Concentrations of ovarian and pituitary hormones following prostaglandin F2 alpha-induced luteal regression in ewes varies with day of the estrous cycle at treatment

Prostaglandin F2 alpha (PGF2 alpha) was injected on d 5, 8 or 11 postestrus in ewes to determine how stage of the estrous cycle would affect PGF2 alpha-induced changes in concentrations of ovarian and pituitary hormones and intervals to the onset of estrus and the preovulatory surge of luteinizing hormone (LH). Initial concentrations of progesterone and average values during the 12 h after PGF2 alpha were related positively to the day of cycle on which PGF2 alpha was administered. Patterns of decline in progesterone after injection of PGF2 alpha were similar among the 3 d. Concentrations of LH in plasma increased in a similar manner from 0 to 12 h in all ewes. After 12 h LH continued to increase, plateaued or declined in ewes treated on d 5, 8 or 11, respectively. Initial concentrations of follicle stimulating hormone (FSH) in plasma were related positively to day of treatment. After treatment with PGF2 alpha, FSH increased within 2 h on d 5 but declined by that time on d 8 or 11. Concentrations of estradiol following treatment did not vary with day. The onset of estrus and the preovulatory surge of LH occurred at 36 and 35, 40 and 45, and 48 and greater than 48 h in ewes treated on d 5, 8 or 11, respectively. It is concluded that: 1) the initial increase in LH is dependent on a decrease in plasma progesterone and 2) differences in patterns of secretion of gonadotropins before the preovulatory surge of LH might be caused by differences in progesterone or progesterone:-estradiol ratio when luteal regression is induced on different days of the estrous cycle.     

Follicular development,oocyte viability and recovery in relation to follicular steroids,prolactin and glycosaminoglycans throughout the estrous period in superovulated heifers with a normal LH surge,no detectable LH surge,and progestin inhibition of LH surge

Estrous cycles of heifers (n = 137) were synchronized with prostaglandin (PGF_2α) and follicular development stimulated with follicle stimulating hormone. Twenty-eight animals were administered Norgestomet implants 12 hr prior to the initial PGF2α injection to suppress the LH surge that initiates ovulation. Animals were ovariectomized every 12 hr after the initial PGF2α (7–9/time, 12–108 hr and at 192 and 240 hr post PGF2α) and divided into three treatment groups to consist of: 1) animals exhibiting a normal luteinizing hormone (LH) surge (n = 86), 2) animals in which no LH surge was detected (n = 23), and 3) suppression of the LH surge via Norgestomet implants (72–108 hr, n = 28). Follicular diameter was measured and follicular fluid was collected for analysis of prolactin, estradiol, progesterone and glycosaminoglycan concentrations. Progesterone concentrations were increased in animals exhibiting an LH surge as compared to animals in which no LH surge was detected; primarily in large follicles (> 8 mm diameter) after the LH surge. Animals not exhibiting an LH surge also had increased follicular progesterone concentrations compared to Norgestomet-implanted animals (242.3 ± 36.3 vs 86.7 ± 6.4 ng/ml, respectively, P < .01), indicating some LH stimulation. Follicular estradiol in animals exhibiting an LH surge increased up to the time of LH surge detection and then declined whereas animals with no LH surge detected had follicular estradiol concentrations that declined after the PGF_2α injection. No differences were noted between those that did not exhibit an LH surge or in which the LH surge was suppressed with Norgestomet in relation to follicular estradiol concentrations. Follicular estradiol concentrations increased with follicular size in all treatment groups (P < .01). Follicular concentrations of prolactin were increased in small follicles (P < .05; ≤ 4 mm diameter) and follicular prolactin increased from 12 to 36 hr post PGF2α injection, then declined after the LH surge. Follicular glycosaminoglycan concentrations decreased with increases in follicular size (P < .01) and were higher in animals that did not exhibit an LH surge (P < .01). No differences in follicular glycosaminoglycans were noted between Norgestomet-implanted animals and those not exhibiting an LH surge. In the animals representing days 4 and 6 of the subsequent estrous cycle (192 and 240 hr post PGF2α), numbers of small-sized follicles were increased. Follicular progesterone and estradiol concentrations were related to atretic large follicles unovulated from the prior estrus and a wave of growth in small and medium follicles. Follicular prolactin and glycosaminoglycans increased with time of the new estrous cycle and were increased in smaller follicles (P < .01). Suppression of LH with progestin implants (Norgestomet) may relate to early effects of progesterone, which may not be totally eliminated at target tissues and subsequently alters the LH surge, steroidogenesis of the follicle, and ovulation. Oocytes were predominantly found in the follicular fluid from animals in which an LH surge was detected and in the buffer wash of follicles in which no LH surge was detected. Oocyte viability was higher in animals exhibiting an LH surge (75% viable) whereas the oocytes of Norgestomet-implanted animals were 75% degenerate.     

Plasma luteinizing hormone and progesterone concentrations in goats with estrous cycles of normal or short duration after prostaglandin F2 alpha administration during diestrus or pregnancy

Plasma luteinizing hormone (LH) and progesterone concentrations were compared in does experiencing short-duration estrous cycles and in does with estrous cycles of normal duration. The short-duration estrous cycles were observed immediately after induction of abortion in pregnant does by use of prostaglandin (PG) F2 alpha. Intramuscular administration of 5 mg of PGF2 alpha was accomplished in 8 does that were 52 to 63 days into gestation and in 9 cycling does at 7 to 10 days after estrus. In both groups, the mean plasma concentration of progesterone decreased from a luteal phase concentration immediately before to less than 1 ng/ml by 24 hours after PGF2 alpha administration. Of the 8 does that aborted, 6 experienced short-duration estrous cycles, and 4 of these 6 had an LH surge during the time of blood sample collection. The mean time from PGF2 alpha administration to the LH surge was significantly (P less than 0.05) longer in does with short-duration estrous cycles (71 hours) than that in does with estrous cycles of normal duration (58 hours). The mean area under the LH concentration curve was significantly (P less than 0.005) less for does with short-duration estrous cycles. Short-duration estrous cycles were associated with delayed preovulatory LH surges of reduced magnitude.     

Characterization of ovine follicles destined to form subfunctional corpora lutea

A study was done to test whether ovulatory follicles destined to form subfunctional corpora lutea differed from normal ovulatory follicles in steroidogenic function. Twenty-five ewes were treated with prostaglandin F2 alpha on d 11 of the estrous cycle, then unilaterally ovariectomized before (n = 13) or after (n = 12) the surge of luteinizing hormone (LH) at the induced estrus to collect "control" follicles, which would have produced normal corpora lutea. In 15 ewes, the second ovary was removed 63 to 84 h later to collect "treated" follicles before (n = 7) or after (n = 8) the second expected surge of LH. Five ewes (control) were allowed to ovulate from the remaining ovary at first estrus and another five (treated) at the second estrus (3 to 4 d later). Treated ewes had lower serum progesterone than control ewes during the ensuing cycle (P less than .05). Treated follicles contained less estradiol in the theca (4.4 +/- .6 vs 10.0 +/- 2.5 ng; P less than .05), less androstenedione (.1 +/- .1 vs 1.0 +/- .2 ng) and estradiol (.5 +/- .1 vs 2.9 +/- 2.2 ng) in the granulosa (P less than .05) and less progesterone in the follicular fluid (.8 +/- .4 vs 3.3 +/- .8 ng; P less than .05) than control follicles, when removed before the surge of LH. Follicles removed after the surge of LH did not differ. In conclusion, ovulatory follicles with low steroidogenic function became corpora lutea that secreted lower-than-normal quantities of progesterone.     

Effects of pituitary stalk-transection and type of barrier on pituitary and luteal function during the estrous cycle of the ewe

Effects of pituitary stalk-transection on plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) prolactin (PRL) and progesterone were investigated during the estrous cycle of ewes. Pituitary stalk (SS) or sham (SH) transection was performed on day 1 (estrus = day 0) of the estrous cycle. A Teflon or Silastic barrier was placed between the cut ends of the stalk to prevent reorganization of the portal vasculature. Immediately following surgery, pulsatile administration of gonadotropin releasing hormone (GnRH, 200 ng/hr) or .9% NaCl was initiated and continued for the duration of the experiment. Estradiol benzoate (EB, 50 μg im) was administered to all ewes on day 3. Mean concentrations of LH were greater in SS ewes than in SH ewes (P<.05). There was a trend (P=.06) for the concentration of LH to be higher in ewes with Teflon compared with Silastic barriers between the cut ends of the stalk. Infusion of GnRH elevated concentrations of LH in both SS and SH ewes (P<.05). Concentrations of progesterone were reduced (P<.01) in saline-infused SS ewes while infusion of GnRH in SS ewes maintained concentrations of progesterone similar to saline-infused SH ewes. The concentrations of FSH or PRL were unaffected by SS, type of barrier or treatment with GnRH. Administration of EB failed to induce a surge of LH except in a SH ewe infused with GnRH. Ewes were more responsive to infusion of GnRH following SS than after SH as reflected by increased plasma concentrations of LH and progesterone.     

Circulating estradiol suppresses luteinizing hormone pulse frequency during dietary restriction

The influence of dietary restriction on the negative feedback potency of 17-beta-estradiol (E2) was evaluated in both castrated male (wethers) and female sheep (OVX ewes) during the breeding season. In study 1, OVX ewes received maintenance or restricted dietary energy for 7 weeks or maintenance energy for 6 weeks prior to a 5 day fast (n=12ewes/feeding group). Estradiol (0.31microg E2/50kg/h) or vehicle (10% EtOH-saline) was continuously infused into half the animals in each dietary treatment for the final 54h of the study. The dynamic pattern of LH secretion was assessed during the final 6h of infusion. Estradiol inhibited luteinizing hormone (LH) pulse amplitude independent of nutrition (P=0.02); fasting increased mean LH, LH peak height, and LH nadir in the absence of E2 (P=0.004, P=0.02, and P=0.02, respectively); while E2 inhibited pulse frequency (P=0.02) and increased peak width (P=0.04) in restricted ewes. Interestingly, despite uniform E2 delivery, serum concentrations of E2 differed with feeding status. Therefore, 12 wethers were infused with 0.31microg E2/50kg/h (6 fed, 6 fasted) and six wethers received 0.19microg E2/50kg/h (fasted) to establish similar serum concentrations of E2 in fed (0.31microg/50kg/h) and fasted (0.19microg/50kg/h) wethers. When fed and fasted wethers had uniform serum concentrations of E2 LH pulse frequency was suppressed (P<0.05) in fasted relative to fed animals, supporting the postulate that energy restriction enhances the E2 negative feedback potency. Collectively, these studies demonstrate that nutrition affects E2 feedback potency and clearance.     

Regulation of pulsatile LH secretion by ovarian steroids in the heifer

Two experiments were conducted to evaluate relationships among luteinizing hormone (LH), estradiol-17 beta (E2) and progesterone secretion during the preovulatory period in the heifer after prostaglandin F2 alpha (PGF2 alpha)-induced regression of the corpus luteum. A second objective was to elucidate the effects of E2 in regulating LH secretion. In Exp. 1, LH, E2 and progesterone concentrations were determined in serial samples collected during the preovulatory period after PGF2 alpha-induced luteal regression in five Red Angus X Hereford heifers. Progesterone declined to 1 ng/ml by 12 h after the second injection of PGF2 alpha. Frequency of LH pulses increased linearly (P less than .01), whereas no change in amplitude of LH pulses was detected before the preovulatory LH surge. This resulted in a linear increase (P less than .01) in mean LH concentrations. Estradiol also increased in a linear manner (P less than .01), and the rise in E2 was parallel to the increase in mean LH concentrations. In Exp. 2, 12 Angus X Hereford heifers were ovariectomized and administered either 13.5- or 27-cm silastic implants containing E2 at ovariectomy. Four heifers served as nonimplanted controls. Thirty-one days after ovariectomy all heifers were bled at 12-min intervals for 6 h. Frequency of LH pulses declined linearly (P less than .03) while mean LH (P less than .09) and pulse amplitude (P less than .01) increased linearly as E2 dose increased. These results indicate that a reduction in progesterone increases the frequency of LH pulses during the follicular phase of the estrous cycle in cattle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of domperidone and thyrotropin-releasing hormone on secretion of luteinizing hormone and prolactin during the luteal phase and following induction of luteal regression in sheep

Effects of domperidone, a peripheral dopamine receptor antagonist, on secretion of LH and prolactin were studied during the luteal phase and following administration of PGF2 alpha. Since hyperprolactinemia has been reported to inhibit secretion of LH in ewes, effects of thyrotropin-releasing hormone (TRH) also were examined. Ewes 8-10 days post-estrus were assigned to be treated with: 1) vehicle (n = 5); 2) 0.3 mg domperidone (n = 6); 3) 1.0 mg domperidone (n = 6); 4) 3 micrograms TRH (n = 6); or 5) 10 micrograms TRH (n = 6) every 4 hours for 60 hr. Luteal regression was induced with PGF2 alpha at 12 hr after initiation of treatments. During the luteal phase, pulses of LH were more frequent (P less than .05) and the amplitudes of these were higher (P less than .05) in ewes treated with domperidone or TRH than in control ewes. These changes in LH occurred even though each treatment elevated markedly concentrations of prolactin in plasma. After induction of luteal regression, mean of LH and frequency of LH discharges were similar in all groups. However, in ewes treated with the 1.0 mg/4 hr dose of domperidone the pulse amplitude was greater than in the other groups (2.3 vs 1.1 ng/ml). Dose-response relationships and the magnitude of the prolactin release following domperidone or TRH varied with time. Treatments did not affect the timing of the LH surge or the increase in progesterone associated with the subsequent cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Melengestrol acetate blocks the preovulatory surge of luteinizing hormone,the expression of behavioral estrus,and ovulation in beef heifers

We tested the hypothesis that melengestrol acetate (MGA), an orally active progestin, blocks estrus and the preovulatory surge of luteinizing hormone (LH) in beef heifers. Cycling yearling Angus heifers were divided randomly into two groups: MGA-treated (n = 6) and control (n = 5). All heifers received injections of prostaglandin F2alpha (PGF) on d -25, -11, and 0 to synchronize estrus. Following the last PGF injection on d 0, heifers were fed either 0.5 mg MGA in a carrier or the MGA carrier each day for 8 d. At 4-h intervals on d 1 through 6, all heifers were observed for expression of estrous behavior, and blood samples were collected and assayed for LH. Daily blood samples were collected at 0800 on d 1 through 10 and assayed for circulating progesterone concentrations. All control heifers exhibited estrus and a preovulatory surge of LH. In each case, this was followed by increases in circulating concentrations of progesterone indicative of ovulation and normal luteal function. In contrast, none of the MGA-treated heifers exhibited estrus, LH surges, or evidence of ovulation. The results of this experiment show that MGA prevents ovulation in cattle by inhibiting the preovulatory surge of LH.     

Relationships between LH and estradiol-17 beta after removal of luteal progesterone in the ewe

Three experiments were conducted to examine the relationship between systemic concentrations of luteinizing hormone (LH) and estradiol-17 beta (E2) after withdrawal of progesterone in cycling ewes. In Exp. 1, ewes were assigned randomly to one of three treatments: laparotomy (C), removal of the luteal ovary (ULO), or ULO plus anesthesia with sodium pentobarbital for 6 h beginning 4 h after surgery. Anesthesia was used in an attempt to block the expected increase in tonic secretion of LH. Patterns of LH and E2 in these three groups did not differ during the 24-h experimental period. In Exp. 2, a longer period of anesthesia was utilized. Forty-eight ewes were assigned at random to one of four treatments: C, ULO, lutectomy or an intrafollicular injection of prostaglandin F2 alpha (PGF2 alpha). One-half of the ewes in each group were anesthetized with sodium pentobarbital from initiation of treatment (0 h) until 10 h after surgery. Sodium pentobarbital did not suppress the increases in LH and E2 after progesterone withdrawal. The regression of concentrations of E2 on concentration of LH was not significant. In Exp. 3, ewes were infused with either saline or dopamine after receiving an im injection of PGF2 alpha. Tonic secretion of LH increased after 4 h in ewes infused with saline, but not in ewes infused with dopamine. Despite the suppression of LH, concentrations of E2 increased in dopamine-treated ewes as in control ewes. Therefore, the initial increase in E2 after a decline of progesterone in cycling ewes is independent of increases in LH.     

Effect of prostaglandin F2 alpha on the adenylate cyclase and phosphodiesterase activity of ovine corpora lutea

The objective of the present study was to determine the temporal relationships among luteal adenylate cyclase activity, luteal phosphodiesterase activity, luteal progesterone concentration and plasma progesterone concentration during prostaglandin F2 alpha (PGF2 alpha)-induced luteolysis in ewes. Corpora lutea (CL) were removed from cycling ewes on d 9 (d 0 = first day of estrus) at 0, 2, 4, 6, 12 and 24 h (seven to eight ewes/group) after PGF2 alpha administration (im). Jugular blood samples were collected at the time of enucleation of CL and analyzed for progesterone. Plasma and luteal progesterone concentrations were decreased (P less than .05) by 4 and 12 h after PGF2 alpha injection, respectively. Basal adenylate cyclase, luteinizing hormone (LH)-activated adenylate cyclase, guanylylimidodiphosphate [Gpp(NH)p]-activated adenylate cyclase and LH plus Gpp(NH)p-activated adenylate cyclase activities were decreased (P less than .05) by 2 h after PGF2 alpha injection. The decrease in adenylate cyclase activity paralleled the decrease in plasma progesterone concentration over time. Luteinizing hormone stimulated (P less than .05) adenylate cyclase activity relative to basal activity at 0, 2, 12 and 24 h post-PGF2 alpha; whereas, Gpp(NH)p stimulated (P less than .01) adenylate cyclase activity relative to basal activity at each time point. In contrast to the decrease in adenylate cyclase activity, phosphodiesterase activity was increased (P less than .05) at 2 and 4 h post-PGF2 alpha. These results suggest that a decrease in adenylate cyclase activity coupled with an increase in phosphodiesterase activity may decrease the intracellular adenosine 3',5' cyclic monophosphate (cAMP) concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Food deprivation stimulates the luteolytic capacity in the gilt

The aims of this study were to study the effects of fasting on progesterone (P4) production in the pig and to verify whether fasting influences luteal expression of PGF(2alpha) receptor (FPr) and prostaglandin secretion. Superovulated prepubertal gilts were used; half of them were fasted for 72h starting on day 2 (F2) or 9 (F9) of the induced estrous cycle, respectively, while two groups (C2 and C9) served as respective controls. Plasma P4 and PGFM concentrations were determined by RIA while FPr mRNA expression in CLs collected at the end of fasting period was measured by real-time PCR. In experiment 1, plasma P4 concentrations in fasted gilts were significantly (P<0.01) higher than in controls starting from day 3 (F2; n=6) and 10 (F9; n=6). FPr mRNA expression was similar in F2 and C2 (n=6) CLs while it was significantly (P<0.05) higher in F9 than in C9 (n=6) CLs. In experiment 2, cloprostenol administered on day 12 significantly (P<0.05) increased FPr mRNA expression in CLs from both F9 (n=6) and C9 (n=6) gilts. At the time of cloprostenol injection PGFM levels were significantly higher (P<0.05) in the fasted group and cloprostenol-induced luteolysis in fasted but not in normally fed gilts. Results from this study indicate that fasting in prepubertal gilts induced to ovulate stimulates luteal P4 and PGFM production as well as FPr mRNA expression, thus increasing luteolytic susceptibility.     

Effect of marketing treatments and transportation on feeder pig performance

During four 6-wk trials, 376 university-raised, crossbred feeder pigs were used to determine the effects of fasting (no feed or water) vs providing feed plus water or water alone at the simulated market and a 563-km transport on shrinkage and subsequent health and performance. Providing feed and water or water alone during a 12-h market simulation for Trials 1, 2 and 4 or a 24-h period for Trial 3 did not affect subsequent rate of gain (ADG) or feed efficiency (F/G) compared with pigs fasted during the market stay. However, overall shrinkage (market phase plus transportation) of pigs provided feed and water at the market was less (P less than .05) than for fasted pigs (4.0 vs 8.4% for Trials 1, 2 and 4; 4.5 vs 11.8% for Trial 3). Transporting the fasted or nonfasted feeder pig 563 k did not affect subsequent health or performance. Overall shrinkage of the fasted pigs that were transported 563 km vs those that were not transported during Trial 4 was not different (8.8 vs 9.1%; P greater than .05). In conclusion, one-owner feeder pigs can cope with the stress of fasting and transporting long distances without any extended detrimental effects on subsequent health and performance.     

Suppressive action of gonadotropin-releasing hormone and luteinizing hormone on function of the developing ovine corpus luteum

Experiments were conducted to examine the effects of exogenous GnRH and LH on serum concentrations of progesterone (P4) in the ewe. Ewes in Exp. 1 and 2 were laparotomized on d 2 of an estrous cycle and ewes with corpora lutea (CL) in both ovaries were unilaterally ovariectomized. Ewes with CL in one ovary only were not ovariectomized. While they were anesthetized, ewes (n = 5) were injected with 25 micrograms GnRH (Exp. 1) or 50 ng GnRH (Exp. 2) into the artery supplying the ovary bearing the CL. Control ewes (n = 5 in each experiment) were injected similarly with saline. In Exp. 3, six ewes were injected i.v. (jugular) on d 2 with 100 micrograms oLH (t = 0) and 50 micrograms oLH at 15, 30 and 45 min; six control ewes were injected similarly with saline. Jugular blood was collected from all ewes at frequent intervals after treatment for LH analysis and on alternate days of the cycle through d 10 or 11 for P4 analysis. Treatment with 25 micrograms GnRH increased serum concentrations of LH at 15, 30, 45 and 60 min postinjection (P less than .001) and reduced serum concentrations of P4 on d 7 through 11 (treatment x day interaction; P less than .05). Injection with 50 ng GnRH caused a slight increase in serum concentrations of LH at 15 min but had no effect on serum concentrations of P4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of charcoal-extracted, bovine follicular fluid on gonadotropin concentrations, the onset of estrus and luteal function in heifers

A study was conducted to determine the effect of charcoal-extracted, bovine follicular fluid (CFF) on plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations, the interval from luteolysis to estrus, and subsequent luteal function in heifers. Fifteen Angus, Simmental and Hereford heifers were allotted by age, weight and breed to a control (C, n = 8) or a CFF (n = 7) group. Heifers received injections of saline or CFF (iv, 8 ml/injection) every 12 h from d 1 (d 0 estrus) through d 5 of the estrous cycle. On d 6, each heifer was injected (im) with 25 mg of prostaglandin F2 alpha (PGF2 alpha). Blood samples were collected every 12 h by venipuncture starting just before the first saline or CFF injection and continuing until estrus. Thereafter, blood samples were collected every other day during the subsequent estrous cycle and assayed for FSH, LH, estradiol-17 beta and progesterone by radioimmunoassay. Injections of CFF had no effect (P greater than .05) on circulating FSH or LH concentrations from d 1 to 5 relative to the C group; however, there was a transient rise (P less than .05) in FSH concentrations 24 h following cessation of CFF injections. This transient rise in FSH was not immediately followed by an increase in plasma estradiol-17 beta concentrations. Although CFF injections did not interfere with PGF2 alpha-induced luteolysis, the interval from PGF2 alpha injection to estrus was delayed (P less than .05) by 5 d in the CFF group compared with the C group.(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.     

Effect of short-term fasting on hepatic steroid hormone metabolism in cows

In the present study, the effect of 4-day fasting on steroid hormone metabolism in the liver and secretion of LH was examined in cows. Six non pregnant, dry Holstein cows were used. The estrous cycle was synchronized in all cows using CIDR-Ovsynch. Cows were allocated to a control group (n=3) and a fasting group (n=3). In the fasting group, cows were fasted for four days from day -4 to day -1 (day 0=day of 2nd GnRH injection) but otherwise were fed ad libitum. The experiment was repeated in a crossover design after an interval of about one month. The peripheral progesterone (P(4)) concentration in the fasting group was significantly higher than in the control group on day -1 and 0. The peripheral estradiol-17β concentration in the fasting group was also significantly higher than in the control group on day -1 and 0. The portal vein P(4) concentration in the fasting group was significantly higher than in the control group. On day 0, there was no difference in LH secretion between groups. The mean percentages of lipid droplets in liver cells in the fasting group were significantly higher than in the control group on day 0. These results suggest that short-term fasting leads to reduced hepatic steroid hormone metabolism by accumulation of fat in the liver, which causes high peripheral steroid hormone concentrations.     

Effect of body fat mass and nutritional status on 24-hour leptin profiles in ewes

This study was designed to determine the effect of feeding or fasting of fat or thin ewes on 24-h leptin profiles. Ewes were assigned, based on ultrasonic assessments of last-rib subcutaneous fat measurements, into fat (fat thickness > 1 cm; mean = 1.52 +/- 0.03 cm; range 1.14 to 2.18 cm) or thin (fat thickness < 1 cm; mean = 0.25 +/- 0.03 cm; range 0.03 to 0.84 cm) groups. Fat and thin ewes were then assigned to either fed or fasted (deprived of feed) groups consisting of five ewes per group. Thus, four groups existed and were designated as fat-fed, fat-fasted, thin-fed, and thin-fasted. Fed ewes had ad libitum access to feed throughout the study. Fasted ewes were prohibited access to feed beginning 48 h preceding the experiment. Plasma samples were collected for leptin analysis from ewes every 15 min for 24 h beginning 48 h after the initiation of feed restriction or the congruent interval in fed ewes. Data were subjected to CLUSTER pulse analysis procedures. Profiles of plasma concentrations of leptin were episodic in nature and did not differ in a diurnal manner. Fed ewes had greater mean concentrations of leptin, area under the curve, number of peaks, peak height, peak nadir, and a shorter interval between peaks than fasted ewes (P < or = 0.05). Fat ewes had greater mean concentrations of leptin, area under the curve, number of peaks, peak height, peak nadir, and a shorter interval between peaks than thin ewes (P < 0.02). There also was a tendency for a body condition x treatment interaction for number of peaks (P = 0.073) and interval between peaks (P = 0.056). These results provide evidence that plasma concentrations of leptin are episodic in nature and are influenced by nutritive state and fat thickness over the ribs, but display no circadian variation.     

Increased ovulation rate of adult ewes treated with anti-bovine LH antiserum during the normal breeding season

Adult Suffolk ewes (n = 14) were treated on d 10 of the estrous cycle with anti-bovine luteinizing hormone (LH) antiserum. Control ewes (n = 10) were treated with normal horse serum. Estrous behavior and the number of corpora lutea and ovarian follicles were examined at the subsequent estrous cycle. Daily plasma concentrations of progesterone (P4), follicle stimulating hormone (FSH) and estradiol were determined before and after treatment. Ewes treated with antiserum had a higher (P less than .05) ovulation rate (2.7 +/- .2) than did controls (2.1 +/- .1). No differences were found in the numbers of large (greater than 5 mm) or small (less than 5 mm) follicles between treatment groups. Estrus was delayed (P less than .025) approximately .6 d/in ewes treated with antisera. Immunoreactive FSH increased (P less than .05) within 1 d after treatment and remained higher than the controls for 5 d. Peak estradiol concentrations occurred on d 17 for treated ewes compared with peak concentrations on d 15 or 16 for control ewes. The P4 concentrations were generally less (P less than .025) in treated ewes throughout the luteal phase of the treatment cycle. These data demonstrate that ovulation rate is increased in ewes treated with LH antiserum. The marked increase in plasma FSH suggests a possible mechanism whereby ovulation rate is enhanced.     

Luteinizing hormone and testosterone response of sexually active and inactive rams.

The objective of this study was to identify rams exhibiting high (HP) and low (LP) levels of sexual performance and to determine whether their respective behavioral responses to ewes in estrus were related to changes in serum testosterone (T) and LH concentrations. Rams were selected on the basis of standardized serving capacity tests. Plasma T and LH concentrations in rams were measured in three experiments: 1) after 15 min of exposure to estrous ewes, 2) after an injection of 500 ng of LHRH, and 3) during an 11-h exposure to estrous ewes. During 15 min of exposure to ewes, HP rams were sexually active, whereas LP rams showed no sexual interest. Secretion of LH was similar (P greater than .05) between ram groups. Sexual arousal, copulation, and ejaculation of HP males were not related (P greater than .05) to LH secretion. Exposure to estrous ewes for 11 h, however, stimulated LH pulse frequency and elevated basal LH and T concentrations in HP but not LP rams (P less than .001). Luteinizing hormone secretion was positively correlated to the frequency of mounts (r = .19; P less than .01) and ejaculation (r = .17; P less than .03). Aggressive behavior of rams directed at ewes was negatively correlated to LH (r = -.22 P less than .003). Concentrations of LH and T after LHRH injection were similar between HP and LP rams (P greater than .05). These results show that the effects of the ewe on LH secretion of rams depend on length of the exposure period and sexual activity of the male.