Effect of Follicle Size and Follicle-Stimulating Hormone on Ovulation Induction and Embryo Recovery in the Mare

The timing of ovulation is an important component to many equine breeding strategies. The action of luteinizing hormone on ovulation induction has been recognized; however, potential effects of follicle-stimulating hormone (FSH) have been less defined. Objectives of this study were to determine whether (1) mares could be induced to ovulate follicles ≤30 mm; (2) equine FSH (eFSH) has a positive effect on ovulation induction, and (3) ovulation of small follicles would affect embryo recovery. Light-horse mares (n = 12) between 4 and 10 years of age were assigned to treatments when they had a dominant growing follicle with a mean diameter of 24, 28, or 35 ± 2 mm and endometrial edema. Treatments were (1) H35, human chorionic gonadotropin (hCG) at 35 ± 2 mm; (2) F35, eFSH at 35 ± 2 mm; (3) H28, hCG at 28 ± 2 mm; (4) FH28, eFSH and hCG at 28 ± 2 mm; (5) D28, deslorelin (gonadotropin-releasing hormone [GnRH] analog) at 28 ± 2 mm; (6) FH24/H24, hCG or eFSH and hCG at 24 ± 2 mm. Mares’ reproductive tracts were scanned at 24 ± 2-hour intervals after treatment to detect ovulation. Mares were inseminated, and embryos were collected. Numbers of mares that ovulated within 48 ± 2 hours after treatment were: H35, 8/8 (100%); F35, 8/14 (57%); H28, 7/12 (58%); FH28, 9/12 (75%); D28, 3/7 (43%) and FH/H24, 4/14 (29%). The number of mares that ovulated in 48 ± 2 hours for H35 was not different from that for FH28 but was higher (P < .05) than all other groups. Embryo recovery rates, diameters, developmental stages, and morphology scores were not different for mares ovulating 48 hours or less versus more than 48 hours after treatment or among treatment groups. Results of this study demonstrate that follicles ≤30 mm can be induced to ovulate with no effect on embryo recovery or quality, as assessed by stereomicroscopy.     

Uterine Inertia due to Severe Selenium Deficiency in a Parturient Mare

A 12-year-old, multiparous, parturient show jumper embryo-recipient mare presented at a veterinary hospital, seven days past her due date and with a dilated cervix, for evaluation of mild colic. Gastrointestinal or metabolic abnormalities and fetal maldispositions were excluded as causes of dystocia, and a diagnosis of uterine inertia was made. There was no uterine response to oxytocin treatment. A live filly was delivered via C-section, and severe selenium deficiency was eventually confirmed in the mare, her offspring, and in the herd of origin. The filly was born with severe white muscle disease and required intensive treatment. This report suggests that selenium deficiency is an underlying cause of equine uterine inertia in the absence of other causes of dystocia.     

Prostaglandin F2α Metabolite Levels Following an Embryo Transfer Procedure in the Mare

Hormonal, chemical, and mechanical stimuli can activate the arachidonic acid cascade and result in formation of prostaglandins and related substances. These compounds can have a profound role in the initiation of the inflammatory process (Higgins & Lees 1984). Prostaglandin (PG) F_2α is the key hormone in reproductive physiology with well-known effects on reproductive performance e.g. luteolysis and abortion. An activation of the arachidonic acid cascade, caused by mechanical manipulation during an embryo transfer procedure, might be one explanation for early embryonic loss.     

Superovulatory Response and Embryo Recovery after Treatment with Different Gonadotrophin during Induced Luteal Phase inCamelus dromedarius

Superovulation, embryo recovery and transfer were attempted in 19 dromedary camels of about 6-10 years of age, and having calved at least once. Superovulation was done using two commercially available porcine FSH preparations, FSH-I (II donors) and FSH-2 (8 donors) during a luteal phase created by inducing ovulation with hCG. The superovulatory response was assessed by ultrasonography. The embryo recovery was attempted non-surgically in sitting position on day 8 and day 7 after first mating in one FSH-1 and one FSH-2 group, respectively. Considerable individual variation in response to the superovulatory stimulus was observed. No significant difference was observed between the two groups in terms of superovulatory response and embryo recovery (p > 0.05). In total 30 embryos were recovered from 17 donors (1.51 embryos/donor). Recipients were synchronized with donors using hCG. Eight embryos were transferred, resulting in two pregnancies and live births.     

Differences in Reproductive Performance, Embryo Development, Interferon-tau Secretion by the Conceptus and Luteal Function in Ewe Lambs Synchronized in Oestrus before or after the Spontaneous Onset of Luteal Activity Preceding Puberty

In mid-September, 1 month before the insertion of intravaginal pessaries to induce sexual activity, blood samples were collected every 4 days from 16 ewe lambs aged 7 months, in order to determine the incidence of ovulations by measurement of plasma progesterone concentrations. It has been studied whether the response to a progestagen treatment of ewe lambs apparently close to puberty could be modified by the onset of the ovarian events preceding puberty. The effect of the presence or absence of ovulations prior to progestagen treatment on the potential reproductive performance (fertility, litter size and fecundity), embryo development [embryo quality and interferon-tau (IFNτ) secretion], luteal function (progesterone secretion in vitro ) and endometrial progesterone content was studied in seven ovulating (Ov+) and nine nonovulating ewe lambs (Ov−) on day 14 after mating. The best potential reproductive results were obtained with Ov+ animals, although these differences could not be initially attributed to either different progesterone secretion in vitro or concentration of endometrial progesterone. Irrespective of the experimental groups, secretion of progesterone by luteal tissue from ewe lambs with normal embryos was significantly greater (p<0.05) than that of animals with abnormal embryos or with no embryos. Normal embryos secreted a higher amount of IFN-τ than those embryos classified as abnormal (p<0.07). In conclusion, ewe lambs which exhibit luteal activity before puberty have the highest levels of reproductive performances after a progestagen treatment. Corpora lutea from ewe lambs with normal embryos had higher rates of progesterone secretion in vitro and their embryos had a higher IFN-τ production by the embryos, indicating greater capacity for subsequent development.     

Peripartal Endocrinology in the Mare and Foetus

The endocrine profiles in the periparturient mares are dominated by increasing concentrations of progestagens and decreasing oestrogens. These hormones are produced by precursors from the foetus, metabolized by the placenta and act primarily on the maternal uterus. The circulating concentrations of hormones in maternal plasma, generally, represent a small proportion of those metabolized by the foetus and utero-placental tissues. There is clear evidence that the foetal hypothalamo-pituitary-adrenal (HPA) axis initiates the process of foetal maturation and the hormonal cascade which culminates in parturition at term. The endocrine changes associated with abnormal pregnancy and abortion in late pregnancy are less well understood, as are the hormonal treatments needed to avert these problems. Further work is needed to establish the biological role of the various hormones present in pregnant mares and, in particular, those hormones which control myometrial quiescence.     

Common Peripartum Problems in the Mare

Reproductive problems in the perinatal period can adversely affect a mare's future fertility or, worse, may be life threatening to her or her foal. A number of abnormalities can occur, including uterine torsion, uterine artery or uterine hemorrhage, retained fetal membranes, metritis, rectovaginal injuries, and necrotic vaginitis. Because hemorrhage, retained placenta, metritis, and necrotic vaginitis can happen after a normal delivery or after dystocia, all mares should be monitored closely in the first days after parturition for signs of lethargy, depression, colic, sore feet, or anorexia. Methods for diagnosing, managing, and treating these conditions and the possible complications are discussed.     

Age-Dependent Effect of Foal Heat Breeding on Pregnancy and Embryo Mortality Rates in Thoroughbred Mares

The aim of the present study was to evaluate the correlation of age and heat cycle to determine reproductive efficiency in young and aged Thoroughbred mares bred on foal heat (FH) or on second heat (SH) after foaling. Embryo mortality (EmbM) was determined every time a mare was found open after a positive pregnancy diagnosis. Parturition to breeding interval, pregnancy rate (PregR) and EmbM rate were the dependent variables and the treatments were breeding on the FH or on SH. The cutoff age to obtain above-average probability for the EmbM was 10 years old. PregR in mares bred on FH was lower compared with SH (P < .01); however, it was neither affected by the age of mares (P > .05) nor by the age group of mares (P > .05). Regarding FH and SH, there was a difference in PregR in young mares (P < .01), unlike in aged mares (P > .05). EmbM rate was not different between mares bred on FH or SH (P > .05) although it was affected by age of mares (P < .01). EmbM was higher in oldest than young mares (P < .01). Aged mares bred on FH had a significantly higher EmbM rate compared with the young group also bred on FH (P < .01). In conclusion, the reproductive efficiency of Thoroughbred mares bred on FH is dependent of the age. Aged mares (≥10 years old) should be bred at their SH to reduce EmbM and improve reproductive performance.     

Some Aspects of Twin-gestation in the Mare

A study has been made of 44 cases of twin pregnancy in mares. The fetuses, foals, fetal membranes and blood groups of parents and foals were examined in order to determine the incidence of chorio-vascular anastomosis, blood chimaerism and freemartinism.

All of the twins proved to be dizygotic and 33 of the 34 pregnancies were bicornual. Fusion of the chorion was seen in 14 of 22 placentas and macroscopic choriovascular bridges were observed in five of these, although blood chimaerism was diagnosed in 11 of 25 cases (44 per cent) examined. This would indicate a high incidence of microchoriovascular anastomosis. The fetal female genital organs of four heterosexual twins were found to be anatomically and histologically normal at autopsy despite the existence of blood chimaerism. Five other sexvalley mature mares born as heterosexual twins with chimaerism all had normal genital organs and estrus cycles and one of these has since become pregnant. The important interspecies differences with respect to the incidence and degree of choriovascular anastomosis and freemartinism are stressed and suggestions for a plausible explanation were advanced.

     

Ovarian Teratoma in a Mare

During a routine trip to a horse slaughterhouse, we found bilateral ovarian teratoma. Macroscopic findings were confirmed by the presence of hair, bones, and cartilage. Under microscopy, these tumors had mature foreign tissues as stratified squamous and respiratory epithelia, sebaceous and sweat glands, as well as follicular endocrine cells, inflammatory cells, hepatocytes, and hyaline cartilage.     

Oviductal Adenoma in a Mare

A 10-year-old Rocky Mountain Saddle Horse mare was initially presented for erratic estrous cycles, infertility, and an enlarged ovary. The initial differential diagnosis list comprised neoplastic and nonneoplastic ovarian conditions. The primary differential diagnosis of granulosa cell tumor was deemed less likely because of clinical findings and laboratory results. Because of the chronic nature and apparent infertility resulting from the abnormal ovary, surgery was elected to remove the affected ovary. Exploratory laparotomy confirmed the presence of the enlarged ovary; however, a larger oviductal tumor was discovered. Both the ovary and tumor were removed and the mare recovered uneventfully. The mare cycled normally, conceived, delivered a healthy foal, and is currently in late gestation with her second pregnancy.