Response of gilts with delayed puberty to pregnant mare serum gonadotropin or estrogen

The effect of pregnant mare serum gonadotropin (PMSG) or estradiol cyclopentylpropionate (EC) on the induction of estrus, duration of estrus, and serum progesterone concentration after estrus was evaluated in 8 gilts with delayed puberty. Four gilts were given 500 IU of PMSG IM and 4 were given 2 mg of EC, IM. The inactive status of the ovaries at the time of treatment was verified by serum progesterone values of less than 0.5 ng/ml in serial samples collected before treatment. The 4 EC-treated gilts came into estrus at a mean of 3.5 days after treatment, but 1 of the gilts did not form corpora lutea. Three PMSG-treated gilts came into estrus at a mean of 4.0 days after treatment. The remaining PMSG-treated gilt remained anestrus and did not form corpora lutea. The mean duration of estrus in EC-treated gilts was 5.25 days compared with 2.0 days for PMSG-treated gilts (P less than 0.05). Serum progesterone concentrations were higher in PMSG-treated gilts than in EC-treated gilts at 8, 11, and 17 days after treatment (P less than 0.05).     

Reproductive performance of sows treated with a combination of pregnant mare's serum gonadotropin and human chorionic gonadotropin at weaning in the summer

During the summer and fall of 1987, sows from eight herds in three states were assigned randomly to receive either a combination of 400 IU of pregnant mare's serum gonadotropin with 200 IU of hCG (P.G. 600) or no treatment at weaning. A treatment x parity interaction was observed for days to first estrus after treatment and percentage anestrus (percentage of sows not achieving estrus within 10 d after weaning). Relative to primiparous control sows, primiparous sows given P.G. 600 expressed estrus sooner (P less than .02) after weaning (6.0 vs 7.8 +/- .6 d) and exhibited less (P less than .02) postweaning anestrus (15.6 vs 29.2 +/- 4.0%). Second parity sows that received P.G. 600 showed estrus sooner (P less than .06) than second-parity control sows (4.7 vs 6.4 +/- .7 d). Days to first estrus after treatment did not differ between groups for parity-three and older sows, and percentage anestrus was not different between treatments for parity-two and older sows. The herd X treatment interaction was significant for percentage recycled (percentage of successfully mated sows that returned to estrus), subsequent farrowing rate, and subsequent number of pigs born dead. Number of pigs born alive was lower for sows treated with P.G. 600 than for control sows (10.55 vs 10.10 +/- .18; P less than .02). In summary, treatment of sows weaned in the summer and fall with P.G. 600 had decreased days to postweaning estrus in parity-one and -two sows and reduced frequency of postweaning anestrus in primiparous sows.     

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.     

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.     

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)     

Altrenogest and fat for summer breeding of primiparous sows

Delaying the onset of estrus after weaning and adding fat to the postweaning diet were studied for their effects on estrus and fertility in 232 crossbred primiparous sows on a commercial swine farm. Sows were assigned randomly to the following treatments after weaning in June, July, August, or September, 1983: 1) altrenogest (20 mg/d) was fed for 7 d after weaning (n = 76), 2) altrenogest was fed for 7 d plus .53 kg dried animal and vegetable fat product (.45 kg actual fat/d) for 14 d after weaning (n = 78), or 3) no treatment (controls, n = 78). While a similar proportion of sows came into heat after weaning (lactation length = 4 wk), sows fed altrenogest (14.4 +/- .2 d) returned to estrus about 9 d later (P less than .01) than controls (5.6 +/- .2 d). Serum progesterone concentration was assayed in blood samples collected from a subgroup (74%) of the cows not observed in estrus by 3 wk after weaning to determine possible causes of anestrus. If serum progesterone (greater than 5 ng/ml) was elevated, we assumed that sows had ovulated without expressing estrus (behavioral anestrus) or ovulated with undetected estrus (less overt estrus or error in estrous detection), whereas low progesterone (less than or equal to 5 ng/ml) indicated that sows were anovulatory. About 53% of the sows not observed in estrus across all treatments had luteal function, probably resulting from post-weaning ovulation. Incidence of anovulation without estrus was 47%. Farrowing rate was higher (P less than .05) for sows fed only altrenogest (64%) compared with controls (46%), but similar to fat supplemented, altrenogest-treated sows (52%).(ABSTRACT TRUNCATED AT 250 WORDS)     

新型激素制剂对母猪诱导发情效果研究

应用PX-700制剂对乏情母猪进行了诱导发情研究，结果表明：700IU是PX-700制剂诱导乏情母猪发情的适宜剂量；而该制剂对断奶后45d以上的乏情母猪诱导发情率较低，但其情期受胎率不受影响；PX-700制剂对诱导发情后母猪的情期受胎率、产仔数及仔猪出生重均无影响。     

Prostaglandin F2 alpha and prolactin in experimental hypogalactia in sows

Peripheral plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F2alpha(PGFM), progesterone, prolactin and oestrone were determined in 20 sows for two days before and three weeks after parturition. Groups of four sows each received one of the following five treatments post partum: 30 ml sterile 0.9 per cent saline solution intrauterinely; ovariectomy and 30 ml saline solution intrauterinely; 10 ml Lugol's iodine plus 20 ml saline solution intrauterinely; ovariectomy and 10 ml Lugol's iodine plus 20 ml saline solution intrauterinely, or progesterone (0.5 mg [kg bodyweight]-1 intramuscularly). Saline solution and iodine were administered every 48 hours, starting immediately after parturition, for one week. Ovariectomy was performed within eight hours of delivery. Progesterone was given every third day for 12 days. Piglet weight gains were used as a reflection of milk yield. In all sows, oestrone values were elevated before parturition, but fell by the end of delivery and were very low during lactation. PGFM concentrations rose during the last two days of pregnancy to reach maximal values at the time of delivery. Plasma progesterone levels declined concomitantly with the rise in PGFM values before parturition. Basal values of progesterone were achieved within 24 hours after delivery in control sows receiving saline treatment. Progesterone values fell immediately after ovariectomy in sows receiving saline or iodine treatment but were slightly elevated for one week in sows that received only intrauterine iodine treatment, suggesting that complete regression of corpora lutea is prevented by suppression of post parturient uterine prostaglandin production. Sows injected with progesterone maintained plasma values of about 5 to 15 nmol litre-1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Technical note: use of slow-release estradiol and prostaglandin F2alpha to induce pseudopregnancy and control estrus in gilts

We determined whether a single injection of slow-release estradiol-17beta (SRE2) would induce pseudopregnancy in gilts and whether PGF2alpha would regress the corpora lutea (CL) of pseudopregnancy. Crossbred gilts (n = 40) were induced to ovulate by treatment with 400 IU of hCG + 200 IU of eCG (PG600, Intervet, Millsboro, DE) given at 180 d of age (d = 0). On d 14, gilts were injected i.m. with one of five doses (n = 8 gilts/dose) of SRE2 (0, 12.5, 25, 50, or 100 mg). Blood samples were collected before SRE2 and twice weekly until d 73 to monitor serum progesterone (P4) and estradiol (E2). On d 59, gilts received (i.m.) 10 mg of PGF2alpha (Lutalyse, Pharmacia Upjohn, Kalamazoo, MI) and were checked for estrus for 7 d. On d 62, mammary development was scored (0 = no development; 1 = some development; 2 = teat and gland development) by a neutral observer. Treatment with SRE2 increased (P < .05) peak E2 concentrations, duration of luteal function, and mammary gland score. There were no differences (chi-square, P > .05) among doses of SRE2 in the percentage of pseudopregnant gilts that showed luteolysis after PGF2alpha. We conclude that a single injection of SRE2 can induce pseudopregnancy and that the CL can be regressed with PGF2alpha, providing a simple method for controlling estrus in gilts.     

Potential treatments for anestrus in gilts and sows

Pregnant mares' serum gonadotrophin (400 IU) combined with human chorionic gonadotrophin (200 IU) was administered to anestrous gilts (n=31) and sows (n=20) in commercial herds. Two-thirds of the treated animals were mated successfully within seven days and, although no control animals were included, the response indicated that this hormone combination would be useful in herds with anestrous problems. A second experiment was conducted to evaluate the occurrence of estrus and/or ovulations in prepuberal gilts (n=eight/treatment) following injection with pregnant mares' serum gonadotrophin/human chorionic gonadotrophin or other hormones that might stimulate ovarian activity. The pregnant mares' serum gonadotrophin/human chorionic gonadotrophin combination and follicle-stimulating hormone produced estrus within ten days of injection in at least half of the treated gilts but the response was lower with gonadotrophin-releasing hormone and a prostaglandin analogue. Combinations of human chorionic gonadotrophin with small amounts of estradiol benzoate stimulated estrus and ovulation in most of the treated gilts.     

A role for the adrenal cortex in the onset of cystic ovarian follicles in the sow.

The corticotrophin (ACTH)-adrenal cortical axis has previously been implicated in the onset of cystic ovaries in the sow. In view of the role of the ACTH-adrenal cortical axis in stress, two sows were subjected to an elevated environmental temperature of 32 degrees C for three hours daily during the follicular phase of the estrous cycle. Plasma concentrations of glucocorticosteroids and progesterone fluctuated markedly in one sow that developed cystic ovaries. Concentrations of these hormones did not vary greatly in the other sow that did not develop cystic follicles. Exposure to an environmental temperature of 32 degrees C for three hours or injection of 1 IU/kg bodyweight of ACTH for each of two ovariectomized sows resulted in an elevation in progesterone values to 5-7 ng/ml plasma from basal levels of 1-2 ng/ml and a rise in total glucocorticosteroids from basal levels of 1 or 2 microgram/100 ml plasma to 4-10 microgram/100 ml. Injection of 2 mg/kg bodyweight of progesterone and 4 mg/kg bodyweight of cortisol into the ovariectomized sows was found to approximate these elevations in plasma steroid values. When either progesterone or cortisol was injected daily during the follicular phase into two intact sows in two successive experiments at these dosage levels, similarly elevated plasma steroid concentrations were seen and cystic ovarian follicles resulted. The results suggest that glucocorticosteroids and progesterone of adrenal origin may be involved in the onset of cystic ovaries in the sow.     

Effect of hCG Treatment on the Oestrous and Ovulation Responses to FSH in Prepubertal Gilts

To ensure sufficient numbers of pregnant females, particularly at hotter times of the year, hormonal induction of gilt oestrus may be necessary. However, the gilt oestrus and ovulation responses to gonadotrophin treatment have often proven unpredictable. The objective of this study was to examine possible reasons for this unpredictability. Prepubertal gilts (approximately 150 days of age, n = 63) were assigned to one of three treatments: injection of 300 IU hCG (n = 15); pre-treatment with 100 mg FSH in polyvinylpyrrolidinone administered as 2 × 50 mg injections 24 h apart, followed by 600 IU eCG at 24 h after the second FSH injection (n = 23); or FSH pre-treatment as above followed by 300 IU hCG at 24 h after the second FSH injection (n = 25). To facilitate oestrus detection, gilts were exposed to a mature boar for 15 min daily for 7 days. Blood samples were obtained on the day of eCG or hCG injection and again 10 days later and gilt ovulation responses determined based on elevated progesterone concentrations. The oestrus responses by 7 days were 6.7%, 17.5% and 64.0% for gilts treated with hCG, FSH + eCG and FSH + hCG, respectively (p < 0.001). The oestrous gilt receiving hCG alone and one oestrous FSH + hCG gilt did not ovulate, all other oestrous gilts ovulated. A further two anoestrous FSH + eCG-treated gilts ovulated. These data suggest that FSH pre-treatment facilitated the development of ovarian follicles to the point where they became responsive to hCG, but had little effect on the response to eCG.     

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.     

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.     

Effect of boar presence before and after weaning on estrus and ovulation in sows

Two hundred sixty-two sows were used to investigate the effects of boar exposure during the last week of nursing (BPRE) and after weaning (BPOST) on the return to estrus. Because approximately one-half of the sows were weaning their first litter, a third factor, primiparous vs multiparous (LITT), was considered in the statistical analysis. To evaluate the effect of treatment on ovarian activity, the sows were also blood-sampled twice weekly for 3 wk after weaning for the measurement of plasma progesterone concentrations as an index of ovulation. Boar exposure after weaning was the most important stimulus of early ovulation and estrus after weaning (P less than .001). A greater proportion of first-litter sows exhibited estrus later (P less than .02) and ovulated later (P less than .09) than did multiparous sows. First-litter sows were unaffected (P greater than .10) by boar exposure before weaning. Multiparous sows were sensitive to boar exposure during nursing. Maximal boar exposure for these sows (BPRE + BPOST) resulted in 95% of sows in estrus and ovulating within 20 d of weaning. No boar exposure resulted in 45% and 38% anestrus and anovulatory sows. Boar exposure, either before or after weaning, was effective in reducing the number of anestrus and anovulatory sows to between 15 to 30%. The effects of BPRE and BPOST on return to ovulation were additive and approximately equal.     

Effects of ACTH injections during estrus on concentrations and patterns of progesterone, estradiol, LH, and inhibin alpha and time of ovulation in the sow

This study investigated whether injections of ACTH for 48 h, from the onset of the second standing estrus after weaning, had any impact on time of ovulation and patterns of progesterone, estradiol, luteinizing hormone (LH), and inhibin alpha. The studied sows (n=15) were fitted with jugular vein catheters and randomly divided into a control (C group) and an ACTH group. From the onset of standing estrus, the sows were injected (NaCl or synthetic ACTH, 5 microg/kg) every 4h; blood samples were collected immediately before and 45 min after each injection. Ovulation was monitored using ultrasonography. The ACTH-group sows stopped displaying signs of standing estrus sooner after ovulation in their second estrus, but no impact was found on time of ovulation. There were no significant differences in the intervals between LH peak, estradiol peak, and the onset of standing estrus between the C and ACTH groups. The cortisol and progesterone concentrations were significantly elevated (p<0.001) in samples taken 45 min after ACTH injection. There were minor differences in estradiol and LH concentrations between the groups. Overall inhibin alpha concentrations were significantly higher during the treatment period in the ACTH than in the C group, but there were no significant differences between samples taken either 45 min or 4h after injection. In conclusion, injections of synthetic ACTH during estrus in the sow apparently disturb the duration of signs of standing estrus and the hormonal pattern of progesterone, and possibly of inhibin alpha, estradiol and LH.     

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.     

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)     

Embryo collection from pigs post‐pseudopregnancy induced by estradiol dipropionate

We aimed to define whether embryo collection carried out after pseudopregnancy was of similar outcome and quality as after artificial abortion. To induce pseudopregnancy, 30 gilts or sows were given 20 mg intramuscular estradiol dipropionate (EDP) 10–11 days after the onset of estrus. Ten additional pigs were inseminated artificially at natural estrus as a control group. Prostaglandin F_2α (PGF_2α) was administered twice with a 24 hr interval beginning 15, 20, or 25 days after EDP‐treatment (n = 10 per group) or between 23 and 39 days after artificial insemination in control pigs. Following this, all pigs were given 1,000 IU equine chorionic gonadotropin and 500 IU human chorionic gonadotropin (hCG) and then inseminated. Embryos were recovered 6 or 7 days after hCG treatment and outcome was recorded. There was no significant difference in the number of normal embryos collected from the pigs with PGF_2α initiated at different time points or from the control group. Embryonic developmental stages 7 days after hCG treatment also did not differ among groups. These results indicate that the use of EDP to induce pseudopregnancy, followed by PGF_2α administration to synchronize estrus for subsequent embryo harvest, is a suitable alternative to the artificial abortion method.