Induction of ovulation in gonadotropin treated gilts with synthetic gonadotropin releasing hormone

Four consecutive trials were conducted to investigate the possibility of controlling the time of ovulation in prepuberal gilts pretreated with PMS and HCG. In trial 1 it was shown that the GnRH analog Hoe 766 was superior to other compounds tested. The following trial revealed that 10 mug of that analog is the optimal dose to elicit an ovulatory response. In trial 3 it was found that the majority (73%) of gilts had started ovulating by 39 h after Hoe 766 injection. Individual gilts started ovulating up to 4 h sooner or up to more than 5 h later. Apparently the ovulatory process of an individual gilt extends over a period of 4 - 5 h. Double insemination of 9 gilts at 34 and 41 h after Hoe 766 resulted in fertilization rates and litter sizes that compared favourably with those of corresponding gilts treated with HCG.     

Control of ovulation with a GnRH analog in gilts and sows

Methods for the control of ovulation with GnRH or the GnRH analog D-Phe6 -LHRH (GnRH-A), were evaluated in gilts and sows as the last step in development of a fixed-time Al protocol. This involved 3 field trials using 2,744 gilts (10 units) and 71,628 sows (33 units). In Trial 1, the GnRH-A (75 microg) was given subsequent to treatment with altrenogest for cycle control or eCG for the stimulation of uniform follicle development in gilts. The release of LH was followed by ovulations which commenced within 36.4 +/- 3.3 hr and were terminated at 39.0 +/- 2.8 hr after administration of GnRH-A. This degree of synchronization of ovulations enabled the use of fixed-time AI. Consequently, subsequent to pretreatment with altrenogest and eCG, in 10 production units 1,285 gilts received 50 microg GnRH-A and 1,459 gilts 500 IU hCG serving as positive controls (Trial 2); all the gilts were inseminated 24 and 42 hr after treatment. Pregnancy rate and piglet index (n of piglets per 100 first inseminations) following GnRH-A vs hCG were 78.8% and 779 vs 74.4% and 728, respectively (P < 0.05). In field trials with first litter gilts and multiparous sows (33 units holding from 250 to 6,000 sows), 1,000 IU eCG was used for estrus control after weaning and 25 microg or 50 microg GnRH-A were given 55 to 58 hours after eCG (n = 19,954 and 20,701) (Trial 3). Sows treated during the same time period with 300 microg GnRH plus 300 IU. hCG (n = 30,973) served as positive controls; all sows were inseminated 24 and 42 hours after treatment. Pregnancy rates for 50 microg GnRH-A, 25 microg GnRH-A and 300 microg GnRH plus 300 IU hCG were 83.0%, 81.7% and 80.7%, and the piglet indices 913, 899 and 880, respectively (P < 0.05). Unit size and parity had significant effects on fertility and productivity. In all studies, results with 50 microg GnRH-A were superior. In year-long studies, highest levels of fertility in response to these treatments were seen from December to May.     

Induction of abortion in feedlot heifers with cloprostenol (ICI 80,996)

Abortion was induced in two groups of feedlot heifers with cloprostenol. Response varied with the stage of gestation and dose of cloprostenol. Results of this limited trial indicate that cloprostenol is a safe and effective abortifacient in feedlot heifers at a dose of 250 μg to day 120 of gestation and at a dose of 500 μg from day 121 to day 150.     

Reversal of indomethacin blockade of ovulation in gilts by prostaglandins

Prepubertal gilts given 750 IU pregnant mares′ serum gonadotropin (PMSG) followed 72 h later by 500 IU human chorionic gonadotropin (hCG) to induce follicular growth and ovulation fail to ovulate when 10 mg/kg indomethacin (INDO) is injected 24 h after hCG administration. This study examines the effects of administration of exogenous prostaglandins F_2α and E₂ (PGF_2α and PGE₂) alone or in combination, and at various times prior to the expected time of ovulation, on the INDO blockade of ovulation in PMSG/hCG-treated gilts. Occurrence of ovulation was determined by visual observation at laparotomy 48 h after hCG. When 5 mg or 10 mg PGF_2α was injected at each of 38, 40 and 42 h after hCG injection, 63% and 79%, respectively, of preovulatory follicles ovulated. In contrast, injection of 5 mg PGE₂ or 5 mg PGE₂ plus 5 mg PGF_2α induced ovulation in 0% and 24% of preovulatory follicles, respectively. In control groups, 100% of folicles in PMSG/hCG-treated gilts ovulated whereas none did so in PMSG/hCG/INDO-treated animals. These results indicate that administration of PGF_2α can induce ovulation in the PMSG/hCG/INDO-treated prepubertal gilt and suggest that PGE₂ is ineffective and may be antagonistic to PGF_2α in overcoming the ovulation blocking effect of INDO.     

Estrus and ovulation in gilts fed a synthetic progestogen

A synthetic progestogen, allyl trenbolone (AT), was fed to sexually mature gilts to determine the effective doses for the control of estrus and ovulation. Gilts were assigned to a control group and 5 treatment groups receiving 10.0, 12.5, 15.0, 17.5 or 20.0 mg of AT mixed in .45 kg of feed/head/day for 18 consecutive days. Ovarian morphology was determined by laparotomy following estrus or at 10 days post-treatment. AT suppressed estrus in all gilts during treatment. Estrus was effectively synchronized in treated gilts. The average interval from withdrawal of progestogen treatment to estrus was 4.5 days for 48 of 50 treated gilts that were in estrus within 10 days after treatment. The average ovulation rate in treated gilts was similar to control gilts. No detrimental side effects, due to treatment, were observed with the possible exception of a slight increase in the incidence of cystic follicles.     

Increased ovulation rate in gilts after oral administration of epostane

In Phase I of this study to enhance ovulation rate and hence litter size, gilts received 0 (sham control), 0.625, 1.25, 2.5 or 5.0 mg epostane/kg body weight on Days 10, 11 and 12 of the oestrous cycle (5 gilts/group). After epostane treatment, plasma progesterone concentrations were reduced (P less than 0.01) in a dose-related manner, % progesterone decline = 21.30 x square root of (dose) + 10.45, R2 = 0.70, but recovered to pretreatment levels by 24 h. In Phase II the effects of epostane on ovulation rate and litter size were tested at two study centres. At each centre 108 gilts were treated with the same doses of epostane as used in Phase I and the doses were given for 7 days (Days 15-21) or 12 days (Days 10-21) during the first oestrous cycle. Gilts were inseminated twice during the oestrus after treatment and were slaughtered 30 days later. Mean (+/- s.d.) ovulation rate was 16 +/- 2.7 (N = 8) and 21 +/- 4.0 (N = 61) for control and epostane-treated gilts in Centre A and 12 +/- 2.4 (N = 5) and 17 +/- 3.8 (N = 55) respectively in Centre B (P less than 0.01 for both) and was dose related (ovulation rate = 3.38 x square root of (dose) + 16.17, R2 = 0.31). The effects of 7- or 12-day epostane treatment on ovulation rate were not different (P greater than 0.05), indicating that effects of treatment after Day 14 of the oestrous cycle are most important to subsequent ovulation frequency.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of estrus in pubertal miniature gilts

Genetic engineering of miniature pigs has facilitated the development of numerous biomedical applications, such as xenotransplantation and animal models for human diseases. Manipulation of the estrus is one of the essential techniques for the generation of transgenic offspring. The purpose of the present study was to establish a useful method for induction of the estrus in miniature gilts. A total of 38 pubertal miniature gilts derived from 4 different strains were treated with exogenous gonadotropins. Estrus and ovulatory response were examined after treatment with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) as 200 IU PMSG and 100 IU hCG, 300 IU PMSG and 150 IU hCG, or 1,500 IU PMSG only, followed by 100, 150 or 750 IU hCG 72 h later, respectively. The optimal protocol was determined to be the combination treatment of 200 IU PMSG and 100 IU hCG followed by 100 IU hCG. The administration of 200 IU PMSG and 100 IU hCG was effective in inducing estrus regardless of the strain, although there was a strain difference in the ovulatory response. These results indicate that treatment with a low-dose combination of PMSG and hCG provides one of the simplest methods for induction of estrus and ovulation in pubertal miniature pigs.     

Induction of ovulation and multiple ovulation in seasonally-anovulatory mares with equine pituitary fractions

Equine pituitary fractions were used to induce ovulation in seasonally-anovulatory pony mares. Over three experiments, 87% of mares ovulated following twice daily injections for 14 days of equine pituitary fractions. Of the mares which ovulated, 58% had 2 or more ovulations/estrus.     

The time of ovulation in relation to estrus duration in gilts

The objective of this study was to determine time of ovulation, monitored by transcutaneous ultrasonography, relative to the duration of estrus in gilts. We exposed 92 cyclic gilts, Camborough x Canabrid terminal line, at Day 19 of their third estrous cycle to vasectomized boars every 6 h for the detection estrus. Transcutaneous ultrasonography was performed every 6 h, starting 24 h after the onset estrus, to determine time of ovulation. Estrus duration was, on average, 52.6 h (range: 30 to 72 h), and ovulation occurred between 30 and 60 h after the onset of estrus (mean: 44 h), about 85 % of the way through the estrus period. The time of ovulation during estrus was dependent on the duration of estrus (Time of ovulation = (duration of estrus) x 0.409 + 22.7; r = 0.57, P = 0.0001). Prediction of the time of ovulation in relation to duration of estrus is important for determining the optimal time for inseminating gilts. This knowledge would contribute to an improvement in the fertilization rate and in reproductive efficiency of the breeding herd.     

The relationship between ovulation rate and embryonic survival in gilts

Norwegian Landrace gilts were inseminated on the second day of their second oestrus and slaughtered 28 to 34 days after insemination. The number of corpora lutea (ovulation rate) and normal embryos was counted and the embryonic survival rate was calculated for the 306 pregnant gilts. Mean (+/-S.D.) ovulation rate, number of normal embryos and embryonic survival rate were 14.17+/-2.48, 10.55+/-3.30 and 74.8%+/-20.7%, respectively. The significant (P<0.001) curvilinear regression of embryonic survival rate on ovulation rate gives a maximum embryonic survival rate at 13.2 ovulations. Increased ovulation rate gives increased number of normal embryos up to 18.1 ovulations. Ovulation rate should be considered when assessing factors affecting embryonic survival in pigs.     

Synchronization of oestrus in gilts with altrenogest: effects on ovulation rate and foetal survival

Previous studies have shown that use of altrenogest resulted in a high rate of fertility and increased litter size compared with controls under conditions of practical pig production. The present study was designed to evaluate whether ovulation rate and/or foetal survival were increased by altrenogest using crossbred gilts derived from one herd (n = 227) and introduced in the same piggery over 12 months. Each gilt was allocated to a treated group (n = 103) receiving an individual daily dose of 20 mg of altrenogest for 18 days in its feed or a control group (n = 124) after puberty had been diagnosed, (197 ± 1 day; mean ± SEM). They were inseminated (double AI) at the second induced or natural oestrus. Pregnancy was diagnosed by ultrasonography at Days 22 and 42 post-insemination in the absence of return to oestrus. Pregnant gilts were slaughtered at 48 ± 3 days of pregnancy following the second examination. The number of living and dead foetuses were recorded before uterine contents (foetuses and placentae) were weighed and the number of corpora lutea (CL) per ovary counted.Precise synchronization of oestrus was observed after the end of the progestogen administration, with 93% of the gilts in oestrus by Days 5 to 7. For the controls, the interval from first to second oestrus ranged from 17 to 25 days in 93% of the control gilts. The pregnancy rate was 89.3% for treated gilts and 77.4% for controls (P < 0.05). The ovulation rate was increased by the treatment (15.4 ± 0.3 vs 14.6 ± 0.3; mean ± SEM, P < 0.02). Although the altrenogest group had more foetuses (11.1 vs 10.6), this difference was not significant (P > 0.14). The percent of foetal survival was similar in both groups (64.9%; P > 0.27). The foetal and placental weights differed only between dams and increased with stage of gestation. The increase in litter size through feeding altrenogest was associated with an increased ovulation rate.     

Postinsemination treatment of primiparous and multiparous cows with cloprostenol failed to affect ovulation and pregnancy rate in dairy cattle

Previous studies have demonstrated the facilitating effect of a single cloprostenol treatment postinsemination on ovulation and pregnancy rate in dairy cattle and Italian buffalos. This study was conducted to test the effects of 500 μg cloprostenol given intramuscularly immediately postinsemination to 55 primiparous and 60 multiparous Holstein cows (Bos taurus; TR) of a typical dairy operation in East Germany and to compare them with 57 primiparous and 48 multiparous saline-treated cows (CON). Animals of the TR and CON groups did not differ or only differed marginally for age at treatment, interval calving–treatment, lactation number, milk production on the day of treatment, body condition score, and their peri- and postparturient case histories. All animals were clinically and reproductively healthy on the day of treatment. They were inseminated once 12 h after the onset of estrus, scanned 24 h after insemination to confirm ovulation, and tested for pregnancy by transrectal palpation between Days 42 and 48 postinsemination. Treatment did not affect the number of cows ovulating. The overall combined pregnancy rate (PR) was 47.3%. Pregnancy rate did not differ statistically between TR and CON (46.1% vs. 48.6%; P > 0.05). In conclusion, this study failed to demonstrate beneficial effects of a postinsemination treatment of primiparous and multiparous cows with cloprostenol on ovulation and PR in a typical dairy cattle operation in East Germany.     

Induction of parturition in pigs by intravaginal application of the prostaglandin analog cloprostenol

Cloprostenol was deposited in the vaginal lumen of sows on Day 111 of pregnancy at dosages of 100, 125 or 175 g and volumes of 1, 2 or 5 ml, respectively. A control group was treated with physiological saline. In 92 out of 93 prostaglandin-treated sows, parturition commenced approximately 22 h after application, with no significant differences between dose levels or volumes. There were also no differences in the average size and weight of litters born, weaning weight, frequency of postpartum complications or post-weaning fertility. Intravaginal application of cloprostenol is thus a simple and efficient means of inducing parturition in sows.     

Effect of time of ovulation and sperm concentration on fertilization rate in gilts

In normal production practices, sows and gilts are inseminated at least twice during estrus because the timing of ovulation is variable relative to the onset of estrus. The objective of this study was to determine if a normal fertilization rate could be achieved with a single insemination of low sperm number given at a precise interval relative to ovulation. Gilts (n=59) were randomly assigned to one of three treatment groups: low dose (LD; one insemination, 0.5 x 10(9) spermatozoa), high dose (HD; one insemination, 3 x 10(9) spermatozoa) or multiple dose (MD; two inseminations, 3 x 10(9) spermatozoa per insemination). Twice daily estrus detection (06:00 and 18:00 h) was performed using fenceline boar contact and backpressure testing. Transrectal ultrasonography was performed every 6 h beginning at the detection of the onset of standing estrus and continuing until ovulation. Gilts in the LD and HD groups were inseminated 22 h after detection of estrus; MD gilts received inseminations at 10 and 22 h after detection of estrus. Inseminations were administered by using an insemination catheter and semen was deposited into the cervix. The uterus was flushed on Day 5 after the onset of estrus and the number of corpora lutea, oocytes, and embryos were counted. Time of insemination relative to ovulation was designated as 40 to >24 h, 24 to >12 h, and 12 to 0 h before ovulation and >0 h after ovulation. The LD gilts had fewer embryos (P<0.04), more unfertilized oocytes (P<0.05) and a lower fertilization rate (P<0.07) compared to MD gilts. The effects of time of insemination relative to ovulation and the treatment by time interaction were not significant. We conclude that a cervical insemination with low spermatozoa concentration may not result in acceptable fertility even when precisely timed relative to ovulation.