End Of Estrus Research Articles

Reproductive hormone secretions in pony mares subsequent to ovulation control during late winter

Beginning in December, pony mares were placed under a schedule of increasing light. Starting in February, onset of estrus was checked by daily teasing with a stallion. Mares were randomly assigned to one of three treatments (6 mares per group) administered in March. Treatments were: Group I — 75 mg progesterone injected intramuscularly every day for 10 days in combination with a 1.25 mg injection of PGF 2α on day 7 of progesterone treatment and a 2,000 IU injection of HCG on day 2 of estrus; Group II — a norgestomet ear implant inserted for 10 days in combination with 1.25 mg PGF 2α given 7 days after insertion and 2,000 IU HCG administered on day 2 of estrus; and Group III — same as II except that 2 mg of GnRH rather than HCG were administered on day 2 of estrus. Blood plasma for radioimmunoassay of progesterone, LH and estradiol was collected from the first day of treatment until 14 days after the end of estrus. Also in March, 6 mares were bled daily from the first day of estrus until subsequent estrus or day 21 (control estrus). Although estrus was detected in all mares, 14 of 18 mares ovulated subsequent to treatments and four of the six control estrus mares ovulated. Only among HCG treated mares was the ovulation rate higher (P < .05) than it was in the control estrus group. The interval from last progesterone injection or norgestomet implant removal to estrus did not differ between treatment groups. Concentrations of estradiol and LH were increased for several days around the time of ovulation and tended to be positively correlated with each other. In the mares that did not ovulate, concentrations of LH and estradiol appeared to be lower than in mares that ovulated. In summary, progestins in combination with PGF 2α and increasing light will synchronize estrus in mares during late winter and HCG will hasten ovulation in some mares.

Some observations of estrous cycle in swamp buffaloes.

The length of estrous cycle, duration of estrus and time of ovulation in swamp buffaloes were studied. Eight adult females in a lot were checked for estrus twice daily by a vasectomized buffalo bull for 3 months. Duration of estrus was estimat-ed by checking male-receptivity every 3 h and time of ovulation was determined by rectal palpation performed every 3 h after the end of estrus.All females came into estrus 3 to 5 times during the experimental period of 91 days. The length of estrous cycle was 19.1±5.8 (Mean±SD) days with a range of 9 to 38 days. The duration of estrus was 17.3±4.6 h (range: 9-24) and time of ovulation was 13.5±3.7 h (range: 6-18) after the end of estrus. External signs of estrus examined were not evi-dent enough to detect estrus and homosexual behavior was seldom observed.These results indicate that characteristics related to estrus and estrous cycle in swamp buffaloes are analogous to those in cattle except for the uncertainty of external signs of estrus.

Effects of progesterone or estradiol on uterine tubal transport of ova in the cow

An experiment was designed to determine the effect of progesterone (P) or estradiol benzoate (EB) on uterine tubal transport of ova in the cow. Intramuscular injections of P, EB, or corn oil (C) were administered to heifers 24 hours after the end of estrus. The heifers were euthanatized 60 hours after the end of estrus and the location of the ovum or zygote was determined. Venous serum levels of progesterone and estradiol-17β were measured by radioimmunoassay. The mean uterine tube (UT) length was 23.9 cm. An ovum or zygote was recovered from 11 of 14 heifers. Serum levels of progesterone and estradiol-17β were above normal bovine levels following the P and EB treatments, respectively. The mean UT ovum transport rates were 0.42, 0.21 and 0.23 cm/hour in the P, EB and C treatment groups, respectively. The UT ovum transport rate was increased (P<0.05) by the P treatment and EB treatment had no effect (P > 0.05) when compared with the C treatment.

Investigation of factors affecting superovulation and non-surgical embryo recovery from lactating British Friesian cows.

Factors affecting the success of superovulation and embryo recovery were examined in two groups of 16 lactating Friesian cows which were superovulated twice at five to six week intervals in a 24 factorial experiment. There were no differences in ovarian response using pregnant mare serum gonadotrophin or human menopausal gonadotrophin. A total of 3000 iu human chorionic gonadotrophin given intravenously at the first insemination significantly (P less than 0.01) affected embryo recovery rate. A single intramuscular treatment with releasing hormone had no effect. A lower proportion of unfertilised eggs was recovered after insemination with semen from a bull of above average fertility than with semen from a bull of below average fertility (P less than 0.03). Insemination routines affected both the proportion of unfertilised eggs (P = 0.06) and embryo recovery rate (P less than 0.03). Antibacterial treatment given when insemination was carried out after the end of oestrus did not affect success. The three-way circulation system of embryo and fluid recovery was significantly (P less than 0.01) more efficient than the two-way to-and-fro system at day 7 after oestrus, but this appeared to alter at day 8 in favour of the two-way system. A more efficient fluid recovery was achieved with the three-way system (P less than 0.001). Catheter location, catheter size, interval from calving and condition of the donor did not affect success, but embryo recovery rate from younger cows (less than 4.5 years) was lower than from older animals (4.5 to 7 years) (P less than 0.05).

A Timetable of Embryonic Development of the Dasyurid Marsupial Antechinus stuartii (Macleay)

The rate of embryonic development was investigated in 278 embryos of A. stuartii. Ovulation occurred when the number of epithelial cells in the urine of the female began to fall at the end of oestrus. The gestation period was 27.2 days (so, & 1.83; s~,kO.55; range, 25-31 days). Most births occurred during the 26th, 27th or 28th days. Data from sequentially sampled embryos was used in preparation of a timetable of development over 27 days from fertilization to birth. The eggs spent 24 h or less in the oviduct, where they were fertilized. After entering the uterus, they rapidly underwent the first and second cleavage divisions, and by the start of the 2nd day had reached the four-cell stage. They then appeared to undergo a period of developmental arrest for up to 4 days. Cleavage was resumed by the end of the 5th day at the latest, after which the blastocyst slowly expanded and cell numbers increased, to 1.0 mm diameter and approximately 100-300 cells at the end of the 11th day. (The unilaminar blastocyst was formed between the 20- and 50-cell stages.) A second period of developmental arrest followed, until the end of the 13th or 14th day, and was followed by slow growth, increase in cell number and differentiation so that by the 16th day the embryo had a cell number of 1000-3000, measured 1.3-1.5 mm and possessed a distinct embryonic area. The bilaminar blastocyst was completed by day 20; primitive streak and notochord formation took a further 2 days. By the end of the 22nd day, the embryo possessed a distinct notochord and the mesodermal mantle had passed the equator of the blastocyst. The first somites, the heart rudiment, neural tube, and early stages in amnion development appeared during the 23rd day. The shell had been lost and implantation, which began during the 23rd day, was complete by the end of the 24th day. Organogenesis, from the advanced primitive streak stage without notochord to birth, took 6 days.

Peripheral plasma levels of progesterone in goats treated with fluorogestone acetate and prostaglandin F2 α during the estrous cycle

Intravaginal pessaries impregnated with 20 mg fluorogestone acetate (FGA) were inserted into fifteen does at various intervals after the end of estrus. After resumption of cyclical activity following withdrawal of the intravaginal pessaries, the does were divided into six groups and treated with prostaglandin F2 α. Each doe received 15 mg Prostaglandin F2 α administered intramusuclarly 2, 4, 6, 12, 14 or 16 days after the end of estrus. The animals were bred naturally on the first estrus following prostaglandin treatment. Jugular blood samples were collected from each doe throughout the experimental period. The plasma samples were assayed for progesterone. Intravaginal fluorogestone acetate treatment in does had no effect on the function of the corpus luteum, however, overt estrus was postponed during treatment and for a few days after removal of the pessaries. Prostaglandin injection into does, 4, 6, 12, 14 or 16 days after the end of estrus induced luteolysis and subsequent ovulatory estrus within 2 to 3 days. Fertility at PGF2 α induced estrus in these does was 77%. Prostaglandin treatment two days after the end of estrus had no effect on the corpus luteum function. It is concluded that prostaglandin is luteolytic when administered into does anytime beyond four days after the end of estrus.

Hormonal control of neutrophil chemotactic activity in the rat vagina.

A sexual-hormone-dependent neutrophil chemotactic factor(s), operative under physiological conditions, is described. Rat vaginal washouts were shown to be both chemotactic and chemokinetic for rat neutrophils in vitro, whereas macrophages were not attracted. Peak activity was observed at the end of estrus and preceded maximal neutrophil infiltration in the vagina. In order to mimic these events, gonadectomized animals were treated with estradiol for a week. They showed a similar peak of chemotactic activity 30-36 h after estradiol withdrawal, accompanied by a massive neutrophil accumulation. These data suggest that a decrease in estradiol level permits the expression of the chemotactic signal. There was no evidence for chemotaxis and/or migration inhibitors before and during estrus or during long-term estradiol treatment of gonadectomized rats. Induced neutrophil accumulation in the peritoneal cavity and chemotactic responsiveness of these cells in vitro were similar in all stages during the estrus cycle. Estradiol, progesterone, testosterone, and hydrocortisone neither promoted nor significantly inhibited the neutrophil migratory behavior over a wide range of concentrations. Our experiments suggest that the periodic neutrophil accumulation in the rat vagina after estrus is triggered by locally expressed chemotactic mechanisms that are controlled by sexual hormones. The data provide the first evidence that hormonal changes can control chemotactic factors and thus indirectly control cell migration.

Repeatability of the duration of oestrus and breed differences in the relationship between druation of oestrus and ovulation rate of sheep.

The duration of oestrus and the time interval from removal of progestagen-impregnated pessaries to the onset and end of oestrus were examined in Texel, Finnish Landrace, Galway and Fingalway (Finnish Landrace X Galway) ewes. The differences among the breeds in the relationship between these variables and ovulation rate at the controlled oestrus were also investigated. Breed differences were significant for all traits except the interval from pessary withdrawal to the onset of oestrus. The relationship between ovulation rate and both the interval from pessary withdrawal to the onset of oestrus and the duration of oestrus differed significantly among the breeds. The repeatability of the duration of oestrus was significant for Texel and Rambouillet ewes (mean = 0.5) and for pooled data from ewe lambs of various breeds. It was concluded that, in view of the breed differences in the relationship between ovulation rate and duration of oestrus and other traits, generalizations should not be made from among-breed to within-breed relationships. The high repeatability for the duration of oestrus may mean substantial heritabilities for the physiological determinants of oestrus duration.

Total unconjugated oestrogen and progesterone concentrations in peripheral blood during the oestrous cycle of the dog.

From the beginning of pro-oestrus to the end of metoestrus, daily peripheral blood samples were withdrawn from six bitches. Further samples were obtained during anoestrus. Oestrogen values rose from the onset of pro-oestrus to attain a peak value of 25-3 +/- 4-8 pg/ml on Day 1 of oestrus. Progesterone concentrations began to rise 2 days before the oestrogen peak, and reached their highest levels of 18-9 +/- 1-0 ng/ml 16 days after the end of oestrus. After oestrus, an oestrogen rise was detected which reached a peak at Day 18 of metoestrus. The duration of oestrus was unrelated to the length of time that oestrogen levels were raised, or the maximum values were attained. No significant oestrogen levels were detected during anoestrus.

Conception rate after uterine transfer of cow eggs, in relation to synchronization of oestrus and age of eggs.

In sheep, the transfer of twoto four-cell eggs from the oviduct of donors to the uterus of recipients results in a poor conception rate, while uterine transfers of Day-3 (eight-cell) eggs (Day 0 = day ofoestrus) give a satisfactory conception rate (Averill & Rowson, 1958). Moore & Shelton (1964) found that transfers to the oviduct were more successful than those to the uterus, but Trounson & Moore (1974) found that the site of transfer of Day-3 eggs had no effect upon their subsequent survival. In sheep, most eggs are present in the uterus 66 hr after ovulation (Holst, 1974), whereas in the cow, which ovulates about 12 hr after the end of standing oestrus, Hamilton & Laing (1946) could find no eggs in the uterus before 96 hr after the end of oestrus. Thus, although the cleavage rates of eggs are approximately similar in relation to oestrus in both sheep and cow, sheep eggs are entering or are already present in the uterus on Day 3, but cow eggs of a comparable age remain in the oviduct for a further 24 hr. In the present study, the conception rate after uterine transfer of cow eggs of different ages has been examined in relation to the degree of synchronization of the donor and recipient. Conception was assessed by rectal palpation 35 to 42 days after the oestrus before transfer. The eggs used for this purpose were collected and transferred as described by Rowson, Moor & Lawson (1969) or with minor modifications. The flushing and transfer medium was either TCM 199 or Dulbecco phosphate-buffered saline. No pregnancies resulted from the transfer of twenty-two 2-day eggs to the uterus of recipients and these results were therefore excluded from the statistical analysis. The number of uterine transfers carried out on Days 3 to 7 to animals with synchronous oestrus or to recipients in which oestrus differed from the donors by +1 or

Development of the implantation chamber in the pregnant bitch

Uteri taken from 25 bitches at various times during the early stages of pregnancy were studies cytologically to determine how the implantation chamber developed and how fetal-maternal relations were established. On day 13 after the end of estrus, knobs of trophoblastic syncytium formed and became wedged between cells of the uterine luminal epithelium. The syncytium quickly spread along the uterine lumen and into the mouths of the glands, dislodging and surrounding maternal cells. As invasion continued trophoblastic villi, consisting of cores of cytotrophoblast covered by a continuous layer of syncytium, penetrated deeper into the endometrium. The syncytium spread to surround maternal vessels and decidual cells. By day 26 the trophoblast had extended down to the large lacunae. Here syncytial trophoblast covering tips of the villi degenerated, leaving cytotrophoblast exposed to the necrotic zone. These cells possessed characteristics of absorbing cells. Hematomas were formed by focal necrosis of fetal and endometrial tissue at the poles of the implantation sites. Large pools of extravasated blood accumulated and red blood cells were phagocytized by surrounding trophoblastic cells. Therefore, the endotheliochorial relationship in the canine placenta appeared to be established by syncytial trophoblast invading a cellular endometrium. In the necrotic zone and hematomas, cellular trophoblast may have lost its syncytial covering, but elsewhere maternal vessels and decidual cells in the placenta were in direct contact only with syncytial trophoblast.

Hormonal control of changes in the direction of uterine contractions in the estrous ewe.

One hundred fifty-three ewes were laparotomized. and their uteri were exteriorized and observed for 10 mm for origin and direction of individual uterine contractions. The number of contractions generally averaged between four and seven per minute. At 5 h after the beginning of estrus. 67 percent of the uterine contractions originated near the body of the uterus and moved anteriorly. At 26 h (late estrus). 35 percent of the contractions originated near the uterine body and 42 percent originated near the tubo-uterine junctions. At 48 h (after the end of estrus). 75 percent of the contractions originated at the tubo-uterine junctions and moved toward the cervix. The administration of either 6, 30 or 150 � of estradiol I 7-� between 20 and 40 h after the beginning of estrus prevented the change in direction of contractions. Removing the ovaries during estrus did not prevent the change. When the ovaries were removed from ewes during the luteal phase of the estrous cycle, the administration of either estradiol or estradiol plus progesterone had, in 48 h, initiated uterine contractions that were typical of early estrus. The data suggest that endogenous estrogen initiates the type of uterine motility seen during early estrus, and that declining estrogen secretion is responsible for the change in direction of contractions during estrus. Uterine contractions have been observed in pre-ovulatory estrous ewes in several experiments (Brinsfield and Hawk, 1969: Mann, 1969: Hawk and Echternkamp, 1973: Hawk, 1973). The number of contractions generally averaged five to six per minute, and, in control ewes, the majority of contractions originated near the uterine body and moved toward the oviducts. Other reports suggest that there might be considerable normal variation in the origin and direction of contractions in the reproductive tract. In the estrous rabbit, contractions in the uterus were reported to be continuations of contractions of the oviducts and to move along the uterine horn from the tubouterine junction toward the cervix (Reynolds, 1965). However, in estrous rabbits observed in this laboratory, only half as many uterine contractions moved toward the cervix as moved toward the oviducts (Warren and Hawk, 1971). In ewes, Croker and Shelton (1973) reported that the greatest number of uterine contractions moved toward the oviducts during early estrus but toward the cervix after the end of estrus. A series of experiments was conducted with the ewe to determine the normal changes in the direction of uterine contractions during and soon after the end of estrus, and to investigate the role of ovarian hormones in causing the changes that were found.

Changes in blood histamine and bradykininogen levels during different periods of the oestrous cycle in goats.

Blood histamine and plasma bradykininogen levels were estimated in eighteen normally cyclic goats at different periods of the oestrous cycle. The histamine level increased significantly (P smaller than 0.05) on Day 18 of the oestrous cycle. The bradykininogen level decreased significantly (P smaller than 0.05) towards the end of oestrus.

The time of entry of ova into the uterus of the ewe.

Precise estimates for the time of entry of the ovum into the uterus from the oviduct are not available for the sheep. Data presented by Clark (1934), Lang (1969) and others suggest that the ovum enters the uterus between 60 and 96 hr after the end of oestrus but the time of ovulation was not accurately assessed. In a study in which the time of ovulation was accurately determined, Holst & Braden (1972) found that the ovum remains in the oviduct for at least 60 hr after ovulation. The experiment described below was undertaken to determine the time and stage of segmentation at which ova entered the uterus. Forty primiparous Border Leicester × Merino ewes and three vasectomized rams were placed in yards where continuous observation could be maintained. To facilitate the conduct of the experiment, observations were made at the second synchronized oestrus following withdrawal of progestagen pessaries (Repromap

Control of the Estrous Cycle with Prostaglandin F2α in Cattle and Horses

After depositing 5 mg PGF2α into the uterus of cows during diestrus, progesterone fell 50% within 12 hr., estradiol more than doubled within 24 hr., LH peaked at 71 hr., estrus began at 72 hr. and ovulation occurred at 95 hours. Intramuscular injection of 30 mg PGF2α into heifers during diestrus caused similar results, but administration of PGF2α on day 3 of the estrous cycle had no luteolytic effect. Intravaginal treatment with 30 mg PGF2α resulted in luteolysis which was more variable and retarded by about 1 day compared to that after im PGF2α. The fertility of cattle inseminated during the estrus after treatment with PGF2α and that of cattle inseminated at 72 and 90 hr., after PGF2α was equivalent to that in controls. After im injection of PGF2α, blood plasma PGF peaked from 10 to 30 min. and declined to basal values within 2 hours. Blood plasma progesterone began to fall within 10 min. and continuously after PGF2α, and estradiol increased continuously possibly beginning within 1 hour. Intramuscular injections of PGF2α caused an increase in blood prolactin (2.5-fold within 10 min.) which persisted for at least 2 hours. Increases in GH were proportional to im dose of PGF2α; GH increased two and one-half-, seven- and 26-fold at 30 min. after 15, 30 and 60 mg PGF2α. Increased growth hormone (GH) persisted for at least 2 hr. after in PGF2α. Relative to changes after im PGF2α, infusion (iv) of 0.5 mg PGF2α per minute for 30 min. resulted in higher blood prolactin and GH. In horses, administration of 10 mg PGF2α into the uterus or 15 mg sc at day 7 to 9 after ovulation caused a 60% reduction in blood progesterone within 12 hr., estrus commenced in about 2.2 days and ovulation occurred at about 2 days before the end of estrus. PGF2α had no detectable or significant residual influence on the subsequent control estrous cycles in either cows or horses. The precise synchrony of ovulation and normal fertility after administration of PGF2α may allow artificial insemination in herds where AI was not possible previously. However, effects of PGF2α on other than reproductive traits should be investigated more thoroughly.

Immunoreactive luteinizing hormones and progesterone during pregnancy and following gonadotrophin administration in beagle bitches.

ABSTRACT Immunoreactive canine luteinizing hormone (IRCLH) and progesterone were measured in the plasma of Beagle bitches. Changes in plasma hormone concentrations during pregnancy were similar to those seen in the non-pregnant animal during metoestrus. Administration of pregnant mares' serum gonadotrophin (PMSG) and human chorionic gonadotrophin (HCG) to anoestrous bitches induced oestrus. However, the duration of progesterone secretion was shorter than that seen in pregnant bitches. Treatment appeared to stimulate the secretion of IRCLH and in some animals plasma levels reached a maximum some weeks after the end of oestrus.

The prenatal development of the dog: preimplantation events.

Prenatal development of purebred beagle dogs was studied from the time of ovulation to the time of implantation. Ovulation occurred 1–2 days after the bitch’s first acceptance of coitus. Primary oocytes were shed from the ovary, and the first evidence of polar body formation was observed 3 days after breeding. The embryos entered the uterus as morulae of 16 cells or more, 8–12 days after breeding, and they became blastocysts shortly thereafter. During the free-floating blastocyst stage, which lasted about 1 week, the blastocysts grew to 2.6 mm in diameter and migrated through the uterus. Implantation, first marked by local endometrial edema at the definitive site of each embryo, began an average of 17-18 days after breeding. Shortly after the occurrence of local endometrial edema, differentiation of the primitive streak and three primary germ layers began in the embryo. The age of embryos was assessed on the basis of the time elapsed from breeding, the time elapsed from refusal to breed, and the time after the vaginal smear showed a change from predominantly cornified to predominantly noncornified epithelial cells. The calculated age of embryos at a given stage of development varied as much as 7 days when either postbreeding or postrefusal ages were used. The variation was reduced to 1–2 days when age was determined according to characteristics of the vaginal smear. The early embryonic development in the dog appears to be more closely associated with hormonal events near the end of estrus than with the time of ovulation. The vaginal smear is the best clinical index of these events.

Effect of corticotrophin and corticosteroids on oestrus, ovulation and oestrogen excretion in the sow.

SUMMARY Corticotrophin (ACTH), hydrocortisone or prednisolone trimethylacetate were administered daily to sows from 24 hr. before oestrus or from day 14 of the cycle until the end of oestrus. Treatment beginning on day 14 delayed the peak in urinary oestrogen excretion normally seen, postponed the onset of oestrus by 1–3 days and shortened the duration of oestrus. Treatment begun before oestrus did not appear to alter the pattern of oestrogen excretion but shortened the duration of oestrus. Administration of ACTH, but not that of corticosteroids, also interfered with ovulation.

The Length of the Uterine Horn and Fallopian Tube in the Sow

Summary Reproductive tracts were examined from sows killed at different times after the onset of oestrus. The uterine horns were thick and oedematous during oestrus, but after the end of oestrus they became thinner and doubled in length as the oedema subsided. During the first post-weaning oestrus the uterine horns were 20% shorter than during subsequent oestrous periods, and this difference appeared to result from a progressive increase in the size of the reproductive tract after weaning. The sows used were of different ages and body-weights. There appeared to be little tendency for the size of the tract to increase with age, and no relationship was found between body-weight and the length of the uterine horn.

Use of probit analysis in a study of the effect of the ram on time of ovulation in the ewe.

Summary. To investigate the relationship between oestrus and time of ovulation from the start of heat and the effect of the ram on this relationship, 200 ewes, half of which had been run with rams continuously during oestrus, were slaughtered at intervals after the end of heat. The method of probit analysis was used to fit multiple regression equations for percentage of ewes ovulated (as a probit) in terms of slaughter time and heat length. From these equations, estimates of mean ovulation times for various heat lengths were calculated. In the control group, which was teased at 4-hr intervals to determine lengths of heat, ovulation occurred, on the average, shortly after the end of oestrus. Although duration of oestrus was shorter when the sexes were continuously associated, ovulation occurred later. In addition, there was a positive correlation between heat length and time of ovulation in this group, but not in the control group.