Effect of hCG on Early Luteal Serum Progesterone Concentrations in PG600‐Treated Gilts

Gilt oestrus and ovulation responses to injection of a combination of equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG) (PG600) can be unpredictable, possibly reflecting inadequate circulating LH activity. The objective of this study was to determine the effect of PG600 followed by supplemental hCG on gilt ovarian responses. In experiment 1, 212 Hypor gilts (160 day of age) housed on two farms in Spain received intramuscular (i.m.) injections of PG600 (n = 47), or PG600 with an additional 200 IU hCG injected either concurrently (hCG‐0; n = 39), or at 24 h (hCG‐24; n = 41) or 48 h (hCG‐48; n = 45) after PG600. A further 40 gilts served as non‐injected controls. Ovulation responses were determined on the basis of initial blood progesterone concentrations being <1 ng/ml and achieving >5 ng / ml 10 d after the PG600 injection. The incidence of ovulating gilts having progesterone concentrations >30 ng/ml were recorded. During the study period, 10% of control gilts ovulated whereas 85–100% of hormone‐treated gilts ovulated. There were no significant differences among hormone groups for proportions of gilts ovulating. The proportions of gilts having circulating progesterone concentrations >30 ng/ml were increased (p ≤ 0.02) in all hCG treated groups compared with the PG600 group. In experiment 2, a total of 76 Hypor gilts at either 150 or 200 days of age were injected with PG600 (n = 18), 400 IU eCG followed by 200 IU hCG 24 h later (n = 20), PG600 followed by 100 IU hCG 24 h later (n = 17), or 400 IU eCG followed by 300 IU hCG 24 h later (n = 21). Blood samples were obtained 10 days later for progesterone assay. There were no effects of treatment or age on incidence of ovulation, but fewer 150‐day‐old gilts treated with PG600 or 400 IU eCG followed by 200 IU hCG had progesterone concentrations >30 ng / ml. We conclude that hCG treatment subsequent to PG600 treatment will generate a higher circulating progesterone concentration, although the effect is not evident in older, presumably peripubertal, gilts. The mechanism involved and implications for fertility remain to be determined.     

Effect of human chorionic gonadotropin on preovulatory luteinizing hormone surge and ovarian hormone secretion in gilts

The influence of varying doses of human chorionic gonadotropin (hCG) on the preovulatory luteinizing hormone (LH) surge, estradiol-17 beta (E2) and progesterone (P4) was studied in synchronized gilts. Altrenogest (AT) was fed (15 mg X head-1 X d-1) to 24 cyclic gilts for 14 d. Pregnant mares serum gonadotropin (PMSG; 750 IU) was given im on the last day of AT feeding. The gilts were then assigned to one of four groups (n = 6): saline (I), 500 IU hCG (II), 1,000 IU hCG (III) and 1,500 IU hCG (IV). Human chorionic gonadotropin or saline was injected im 72 h after PMSG. No differences in ovulation rate or time from last feeding of AT to occurrence of estrus were observed. All gilts in Groups I and II expressed a preovulatory LH surge compared with only four of six and three of six in Groups III and IV, respectively. All groups treated with hCG showed a rapid drop (P less than .01) in plasma levels of E2 11, 17, 23 h after hCG injection when compared with the control group (35 h). The hCG-treated gilts exhibited elevated P4 concentrations 12 h earlier than the control group (3.1 +/- .5, 3.4 +/- .72, 3.1 +/- .10 ng/ml in groups II, III and IV at 60 h post-hCG vs .9 +/- .08 ng/ml in group I; P less than .05). These studies demonstrate that injections of ovulatory doses of hCG (500 to 1,500 IU) had three distinct effects on events concomitant with occurrence of estrus in gilts: decreased secretion of E2 immediately after hCG administration, failure to observe a preovulatory LH surge in some treated animals and earlier production of P4 by newly developed corpora lutea.     

Effect of eCG or eCG Plus hCG on Oestrus Expression and Ovulation in Prepubertal Gilts

To meet weekly breeding targets, it is occasionally necessary to inject exogenous gonadotrophins to induce oestrus in prepubertal gilts. However, the gilt oestrus response to equine chorionic gonadotrophin (eCG) either alone or in combination with human chorionic gonadotrophin (hCG) can be unpredictable. The objective of the present study was to examine possible reasons for this unpredictability. Prepubertal gilts (90 kg and 153 days of age, n = 109) received an injection of either 600 IU eCG or a combination of 400 IU eCG and 200 IU hCG (PG600), or were non-injected controls, and were then exposed to a mature boar for 15 min daily for 7 days for oestrus detection. At the time of injection, real-time ultrasound revealed that the gilt ovaries had primarily 1–2 mm follicles. Blood samples were obtained at time of hormone injection (day 0) and at days 3, 7 and 10 for assay of serum progesterone concentrations. The oestrus responses by 7 days were15.5%, 73.3% and 0%, for eCG, PG600, and control gilts, respectively (p < 0.001). The oestrus response improved (p < 0.05) with increasing body weight. Based on circulating progesterone levels, all oestrous gilts ovulated except for four of the PG600 gilts. Failure to express oestrus in PG600 gilts was not associated with a premature rise in progesterone.     

Case Study: Synchronization of Estrus and Fertility in Gilts Administered P.G. 600® After Treatment with Regu-mate® for 14 or 18 Days

The objective was to determine the effects of duration of progestin exposure prior to gonadotropin treatment on the synchronization of estrus and fertility in gilts. Gilts were fed daily a complete diet containing 15 mg Regu-mate® (Intervet America Inc., Millsboro, DE) for 14 (n = 19) or 18 (n = 18) d. Twenty-four hours after the last feeding of Regu-mate®, all gilts received an i.m. injection of P.G. 600® [400IU pregnant mare serum gonadotropin (PMSG) and 200 IU human chorionic gonadotropin (hCG); Intervet America Inc.]. Gilts were bred artificially 12 and 24 h after first detection of standing estrus. More 18-d (33.3%) than 14-d treated gilts (5.3%) were in estrus on the peak day (d 4.0) after P.G. 600® injection (P=0.02). The percentage of gilts displaying estrus < 7 d after P. G. 600® injection was greater (P=0.06) for the 18-d treatment (88.9%) than for the 14-d treatment (63.2%). Farrowing rate tended to be greater (P=0.17) for gilts exposed to Regu-mate® for 18 d (75%) compared with 14 d (50%). Total pigs born (P=0.43), pigs born live (P=0.63), stillborns (P=0.62), and total litter weight (P=0.52) were similar between groups. The number of mummified fetuses tended to be higher (P=0.11) for gilts in the 18-d treatment group (0.8 ± 0.2) compared with the 14-d treatment group (0.2 ± 0.3). In summary, the precision of estrus synchronization and reproduction was greater in gilts given P.G. 600® after 18 d compared with 14-d Regu-mate® treatment.     

Blood LH level and induced ovulation after hCG and PMSG treatment in ovarian quiescent cattle

Ovarian quiescent cattle bearing follicle with palpable size were treated with single intramuscular injection of 750-6,000 IU of human chorionic gonadotrophin (hCG) in 13 cases and 1,000-2,000 IU of pregnant mare serum gonadotrophin (PMSG) in 5 cases. Changes of blood luteinizing hormone (LH) level, estrus and ovulation after the treatments were examined. After the hCG treatment LH level became slightly high from 0.2-0.6 ng/ml of pre-treatment to 0.3-1.9 ng/ml of post-treatment and maintained the level up to ovulation without the ovulatory LH surge. Ovulation was induced about 36 hr after the treatment in 12 cases. The ovulations were all silent ovulations. After the PMSG treatment LH level became slightly high from 0.6 ng/ml of pre-treatment to 1.3 ng/ml of post-treatment and the level lasted until the ovulatory LH surge. The ovulatory LH surge occurred about 39 hr after the PMSG treatment in 4 cases with a peak of about 32 ng/ml. Ovulation was induced about 74 hr after the treatment in all 5 cases. Four cases showed estrus but one in which the LH surge could not be confirmed did silent estrus preceding the induced ovulations. It was demonstrated that hCG induced ovulation without the LH surge but PMSG induced the ovulatory LH surge and the subsequent ovulation in ovarian quiescent cattle.     

Endocrine pathogenesis of postweaning anestrus in swine: response of the persistently anestrous sow to hormonal stimuli

The endocrine function of the individual components of the hypothalamo-hypophyseal-ovarian axis of the postweaning anestrous sow was evaluated by monitoring the sow's response to exogenous estradiol, gonadotropin releasing hormone (GnRH), and gonadotropins. Sows (4 to 6/group) not returning to estrus by 42.8 +/- 3.1 days after weaning were assigned to 1 of the following treatments: 10 micrograms of estradiol benzoate (EB)/kg of body weight; 200 micrograms of GnRH, 1,000 IU of pregnant mare's serum gonadotropin (PMSG); 1,000 IU of human chorionic gonadotropin (HCG); or 4 ml of saline solution plus 2 ml of corn oil. A preovulatory-like surge of luteinizing hormone [(LH) greater than 12 hours in duration] was observed in all weaned sows treated with EB. All EB-treated sows exhibited estrus and ovulated but none conceived. Sows given GnRH had transiently increased (less than 3 hours) LH concentrations that were not associated with estrus or ovulation. Treatment with PMSG caused an increase in peripheral concentrations of 17 beta-estradiol that was followed by an LH surge, estrus, ovulation, and conception. Treatment with HCG caused an increase in circulating concentrations of 17 beta-estradiol that was accompanied by a surge of LH in some sows and ovulation in all sows. Not all sows treated with HCG exhibited estrous behavior, but conception occurred in 2 of 3 sows that were mated at estrus. None of the sows treated with saline plus corn oil had consistent changes in circulatory concentrations of 17 beta-estradiol or LH and none exhibited estrus or ovulated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of fertile estrus in prepuberal gilts by treatment with a combination of pregnant mare's serum gonadotropin and human chorionic gonadotropin

Ten trials involving 678 presumed prepuberal gilts (5.5 to 7.5 mo old) were conducted in North Carolina, Illinois and Missouri to evaluate the reproductive performance of gilts given a combination of 400 IU of pregnant mare's serum gonadotropin and 200 IU of human chorionic gonadotropin (P. G. 600). Gilts that were presumed to be prepuberal received P. G. 600 or no treatment (control) on the day of movement from finishing facilities to pens for breeding. Detection of estrus, with the aid of mature boars, was conducted daily for 28 d; gilts in estrus were mated naturally. Treatment with P. G. 600 increased the percentage in estrus within 7 (57.5 vs 40.9%) or 28 d (72.9 vs 59.5%); average interval to estrus was reduced (P less than .05) from 10.4 to 7.5 d. Farrowing rate (78.5 +/- 3.1%), number of pigs born alive (8.6 +/- .2) or dead (.26 +/- .06) and number of pigs weaned (8.0 +/- .2) were unaffected by treatment. Gilts that were heavier than the median for each farm were in heat sooner and more were detected in heat, but no other reproductive traits differed between heavy and light gilts. Overall, the results reveal that P. G. 600 was useful for induction of fertile estrus in prepuberal gilts.     

Reproductive performance of totally confined sheep bred with semen extended in a lactose-egg yolk-glycerol buffer and stored at 5 degrees C.

Two experiments were carried out in January and May 1975 to study reproductive performance (fertility, prolificacy and fecundity) of totally confined sheep synchronized for estrus. The main objective of the first experiment was to compare reproductive performance of ewes bred naturally to those bred by artificial insemination. Semen for artificial insemination was collected by either artificial vagina or electroejaculation and stored for up to 36 hours at 5 degrees C. A second objective was to evaluate the effect of pregnant mares' serum gonadotrophin on the reproductive performance of ewes synchronized for estrus. Fertility was 53% for ewes bred by natural mating, 34% for ewes receiving pregnant mares' serum gonadotrophin and bred by artificial insemination, and 9% for those not receiving pregnant mares' serum gonadotrophin and bred by artificial insemination. There was no difference in fertility between ewes bred with semen collected by artificial vagina or by electroejaculation. A similar pattern was observed for fecundity. Average prolificacy was 2.0 with no significant differences among mating methods or pregnant mares' serum gonadotrophin application being observed. In the second experiment, the reproductive performance of ewes inseminated with semen stores at 5 degrees C for 48 to 60 hours was compared to that of ewes inseminated with semen stores for 24 to 36 hours. No significant differences in the reproductive performance were detected. Although average fertility (9%) and fecundity (19%) were low, prolificacy averaged 2.0 lambs per ewe lambing.     

Effects of progesterone and human chorionic gonadotrophin administration five days postinsemination on plasma and milk concentrations of progesterone and pregnancy rates of normal and repeat breeder dairy cows.

Treatment with a progesterone-releasing intravaginal device between days 5 and 12 after estrus elevated (p less than 0.05) plasma progesterone concentrations between days 6 and 8 in comparison with controls. Treatment with injectable progesterone (200 mg) on days 5, 7, 9 and 11 postestrus did not increase plasma progesterone concentrations over controls. The administration of 1500 IU human chorionic gonadotrophin (hCG) on day 5 after estrus resulted in a sustained increase (p less than 0.01) in plasma progesterone concentrations from day 8 until day 20 when measurements ceased. Pregnancy rates, as a result of artificial insemination (AI) at the pretreatment estrus, in these treatments (n = 12-14 each), were unaffected by any of the treatments and ranged from 57.1 to 75.0% at 45-60 days post-AI. In a field trial, of 36 repeat breeder cows treated with 1500 IU hCG 5.5 days after insemination, 47.2% were pregnant at 60 days, whereas 39.5% of saline-treated controls were diagnosed pregnant. Treatment with hCG significantly (p less than 0.05) increased milk progesterone concentrations over controls on days 14 and 20 after insemination.     

Effects of equine chorionic gonadotropin on reproductive performance in anestrous mink.

The incidence of anestrous mink during the normal breeding season has been reported to be as high as 5%. We sought to induce estrus in these mink by using various doses of equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). Seventy-five female mink maintained under standard ranch conditions failed to demonstrate estrus during the annual breeding season in March. These anestrous mink were randomly assigned to treatment groups. Treatments were given on March 16 and again on March 18. On these 2 d, mink were treated with equal doses of saline, 25, 50, or 100 IU of eCG, or 50 IU of eCG on March 16 and 50 of IU of eCG + 100 IU of hCG on March 18. Females were paired with males beginning on March 22. None of the saline-treated mink mated. In contrast, reproductive performance of the anestrous mink was significantly improved by treatment with eCG. This included proportion of mink breeding (47 to 100%), proportion giving birth (33 to 80%), and average litter size (2.6 to 4.0 kits per whelping female). Reproductive efficiency improved with increasing doses of eCG and was not further improved by addition of hCG. These results demonstrate that eCG has a potential application for treating anestrous mink during the breeding season.     

Influence of Gonadotrophin‐Induced First Oestrus on Gilt Fertility

The aim of this study was to determine the association between the oestrous response of pre‐pubertal gilts to gonadotrophin injection or boar exposure and their subsequent farrowing rate and litter size. At 154 days of age, randomly selected pre‐pubertal gilts received an intramuscular injection of 400 IU equine chorionic gonadotrophin plus 200 IU human chorionic gonadotrophin (PG600^®; Merck Animal Health; n = 181). From the remaining pool of animals not treated with hormones, the first gilts showing signs of oestrus were selected to act as controls (n = 201). Boar exposure began at 155 days of age for both groups, and gilts were bred at a weight of approximately 130 kg. Comparisons were made between PG600^®‐treated gilts exhibiting oestrus or not within 7 days post‐injection (early and late responders, respectively) and control gilts exhibiting oestrus or not within 30 days after beginning of boar exposure (select and non‐select control gilts, respectively). By 162 days, oestrus was detected in 67.5% of PG600^®‐treated gilts compared with 5.7% of control gilts (p < 0.0001). The proportion of animals observed in oestrus at least three times before breeding was greater for select control gilts compared with early and late responder PG600^®‐treated gilts (p ≤ 0.001). There were no significant differences in farrowing rate and litter size between the four treatment groups. These data indicate that PG600^® is an effective tool to induce an earlier oestrus in gilts, that subsequent farrowing rate and born alive litter size compare favourably to that of select gilts and that gilts failing to respond promptly to hormonal stimulation do not exhibit compromised fertility.     

Endometrial and conceptus expression of HoxA10, transforming growth factor β1, leukemia inhibitory factor,and prostaglandin H synthase-2 in early pregnant pigs with gonadotropin-induced estrus

This study was conducted to evaluate the effect of estrus induction with gonadotropins on endometrial and conceptus expression of HoxA10, transforming growth factor (TGF) β1, leukemia inhibitory factor (LIF), and prostaglandin H synthase-2 (PGHS-2) during early pregnancy in pigs. Twenty-four prepubertal gilts received 750 IU of pregnant mare serum gonadotropin (PMSG) and 500 IU of human chorionic gonadotropin (hCG) 72 h later. Gilts in the control group (n = 23) were observed daily for estrus behavior. Endometrial tissue samples, conceptuses, blood serum, and uterine luminal flushings (ULFs) were collected on days 10, 11, 12, and 15 after insemination. There was no effect of estrus induction on estradiol content in ULFs, or on ovulation and fertilization rates in studied gilts. However, the content of progesterone in the blood serum was greater in naturally ovulated gilts in comparison to gonadotropin-treated animals on day 12 of pregnancy (P < 0.05). HoxA10 expression was up-regulated in the endometrium of pregnant gilts, with natural ovulation on days 12 (P < 0.05) and 15 (P < 0.001) in comparison to days 10 and 11. When compared to control gilts, administration of PMSG/hCG resulted in decreased expression of endometrial HoxA10, TGFβ, LIF, and PGHS-2 on day 12 of pregnancy (P < 0.05). Conceptus expression of studied factors was not affected by gonadotropin treatment. Overall, these results suggest improper endometrial preparation for implantation in prepubertal gilts induced to ovulate with PMSG/hCG.     

Regression of induced corpora lutea by human chorionic gonadotropin in prepuberal gilts

The effect of daily injections of human chorionic gonadotropin (HCG) on luteal maintenance in hysterectomized prepuberal gilts induced to ovulate and in hysterectomized mature gilts was studied. Twenty-four pre-puberal gilts, 120 to 130 d of age, were induced to ovulate with 1,000 IU pregnant mare serum gonadotropin followed 72 h later with 500 IU HCG. Nine of the 24 prepuberal gilts (bred controls) were artificially inseminated on d 0 (d 0 = d after HCG). Mature gilts that had displayed one or more estrous cycles of 17 to 22 d were used (d 0 = onset of estrus). All gilts, except the bred controls, were totally hysterectomized on d 6 to 9 and their corpora lutea (CL) marked with charcoal. From d 10 through 29, eight prepuberal and 10 mature hysterectomized gilts received daily injections of 500 IU HCG in saline while seven prepuberal and eight mature hysterectomized gilts received daily injections of saline vehicle. Jugular blood samples were quantitated by radioimmunoassay for estrogen and 13,14-dihydro-15-keto prostaglandin F2 alpha (PGFM), a metabolite of prostaglandin F2 alpha. One bred control gilt was pregnant on d 30, indicating that the prepuberal gilts used in the experiment were prepuberal. All mature gilts and six of seven prepuberal gilts that received saline had maintained CL to d 30. Eight of 10 mature gilts that received HCG had maintained CL to d 30, while only two of eight (P less than .05) prepuberal gilts that received HCG maintained CL to d 30. All gilts receiving HCG had numerous follicles and accessory luteal structures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Luteinizing hormone receptor number and affinity in corpora lutea from prepuberal gilts induced to ovulate and spontaneous corpora lutea of mature gilts

This study was designed to determine if luteal cell receptors for luteinizing hormone/human chorionic gonadotropin (LH/hCG) contribute to the previously demonstrated abnormal function of induced corpora lutea (CL) in gilts. Twenty-five prepuberal (P) gilts, induced to ovulate with 1,500 IU pregnant mare serum gonadotropin followed 72 h later with 500 IU hCG (d 0 = day of hCG), and 22 mature (M) gilts that had displayed two or more estrous cycles were ovariectomized (OVX) on d 10, 14, 18, 22 or 26 after the onset of estrus. All gilts except those OVX on d 10 were hysterectomized between d 6 and 9 to ensure luteal maintenance. The CL were stored at -196 degrees C until determination of LH/hCG receptor number and dissociation constant (KD) by saturation analysis. Receptor number was greater for M than for P gilts on d 14 (P less than .07) and d 18 (P less than .01). The KD was greater in M than in P gilts on d 14 (P less than .01) and d 18 (P less than .0001). The LH/hCG receptor number and KD of P gilts remained the same throughout the days studied. The LH/hCG receptor number (fmol/mg protein) of M gilts was elevated on d 10, 14, and 18 (50.8, 50.4 and 51.4, respectively) and decreased on d 22 (26.5) and d 26 (25.4) to values similar to those of P gilts. In M gilts, KD increased on d 14, remained high on d 18 and decreased on d 22. We suggest that abnormal function of induced CL in P gilts may be due to an elevated LH receptor number.     

Observations on the influence of exogenous gonadotrophins and cloprostenol on ovulation in gilts

We studied the effects of gonadotrophins and prostaglandin (PG) F_2α on ovulation in gilts. Twenty-eight gilts were induced to ovulate using 750 IU pregnant mares serum gonadotrophin (PMSG) and 500 IU human chorionic gonadotrophin (hCG), administered 72 h apart. At 34 and 36 h after hCG, gilts received injections of either 500 μg or 175 μg PGF_2α (cloprostenol), or had no injections. Laparotomies were performed at 36 h (cloprostenol gilts) or 38 h (controls) after hCG injection. The ovaries were examined and the proportion of preovulatory follicles that had ovulated (ovulation percent) was determined at 30 min intervals for up to 6 h. The number of gilts in which ovulation was initiated and the ovulation percent increased (p<0.001) with time, but was not affected by treatment. Many medium sized follicles (≤6 mm) were also observed to ovulate, or to exhibit progressive luteinization without overt ovulation, during the surgical period. A discrepancy between numbers of preovulatory follicles and corpora lutea suggests that luteal counts may not be an accurate assessment of ovulation rate following gonadotrophic stimulation.     

The effect of various doses HCG on ovulation stimulation in gilts following previous biotechnical puberty induction

The effects of various doses of human chorionic gonadetropine (HCG) to stimulate ovulation in 86 gilts in which puberty had been induced by administration of 500 IU of pregnant mare serum (PMS) and 250 IU of HCG were established by slaughter. Only 26.9 per cent of the group without HCG had completed ovulation 120 hours from puberty induction, but 93.5 per cent had done so in the group which had received additional 500 IU or HCG 78 hours after the PMS/HCG injection. Ovulation was completed by 71.4 per cent of those sows which had been stimulated, using 250 IU of HCG. More accurate timing of ovulation in animals of one and the same group can be helpful in better insemination timing.     

Orientation studies of ovulation release in mice to test gonadotropic preparations. 2. FSH, PMSG and Gn-RH activity

The doses of FSH (follicle-stimulating hormone), PMSG (pregnant mare serum gonadotrophin), and gn-RH (gonadotrophin-releasing hormone) effective in terms of triggering ovulation were determined in a mouse ovulation test. Varying doses of the above preparations were subcutaneously injected, 48 hours after overstimulation by injection of 0.5 or 1.0 IU of PMSG. The animals were sacrificed for examination, after another 18-20 hours had passed. Roughly 50 per cent of all animals treated (threshold) in one and the same dosage group (n = 5) had ovulated in response to 0.02-0.1 IU of FSH per animal. The following FSH and PMSG dosages are recommended: 0.02, 0.04, 0.06, 0.08, and 0.1 IU of FSH, 0.6, 1.0, 1.4, 1.8, 2.2, 2.6, 3.0 IU of PMSG. When mouse ovulation tests were used in orientation studies, ovulation was regularly induced by Gn-RH doses per animal between 0.01 and 1.0 micrograms. Dosage spacings or increments should be specified with higher accuracy by further studies.     

The influence of exogenous pituitary growth hormone on the ovulatory response to PMSG and hCG and the LH response to estradiol benzoate in prepubertal gilts

Two experiments were performed to examine the influence of exogenous growth hormone on the reproductive axis in gilts. Experiment one employed 26 Yorkshire × Landrace prepubertal gilts, which were selected at 150 d and 86.5 ± 1.5 kg bodyweight (BW) and assigned equally to two treatments. Gilts received injections of either porcine growth hormone at 90 μg/kg BW, or vehicle buffer, from 150 to 159 d. At 154 d gilts received 500 IU PMSG, followed 96 hr later by 250 IU hCG. Gilts were slaughtered at 163 days and their ovaries recovered to determine ovulatory status. In each treatment, gilts failed to show any ovarian response to PMSG/hCG. All remaining control gilts ovulated and their ovaries appeared morphologically normal. In gilts receiving exogenous growth hormone, fewer ovaries (4/11, P<.01) appeared morphologically normal. The ovaries of all other growth hormone injected gilts had very large (12–25 mm) non-luteinized follicles. In experiment two, 20 prepubertal Yorkshire × Landrace gilts were selected at 138 days and 85 kg BW. These gilts received injections of growth hormone at 90 μg/kg BW (n=9) or vehicle (n=11) from 138 to 147 days. At 143 days, all gilts were given an injection of estradiol benzoate (EB) at 15 μg/kg BW. Blood samples were taken at the time of EB injection, at 24 and 36 hr and then at 6 hr intervals until 78 hr. All samples were assayed for serum LH concentrations. The EB induced LH peak height was lower (P<.04) in gilts receiving exogenous growth hormone than in controls. The results presented indicate that the daily injection of growth hormone at 90 μg/kg BW reduced the estradiol-induced release of LH in addition to reducing the number of corpora lutea in gonadotrophin stimulated gilts.     

Ovulation and embryonic survival in pubertal gilts treated with gonadotropin releasing hormone

An experiment was conducted to evaluate the effect of exogenous gonadotropin releasing hormone (GnRH) on ovulation and embryonic survival in pubertal gilts. Gilts were assigned in replicates to a control (n = 10) and treatment (n = 10) group. Treatment consisted of an iv injection of 200 micrograms of GnRH immediately after initial mating on the first day of detected estrus. Control gilts were similarly injected with physiological saline. Blood samples were collected from the anterior vena cava immediately prior to injection, thereafter at 15-min intervals for 90 min, and subsequently, before slaughter on d 30 of gestation. Serum samples were analyzed for luteinizing hormone (LH) and progesterone by radioimmunoassay. Treatment with GnRH increased the quantity of LH released (P less than .05), with highest serum concentrations (ng/ml, means +/- SE) of gonadotropin in treated gilts (17.3 +/- 3.5) occurring at 75 min post-injection. In control gilts, serum concentrations of LH were not affected by injection of saline. Mean number of ovulations in treated gilts was also greater (P less than .05) than that of control animals (14.5 +/- .7 vs 12.1 +/- .6). However, treatment with GnRH did not enhance the number of attached conceptuses (normal and degenerating) present (treated, 10.9 +/- .9 vs control, 10.5 +/- .7) nor the percentage of viable fetuses (treated, 74.7 +/- 6.9 vs control, 83.5 +/- 5.0%) on d 30 of gestation. Although GnRH increased ovulation rate, mean weight of corpora lutea of treated and control gilts did not differ (402.8 +/- 16.3 vs 389.5 +/- 11.3 mg, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Regression of induced corpora lutea in mature cyclic gilts by human chorionic gonadotropin.

This study was conducted to determine whether chronic hCG treatment would cause regression of induced corpora lutea (CL) in mature cyclic gilts. Thirty-two mature gilts that had displayed one or more estrous cycles of 18 to 22 d were used. Sixteen gilts were hysterectomized (HYSTX) on d 6 to 9 (d 0 = onset of estrus) and their CL were marked with charcoal (spontaneous group). Sixteen gilts (induced group) were injected with 1,500 IU of pregnant mare's serum gonadotropin (PMSG) on d 6 and 500 IU of hCG on d 9 (day of hCG = d 0 of the induced cycle). Ovulation was assumed to occur on d 2 of the induced cycle. Induced gilts were HYSTX on d 8 to 9 (d 17 to 18 of the original spontaneous cycle) and their CL were marked with charcoal. Only gilts (n = 14) in which induced CL were present and in which the original CL had regressed were then subjected to treatment with saline or hCG. From d 10 to 29, gilts with spontaneous CL were injected daily with 500 IU of hCG (n = 8) or saline (n = 8). From d 10 to 29 of the induced cycle, induced gilts were injected daily with 500 IU of hCG (n = 6) or saline (n = 8). Jugular blood samples were collected every other day from all gilts beginning on the 1st d of daily hCG treatment and quantified for estradiol and progesterone by RIA. On the day after the last hCG injection, the number of charcoal-marked CL and charcoal-marked corpora albicantia (CA) were determined.(ABSTRACT TRUNCATED AT 250 WORDS)