individual wave profiles in 5 of 17 (29%) minor waves. Minor waves, compared with major waves, had larger diameter of follicles on the day of wave emergence (15.0 versus 12.1 mm), and significantly greater variation in the day of attainment of maximal diameter of largest follicle and small follicles. A mean increase in FSH was temporally associated with the emergence of both major and minor waves. In mares with minor waves, concentrations of FSH were higher, on average, over Days 11 to 40, which seemed consistent with the origin of follicular waves from larger follicles in the basal populations. The lower overall FSH levels in mares with major waves seemed at least partly due to depression of FSH levels beginning at the time of divergence between the 2 largest follicles.

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PubMed1992

Embryo loss following GnRH-induced ovulation in anovulatory mares.

Two experiments were conducted using a 21-day GnRH analogue treatment regimen to induce ovulation in seasonally anovulatory mares. In Experiment 1, nontreated (n=20) and treated (n=83) mares were defined as having inactive ovaries (largest follicle <or=15 mm) at the start of treatment (February). In Experiment 2, nontreated (n=7) and treated (n=10) mares were defined as having active ovaries (largest follicle 21 to 29 mm) at the start of treatment (April). Fewer mares ovulated that had inactive ovaries at the start of treatment compared to mares that had active ovaries (26% versus 70%). In mares that had inactive ovaries at the start of treatment, the pregnancy rate on Day 11 (ovulation=Day 0) was not different between treated (14/22; 64%) and nontreated (14/20; 70%) mares. However, the embryo-loss rate between Days 11 and 40 was significantly higher in treated (9/14; 64%) than in nontreated (1/14; 7%) mares. Losses tended to occur more frequently between Days 15 and 25. Averaged over Days 3 to 18, there was a significant main effect of group for the diameter of the largest follicle and for circulating concentrations of FSH, LH and progesterone in mares that had inactive ovaries at the start of treatment. The group effect was attributable to decreased mean values for each end point in treated mares, especially in treated mares that had embryo loss. A significant decrease in progesterone on Day 15 in treated mares with embryo loss corresponded to the first day that embryo loss was detected. In mares that had active ovaries at the start of treatment, pregnancy rate, embryo-loss rate, and ovarian and hormonal end points were not significantly different between the treated and nontreated mares. The results indicated that hormonal capacity was reduced and embryo-loss rate was high following GnRH-induced ovulation in mares that had inactive ovaries at the start of treatment.

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PubMed1992

Role of the embryonic vesicle and progesterone in embryonic loss in mares.

Characteristics of spontaneous embryonic loss in 21 mares were compared with those of 52 contemporary mares that maintained pregnancy. Embryonic losses were, in retrospect, grouped according to day of loss and length of the interovulatory interval, respectively, as follows: group 1, less than or equal to day 20 and less than or equal to 30 days (n = 10); group 2, less than or equal to day 20 and greater than 30 days (n = 3); and group 3, greater than day 20 and greater than 30 days (n = 8); ovulation was day 0. Mean diameter of the embryonic vesicle in group 1 was smaller (P less than 0.05) on days 12-18 than in the pregnancy-maintained group, but among the pregnancy-maintained group and the embryonic-loss groups, the mean individual growth rates of vesicles was similar (no significant difference). A more frequent (P less than 0.05) location of the vesicles in the uterine body on day 13 in group 1 was due to a greater proportion of small vesicles and for day 18 was due to a greater incidence of fixation failure. Luteal regression occurred at the expected time in 77% of the mares with loss sooner than day 20. Low concentration of progesterone on days 12, 15 and 18, a detected decrease in diameter of the corpus luteum on days 15 and 18, and an interovulatory interval of less than or equal to 30 days indicated that luteolysis was not prevented by the embryonic vesicle in group 1.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1991

Ultrasonic detection of the conceptus and characterization of intrauterine fluid on days 10 to 22 in heifers.

Nonbred and pregnant heifers were examined ultrasonically on alternate days from Days 10 to 22 in three experiments. The goal was to define criteria that could be used for identification of the early conceptus. The location and size of circular and elongated nonechongenic structure (apparently free intrauterine luminal fluid) were recorded (Experiment 1). On Day 12, there was a significantly greater number of circular nonechogenic structures in the ovarian half of the uterine horn ipsilateral to the corpus luteum in pregnant heifers than in nonbred heifers (means, 5.1 vs 3.5). Therefore, the embryonic vesicle was apparently detected on Day 12, but was not distinguished from circular nonechogenic structures representing free luminal fluid. The number of circular nonechogenic structures decreased after Day 14, with a corresponding increase in elongate nonechogenic structures associated with luteal regression (nonbred heifers) or elongation of the blastocyst (pregnant heifers). On Day 16, there were more elongated than circular nonechogenic structures in pregnant heifers than in nonbred heifers. In nonbred heifers, there was no evidence of a local utero-ovarian relationship between the amount of intrauterine luminal fluid and the location of either the corpus luteum or the next ovulatory follicle. Uterine luminal fluid in each horn increased several fold between Days 16 and 18 in nonbred heifers; there was significantly more lumina fluid in nonbred than in pregnant heifers on Days 18 and 20. In pregnant heifers, intrauterine luminal fluid area increased first in the ovarian end of the uterine horn ipsilateral to the corpus luteum; this was apparently due to detection of the elongating blastocyst. The length of the longest specular reflector on the endometrial surface of the uterine lumen increased over Days 10 to 22 in nonbred and pregnant heifers, but was not a useful criterion for detection of the conceptus (Experiment 2). The accuracy of a 7.5 MHz transducer for pregnancy diagnosis was not greater than a guess (50%) before Day 16 (Experiment 3). Results indicated that early pregnancy diagnosis in heifers was confounded by the presence of intrauterine fluid.

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PubMed1990

Effects of time of insemination relative to ovulation on pregnancy rate and embryonic-loss rate in mares.

The effects of pre-ovulatory and post ovulatory insemination on pregnancy rate and embryonic-loss rate were studied in 268 mares in two experiments. Within each experiment mares were randomised within replicates as follows: to be inseminated on the day the pre-ovulatory follicle reached 35 mm (pre-ovulatory group), to be inseminated on the day of ovulation (Day 0 group), and to be inseminated on the day after ovulation (Day 1 group). Ultrasonic pregnancy diagnoses were performed on Days 11, 12, 13 and 14 (Experiment 1) and Days 11, 12, 13, 14, 15, 20 and 40 (Experiment 2). Combined for the two experiments, pregnancy rates were different (P less than 0.01) among the three groups. For Experiment 2, pregnancy rate within the pre-ovulatory group was lower (P less than 0.05) for insemination 4 days or more before ovulation than for up to 3 days before ovulation. Pregnancy rate was lower (P less than 0.05) for the Day 0 group than for the pre-ovulatory group inseminated up to 3 days before ovulation. In Experiment 2, ovulation was detected by examinations every 6 h; pregnancy rate was greater (P less than 0.05) for mares inseminated 0 to 6 h after ovulation than for mares inseminated at 18 to 24 h. No pregnancies occurred when mares were inseminated 30 h or more after ovulation. The mean day of first detection of the embryonic vesicle was different (P less than 0.0001) among the three groups. Diameter of embryonic vesicle averaged over Days 11 to 15 also differed (P less than 0.0001) among groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Effect of GnRH treatment during the anovulatory season on multiple ovulation rate and on follicular development during the ensuing pregnancy in mares.

Seasonally anovulatory mares were injected, i.m., twice daily with a GnRH analogue (GnRH-A), and hCG was given when the largest follicle reached 35 mm in diameter. In Exp. 1, treatment was initiated on 23 December when the largest follicle per mare was less than or equal to 17 mm. An ovulatory response (ovulation within 21 days) occurred in 17 of 30 (57%) GnRH-A-treated mares on a mean of 15.8 days. The shortest interval to ovulation in control mares (N = 10) was 57 days. The diameter of the largest follicle first increased significantly 6 days after start of treatment. In Exp. 2, treatment was begun on 15 January and mares were categorized according to the largest follicle at start of treatment. The proportion of mares ovulating within 21 days increased significantly according to initial diameter of largest follicle (less than or equal to 15 mm, 9/25 mares ovulated; 15-19 mm, 13/21; 20-24 mm, 20/24; greater than 25 mm, 3/3). The multiple ovulation rate was greater (P less than 0.01) for treated mares (27/86 mares had multiple ovulations) than for control mares (2/35). Treated mares in which the largest follicle at start of treatment was greater than or equal to 25 mm had a higher (P less than 0.01) multiple ovulation rate (9/14) than did mares in which the largest follicle was less than 25 mm (18/72). The pregnancy rate for single ovulators was not different between control mares (26/30 pregnant mares) and treated mares (43/54).(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1988

Embryo reduction before day 11 in mares with twin conceptuses.

Incidence of embryo reduction (natural elimination of one member of a twin set) before d 11 was studied by comparing the number of ultrasonically detected conceptuses per ovulation between single and double ovulators. Effect of unilateral (n = 24) vs bilateral (n = 26) double ovulations on the incidence of embryo reduction also was considered. Each of 50 double-ovulating mares was matched with two single ovulators yielding 100 ovulations, or potential embryos, per group. Frequency with which an ovulation resulted in a conceptus was greater for single ovulators (85%, P less than .01) and for bilateral double ovulators (77%, P less than .05) than for unilateral double ovulators (60%). The difference between single and bilateral ovulators was not significant. Expected frequencies for none, one or two conceptuses per mare for double ovulators were calculated using the d-11 pregnancy rate for the single ovulators (85%). For unilateral ovulators, but not for bilateral ovulators, observed frequencies of none, one or two conceptuses were different (P less than .05) from expected (observed and expected, respectively, for no conceptuses, 29% and 2%; one conceptus, 21% and 26%; two conceptuses, 50% and 72%). Results did not indicate the existence of an embryo reduction phenomenon before d 11 in bilateral ovulators; each ovum had the same chance (no significant difference) of developing into a d-11 conceptus as an ovum in single ovulators. In unilateral double ovulators, the lower d-11 pregnancy rate per ovum, compared with bilateral ovulators and single ovulators, was attributable to a greater frequency of mares with no embryonic vesicles rather than to a greater frequency of mares with one vesicle.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1987

Reproductive seasonality of the jenney.

Reproductive seasonality was studied in 12 jennies in southern Wisconsin for 12 mo. The proportion of jennies ovulating differed (P<0.05) among months due primarily to a lower proportion ovulating during December (64%) than during the other months (82 to 100%). Of 114 interovulatory intervals, eight were considered prolonged (>35 d) due to persistent corpus luteum (two intervals) and a follicular-related anovulatory period (six intervals). Four of the six follicular-related anovulatory periods were attributed to seasonal effects. The anovulatory season in these four jennies occurred in winter, was relatively short (39 to 72 d), and was terminated by a long period (17 to 41 d) of estrous behavior in the continued presence of large follicles (>20 mm). The prolonged estrus accounted for the lower incidence of ovulations during December and seemed similar to the transition between anovulatory and ovulatory seasons in mares. There was a significant effect of month on length of the interovulatory interval, even after removal of the eight prolonged intervals, due primarily to shorter intervals during May to September (means, 23.0 to 24.3 d) than during October to April (25.0 to 27.3 d). Length of estrus differed significantly among months due primarily to shorter periods during May to October (means, 5.7 to 6.9 d) than during November to April (7.4 to 15.2 d). These results indicated that this species is subjected to seasonal effects on reproductive function. However, contrary to the literature, the dramatic partitioning of the year into ovulatory and anovulatory seasons, as occurs in mares, was absent (eight jennies) or limited (four jennies).

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PubMed1987

Effect of uterine inflammation and ultrasonically-detected uterine pathology on fertility in the mare.

The incidence of intrauterine fluid collections during dioestrus (12/43, 28%) and uterine cysts throughout the oestrous cycle (11/73, 15%) found in this study indicates that these ultrasonically detectable abnormalities are prevalent in mares. The hypothesis that uterine cysts do not affect pregnancy was not supported. Intrauterine fluid collections at dioestrus represented the presence of an inflammatory process as indicated by a high biopsy score, reduced progesterone concentrations, and a shorter interovulatory interval. Mares with fluid collections at dioestrus had a lower pregnancy rate at Day 11 and a higher embryonic loss rate by Day 20 than did mares without such collections. The progesterone profile and length of interovulatory interval for mares with uterine inflammation supported the hypotheses that embryonic loss in this herd was due to uterine-induced luteolysis rather than primary luteal inadequacy.

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PubMed1985

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.

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PubMed1985

Effects of 6-MBOA on reproductive function in ponies, mice, rats and mink.

The effect on reproduction of the plant derivative 6-methoxybenzoxazolinone (6-MBOA), which stimulates reproductive function in voles, was tested in pony mares, laboratory mice and rats, and mink. There was not a significant effect of intravenous injections of 6-MBOA on the ovarian follicles during the transition between the anovulatory and ovulatory seasons in mares. No significant effect of intraperitoneal injections of 6-MBOA on the weight of uterus or ovaries was found in eight-week-old mice, failing to confirm the results of an earlier report. In immature white rats, 6-MBOA treatment resulted in an increase in uterine weight (P<0.05) at the lowest dose tested (0.03 mug/rat; mean for controls, 34 +/-2 mg; treated, 47 +/-5 mg). However, no significant effect was found on the weights of the ovaries and other glands or in coded scores for ovarian stimulation and uterine fluid distention. Adding 1.5 mg 6-MBOA to the daily feed ration of mink beginning two weeks before the mating season did not affect the mean number of kits born. Nulliparous female mink had smaller (P<0.001) litter size than multiparous females. In addition, of the mink that whelped, there were more (P<0.01) nulliparous females (25 118 ) than multiparous females (9 144 ) that lost one or more kits within 48 hours. These results, however, were not altered by 6-MBOA treatment.

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PubMed1985

Embryonic loss in mares: Incidence and ultrasonic morphology.

Pregnancy was determined by ultrasound on Days 11, 15, 20, 25, 30, 35, 40, 45, and 50 in 154 ponies and 27 horses. In ponies, the embryonic loss rate for Days 11 to 15 (28 154 , 18.2%) was greater (P<0.01) than for any of the subsequent five-day intervals (0% to 3.3%). There were no losses during Days 11 to 15 in horses (0 27 ), and the difference between ponies and horses was significant. The loss rates for the seven periods encompassing Days 15 to 50 were not significantly different among periods. Pseudopregnancy occurred more frequently (P<0.01) following embryonic loss after Day 20 (Days 11 to 15, 26%; Days 15 to 20, 33%; after Day 20, 100%). Embryonic vesicles that were lost during Days 11 to 15 were smaller on the average than control vesicles. However, most of the vesicles grew at an apparently normal rate. Two of five vesicles that were lost between Days 15 and 20 and three of four that were lost between Days 20 and 25 were undersized during preceding examinations. Undersized vesicles were found during 13 415 (3%) examinations during Days 11 to 20 in mares that maintained the embryo and in 21 106 (20%) in mares that lost the embryo. Embryonic vesicles that were lost during Days 11 to 15 usually disappeared without previous indications, except in three mares in which the vesicle was floating in a small collection of fluid. Ultrasonic indications of impending loss at later stages included failure of fixation, an echogenic ring (vesicle) or mass floating in a collection of fluid, an echogenic area in the dead embryo, absence of heart beat, and a gradual decrease in volume of placental fluids with disorganization of the placental membranes. The solid remnants and at least some of the fluids resulting from late embryonic and early fetal death were retained sometimes for weeks or months until the debris was apparently expelled through an open cervix.

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PubMed1985

Delayed follicular development and ovulation following inhibition of FSH with equine follicular fluid in the mare.

In two experiments, PGF(2alpha) was given to all mares on Day 10 (ovulation = Day 0). In experiment 1, mares received either whole follicular fluid or saline i.v. every 12 hours on Days 10 to 14. Experiment 2 was similar to experiment 1, except the follicular fluid was extracted with charcoal to remove steroids. Analysis of the FSH data for Days 10 to 21 indicated an effect of treatment (P<0.08) with whole follicular fluid, but not with charcoal-extracted follicular fluid. However, there was an effect of day (P<0.05) and an interaction (P<0.01) of treatment with day for both experiments. The interaction of treatment with day seemed primarily due to a marked post-treatment increase in FSH concentrations between Days 15 and 17 for mares treated with either whole follicular fluid or charcoal-extracted follicular fluid. Analysis of the diameter of the largest follicle for Days 10 to 18 indicated a main effect of treatment (P<0.05) and day (P<0.05) and an interaction (P<0.05) of treatment with day for both experiments. The interaction of treatment with day was attributable to the inhibition of follicular growth by Day 14 for mares treated with whole follicular fluid and by Day 15 for mares treated with charcoal-extracted follicular fluid. The length of the interovulatory interval was longer (P<0.05) in the treated group than in controls for both experiments. Results indicated that equine follicular fluid contained a proteinaceous substance that suppressed circulating concentration of FSH. The inhibited follicular growth and the delay in ovulation were attributed to the reduced concentrations of circulating FSH.

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