Serum profiles of progesterone, LH, FSH and prolactin immediately preceding induced puberty in gilts

Two experiments were conducted to determine if the secretory patterns of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) and serum concentrations of progesterone change immediately preceding induced puberty in gilts. To help predict when prepubertal gilts would attain puberty, gilts were induced into puberty by relocation from confinement housing to an outdoor lot and exposure to mature boars. In Exp. 1, 17 prepubertal gilts were bled on two successive days from 0800 to 1200 h before relocation and boar exposure and until the second day of estrus or for 8 d in gilts that failed to exhibit estrus. Blood samples were collected from indwelling cannulas at 20-min intervals for 4 h. In Exp. 2, blood samples were collected from 20 prepubertal gilts at 20-min intervals from 0800 to 1200 h and from 2000 to 2400 h until the second day of estrus or for 6 d if the gilt failed to exhibit estrus. In each experiment, 11 gilts exhibited pubertal estrus 3 to 6 d after relocation and boar exposure. When the frequency of LH spikes in each gilt was normalized to the day of her preovulatory surge of LH (d 0), a decline in the frequency of LH secretory spikes was observed as gilts approached puberty. However, neither the average magnitude of LH spikes nor mean LH concentrations were different among these days. Mean serum concentrations, frequency of spikes or average magnitude of secretory spikes of FSH or PRL did not change on the days preceding the preovulatory peak of LH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pituitary responsiveness to GnRH, hypothalamic content of GnRH and pituitary LH and FSH concentrations immediately preceding puberty in gilts

To determine whether pituitary concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) or hypothalamic content of gonadotropin releasing hormone (GnRH) change before puberty, 40 prepubertal gilts averaging 7 mo of age were slaughtered before or on the second, third or fourth day after relocation and boar exposure. Some gilts responded to relocation and boar exposure as indicated by swollen vulvae, turgid uteri and enlarged ovarian follicles at the time of slaughter. Pituitary concentrations of LH and FSH and hypothalamic content of GnRH were similar between gilts that responded to relocation and boar exposure and gilts that did not respond. In addition, boar exposure and relocation had no effect on pituitary concentrations of LH and FSH or on hypothalamic content of GnRH. To determine whether pituitary responsiveness to GnRH changes before puberty, a third experiment was conducted in which 72 gilts were injected with 400 micrograms of GnRH either before or on the second, third or fourth day after relocation and boar exposure. In gilts that subsequently responded (i.e., ovulated) as a result of relocation and boar exposure, pituitary responsiveness to GnRH was reduced as compared with gilts that failed to ovulate after relocation and boar exposure. Peak concentrations of serum LH after GnRH injection were 4.6 +/- 1.3 vs 9.8 +/- .8 ng/ml for responders vs nonresponders. Peak serum FSH after GnRH injection was also lower for responders than for nonresponders (29.5 +/- 4.2 vs 41.2 +/- 2.4 ng/ml). When compared with controls, relocation and boar exposure did not significantly affect GnRH-induced release of LH and FSH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prepubertal consumption of zearalenone on puberty and subsequent reproduction of gilts

Forty-eight prepubertal gilts (178.7 +/- 4.1 d; 94.2 +/- 4.1 kg), 16 in each of three trials, were assigned randomly to receive 0 (C) or 10 ppm zearalenone (Z) daily in 2.5 kg of a 14% protein finishing ration for 2 wk. Blood samples were collected at 20-min intervals for 4 h 1 wk after the start of the experiment and 1 wk after Z was withdrawn. Two weeks after Z was withdrawn, gilts were exposed to mature boars 15 min per day for 3 wk. Gilts in estrus were mated to two different boars 12 h apart. Twice each week, blood was sampled and analyzed for progesterone to establish age of puberty. Age at puberty differed (P = .008) among replicates but was similar (P = .13) between Z and C gilts within each replicate. Mean serum concentrations of LH were suppressed (P = .025) during consumption of Z (.25 vs .42 ng/ml) but were similar (P = .16) to concentrations in C gilts 1 wk after Z was withdrawn (.35 vs .45 ng/ml). Frequency and amplitude of LH secretory spikes did not differ (P greater than .50) between Z and C gilts during either sampling period. Mean serum concentrations of FSH were similar (P = .25) between Z and C gilts. Number of corpora lutea and live fetuses were similar (P = .29 and P = .94, respectively) between Z and C gilts. Fetal weights were greater (P = .025) and crown to rump length tended to be greater (P = .10) in fetuses from Z gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of daily injections of porcine somatotropin on growth, puberty, and reproduction in gilts

To determine whether recombinant porcine somatotropin (rpST) alters reproduction, 40 crossbred gilts weighing 59.1 +/- .5 kg at 125 +/- 1 d of age were assigned randomly to an experiment arranged as a 2 x 2 factorial. Eight gilts were given daily injections of diluent until they reached 104 kg BW (DW), and eight received diluent injections until puberty (DP). Twelve gilts were given rpST (4 mg/d) until 104 kg BW (PW) and 12 were given rpST injections until puberty (PP). All gilts were individually fed on an ad libitum basis an 18% CP corn-soybean meal diet (1.2% lysine and 3.1 Mcal/kg of ME). Beginning at 5 mo of age, gilts were exposed 20 min daily to mature boars. Serum concentrations of progesterone were measured weekly from 5 to 8 mo of age to verify age of puberty. Gilts observed in pubertal estrus were mated to two different boars 10 h apart. At 47 +/- 1 d of gestation, gilts were slaughtered to assess fetal development. After 60 d of treatment, serum LH and FSH profiles were determined in blood samples drawn at 20-min intervals for 4 h from eight diluent- and eight rpST-treated gilts fitted with indwelling jugular catheters. By 28 d, feed intake, feed/gain, and blood urea nitrogen were decreased (P less than .005) by rpST. Treatments did not affect (P greater than .05) the proportion of gilts attaining first ovulation (DW = 6/6; DP = 10/10; PW = 7/9; PP = 14/14) or conception rate (DW = 5/6; DP = 7/10; PW = 4/6; PP = 11/12).(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormonal patterns of boars exposed to natural or supplemental lighting during pubertal development

Thirty-two crossbred boars (Hampshire X Duroc X Yorkshire) were reared under natural lighting (35 lx) or supplemental lighting (1,400 lx) beginning at 4 wk of age. Boars received supplemental lighting from six 40-W fluorescent bulbs between 0530 and 2030 in a nursery unit. From 9 to 32 wk of age, boars received either natural lighting (30 lx) or supplemental lighting (100 lx) in a growing-finishing unit. Blood samples were collected from indwelling cannulae at 20-min intervals for 6 h every 2 wk from 2.5 to 7 mo of age. Libido scores were evaluated during alternate weeks when intensive blood samples were not taken. Libido scores were not different between natural and supplemental lighting treatments (P greater than .30). However, at 122 d of age, libido scores of boars exposed to supplemental lighting tended to be higher (P = .10) than those exposed to natural lighting. Although mean serum concentrations of luteinizing hormone (LH) were higher (P less than .05) in boars at 75, 89, 103 and 131 d of age reared under supplemental lighting than boars of the same age reared under natural lighting, the number of LH secretory spikes was similar between the treatment groups (P = .39). Serum concentrations of LH decreased in both treatment groups as boars became older (P less than .05). However, the incidence of LH spikes was similar across ages and between treatment groups from 2.5 to 7 mo of age. Mean serum concentrations of follicle stimulating hormone and testosterone were similar between treatments (P greater than .75).     

The effect of confinement on days to puberty in gilts

In the late fall and winter of 1982 to 1983, 112 crossbred gilts were used in a factorially arranged experiment to determine the effect of confinement on the age at which a gilt reaches first estrus (puberty). Two environments (confinement and non-confinement) and three ages at movement to non-confinement (100, 140, and 180 d) were studied. No differences were detected (P greater than .05) between confinement and non-confinement in the proportions of gilts reaching puberty by 210 d of age. Gilts were older at puberty (P less than .05) in confinement than in non-confinement (192.0 vs 187.7 d) and had a longer interval (P less than .05) from first boar contact to first estrus (12.1 vs 7.8 d). Age at puberty (192.1 vs 187.0 vs 190.5 d) and the proportion reaching puberty (56.4 vs 45.7 vs 65.8%) were not different (P greater than .05) between age-of-movement groups. However, a higher (P less than .05) proportion of the non-confinement gilts reached puberty within 10 d after the beginning of boar exposure than confinement (44.6 vs 26.8%). Moving gilts from confinement to non-confinement (pasture) at 180 d appeared to be the most effective method tested for inducing puberty in gilts.     

Reduction in age of puberty in gilts consuming melatonin during decreasing or increasing daylength

Two experiments were conducted to determine whether oral administration of melatonin alters the onset of puberty in gilts during naturally increasing or decreasing daylength. In Exp. 1, 20 crossbred prepubertal gilts weighing 77.5 +/- .5 kg at 171.8 +/- 1.0 d of age were assigned randomly to receive either a daily oral dose of 3 mg of melatonin (MEL) or ethanol vehicle (ETH) at 1530 from August 31 to December 1, 1987 (decreasing daylength). Gilts were exposed to mature boars for 20 min thrice weekly and blood samples were collected twice weekly. Serum concentrations of progesterone were used to establish age at puberty and length of estrous cycle. In Exp. 2, 20 crossbred prepubertal gilts weighing 67.7 +/- .7 kg at 143.8 +/- 1.1 d of age received either MEL or ETH treatment from February 1 to May 15, 1988 (increasing daylength). Age of puberty was less in gilts that received MEL than in gilts that received ETH in both Exp. 1 (198 +/- 3 vs 228 +/- 7 d; P less than .01) and Exp. 2 (183.8 +/- 2.7 d vs 194.3 +/- 3.3 d; P less than .05). Gilts that received MEL reached puberty at a lighter weight than gilts that received ETH in Exp. 1 (95.6 +/- 2.1 vs 112.4 +/- 3.9 kg; P less than .01) and Exp. 2 (88.1 +/- 1.5 vs 96.0 +/- 1.8 kg; P less than .01). Serum concentrations of LH and FSH, length of estrous cycles, and percentage of muscle of carcasses were similar between MEL and ETH gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of physiological indicators of chronic stress in confined and nonconfined gilts

Two experiments were conducted to determine if confinement-induced delayed puberty in gilts was due to chronic physiological stress imposed by confinement housing. In both experiments, crossbred gilts, raised in total confinement, were moved to an outside dirt lot (nonconfined) or to a single pen in a confinement finishing unit (confined) at 100 to 110 d of age. Beginning at 150 d of age, estrus was checked daily with a boar to determine age at first estrus. Gilts were necropsied at 270 d of age. In Exp. I, 19 confined and 19 nonconfined gilts were cannulated by jugular puncture at 185 d of age. The day after cannulation, blood samples were collected for 4 h, 200 IU porcine adrenocorticoptropic hormone (ACTH) was injected via the cannulae and blood samples were collected for an additional 8 h. Serum cortisol, progesterone, luteinizing hormone (LH) and prolactin (PRL) concentrations were determined. In Exp. II, both jugular veins of six confined and six nonconfined gilts were cannulated at 204 d of age. The day after cannulation, blood samples were collected for 4 h and cortisol was continuously infused for the last 2 h of the blood collection period. Cortisol metabolic clearance rate (MCR) and secretion rate (SR) were determined. By 270 d of age, 21 of 28 (75%) nonconfined gilts and 11 of 31 (35.5%) confined gilts (P less than .01) in Exp. I and 18 of 25 (72%) nonconfined gilts and 12 of 25 (48%) confined gilts (P less than .06) in Exp. II had exhibited estrus and ovulated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of adrenalectomy and glucocorticoids on puberty in gilts reared in confinement

The effect of adrenal function and flumethasone (FM, a synthetic glucocorticoid) on induction of puberty in crossbred gilts raised in confinement was examined in two experiments. In Exp. 1, gilts were adrenalectomized (Adx) or subjected to sham adrenalectomy (Sham) between 140 and 160 d of age. Twenty days later indwelling jugular catheters were implanted in Adx, Sham and another group of intact gilts designated as Controls, and the gilts were moved from confinement to outdoor pens and checked daily for estrus with a mature boar. Fewer (P less than .05) Adx (1/11) than Sham (9/14) gilts showed estrus and ovulated by 205 d of age. Response of Control gilts (6/14) was not different from the other groups. Although Adx gilts received 40 mg cortisone acetate and 10 mg deoxycorticosterone acetate daily throughout the experiment, mean plasma glucocorticoids were lower (P less than .05) in Adx (24 +/- 4.7 ng/ml) than in either Sham (47 +/- 8.1 ng/ml) or Control (44 +/- 6.1 ng/ml) gilts. Experiment 2 was conducted to determine whether FM given to Adx gilts immediately after surgery could have inhibited estrus and ovulation. Intact gilts received a total of 27.5 (FM1) or 17.5 (FM2) mg FM over 4 d between 150 and 160 d of age before relocation and boar exposure 20 d later. Control gilts received no injections. Nine of 13 FM-treated but none of the Control gilts showed estrus. It is concluded from these results that the adrenal glands may facilitate the onset of puberty in gilts through increases in glucocorticoid production, but that this is not required for puberty to occur.     

Active immunization of prepubertal boars against testosterone: testicular and endocrine responses at 14 months of age

Thirteen crossbred boars were immunized at 1 mo of age against either testosterone-3-oxime-equine serum albumin (treated boars) or equine serum albumin (control boars) to test the hypothesis that active immunization against testosterone stimulates testicular growth and development in the prepubertal boar. All boars were injected with the appropriate antigen at 2, 3, 4, 5 and 6 mo of age and were slaughtered at 14 mo of age. Active immunization against testosterone resulted in an increase (P less than .05) in tritiated-testosterone binding by plasma within 60 d after the primary immunization; the degree of binding decreased by 6 mo but remained elevated (P less than .05) relative to controls through 12 mo of age. There was no effect of treatment on body weights through 12 mo of age. Concentrations of testosterone in plasma were higher (P less than .05) in testosterone-immunized boars than in controls; this increase was likely due to antibody binding rather than increased testosterone secretion because (1) concentrations of androgen in testicular parenchyma at slaughter were not altered by treatment and (2) plasma concentrations of estrogens were generally not affected by treatment. Concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were markedly suppressed in testosterone-immunized boars during the time when concentrations of these gonadotropins were high in control boars (greater than 3 mo of age). In spite of suppression of average LH and FSH concentrations, testicular weights, daily sperm production rates and seminal characteristics were similar for the two groups of boars at slaughter. (ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of space allowance during rearing and selection criteria on performance of gilts over three parities in a commercial swine production system

A total of 1,257 gilts were used to determine the effect of space allowance during rearing and age at puberty on total pigs produced and removal rate over 3 parities. There were 2 treatments. In treatment 1, gilts were given a space allowance of 1.13 m(2)/gilt (15 gilts per pen), and in treatment 2, gilts were given 0.77 m(2)/gilt (22 gilts per pen). Gilts (38 kg and 75 d of age) were individually weighed upon entry and before leaving the rearing site. They were scanned for backfat thickness and loin depth and had their feet and legs scored for structure, movement, and toe evenness before leaving the rearing site. Commencing at approximately 140 d of age, gilts were exposed to a vasectomized boar once daily with age of puberty recorded for all gilts attaining puberty before leaving the rearing site. Gilts were then moved to a specialized gilt breeding farm. When confirmed pregnant, they were moved to 1 of 9 sow farms at random, where gilts remained until removal from that herd. Space allowance in rearing had no effect (P > 0.29) on growth rate in rearing, backfat thickness and loin depth, total pigs produced, or removal rate. A greater percentage of gilts attained puberty (P = 0.02) and attained puberty at a younger age (P < 0.01) when given the greater space allowance in rearing. Gilts given the lower space allowance in rearing had more (P = 0.04) cracks on their rear hooves. Gilts attaining puberty at a younger age (<185 d) had a greater growth rate in rearing, greater backfat thickness at 200 d of age, and produced more (P < 0.05) pigs over parities 1 to 3. Gilts in the fastest growth-rate group in rearing (>860 g/d) had greater (P < 0.05) total born in parity 1, but total pigs produced to the end of parity 3 was not different (P = 0.47). Contrary to expectation, a fast growth rate in rearing did not negatively affect removal rate. Gilts served between 240 to 260 d of age produced more (P < 0.01) pigs by the end of parity 3 than those served at >260 d of age, whereas a greater (P < 0.01) percentage of gilts served at >280 d of age were removed by the end of parity 3. In conclusion, space allowance in rearing did not affect total pigs produced or removal rate; however, gilts that attained puberty at a younger age produced more pigs over parities 1 to 3.     

Influence of manure gases on puberty in gilts

To determine whether manure gases can influence onset of puberty in gilts, 42 crossbred gilts were reared from 10 to 40 wk of age on concrete slats over a 1.22-m deep pit that was drained and refilled with clean water biweekly (clean group). Forty-one gilts were reared over a similar type pit where manure was allowed to accumulate (control group). Treatments were in two separate rooms of the same building with similar feeding, water, floor space, lighting and room temperature. Ventilation fans with timer controls in each room were set so fans in the clean environment ran twice as long as fans in the control environment. Aerial concentrations of ammonia in the control room were fourfold higher than in the clean room (21 vs 5 ppm), while aerial concentrations of hydrogen sulfide were similar. Average daily gain and feed efficiency were similar for both groups [.69 vs .72 kg/d (P = .31) and 1.61 vs 1.54 kg feed/kg gain (P = .52)]. From 20 to 40 wk of age, all gilts were exposed to a mature boar three times weekly, utilizing four boars in rotation. Blood samples were collected weekly from each gilt by venipuncture and analyzed for progesterone to establish time of first ovulation. A greater proportion of gilts in the clean group attained puberty by 24 to 26 wk (P less than .05) and 27 to 29 wk of age (P less than .10) compared with the control group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine changes associated with a dietary-induced increase in ovulation rate (flushing) in gilts

Effects of an increased level of dietary energy (flushing) on plasma concentrations of FSH, LH, insulin, progesterone and estradiol-17 beta and ovulation rate were studied in 16 gilts. Gilts received 5,400 kcal ME/d for one estrous cycle and the first 7 d of a second. On d 8 of the second estrous cycle, gilts received either 5,400 kcal ME/d (control [C], n = 8) or 11,000 kcal ME/d (flushed [F], n = 8) for the remainder of the estrous cycle. Blood was collected daily at 15-min intervals for 6 h from d 8 through estrus. Gilts were examined by laparotomy 6 d after estrus. Ovulation rate was greater (P less than .05) in F than C gilts (16.0 vs 9.4). Mean daily concentrations of FSH were greater (P less than .05) in F gilts at 5 d, 4 d and 3 d prior to estrus compared with C females. In both C and F gilts, FSH decreased (P less than .05) prior to estrus. Mean daily concentrations of LH and LH pulse amplitude were not different (P greater than .05) between treatments. Mean number of LH pulses/6 h at 4 d, 3 d and 2 d prior to estrus were greater (P less than .05) in F than in C gilts. In both treatments, LH pulse amplitude decreased (P less than .05) and pulse frequency increased (P less than .07) prior to estrus. Mean plasma concentrations of insulin tended to be higher (P less than .07) in F than in C females during the 7-d period before estrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of gonadotropic and ovarian steroid hormones during the periovulatory period in high ovulating select and control line gilts

Cyclic gilts from Control (C, randomly selected, n = 11) and Relax Select (RS, nine generations of selection for increased ovulation rate followed by seven generations of relaxed or random selection, n = 9) lines of the University of Nebraska Gene Pool population (derived from 14 different breeds) were utilized to characterize differences in gonadotropic and ovarian steroid hormones during preovulatory and postovulatory phases of the estrous cycle. Blood samples were collected during four periods (0500, 1100, 1700 and 2300) daily beginning 2 d prior to anticipated estrus (d -2, d 18 of a 20-d estrous cycle), and continuing through d 4 postestrus (d 0 = 1st of standing estrus). Sampling within a period consisted of five blood samples at 15-min intervals. All plasma samples were analyzed for concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH). Neither mean LH nor peak concentration of LH during the preovulatory surge differed between genetic lines (P greater than .10). Concentrations of FSH increased faster (line X period, P less than .05) and tended (P less than .1) to peak at a higher concentration in RS (.88 ng/ml) than in C (.54 ng/ml) gilts (P less than .05) during the 12 h preceding the FSH and LH preovulatory peaks. The second FSH surge began approximately 24 h after the preovulatory FSH peak. Peak FSH concentrations were observed at 42 h in both lines (1.46 vs 1.74 ng/ml for C and RS gilts, respectively). The higher FSH concentration in RS gilts established during the preovulatory surge was maintained through the second FSH surge (P less than .01). No line differences were detected in plasma concentrations of estradiol-17 beta and progesterone.     

Plasma prolactin, LH, FSH and estrogen excretion patterns in gilts during sexual development

Plasma prolactin (PRL), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured by radioimmunoassay in groups of eight gilts sampled every 20 min for 6 h at about 2-wk intervals between 15 and 192 d of age. The PRL levels were high at 15 and 28 d, declined at 40 d just after weaning and then rose slowly until 192 d of age. The number of LH pulses during 6 h was higher between 83 and 125 d than at the other periods. Magnitude of LH pulses was highest at 15 d, constant from 54 to 125 d, fell at 137 d and remained low until 192 d. Plasma FSH was high from 15 to 125 d, with a maximum at 54 d. It declined slowly until 168 d and did not change thereafter. Estrogen excretion was estimated from urine excretion of estrone (E1; conjugated plus nonconjugated E1) per 24 h from 40 d until puberty in three gilts and at 156 and 174 d in two other animals. The E1 excretion increased with age and four levels were described before peak values with the onset of first estrus. The first increase in E1 excretion occurred between 68 and 110 d, when antral follicles appeared in the ovaries. It was subsequent to the highest levels of FSH and concomitant with the increased frequency of LH pulses. The drop in levels of both gonadotropins after 125 d probably corresponded to the development of the negative feedback as a result of greater ovarian activity in these gilts.     

Changes in plasma follicle-stimulating hormone, luteinizing hormone, estrogen and progesterone during growth of ovulatory follicles in the pig

This experiment was conducted to determine the changes in secretion of LH, FSH, estrogen and progesterone during follicle maturation. Ovaries were recovered from 11 non-treated (control) gilts, three on day 13, four on day 16, and four on day 19 of the estrous cycle, and from four altrenogest-treated gilts on day 19. Altrenogest, a progesterone agonist, was fed at a dose of 20 mg once daily from days 13 to 18 to block spontaneous follicle maturation. Gilts were bled daily from day 12 until slaughter. For control gilts, the number of follicles/gilt 1-6 mm in diameter decreased (P less than .05) from 93.5 on day 13 to 21.5 on day 19, and the number of large (greater than 6 mm) follicles increased (P less than .05) from 5.3 to 13.2. Altrenogest treatment blocked loss of small follicles and growth of large follicles between days 13 and 19. Plasma progesterone decreased (P less than .001) between days 12 and 16 in both control and altrenogest-treated gilts. Plasma FSH decreased (P less than .05) between days 12 and 16 only in control gilts. Plasma LH was not significantly affected by day or altrenogest treatment. Plasma estrogen increased (P less than .05) between days 15 and 19 only in control gilts. These results indicate that 1) no increased LH secretion was detected in conjunction with emergence of ovulatory follicles, and 2) atresia of nonovulatory follicles was associated with decreased secretion of FSH. Both atresia and decreasing FSH secretion began before estrogen concentration increased in the systemic circulation.     

Luteinizing hormone secretion in ovariectomized gilts: effects of age, reproductive state and estrogen replacement

Crossbred gilts were ovariectomized (OVX) at 120, 150, 180 and 210 d of age to determine whether various characteristics of luteinizing hormone (LH) concentrations are influenced by age and reproductive state (prepuberal vs postpuberal). All 120-d-old gilts were prepuberal and all 210-d-old animals were postpuberal, whereas gilts 150 and 180 d old included both prepuberal and postpuberal animals. Blood was collected at 15-min intervals for 2 h, 2 d before OVX (d -2), and 2 (d +2), 8 (d +8) and 14 (d +14) d after OVX. Mean LH concentrations for prepuberal gilts were similar among age groups (P greater than .05) on d -2 and +2; however, LH increased (P greater than .05) from d -2 to +2. No change in LH secretion was found in postpuberal gilts during these two periods. After OVX, LH increased from d +2 to +14 in both prepuberal and postpuberal gilts in all age groups. In postpuberal gilts, LH increased linearly (P less than .05) between d +2 and +14; rate of increase accelerated with advancing age (P less than .01). In prepuberal gilts, LH increased in a nonlinear manner, but it did not increase between d +2 and +8. The increase observed in prepuberal and postpuberal gilts after OVX resulted primarily from an increase in magnitude of peak concentrations of LH. Implants of estradiol-17 beta (E2) were used to determine whether the postovariectomy increase in LH is affected differently by E2 in prepuberal and postpuberal gilts during advancing ages.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lack of an association between plasma follicle-stimulating hormone concentrations and ovarian weight in prepubertal gilts

Selection for increased number of corpora lutea in gilts is associated with increased plasma FSH concentrations during pubertal development. In the current study, 270 gilts from a control (CO) line and a line selected for increased ovulation rate (OR) were unilaterally ovariectomized at 85 d of age, and this ovarian weight was related to FSH concentrations at 65, 75, and 85 d of age. Gilts were produced during two farrowing seasons, spring and fall, and the age at first estrus was monitored from 160 to 250 d. Plasma FSH was greater in OR than in CO gilts at 65 (P < 0.01) and 75 d (difference in spring greater than in fall, P < 0.01), but FSH at these ages was not correlated with ovarian weight at 85 d. At 85 d, FSH did not differ in gilts of these lines; however, FSH was negatively correlated (r = -0.27, P < 0.01) with ovarian weight. The proportion of gilts detected in estrus was less for spring-born CO gilts than for spring-born OR or for fall-born CO and OR gilts (78 vs. 92%, season x line, P < 0.02). The age at first estrus was similar in the two lines but was earlier (P < 0.01) for spring-born than for fall-born gilts (194 vs. 204 d). Concentrations of FSH at each of the ages examined were not correlated with the age at first estrus. These observations support the conclusion that selection for a greater number of corpora lutea produces a correlated increase in plasma FSH during early pubertal development. This increase in FSH most likely reflects differences in FSH synthesis and release and not differences in the stage of pubertal development.     

Ovarian function and hormone secretion of gilts actively immunized against androstenedione

Fifty crossbred gilts immunized against bovine serum albumin (BSA) or androstenedione conjugated to BSA (AD) were used in three experiments. Primary immunizations were given at 120 d of age and boosters at 148 and 176 d. Gilts were moved to pens containing four to five animals each and exposed to boars beginning at 180 d of age. Immunization against AD did not affect age at puberty, percentage of gilts exhibiting estrus or duration of first estrous cycle. Over the three experiments, ovulation rate was 24% greater for AD-immunized gilts than for controls, and the number of corpora lutea was related positively (r = .82) to the log of the antibody titer. Number of ovulations decreased as interval from booster immunization to onset of estrus increased. During diestrus of the first estrous cycle, gilts immunized against AD had more follicles 5 to 10 mm in diameter, more total ovarian follicles and more total ovarian structures (corpora lutea plus follicles) than controls. Immunization against AD increased the frequency of LH pulses on d 16 but not on d 17 or 18, of the estrous cycle. However, average serum concentrations of LH, FSH and estradiol from 5 d before until 2 d after expected estrus were not different between treatment groups. Concentrations of AD in follicles 4 to 6 and greater than 7 mm in diameter were greater in gilts immunized against AD. Mean serum progesterone was higher on d 9 and 12 after mating in AD immunized gilts than in controls. Immunization against AD had no effect on maintenance of pregnancy or embryo survival rate.     

Pulsatile administration of gonadotropin-releasing hormone agonist to gilts actively immunized against gonadotropin-releasing hormone

Sexually mature gilts (n = 20) were actively immunized against GnRH. Primary and booster immunizations of GnRH conjugated to bovine serum albumin induced production of antibodies in all gilts. Nineteen of the gilts became acyclic with suppressed concentrations of gonadotropins and estradiol. Intravenous challenges with 100 micrograms GnRH and 5 micrograms D-(Ala6, des-Gly-NH2(10)) ethylamide GnRH (a GnRH agonist that did not cross-react with antibodies produced by the gilts) caused release of LH and FSH, indicating maintenance of secretory capacity of pituitary gonadotropes in the immunized animals. Gilts were given 100 ng GnRH agonist at 2-h intervals for 72 h (n = 4) or 144 h (n = 10) or did not receive agonist (n = 5). Blood samples were taken every 6 h, and detectable concentrations of LH were observed in 42% and 52% of samples taken from gilts treated with or without agonist. In contrast, serum concentrations of FSH and estradiol were undetectable. Reproductive tracts and anterior pituitaries were taken from gilts at the conclusion of pulsatile administration of GnRH agonist or at 144 h for controls. Pituitary concentration of LH and FSH, uterine wet and dry weight, and size of the uterus were similar among groups. Paired ovarian weights for treated gilts pulsed with GnRH agonist for 72 h were heavier (P less than .05); however, ovaries from all immunized gilts were atrophied without follicular structures.(ABSTRACT TRUNCATED AT 250 WORDS)