Biomedical subjects

E L Squires

Publications and source records attributed to E L Squires.

At least 19 recordsLinked to original sources

PubMed1996

Effects of phosphatidylserine and cholesterol liposomes on the viability, motility, and acrosomal integrity of stallion spermatozoa prior to and after cryopreservation.

Computer-assisted motion analyses (CASA) and flow cytometry were used to evaluate stallion spermatozoa prior to and after cryopreservation. Spermatozoa were pretreated with: (1) Hepes-buffered medium (SHB); (2) phosphatidylserine (PS) liposomes; or (3) liposomes composed of both PS and cholesterol (PSCH) prior to dilution in either SHB or skim milk-egg yolk extender (SMEY). After cooling to 5 degrees C in SHB, PS and PSCH pretreatment (23%). Spermatozoal motion parameters were higher for spermatozoa diluted in SMEY than dilution in SHB. In Experiment 2, motion parameters were compared for spermatozoa pretreated with PSCH liposomes and cryopreserved in either SMEY or a high salt-skim milk-egg yolk extender (CO). Spermatozoal motion characteristics were similar for all spermatozoal treatments after cooling at 5 degrees C. After cryopreservation, PSCH liposome-treated samples had higher percentages of motile spermatozoa than untreated samples regardless of freezing extender. Samples frozen in CO medium had higher percentages of motile spermatozoa than samples frozen in SMEY (P < 0.05; 63% in CO + PSCH and 54% in CO vs 55% in SMEY + PSCH and 48% in SMEY, respectively). In Experiment 3, spermatozoa were treated with dilauroylphosphatidylcholine (PC12) to induce the acrosome reaction. The percentages of viable cells and viable acrosome-reacted spermatozoa were higher for fresh spermatozoa than for cryopreserved spermatozoa (P < 0.05), but were not affected by PSCH liposome treatment (P > 0.05). Addition of PSCH liposomes improved recovery of motile spermatozoa after cryopreservation but did not affect the ability of spermatozoa to undergo a PC12-induced acrosome reaction.

Acrosome↗

PubMed1996

Transvaginal aspiration.

This article describes in detail the procedures for collection of equine oocytes using a transvaginal ultrasound probe. Success in obtaining oocytes from humans, bovines, and horses are presented. The effect of repeated follicular aspiration of both cattle and horses is reviewed.

Animals↗

PubMed1996

Maturation and fertilization of equine oocytes.

Equine oocytes obtained either by transvaginal ultrasound-guided follicular aspiration or from slaughterhouse ovaries can be matured in vitro. This generally requires culture in TCM-199 containing serum and hormones for 30 to 36 hours. With this protocol, approximately 50% to 60% of the oocytes are at metaphase-II at the end of the culture period. At least some of these oocytes appear viable based on production of fertilized eggs either through in vitro fertilization or fertilization in vivo of a recipient mare. The success of producing equine embryos in vitro is still extremely low. More than likely the conditions for in vitro oocyte maturation are not optimized, and the techniques for capacitating equine spermatozoa are not adequate. The stallion sperm would appear more difficult to capacitate and many of the approaches used in other species have not worked in horses. To date, the only fertilization that has occurred with in vitro matured oocytes has been with sperm treatments containing the calcium ionophore A23187. Increased success with in vitro production of equine embryos may be gained through the use of assisted reproductive techniques such as partial zona dissection or intracytoplasmic sperm injection.

Animals↗

PubMed1996

Use of transvaginal ultrasound-guided puncture for elimination of equine pregnancies.

Twinning is a major cause of abortion in mares. Although early management of twins is quite successful, twins that remain after 40 days are difficult to manage. This article reviews the current knowledge of the use of transvaginal ultrasound probe for elimination of twins. Several techniques are presented, as well as discussion on the best time during gestation for this technique to be used.

Abortion, Induced↗

PubMed1996

Factors affecting motion characteristics of frozen-thawed stallion spermatozoa.

Five experiments were conducted to evaluate damage incurred in each processing step for cryopreservation of stallion spermatozoa. In Experiment 1, semen was centrifuged for 9 centrifugation times and the percentage of spermatozoa recovered after each treatment was calculated and spermatozoal motion characteristics analysed. Recovery of spermatozoa was > or = 80% when spermatozoa were centrifuged for > or = 10 min. Experiment 2 evaluated spermatozoa cryopreserved at 5 different concentrations in each of 2 extenders (skim milk-egg yolk-glycerol, SM-EYG; and lactose-EDTA, LAC). In SM-EYG, TMOT and PMOT were higher at spermatozoal concentrations of 20, 200 and 400 x 10(6)/ml (51%/41%, 52%/44%, 50%/43%, respectively) than for samples frozen at > or = 800 x 10(6) spermatozoa/ml (41%/35%, 32%/27%; P < 0.05). Spermatozoa frozen in LAC at a concentration of 20 x 10(6)/ml resulted in the highest TMOT and PMOT (43% and 30%, respectively, P < 0.05). The effect of freezing rate on motion characteristics of spermatozoa was evaluated in Experiment 3. The VCL of spermatozoa frozen in SM-EYG was the only parameter affected by freezing rate (P < 0.05). Experiment 4 evaluated motion characteristics after cryopreservation of spermatozoa in different sized straws (0.5 or 2.5 ml) in each of 2 extenders (SM-EYG and LAC). In SM-EYG, PMOT (38%) and VCL (109 microns/s) were highest when spermatozoa were frozen in 0.5 ml straws (P < 0.05). In Experiment 5, spermatozoa thawed immediately after cryopreservation or thawed after storage in liquid nitrogen for 24-48 h were evaluated. There was no effect of length of storage in liquid nitrogen on spermatozoal motion characteristics (P < 0.05). Experiment 6 evaluated the effects of cooling time to 5 degrees C (0, 2.5 and 5 h) on motion characteristics of spermatozoa cryopreserved in 2 extenders (SM-EYG and LAC). TMOT and PMOT were effected by cooling time, and there was a cooling-time-by-extender interaction (P < 0.05). In SM-EYG, TMOT and PMOT were higher if spermatozoa were cooled to 5 degrees C prior to initiation of freezing than if freezing was initiated at 20 degrees C (P < 0.05). A suggested protocol for cryopreservation of stallion spermatozoa would include: 1) centrifugation at 400 g for 14 to 16 min; 2) extension at 23 degrees C with SM-EYG to 400 x 10(6) spermatozoa/ml; 3) cool to 5 degrees C for 2.5 h; 4) package in 0.5 ml straws at 5 degrees C; 5) freeze in liquid nitrogen vapour at -160 degrees C; and 6) thaw for 30 s in 37 degrees C water.

Animals↗

PubMed1994

Use of gonadotropin-releasing hormone, estrogen, or a combination to increase releasable pituitary luteinizing hormone in early transitional mares.

A lack of pituitary LH stores has been implicated as the cause of seasonal anestrus and failure to ovulate during the spring transition period in mares. In this experiment, 40 mares were used to study the effects of GnRH, estrogen, and an estrogen-GnRH combination on increasing releasable pituitary LH. Mares were stratified based on their ability to secrete LH in response to a 950-micrograms challenge of GnRH (n = 10 per group) and then assigned to one of four treatment groups: 1) controls, given no treatment; 2) 1 mg of estradiol-17 beta in oil i.m. daily for 8 d; 3) 200 micrograms of GnRH analogue des-Gly10, [D-ala6]-LHRH ethylamide in saline i.m. twice daily for 8 d; or 4) estradiol for 4 d then estradiol plus GnRH for four subsequent days. Blood was collected on d 1, 3, 5, and 7 of treatment, and serum was assayed for LH. On d 10 after initiation of treatment, mares were again challenged with GnRH (950 micrograms), and blood was collected for 4 h. Concentrations of serum LH did not vary significantly in control, estradiol-treated, or estradiol plus GnRH-treated mares among treatment days. In contrast, administration of GnRH alone increased (P < .05) concentrations of LH on d 5 and 7. Response to GnRH challenge, as measured by area under the LH curve (AUC) and peak LH, was greater (P < .05) for mares administered GnRH (7,307.1, 67.6 ng/mL, respectively) and GnRH plus estradiol (5,691.4, 60.3 ng/mL) than for mares given estradiol alone (1,519.4, 22.1 ng/mL) or no treatment (1,213.8, 19.4 ng/mL.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1994

Effect of various doses of a gonadotropin-releasing hormone analogue on induction of ovulation in anestrous mares.

One hundred anestrous mares (early February) were injected s.c. with implants containing 0, .9, 1.8, 3.6, or 5.4 mg of a GnRH analogue (goserelin acetate) in an attempt to induce ovarian cyclicity. Follicular activity and concentrations of progesterone and LH were determined every 3 d, or daily during estrus. In treated mares that ovulated, the interval to the second ovulation of the season was compared to that for an additional group receiving 16 h/d of light beginning December 16 (positive controls). Of the mares that did not ovulate in 30 d, eight from each dose group were challenged on d 33 or 34 with an i.v. bolus of 950 micrograms of GnRH. Blood collected at -2, -1, and 0 h before GnRH and at 15, 30, 45, 60, and 90 min and 2, 3, and 4 h after injection was assayed for serum LH. More mares (P < .05) ovulated when given 3.6- (n = 7) or 5.4-mg (n = 6) implants than when given .9-mg implants (n = 0) or placebo (n = 0). Mares with initial follicles < or = 15 mm in diameter were less (P < .05) likely to ovulate (10 of 88) than were those with follicles 16 to 20 mm in diameter (5 of 12). Area under the curve (AUC) for LH was greater for mares receiving larger doses of GnRH. The AUC and peak LH were similar between ovulating and nonovulating mares. Luteinizing hormone peaked in all mares on approximately d 12. There was no difference (P > .05) in either peak LH or AUC among treatment groups in response to the GnRH challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗

PubMed1992

Assessment of Pisum sativum agglutinin in identifying acrosomal damage in stallion spermatozoa.

The use of fluorescein-conjugated Pisum sativum agglutinin (FITC-PSA) was evaluated for its ability to distinguish acrosome-intact from acrosome-damaged stallion spermatozoa. Incubation of fresh (acrosome-intact) and frozen-thawed (acrosome-damaged) spermatozoa with FITC-PSA resulted in acrosome-intact spermatozoa that exhibited no fluorescence, while acrosome-damaged spermatozoa exhibited fluorescent staining over the rostral portion of the head and equatorial segment. Experiments using mixtures of various ratios of acrosome-intact and acrosome-damaged spermatozoa determined the precision (intrasample coefficient of variation), and linearity (increased percentage of spermatozoa with PSA binding, with increased percentage of frozen-thawed spermatozoa in a sample) of FITC-PSA binding. The binding of FITC-PSA increased in samples as the portion of frozen-thawed (acrosome-damaged) to fresh (acrosome-intact) spermatozoa increased. A positive correlation existed (r = 0.98, P less than 0.05) between the percentage of FITC-PSA bound sperm and the proportion of damaged spermatozoa added to a sample. Location of PSA lectin binding on acrosome-damaged spermatozoa, determined by electron microscopy using gold-conjugated PSA, was to components of the outer acrosomal membrane and acrosomal matrix. These results demonstrate that FITC-PSA binding may be useful in determining acrosomal integrity of fresh and frozen-thawed stallion spermatozoa.

Acrosome↗

PubMed1992

Ultrasonographic and quantitative histologic assessment of sequelae to testicular biopsy in stallions.

A sample of testicular parenchymal tissue, approximately 2 x 7 x 7 mm, was aseptically removed from 1 testis in each of 9 stallions on day 0. Slight to moderate hemorrhage from the tunica albuginea was observed in 8 stallions, but bleeding from the parenchyma was detected in only 2 stallions. Stallions were castrated 27 days later. Normal development of granulation tissue was evident at the biopsy site, but hematomas were not observed. In situ measurement of the widths of the right and left testes, total scrotal width, and evaluation of testicular echogenicity during ultrasonography were variables used to monitor changes in the testicular parenchyma from 14 days before biopsy through 27 days after biopsy. The control testis was consistently larger than the biopsied testis, except for day 3. Ultrasonography revealed signs of a localized change in the parenchyma of the biopsied testis in 4 stallions, but each lesion decreased in size by day 27. Tissues removed during biopsy enabled an excellent appraisal of spermatogenesis at that time. Detailed examinations of seminiferous tubules in the testes were performed to assess for damage to testicular function. At castration, samples were taken from 6 sites in each testis. Quantitative histologic evaluations of testicular tissues revealed low numbers of spherical spermatids and pachytene spermatocytes in biopsied testes, compared with control testes. It was concluded that there was a transitory increase in degeneration of preleptotene spermatocytes and B spermatogonia at the time of biopsy. A mild inflammatory response at the biopsy site in some testes was evidenced by an increased number of leukocytes at the biopsy site and at a dorsal site.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Effect of pulsatile or continuous administration of GnRH on reproductive function of stallions.

Gonadotrophin-releasing hormone (GnRH) was administered subcutaneously to reproductively normal stallions, either in a pulsatile manner (10 micrograms GnRH/2 h; n = 6) or as a continuous infusion (10 micrograms GnRH/2 h; n = 6), and in a pulsatile manner to 9 reproductively abnormal stallions, from February to July, 1988. Hormonal secretion patterns, testicular parameters and semen characteristics were monitored before and during treatment. In general, pulsatile GnRH caused a significant increase (P less than 0.05) in luteinizing hormone (LH) concentrations in the peripheral blood of normal stallions. LH levels also appeared to increase in abnormal stallions but the rise was not significant (P greater than 0.05). Stallions given GnRH by continuous infusion and the untreated control stallions did not show an increase in LH concentrations during the treatment period. None of the treatments resulted in significant increases in peripheral blood concentrations of testosterone, although individual stallions that showed an increase in LH secretion appeared to show some increase in testosterone secretion rate. In general, and for individual stallions, none of the treatments resulted in increased total scrotal width, total number of spermatozoa per ejaculate or the percentage of progressively motile spermatozoa in the ejaculate. It was concluded that although pulsatile administration of GnRH may increase the secretion rate of LH and, consequently, testosterone, this adjustment does not increase testicular size or output and motility of spermatozoa.

Animals↗

PubMed1990

Testicular growth, hormone concentrations, seminal characteristics and sexual behaviour in stallions.

Puberty was studied using 15 colts of Quarter Horse phenotype. Total scrotal width was measured every 8 weeks from 48 to 96 weeks. Blood samples were taken from 8 colts at 8, 16 and 24 weeks and then every 4 weeks until 100 weeks to measure changes in LH, FSH and testosterone concentrations. Seminal collections were attempted monthly from 48 to 64 weeks and every 2 weeks thereafter until puberty resumed every 3rd day from 96 weeks for 15 ejaculates. For all collections, times to erection, mount and ejaculation and seminal characteristics were recorded. Age at puberty was defined as the first ejaculate containing 50 x 10(6) spermatozoa, with greater than or equal to 10% motile. Colts were castrated at 2 years to enable determination of daily sperm production (DSP), epididymal sperm reserves and normality of spermatogenesis. Total scrotal width increased linearly from 48 to 96 weeks. Age at puberty averaged 83 weeks (56-97 weeks). Changes in serum concentrations of LH and FSH were parallel, rising at 36-40 weeks, declining after 40 weeks and rising again at 68-80 weeks. Testosterone was low until 68 weeks after which concentrations rose slowly to 80 weeks and increased rapidly to a plateau at 92 weeks. Sexual behaviour and seminal characteristics differed (P less than 0.05) between puberty and 2 years, except for time to erection, time to mount, and percentage of motile spermatozoa. DSP at 2 years averaged 1.7 x 10(9) and daily sperm output (DSO) averaged 1.1 x 10(9). The correlation between DSP and DSO was 0.83 (P less than 0.01). There were 9.57 x 10(9) spermatozoa/epididymis of which 67% were in the cauda.

Animals↗

PubMed1990

Effect of maternal treatment with altrenogest on pituitary response to exogenous GnRH in pubertal stallions.

The pituitary response to exogenous GnRH was studied in 8 colts of Quarter Horse phenotype from 32 to 96 weeks of age. Colts were from dams treated daily from Day 20 to 325 of gestation with (1) 2 ml neobee oil per 50 kg body weight (controls); or (2) 2 ml altrenogest per 50 kg body weight. GnRH challenges (5 micrograms/kg body weight) were administered every 8 weeks from 32 to 96 weeks of age to estimate pituitary content of LH. Blood samples were collected every 20 min for 4 h before GnRH and 15, 30, 45, 60, 90, 120, 180, 240 and 360 min after GnRH. Serum concentrations of LH and FSH were determined for the 2 pre-GnRH and all post-GnRH samples. Baseline concentrations (mean of 2 pre-GnRH samples) of LH and FSH were not affected by treatment (P greater than 0.05). Serum concentrations of LH declined from 40 to 56 weeks and rose again between 72 and 80 weeks. Basal concentrations of FSH declined from 32 to 56 weeks, and varied widely after 56 weeks. The maximum LH response to GnRH (highest concentration after GnRH minus baseline) declined steadily in both groups for 48 to 64 weeks but remained relatively constant in both groups after 64 weeks. The maximum FSH response to GnRH declined from 32 to 64 weeks then remained relatively constant in both groups. The GnRH-induced gonadotrophin release remained low with a transient increase at 72 weeks for both hormones.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Effect of maternal treatment with altrenogest on age at puberty, hormone concentrations, pituitary response to exogenous GnRH, oestrous cycle characteristics and fertility of fillies.

Puberty was studied using 15 fillies of Quarter Horse phenotype. Fillies were from dams treated daily from Days 20 to 325 of gestation with: (1) 2 ml neobee oil per 50 kg body weight (controls); or (2) 2 ml altrenogest (2.2 mg/ml) per 50 kg body weight. The clitoris was measured at birth and approximately every 12 weeks until 84 weeks of age. Blood samples were collected from 9 fillies (5 treated, 4 controls) every 4 days over a 28-day period at 8-week intervals from 4 to 68 weeks of age; sampling continued every 4 days after 72 weeks of age until first oestrus. Blood samples were collected daily during oestrus (greater than or equal to 35 mm follicle) and on Days 4, 6, 10, and 14 after ovulation for the first 2 oestrous cycles. GnRH challenges (5 micrograms/kg) were administered every 8 weeks from 32 to 96 weeks of age. Puberty was defined as the first oestrus with ovulation. Beginning 1 February 1987, fillies were teased daily and their ovaries were examined by ultrasonography every 3 days (daily during oestrus). Fillies were inseminated with 500 x 10(6) motile spermatozoa from one stallion. Pregnancy was diagnosed by ultrasonography on Days 11, 12, 15 and every 5 days until Day 50 after ovulation. Prenatal altrenogest treatment caused clitoral enlargement (P less than 0.05) and increased serum concentrations of LH from 1 to 7 months of age. The amount of LH released in response to exogenous GnRH was greater (P less than 0.05) in treated fillies at 32, 64, and 72 weeks of age. Treated fillies had higher serum concentrations of FSH from 1 to 4 months (P less than 0.05), but FSH was lower (P less than 0.05) in treated fillies before and during first oestrus. Serum concentrations of LH and FSH peaked transiently at 10 months and LH was depressed from 64 to 88 weeks and began to rise 14 days before first oestrus. Concentrations of FSH began to decline 14 days before first oestrus. The median age at puberty was 90 weeks. Durations of oestrus, dioestrus, and the oestrous cycle were not different between groups and were similar to those for adult mares. First cycle pregnancy rates and overall rates were 100 and 82% and 100 and 91.7% for control and treated fillies, respectively (P greater than 0.05). Maternal treatment with altrenogest did alter gonadotrophin secretion before puberty, but had no effect on functional reproductive performance in fillies.

Animals↗

PubMed1990

Effects of transportation on early embryonic death in mares.

Incidence of early embryonic death (EED) and associated changes in serum cortisol, progesterone and plasma ascorbic acid (AA) in transported mares were investigated. Mares were transported for 472 km (9 h) during either d 16 to 22 (T-3 wk, n = 15) or d 32 to 38 (T-5 wk, n = 15) of gestation. Blood samples were drawn from control, nontransported mares (NT-3 wk, NT-5 wk, n = 24) and transported mares pre-trip, midtrip, and at 0, 12, 24, 48 and 72 h post-transport and daily for the next 2 wk. Incidence of EED between transported and nontransported mares was not different (P greater than .05). Serum cortisol in all transported mares increased (P less than .05) relative to pre-trip values at midtrip and 0 h post-transport. Relative to NT mares, serum cortisol was higher (P less than .05) at midtrip in T-3 wk mares and 0 h post-transport in T-5 wk mares. Serum progesterone in all T mares increased (P less than .05) at midtrip relative to pre-trip values and was higher (P less than .05) in T-3 wk mares than in NT-3 wk mares at midtrip and 0 h post-transport. Post-transport decreases (P less than .05) in concentrations of progesterone were observed in mares that aborted. Plasma AA in transported mares increased (P less than .05) at midtrip in T-5 wk mares and decreased (P less than .05) relative to pre-trip values at 24 and 48 h post-transport (T-3 wk and T-5 wk mares, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

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)

Animals↗

PubMed1990

Use of gonadotropin-releasing hormone for hastening ovulation in transitional mares.

Natural GnRH and its analog have potential for hastening ovulation in mares. A study was conducted to evaluate the efficacy of a GnRH agonist given either as an injectable or s.c. implant for induction of ovulation in mares. Forty-five seasonally anestrous mares (March) were assigned to one of three groups (n = 15/group): 1) untreated controls; 2) i.m. injection of the GnRH agonist buserelin at 12-h intervals (40 micrograms/injection for 28 d or until ovulation) and 3) GnRH agonist administered as a s.c. implant (approximately 100 micrograms/24 h for 28 d). Six mares per group were bled on d 0, 7, 14 and 21 after injection or insertion of implant. Samples were taken at -1, -.5 and 0 h and at .5, 1, 1.5, 2, 4, 6 and 8 h after GnRH. Additional daily samples were drawn for 28 d after injection or until ovulation. Samples were assayed for concentration of LH and FSH. Progesterone concentrations were determined in samples collected on d 4, 6 and 10 after ovulation. Number and size of follicles and detection of ovulation were determined by ultrasonography. Number of mares induced to ovulate within 30 d was 0 of 15, 7 of 15 and 9 of 15 for groups 1, 2 and 3, respectively. During treatment, follicle sizes were smaller for mares in group 3 (implant). The LH response to GnRH agonist (area under curve) was similar among groups at d 0 but was greater (P less than .05) for mares in group 3 on d 7 and 14 and groups 2 and 3 on d 21 than for controls. A similar pattern was detected for peak concentrations of LH after GnRH on d 0, 7, 14 and 21. Daily concentrations of LH remained low in untreated control mares compared with GnRH-treated mares throughout the sampling period. Concentrations of LH for mares in group 3 that ovulated were elevated greatly above those for group 2 mares, whereas concentrations of FSH were similar in both treatment groups prior to ovulation.

Anestrus↗

PubMed1990

Gonadotropin response by postpartum mares to gonadotropin-releasing hormone.

We hypothesized that the LH response to GnRH would be greater as the interval from foaling increases, whereas the FSH response would decrease, and that corpus luteum function after the first ovulation would be similar to that after the second ovulation. At parturition, mares were assigned to receive GnRH (2 micrograms/kg) intravenously on 1) d 3 postpartum (n = 6); 2) d 6 postpartum (n = 6); 3) d 1 of first postpartum estrus (foal estrus) and again on d 1 of second postpartum estrus (n = 8). Blood was collected through an indwelling cannula at -2, -1 and 0 h relative to GnRH stimulation (basal concentrations) and at .25, .5, .75, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0 h post-GnRH. Samples were assayed for concentrations of LH and FSH. Basal concentrations of LH were lower (P less than .05) for mares given GnRH on d 3 postpartum than for mares on d 1 of foal estrus. A rise in concentrations of LH was noted within 30 min in all groups, but the response to GnRH on d 1 of the first estrus was less (P less than .05) than on d 1 of second postpartum estrus. As the interval from parturition increased, the amount of LH secreted in response to GnRH increased. The maximum response to GnRH was greater (P less than .05) during d 1 of the first estrus than on d 3 or 6 postpartum and was greater on d 1 of cycle 2 than on d 1 of cycle 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Influences of season and artificial photoperiod on stallions: pituitary and testicular responses to exogenous GnRH.

Effects of season and photoperiod on the anterior pituitary gland and testes were studied by responses to exogenous GnRH. Stallions were assigned to one of three treatments: 1) control, exposed to natural day length; 2) S-L, 8 h of light and 16 h dark (8:16) for 20 wk beginning July 16, 1982 then 16:8 from December 2, 1982 until March 5, 1984; or 3) S-S, 8:16 from July 16, 1982 until March 5, 1984. Approximately every 8 wk, stallions were administered GnRH (2 micrograms/kg BW) and blood was sampled at 20-min intervals for 2 h before and 8 h after GnRH administration. Concentrations of LH, FSH and testosterone were determined. Baseline concentrations (mean of pre-GnRH samples) of all hormones fluctuated seasonally (P less than .05), but only LH and testosterone displayed seasonal changes (P less than .05) in maximum response to GnRH (highest concentration above baseline after GnRH). The FSH response to GnRH was not affected (P greater than .05) by season, photoperiod or the season X treatment interaction. Exposure of S-L stallions to 16:8 in December resulted in early recrudescence of baseline concentrations of LH, FSH and testosterone. Maximum concentration of testosterone in response to GnRH was stimulated by 16:8, but the increase in baseline LH concentrations in S-L stallions was not associated with an increase in maximum LH response to GnRH. Seasonal patterns of baseline concentrations of FSH and testosterone and maximum LH response to GnRH in S-S stallions were similar to those for control stallions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗