Prolactin administration to seasonally anestrous mares: reproductive, metabolic, and hair-shedding responses

Effects of blue monochromatic light directed at one eye of pregnant horse mares on gestation, parturition and foal maturity

Blue light directed at 1 eye advances the equine ovulatory season but may also advance foaling. In this study, effects of blue LED light on pregnancy outcome were assessed. A total of 20 mares with singleton pregnancies were studied over 2 consecutive years in a cross-over design. In 1 year, mares received an extended photoperiod using 50 lux of blue LED light (468 nm) directed at a single eye from 08:00 until 23:00 daily via head-worn light masks starting mid-December and in the other year remained untreated as controls. Gestation was shorter in blue LED light-treated than in control pregnancies (median 333.0 vs 338.5 days, P = 0.036). Foals born to blue LED light-treated mares had lower wither heights (median 103.0 vs 104.5 cm, P = 0.023), similar weights (median 55.8 vs 54.8 kg, P = 0.732) and took less time to stand after birth than control foals (median 35.0 vs 53.5 min, P = 0.036). Foals born to blue LED light-treated mares had reduced hair length compared to controls (median 12.0 vs 20.0 mm, P = 0.009) and hair regrowth in treated mares was reduced (P = 0.036). In conclusion, blue LED light directed at 1 eye advanced foaling and influenced height and hair coat but not weight in foals.

hCG is more effective than the GnRH agonist buserelin for inducing the first ovulation of the breeding season in mares

Background

Human Chorionic Gonadotropin (hCG) and Gonadotropin Releasing Hormone agonists (GnRHa) are routinely used to induce ovulation in mares. However, GnRHa efficacy in transitional mares has been suggested to be low.

Objectives

The aims of this study were as follows: (a) to compare the efficacy of hCG and GnRHa in inducing the first ovulation of the breeding season and (b) to evaluate the correlation between ovulatory response, uterine oedema and teasing score at the time of treatment during the early or late transitional phase.

Study design

Randomised controlled superiority trial.

Methods

Mares in winter anoestrus were treated with sulpiride when at least two follicles reached a diameter of 25 mm. The day after the follicle reached 35 mm in diameter, mares in oestrus were treated with GnRHa buserelin (N = 29) or hCG (N = 33) and checked daily for ovulation.

Results

More mares (30/33, 90.1%) ovulated when the first ovulation after winter anoestrus was induced with hCG, than with GnRHa, (11/29, 38.0%) (P = .0001). Ovulation rate was lower in mares that did not show uterine oedema and full acceptance of the teaser stallion for at least three days before the treatment (32/41, 78% vs 9/21, 42.9%) P = .01.

Main limitations

Plasma LH and oestrogen concentrations were not performed.

Conclusions

These results demonstrate that hCG was more effective than GnRHa for inducing ovulation in the first cycle after winter anoestrus. Uterine oedema and behavioural signs of oestrus, for at least three days before the treatment, were predictors for a positive response to ovulation induction.

Impact of Ergot Alkaloids on Female Reproduction in Domestic Livestock Species

Fescue toxicosis is a multifaceted syndrome that elicits many negative effects on livestock consuming ergot alkaloids produced by endophyte-infected tall fescue. The economic losses associated with fescue toxicosis are primarily due to reproductive failure including altered cyclicity, suppressed hormone secretion, reduced pregnancy rates, agalactia, and reduced offspring birth weights. For decades, a multitude of research has investigated the physiological and cellular mechanisms of these reproductive failures associated with fescue toxicosis. This review will summarize the various effects of ergot alkaloids on female reproduction in grazing livestock species.

Effects of Combined Estradiol-Sulpiride Treatment and Follicle Ablation on Vernal Transition in Mares: Evaluation of Plasma and Follicular Fluid Hormones and Luteinizing Hormone Receptor Gene Expression

This experiment assessed the hormonal production, secretory aspects, and changes in luteinizing hormone (LH) receptor gene expression of early induced ovulatory-sized follicles relative to the first ovulatory-sized follicles occurring naturally in the spring. Anovulatory mares were treated on January 21 with (1) 50 mg of estradiol cypionate (ECP, n = 8) alone or (2) with ECP followed by two 3-g sulpiride injections (n = 8), 5 and 12 days later. Half of each group also received complete follicle ablation via transvaginal aspiration before ECP treatment. Ovaries were scanned regularly until detection of a 32-35 mm follicle; follicular fluid was recovered via aspiration for analysis of hormonal concentrations. Blood was collected regularly to characterize plasma prolactin, LH, follicle stimulating hormone, progesterone, and estradiol concentrations. Mean date to first 35-mm follicle was earlier (P < .05) in sulpiride-treated mares: five of eight (63%) responded within 28 days of the first sulpiride injection. Ablation did not affect ovarian response. Plasma prolactin was stimulated (P < .0001) in ECP-sulpiride-treated mares for 16 days but did not dictate ovarian response. Estradiol stimulated plasma LH (P < .05), which was higher (P < .05) in treated mares that responded. There was no effect of treatment or ablation on follicular fluid concentrations of estradiol, progesterone, leptin, or insulin-like growth factor 1 or on LH receptor gene expression. These latter similarities indicate that ECP-sulpiride early induced follicles have apparently reached a degree of maturity equivalent to naturally occurring ovulatory-sized follicles later in the spring.

Seasonal changes in reproductive and pelage status during the initial ‘quiescent’ and first ‘active’ breeding seasons of the peripubertal pony colt

Pony colts (~12 m) are generally infertile during the breeding season of mature stallions. The mechanism which ‘delays’ puberty beyond the first potential breeding opportunity has not been described. Four pre- and four post-pubertal colts were monitored from November for 13 (group 1, 6 to 19 months of age) and 9 months (group 2, 18 to 27 months of age). Fortnightly, 15 blood samples were collected at hourly intervals from each colt to determine concentrations of prolactin (PRL), LH, FSH and testosterone (T). Testicular biopsies were collected monthly to evaluate spermatogenic activity. Puberty occurred between 17 and 19 months, and at the onset of the 2-year-old breeding season, all colts were fertile. Seasonal changes in the concentrations of all four hormones were observed in both groups. Prolactin concentrations were correlated with changes in day length (r = 0·88) in both groups, but a biphasic profile was noted in group 1. Moulting of the winter coat was coincident with seasonally increased PRL concentrations (P < 0·001). Seasonal changes in FSH, LH and T concentrations were similarly timed between groups and levels were maximal in mid April, mid March and mid May, respectively. However, overall mean concentrations of LH and T in group 1 animals were only 0·33 and 0·22 of group 2 values (P < 0·001). Suppression of gonadal activity during the colts’ first ‘quiescent’ breeding season was associated with low concentrations of circulating LH. Appropriately timed changes in plasma PRL, FSH and T concentrations and pelage indicated that the photoperiodic mechanism was functional in the pre-pubertal colt but pituitary LH release may be blocked by immaturity or active suppression.

Different effects of an extended photoperiod treatment on growth, gonadal function, and condition of hair coats in Thoroughbred yearlings reared under different climate conditions

One- to two-year-old Thoroughbred colts and fillies being reared in Miyazaki (warm climate) and Hidaka (cold climate), Japan, were administered extended photoperiod (EP) treatment between December 20 and the following April 10, and its effect on growth, endocrine changes, gonadal activation, and hair coat condition was investigated. In colts reared in Miyazaki, no effect of EP treatment was noted on the growth indices, including body weight (BW), height at withers (HW), girth, and cannon circumference (CC), whereas the BWs and CCs of fillies were significantly higher in the EP treatment group than the control. In Hidaka, the BWs and HWs of colts and HWs of fillies were significantly higher in the EP treatment group. Gonadal activation characterized by an increase in circulating hormone concentrations was earlier in the EP treatment group for fillies reared in Miyazaki [luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone (P4), and estradiol-17β (E2)] and in colts (LH, testosterone, and E2) and fillies (LH, FSH, P4, and E2) reared in Hidaka. Regardless of sex and climate, prolactin was significantly higher in the EP treatment group, whereas insulin-like growth factor (IGF-I) was not. Initial ovulation occurred before April in more of the EP treatment group than the control regardless of the climate. Molting of the hair coat, examined in March, was advanced in the EP treatment group regardless of sex and climate. These results suggest that EP treatment may promote growth and gonadal activation in fillies reared in Miyazaki and in colts and fillies reared in Hidaka and that the effect may be mediated by prolactin.

Activities and Effects of Ergot Alkaloids on Livestock Physiology and Production

Consumption of feedstuffs contaminated with ergot alkaloids has a broad impact on many different physiological mechanisms that alters the homeostasis of livestock. This change in homeostasis causes an increased sensitivity in livestock to perturbations in the ambient environment, resulting in an increased sensitivity to such stressors. This ultimately results in large financial losses in the form of production losses to livestock producers around the world. This review will focus on the underlying physiological mechanisms that are affected by ergot alkaloids that lead to decreases in livestock production.

Effects of an extended photoperiod on gonadal function and condition of hair coats in Thoroughbred colts and fillies

The effects of an extended photoperiod (EP) in Thoroughbreds colts and fillies from winter at one year old to spring at two years old on the gonadal functions, coat condition, and endocrine changes were investigated. Sixty-two Thoroughbreds (31 colts and 31 fillies) reared in the Hidaka Training and Research Center (Hidaka), Japan Racing Association were used. Thirty of them (15 colts and 15 fillies) were reared under EP conditions from December 20 to April 10, and the remaining 32 horses were reared under natural light alone as a control group. For EP, a 100-watt white bulb was set near the ceilings of stalls, and lighting conditions of 14.5-hr light and 9.5-hr dark periods were established. Blood was collected from the jugular vein once a month from October at one year old to February at two years old in both colts and fillies, and then twice a month in colts and weekly in fillies after March, and the coat condition was evaluated in January and April in 56 horses. To investigate endocrine changes, the plasma concentrations of prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), immunoreactive (ir-) inhibin, testosterone, estradiol-17β and progesterone were measured. No significant difference was noted in the coat condition between the two groups in January, but they changed from winter to summer coats (molting of winter coats) in April in the EP group compared with the control group. Regarding endocrine changes, the plasma concentrations of prolactin, FSH, ir-inhibin and testosterone were significantly higher in the EP colts than in the control group from January to April. The plasma concentrations of LH tended to rise in the EP colts from January to April compared with the control group. In the EP fillies, the plasma concentrations of prolactin, LH, ir-inhibin, estradiol-17β and progesterone were significantly higher during January and April, but a significantly high level of FSH was noted in the control than EP group in January. The ovulation day was advanced in the EP fillies compared with the control group. The present study clearly demonstrated that EP treatment during rearing advanced the molting of winter coats in both colts and fillies. These results suggested to be due to the action of prolactin being increased by EP treatment. In addition, EP treatment stimulated the hypothalamus-pituitary-gonadal axis even in yearlings, and advanced ovulation in fillies. Since EP treatment-induced changes in the yearlings were within the physiological range, and the method is safe and simple, EP treatment may be an effective technique in horse husbandry.

Genetic effect of the prolactin receptor gene on egg production traits in chickens

The identification and utilization of potential candidate genes with significant effects on economically important traits have become increasingly important in poultry breeding programs. The prolactin (PRLR) receptor is a specific receptor for prolactin, which is an anterior pituitary peptide hormone involved in various physiological activities and is essential for reproductive success. In chickens, the PRLR gene resides on the Z chromosome. We used a pooled DNA sequencing approach for identifying SNPs of the PRLR gene. Three hundred and nine-six Erlang Mountainous chicken hens were genotyped for six SNPs using PCR-SSCP and PCR-sequencing methods; the association with chicken egg production traits was studied using general linear model procedures. Three linked SNPs (G14952A, A14969C and G14984A) at the P1 locus, two linked SNPs (G17560A and T17626A) at the P2 locus, and one SNP (T20868C) at the P3 locus were identified. Eight haplotypes were reconstructed on the basis of the six SNPs. The general linear model analysis indicated that there were significant associations of certain genotypes and haplotypes with some egg production traits. We conclude that chicken PRLR gene polymorphisms are associated with egg production traits and have potential as molecular markers for chicken breeding.

Reproductive seasonality in the mare: neuroendocrine basis and pharmacologic control

Reproductive seasonality in the mare is characterized by a marked decline in adenohypophyseal synthesis and secretion of LH beginning near the autumnal equinox. Thus, ovarian cycles have ceased in most mares by the time of the winter solstice. Endogenous reproductive rhythms in seasonal species are entrained or synchronized as a result of periodic environmental cues. In the horse, this cue is primarily day length. Hence, supplemental lighting schemes have been used managerially for decades to modify the annual timing of reproduction in the mare. Although a full characterization of the cellular and molecular bases of seasonal rhythms has not been realized in any species, many of their synaptic and humoral signaling pathways have been defined. In the mare, neuroendocrine-related studies have focused primarily on the roles of GnRH and interneuronal signaling pathways that subserve the GnRH system in the regulatory cascade. Recent studies have considered the role of a newly discovered neuropeptide, RF-related peptide 3 that could function to inhibit GnRH secretion or gonadotrope responsiveness. Although results that used native peptide sequences have been negative in the mare and mixed in all mammalian females, new studies that used an RFRP3 antagonist (RF9) in sheep are encouraging. Importantly, despite continuing deficits in some fundamental areas, the knowledge required to control seasonal anovulation pharmacologically has been available for >20 yr. Specifically, the continuous infusion of native GnRH is both reliable and efficient for accelerating reproductive transition and is uniquely applicable to the horse. However, its practical exploitation continues to await the development of a commercially acceptable delivery vehicle.

Reproductive performance of donor mares subsequent to eFSH treatment in early vernal transition: Comparison between the first, second, and mid-season estrous cycles of the breeding season

The objective was to compare the reproductive performances associated with the first (Cycle-1), second (Cycle-2), and mid-season (MS-Cycle) ovulations of the breeding season in donor mares that were treated with equine-FSH (eFSH) in the early vernal transition. Mares (n=15) kept under ambient light were examined ultrasonographically per-rectum starting January 30. When an ovarian follicle > or =25mm in diameter was detected, twice daily eFSH treatments were initiated. The eFSH treatments ceased when a follicle > or =35mm was detected, and 36h later hCG was administered. Thereafter, mares were artificially inseminated every 48h until ovulation (Day 0). Trans-cervical embryo recovery attempts were performed on Day 8, and subsequently PGF2alpha was administered. Equine FSH was not administered in the subsequent estrous cycles. In Cycle-2 and in the MS-Cycle, hCG was administered when a follicle > or =35mm was detected; breeding, embryo recovery, and PGF2alpha administration, were similar to Cycle-1. Mares had an untreated estrous cycle (no treatment or breeding) between Cycle-2 and the MS-Cycle. All mares developed follicle(s) > or =35mm after 4.9+/-0.6 days of eFSH treatment, and subsequently ovulations occurred; mean (95% CI) interval from treatment initiation to ovulation was 7.9 (6.5-9.3) days. The number of preovulatory follicles (> or =30mm) at the time of hCG administration (Cycle-1: 2.2+/-0.3 compared with Cycle-2: 1.0+/-0 compared with MS-Cycle: 1.1+/-0.1 follicles), and the number of ovulations (2.5+/-0.4 compared with 1.0+/-0 compared with 1.1+/-0.1 ovulations) were greater (p<0.05) in Cycle-1. Nevertheless, mean embryo numbers did not differ among cycles (0.8+/-0.2 compared with 0.5+/-0.1 compared with 0.5+/-0.1 embryo/mare). On average, embryo morphology grade was less (p<0.05) in Cycle-1 as compared to non-eFSH cycles (combined Cycle-2 and MS-Cycle). This impaired embryo quality could be due to a seasonal effect, or negative effect of the eFSH treatment, which was possibly related to alterations in the hormonal environment (estradiol-17beta and progesterone). A prolonged IOI (>21 days) was recorded in 7 of 15 mares following the Cycle-1 ovulation, but not subsequently. In conclusion, eFSH treatment of vernal transitional donor mares stimulated ovulation within only few days of treatment, and the following embryo recovery rate was at least as good as in the subsequent estrous cycles; however, on average, embryos were morphologically impaired. In subsequent estrous cycles in the breeding season, ovulations, embryo recovery rates, and embryo variables did not appear to be negatively affected; however, the first inter-ovulatory interval of the breeding season was prolonged in approximately half of the mares.

Follicle development in mares

The mare provides a unique experimental model for studying follicle development in monovular species. Development of antral follicles in horses is characterized by the periodic growth of follicular waves which often involve the selection of a single dominant follicle. If properly stimulated, the dominant follicle will complete development and eventually ovulate a fertile oocyte. Regulation of follicular wave emergence and follicle selection involves an interplay between circulating gonadotropins and follicular factors that ensures that individual follicles are properly stimulated to grow (or to regress) at any given stage of follicular wave development. Periodic development of follicular waves continuously occurs during most of post-natal life in the mare and is influenced by factors such as stage of oestrous cycle, season, pregnancy, age, breed and individual so that different types of follicular waves (minor or major, ovulatory or anovulatory) and different levels of activity within waves may develop under different physiological conditions. Changes in gonadotropin levels and/or in the sensitivity of follicles to circulating gonadotropins seem to account largely for these physiological variations in follicle development.

Spaying-induced coat changes: the role of gonadotropins, GnRH and GnRH treatment on the hair cycle of female dogs

Although spaying can result in qualitative hair coat changes in dogs, the influence of spaying on the hair growth cycle has never been described. The study aims were to examine the effect of spaying and gonadotropin-releasing hormone (GnRH) treatment on canine hair coat, cycle stages of hair follicles, plasma gonadotropin concentrations and mRNA transcription of luteinizing hormone (LH) and GnRH receptors in hair follicles. Fifteen female dogs were examined before and 1 year after spaying and 24 spayed dogs before and after GnRH treatment. Spaying resulted in increased plasma gonadotropin concentrations and increased anagen : telogen ratio of hair follicles, but only 20% of the dogs developed coat changes. No differences were found in mRNA transcription of LH and GnRH receptors. GnRH treatment resulted in reduced plasma gonadotropin concentrations and improvement of coat changes in 79% of patients. This was associated with an increase in catagen hair follicles without changes in the anagen : telogen ratio. The present study demonstrated that spaying had an effect on the anagen : telogen ratio of hair follicles. Spaying-induced coat changes did not correlate with the anagen : telogen ratio. GnRH treatment reduced gonadotropin concentrations and reversed coat changes in some dogs, but had no effect on the hair growth cycle other than increasing the number of catagen hair follicles. A weak positive correlation between the plasma LH concentration and the anagen : telogen ratio was noted; however, our data did not suggest a direct receptor-mediated hormonal effect on the hair follicle. The present study did not identify the pathomechanism of spaying-induced coat changes.

Seasonal relationships between dopamine D1 and D2 receptor and equine FSH receptor mRNA in equine ovarian epithelium

Dopamine (DA) blockade during anestrus or early spring transition can facilitate ovarian recrudescence and advance the timing of the first ovulation of the season. Some laboratories have reported variable results using DA antagonists to stimulate follicular growth during the mid-portion of the anestrual period. Differences in DA antagonist efficacy may be due to the FSH secretory status of the anestrous mare and the presence or absence of functional ovarian FSH receptors. We hypothesize that direct ovarian dopaminergic input can affect follicular growth through regulation of FSH receptor (FSHr) populations. To investigate this, the amount of DA D1 and D2 receptor (D1r, D2r) and FSHr mRNA was quantified in ovarian tissues in anestrous and mares expressing estrus at typical intervals that are detected during the breeding season. Ovaries (n=26) were collected from 10 anestrous mares and 13 mares that had initiated estrous cycles (n=8 luteal; n=5 follicular phase). The quantity of D1r and D2r mRNA and FSHr mRNA was determined in cortex of both groups and granulosa/theca (those having initiated estrous cycles) tissues by semi-quantitative polymerase chain reaction using the comparative cycle time method. The reference gene was glyceraldehyde-3-phosphate dehydrogenase. The fold-change for each sample was calculated based on a calibrator sample. Fold-change values for D1r and D2r were the dependent variable and tissue was the independent variable in a one-way ANOVA. Results of fold-change in FSHr were compared by ANCOVA due to unequal sample sizes from each mare. Correlations between receptors within each tissue type were determined. For each receptor type and tissue, correlations between follicular and luteal phases were determined. The fold-change of D1r mRNA was less than D2r mRNA in all tissue types and between seasons. The quantity of D2r message in ovarian cortex was greater (p<0.05) during anestrus than after estrous cycles had been initiated. Fold-change in D2r in granulosa/theca was not different dependant on estrous cycle phase or follicle size. Quantity of FSHr mRNA was less in anestrous ovarian cortex and greater after estrous cycles had been initiated. FSHr mRNA fold-change in the ovarian cortex after estrous cycle initiation was not different between estrous cycle phases, but was greater in smaller (<30mm) follicles compared with larger (> or =30mm) follicles. We have demonstrated an inverse temporal relation between ovarian D2r and FSHr in mares dependant upon season. The functional significance of this relationship deserves further study.

Seasonal changes in ovarian activity: Lessons learnt from the horse

The annual reproductive cycle in the horse involves a reduction in ovarian activity during short days. The absence of ovulatory activity during winter has important consequences for an equine industry eager to breed mares early during the year. The anovulatory season results from a reduction in the secretion of pituitary gonadotropin that is in turn triggered by the inhibitory effects of short photoperiod on the hypothalamus-pituitary axis. Recent studies have provided evidence that the response of the ovaries to endocrine stimuli during the anovulatory season is affected not only by circulating concentrations of trophic hormones but also by locally produced growth factors that are putative modulators of follicular responses to gonadotropins. The present review summarises current knowledge on ovarian dynamics during the equine anovulatory season and the regulatory mechanisms involved at both systemic and local levels.

Recurrent flank alopecia in a Tibetan Terrier

Recurrent flank alopecia is described in a 2-year-old, male, neutered Tibetan Terrier with concurrent atopic dermatitis. The diagnosis of recurrent flank alopecia was made after 3 consecutive years of localised, winter-onset alopecia. The diagnosis was based on history, compatible clinical signs and supportive histopathology. The diagnosis was complicated by the presence of concurrent pruritic dermatitis. To our knowledge this is the first report of recurrent flank alopecia in this breed.

Administration of sulpiride to anovulatory mares in winter: effects on prolactin and gonadotropin concentrations, ovarian activity, ovulation and hair shedding

Sixteen seasonally anovulatory mares were randomly allotted to two groups and injected daily with either sulpiride (1 mg/kg body weight) or vehicle from 14 January to 14 February. Sulpiride administration increased daily plasma prolactin concentrations (P < 0.05), although the prolactin response during the 6 h following sulpiride injections decreased markedly from the 1st to the 6th day of treatment (treatment by day, P < 0.0001). Plasma concentrations of LH and FSH were not affected by treatment (P > 0.1). Injection of GnRH and TRH on 15 February showed that the response of plasma prolactin to secretagogue was increased in sulpiride-treated mares (P < 0.005), while there was no effect (P > 0.1) of sulpiride treatment on the response of LH or FSH. Both treatment groups had similar changes in numbers of follicles 10-19 and > or = 20 mm during the experiment (P > 0.1). Similarly, the mean change in maximal follicular size was not affected by treatment (P > 0.9). No mare ovulated during the study, and plasma progesterone concentrations were similar in both groups (P > 0.1), always at levels < 1 ng/ml. Hairshedding increased with time in all mares (P < 0.001) and was increased by sulpiride injections (P = 0.09). It was concluded that sulpiride administration to seasonally anovulatory mares under the conditions of our experiment increased daily plasma prolactin levels but did not stimulate gonadotropin secretion or ovarian activity.

Seasonality in mares

In this review, we have attempted to summarize, based on recent data obtained in our laboratory and elsewhere, our current understanding of the regulatory mechanisms of seasonality and discuss the implications with regard to treatment strategies to advance the onset of cyclic reproductive activity in the early spring.