Ovarian response to pregnant mare serum gonadotropin and porcine pituitary extract in gilts actively immunized against gonadotropin releasing hormone

Two experiments were conducted to determine the effect of exogenous gonadotropins on follicular development in gilts actively immunized against gonadotropin releasing hormone (GnRH). Four gilts, which had become acyclic after immunization against GnRH, and four control gilts were given 1,000 IU pregnant mare serum gonadotropin (PMSG), while four additional control gilts were given saline. Control animals were prepuberal crossbred gilts averaging 100 kg body weight. Control gilts given saline had ovaries containing antral follicles (4 to 6 mm in diameter). Control gilts given PMSG exhibited estrus and their ovaries contained corpora hemorrhagica and corpora lutea. PMSG failed to stimulate follicular growth in gilts immunized against GnRH, and ovaries contained regressed corpora albicantia and small antral follicles (less than 1 mm in diameter). Concentrations of luteinizing hormone (LH) and estradiol-17 beta (E2) were non-detectable in gilts immunized against GnRH and given PMSG. In the second experiment, five gilts actively immunized against GnRH were given increasing doses of PMSG every third day until unilateral ovariectomy on d 50. PMSG failed to stimulate follicular growth, and concentrations of follicle stimulating hormone (FSH), E2 and LH were not detectable. Six weeks later, gilts were given a booster immunization and then were given 112 micrograms LH and 15 micrograms FSH intravenously every 6 h for 9 d. The remaining ovary was removed on d 10. Although LH and FSH concentrations were elevated, administration of gonadotropins did not stimulate follicular growth or increase E2 concentrations. These results indicate that neither PMSG or exogenous LH and FSH can induce E2 synthesis or sustain follicular development in gilts actively immunized against GnRH.     

Serum prolactin response to thyrotropin releasing hormone in estrogen treated hypophysial stalk-transected gilts

Twelve crossbred gilts, 169 ± 3 days of age and 72.8 ± 3.4 kg body weight, were hypophysial stalk-transected (HST)1 or sham hypophysial stalk-transected (S-HST). Gilts were ovariectomized 6 days later and assigned to four treatments of 3 gilts each in a 2 × 2 factorial arrangement. One-half of the HST and S-HST gilts received 5 mg estradiolbenzoate (EB) or corn oil vehicle im at 0800 hr daily for 5 days beginning 64 ± 3 days after HST or S-HST. Blood was collected by jugular vein cannula at 0830 and 0900 hr the day after the last injection of EB or oil. Immediately after the 0900 hr sample, 200 μg thyrotropin releasing hormone (TRH) were injected (iv). Mean basal serum prolactin (PRL) concentration was similar for HST (10.3 ± 1.0 ng/ml) and S-HST (12.3 ± 1.7 ng/ml) gilts, however mean basal serum PRL concentration was greater (P<.05) for EB-treated gilts (13.7 ± 1.3 ng/ml) than for oil-treated gilts (8.8 ± .5 ng/ml). Mean serum PRL concentration of all gilts increased within 10 min and returned to approximately 20 ng/ml by 150 min after TRH. Maximum serum PRL concentrations at 10 min after TRH were greater (P<.01) for S-HST (255.9 ± 29.6 ng/ml) than HST gilts (83.4 ± 18.8 ng/ml), but were not different for EB (198.0 ± 50.6 ng/ml) and oil-treated gilts (141.4 ± 36.3 ng/ml). Area under the serum PRL response curve after TRH was greater (P<.005) for S-HST than HST gilts and for EB than oil-treated gilts (P<.05). These results do not eliminate the possible influence of estrogen on PRL secretion at the hypothalamus, but do indicate that estrogen directly stimulated the anterior pituitary gland to secrete PRL.     

Luteinizing hormone (LH) response to different doses of synthetic gonadotropin releasing hormone (GnRH) in prepubertal gilts

The object of this investigation was to study luteinizing hormone (LH) response to different doses of synthetic gonadotropin-releasing hormone (GnRH) in prepubertal gilts. Four crossbred prepubertal gilts, 128–134 days old and body weight 57–63 kg, were used in this study. Four doses, 0. 5, 25 and 125 μg, of GnRH were administered via a jugular vein catheter in a latin square design. Each treatment consisted of 3 injections at 90 min intervals. Frequent blood samples were taken during a period of 90 min before up to 90 min after treatment. Total LH responses were measured from post-treatment samples as the area under the curve above base level obtained from pre-treatment samples. A positive relationship between GnRH dose and LH release was obtained in all gilts, except for 1 treatment given to a gilt with high plasma level of oestradiol-17β on the day of treatment. This study has demonstrated the responsiveness of the pituitary gland by LH release to different doses of GnRH in 4.5-month-old prepubertal gilts.     

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.     

Response of postpartum beef cows to exogenous progestogens and gonadotropin releasing hormone

Plasma progesterone (P4) profile and estrous detection were used during three experiments to evaluate the effects of exogenous progestogens on the life span of gonadotropin releasing hormone (GnRH)-induced corpora lutea (CL) in postpartum (pp) beef cows. Experiment 1 utilized primiparous fall-calving cows (n = 28, trial 1); and spring-calving cows (n = 29, trial 2). On d 18 to 27 pp (d 0) all cows received intravaginal devices containing either P4 or no P4 (NP) for 5 d. On d 5 the devices were removed and calves were either removed (CR) or were present (CP) with half of the cows within steroid group. At 50 h after device removal, 500 micrograms of GnRH was given (iv) to all cows, and weaned calves were reunited with their dams. The induced CL had a normal life span (greater than 16 d) in 17 and 86% (trial 1) and 8 and 79% (trial 2) of NP and P4 cows, respectively. Calf removal did not affect (P greater than .10) the life span of the CL. In Exp. 2, spring-calving multiparous cows (d 18 to 24 pp; d 0) received either no P4 (NP; n = 19), P4 for 6 d via intravaginal devices (P4H; n = 19) or a single im injection of 300 mg P4 (P4 IM; n = 18). At 48 h after device removal or at 8 d after the injection of P4, half of the cows within steroid group received either 500 micrograms GnRH or saline. Corpora lutea had a normal life span in 0, 11, and 80% of NP, P4 IM and P4H cows, respectively, that received GnRH and in 22% of P4-saline cows. In Exp. 3, fall-calving multiparous and primiparous cows (d 25 to 31 pp) received either no progestogen (NP; n = 20), P4 via intravaginal devices for 5 d (P4H; n = 21) or melengestrol acetate (MGA; .5 mg.head-1.d-1 for 5 d orally, n = 15). At 48 d after device removal or at 72 h after the last MGA feeding, all cows received 500 micrograms GnRH. Progesterone post-GnRH injection was increased (greater than 1 ng/ml) at d 7 in 64, 100 and 100%, and remained elevated at d 14 in 11, 46 and 100% of NP, MGA and P4H cows, respectively. For all experiments plasma P4 was increased (range 2 to 5 ng/ml) when the devices containing P4 were in place, then decreased (less than 1 ng/ml) by 48 to 50 h after device removal.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of unilateral castration and unilateral cryptorchidism on gonadotropin and testosterone response to gonadotropin releasing hormone in the bull

The effects of unilateral castration (UC) and induced unilateral cryptorchidism (UCR) on basal plasma luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone, and on the responses of these hormones to gonadotropin releasing hormone (GnRH), were investigated in bulls altered at 3, 6 or 9 months of age. Blood plasma was collected before and after GnRH (200 micrograms) stimulation approximately 1 year following gonadal manipulation. Neither mean baseline concentrations nor GnRH-induced increases in plasma testosterone were altered (P greater than .1) by hemicastration or UCR (P greater than .1). Both mean baseline LH and GnRH-induced LH release were greater (P less than .05) in bulls altered at 3 months of age than in bulls altered at 9 months of age. UC increased (P less than .05) plasma LH response to GnRH over that observed in intact bulls, but not above that in UCR bulls. UCR had no detectable effect on either baseline concentrations or GnRH-stimulated LH release. FSH was increased (P less than .05) in hemicastrates, while UCR had a variable effect on peripheral FSH: FSH was reduced (P less than .05) in UCR animals altered at 3 months of age but increased (P less than .05) in UCR bulls altered at both 6 and 9 months of age when compared to FSH in intact bulls. The results indicate that, compared with intact bulls, UC bulls release increased amounts of both gonadotropins but similar amounts of testosterone in response to GnRH stimulation. UCR had a variable effect on FSH release and did not alter either LH or testosterone.     

配种前营养策略对母猪妊娠早期胚胎成活率的影响

提高母猪妊娠早期胚胎成活率可以增加产仔数，提高经济效益。配种前营养对妊娠早期胚胎成活率具有重要的影响．这种影响的途径与卵泡发育和卵母细胞质量密切相关。本文综述了配种前营养．包括营养水平、能量来源、蛋白质、纤维等对后备母猪和哺乳母猪妊娠早期胚胎成活率的影响。     

Effects of active immunization against gonadotropin releasing hormone on gonadotropin secretion after ovariectomy and testosterone propionate administration to mares

Five lighthorse mares were actively immunized against gonadotropin releasing hormone (GnRH) conjugated to bovine serum albumin (BSA) to study the involvement of GnRH in luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion following ovariectomy (OVX) and after administration of testosterone propionate (TP). Five mares immunized against BSA served as controls. Immunizations were started on November 1, and OVX was performed in June (d 1). All mares were treated with TP from d 50 to 59 after OVX. On the day of OVX, concentrations of LH were lower (P less than .05) in GnRH-immunized mares than in BSA-immunized mares and were generally nondetectable; FSH concentrations were reduced (P less than .05) by 50% in GnRH-immunized mares relative to BSA-immunized mares. In contrast to BSA-immunized mares, plasma concentrations of LH or FSH did not increase after OVX in GnRH-immunized mares. The LH response to GnRH analog (less than .1% cross-reactive with GnRH antibodies) on d 50 was reduced (P less than .05) by 97% in GnRH-immunized mares relative to BSA-immunized mares, whereas the FSH response was similar for both groups. Treatment with TP for 10 d reduced (P less than .01) the LH response and increased (P less than .01) the FSH response to GnRH analog in BSA-immunized mares, but it had no effect (P greater than .1) on the response of either gonadotropin in GnRH-immunized mares.(ABSTRACT TRUNCATED AT 250 WORDS)     

Response of the lactating and postweaning sow to gonadotropin releasing hormone (GnRH)

Clinical and endocrinological responses to administration of gonadotropin releasing hormone analog (LH-RH-A) during the lactation period and postweaning in the sow were investigated. Plasma LH concentrations in lactating sows rose immediately after administration of LH-RH-A. However, in postweaning sows the increase of LH level was more slowly. Three of 5 postweaning sows came into estrus and ovulated after LH-RH-A treatment. One sow exhibited a distinct LH response, but her ovaries remained quiescent. The remaining one with feeble estrus for a short period became cystic ovaries. Thus, LH response to GnRH in the sow seems to be higher during early lactation than at 2 days postweaning.     

Induction of ovulation in the prepuberal gilt by pulsatile administration of gonadotropin releasing hormone

An attempt was made to induce precocious puberty in gilts approximately 164 days of age by stimulating a luteinizing hormone (LH) secretory pattern similar to that which occurs before normal onset of puberty. Hourly iv administration of 1 μg synthetic gonadotropin releasing hormone (GnRH) for 7 or 8 days resulted in a mean serum LH concentration of 1.7 ± .3 ng/ml in three treated gilts compared with .9 ± .1 ng/ml in three control gilts (P<.08). Serum LH peak frequency was also greater (P<.05) in treated (3.4 ± .5 peaks/4 hr) than in control gilts (1.2 ± .1 peaks/4 hr), but serum LH peak amplitude was not altered (P>.33) by GnRH treatment. All treated gilts displayed estrus and ovulated within 6 days after treatment began, and all control gilts remained prepuberal throughout the study (P=.05). Only one of the three treated gilts displayed a normal estrous cycle and reovulated after treatment. Precocious ovulation but not puberty was induced in gilts by hourly administration of 1 μg synthetic GnRH, indicating that the pituitary and ovaries of 164-day-old gilts are competent and that final sexual maturation occurs at the hypothalamic level.     

Immunization of sheep against modified peptides of gonadotropin releasing hormone conjugated to carriers

The efficacy of antigens based on modified GnRH peptides in stimulating the production of antibodies against GnRH in sheep was tested. In the first study cysteine-containing GnRH peptides were conjugated to keyhole limpet haemocyanin (KLH) in 3 different orientations. The 3 conjugates were prepared in an emulsion of Freund's complete adjuvant (FCA) and were injected into 3 groups of 6 castrated male lambs. The 3 vaccines efficiently induced anti-GnRH titers in all the animals treated. The specificity of the GnRH antisera raised varied depending on the orientation of the GnRH molecule in the antigen and on the individual animal.

In a second trial designed to evaluate carrier molecules, a cysteine-containing GnRH peptide was conjugated to either KLH, equine serum albumin, ovalbumin or tetanus toxoid. The conjugates were prepared with FCA and injected into intact male lambs. All 4 vaccines stimulated the production of antibodies against GnRH in all the animals treated. The conjugates prepared with equine serum albumin or ovalbumin were the most effective in raising high anti-GnRH titers. In 18 of 20 lambs treated, anti-GnRH titers resulted in a marked atrophy of the testes.

We conclude that: 1) the different epitopes of the GnRH molecule are equally immunogenic in sheep; 2) the GnRH antibody response is affected by the carrier used; and, 3) anti-GnRH vaccines based on cysteine-substituted GnRH analogues show potential for use in immunocastration of livestock.     

Ovulation in postpartum beef cows treated with estradiol

The effect of implants of estradiol on initiation of ovarian cycles postpartum was studied in 201 anestrous beef cows. Cows from four farms were used over a 2-yr period in a 2 x 3 factorial arrangement of treatments with estradiol implants and stage postpartum as main effects. Cows were assigned at random within date of calving within farm to receive an ear implant containing estradiol-17 beta (24 mg) for 21 d or to serve as controls. Stages postpartum at implantation were divided into less than or equal to 25, 26 to 39, and greater than or equal to 40 d, three stages that should reflect potential changes in hypothalmic-hypophysial sensitivity to estradiol. Blood samples for determination of progesterone were obtained and rectal examinations of the ovaries performed at implant insertion, 14 d after insertion, at implant removal (d 21), and 14 d after removal (d 35) to assess ovulatory response to treatment. Circulating concentrations of estradiol on d 14 of treatment averaged 3.2 +/- 1.0 and 23.1 +/- 4.7 pg/ml for control and estradiol-treated cows, respectively. Compared with control cows, treatment with estradiol initiated after d 26 postpartum increased the proportion of cows that ovulated during the experimental period. No differences were seen in the average days postpartum when cows were first determined to have ovulated.     

Effects of estradiol-17 beta, naloxone and gonadotropin releasing hormone on postpartum secretion of luteinizing hormone in fall-lambing ewes

The interaction among exogenous estradiol-17 beta, naloxone and gonadotropin releasing hormone (GnRH) in the control of luteinizing hormone (LH) secretion was studied in intact postpartum ewes nursing their offspring. One-half of 30 fall-lambing ewes were implanted subcutaneously with an estradiol-17 beta containing Silastic capsule between postpartum d 1 and 12 which doubled their serum concentrations of estradiol (16.0 +/- .1 vs 8.4 +/- .1 pg/ml). Blood samples were collected from implanted and non-implanted ewes at 15-min intervals for 5 h on d 3, 8, 13, 20 and 28 postpartum. Pre-injection samples were collected for 1 h, and ewes were injected with saline, naloxone (NAL;1 mg/kg) or GnRH (100 micrograms/ewe). When averaged across all days and implant groups, serum LH in the three post-NAL samples was higher (P less than .05) than in the three pre-NAL samples (3.6 +/- 1.2 vs .6 +/- .2 ng/ml). Post-GnRH concentrations of serum LH were lower (P less than .05) in estradiol-implanted ewes than in non-implanted ewes on d 8 and 13, but there were no differences in any LH characteristics on d 20 and 28 after implant removal on d 12. In non-implanted ewes, serum LH responses to GnRH increased (P less than .05) eightfold from d 3 (3.8 +/- 1.4 ng/ml) to d 8 (31.6 +/- 1.4 ng/ml), remained elevated through d 20, but declined by d 28 (10.8 +/- 1.4 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovulation rate and litter size in gilts immunized against androstenedione and 17alpha-hydroxyprogesterone

Two experiments were conducted to evaluate the effects of the immunization of gilts against ovarian steroids on ovulation rate and litter size. In Exp. 1, gilts (n = five gilts/treatment) at 165+/-1.6 d of age were immunized against either carrier (Control), androstenedione, or 17alpha-hydroxyprogesterone. Age at puberty and estrous cycle length averaged 208+/-5.5 (P = 0.67) and 20.3+/-2.8 d (P = 0.41), respectively, and were not affected by treatment. The androstenedione- and 17alpha-hydroxyprogesterone immunized gilts had higher (P < 0.02) ovulation rates than Controls (14.2, 14.2, and 11.4+/-0.8, respectively). Total pigs born (P = 0.66) and pigs born live (P = 0.65) for the androstenedione-treated group were not different from Controls. Gestation length was not different (P = 0.36) between any of the treatments and the Controls (115+/-0.9 d). Procedures used in Exp. 2 were similar to those in Exp. 1, except that only Control (n= 18) and 17alpha-hydroxyprogesterone (n = 16) treatments were included and only litter size at farrowing was measured. Total pigs and pigs born live were higher in the 17a-hydroxyprogesterone-treated gilts than in the Controls (12.6 vs 10.5+/-0.6, P < 0.02; and 11.4 vs 9.2+/-0.6; P < 0.01, respectively). Data from this study indicate that litter size in gilts can be increased by immunization against 17alpha-hydroxyprogesterone.