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.     

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.     

Use of an enzyme immunoassay to determine concentrations of progesterone in caprine plasma and milk

Concentrations of progesterone (P4) were determined using enzyme immunoassay kits on plasma and milk samples obtained on the same days from 18 lactating dairy goats. Progesterone profiles documenting anestrus, short estrous cycles, normal estrous cycles, a prolonged follicular phase, and prolonged luteal phases were established. When plasma P4 concentrations were used as an accurate indication of the presence or absence of functional luteal tissue, milk P4 concentrations agreed with plasma determinations in 79.4% of the 465 samples tested. Milk samples could not be used to make a definitive decision because of marginal values in 11.2% of the determinations. Milk P4 concentrations were high when plasma P4 concentrations were low in 6.2% of the paired samples, especially those obtained around the time of estrus when peripheral P4 concentrations were changing rapidly. The remaining 3.2% of milk samples had low milk P4 concentrations when plasma P4 concentrations were high. Composite milk from 8 does in estrus or 8 does in the luteal phase was not consistently different from strippings in butterfat percentage or P4 concentration.     

Induction of estrus during the non-breeding season in Egyptian Baladi goats

The induction of estrus during the non-breeding season was investigated in 100 Egyptian Baladi goats (Capra hircus). All animals assigned to treatments had low progesterone concentrations (<0.5 ng/ml) tested 2 times 10 days apart to confirm anestrous condition. Animals were assigned to three experimental groups. A group of animals received subcutaneous norgestomet ear implant for 11 days and a single i.m. injection of PGF2alpha 24 hr before implant removal (group I; n=40). Second group of animals received subcutaneous norgestomet ear implant for 11 days and a single i.m. injection of PGF2alpha 24 hr before implant removal and gonadotropin releasing hormone 24 hr after implant removal (group II; n=40). Third group of animals received no treatment (control group; n=20). The percentage of goats that showed estrous behavior during the first 72 hr after implant removal was 77.5, 85.0% and 10.0% in group I, group II and control group, respectively. The fertility rate was 57.5, 70.0% and 10.0% in group I, group II and control group, respectively. In conclusion, estrus can be induced in seasonally anestrous Egyptian Baladi goats using norgestomet and PGF2alpha and the injection of GnRH 24 hr after norgestomet implant removal synchronized ovulation in a higher percentage of goats.     

Production of estradiol by each ovary during the estrous cycle of cows

The objective of our experiment was to examine changes in serum concentrations of estradiol in each utero-ovarian vein before, during and after gonadotropin surges. Four cows were given prostaglandin F2 alpha (PGF2 alpha) during diestrus and three cows were allowed to cycle spontaneously. All cows had a cannula in each utero-ovarian vein and in one jugular vein. Most cows had two transient rises in estradiol, primarily coming from a single ovary, preceding and after luteinizing hormone (LH) surges. The first rise in estradiol began after luteal regression and was sustained from 48 h before a pre-ovulatory LH surge to the end of the LH surge. The second rise in estradiol was sustained from 72 to 168 h after the end of an LH surge. To determine how rapidly asymmetrical production of estradiol began during luteolysis, several cows were injected with PGF2 alpha during the luteal phase. Blood samples were taken from a jugular and both utero-ovarian veins at hourly intervals before and after PGF2 alpha. Asymmetrical production of estradiol began within 3 h after an injection of PGF2 alpha. We concluded: (1) that a single ovary was responsible for the sustained increases in concentration of estradiol that occur during proestrus to estrus and early diestrus in cows and (2) that cows may have at least one follicle capable of producing estradiol during most days of an estrous cycle, thus little delay in selection of which follicle eventually ovulates occurs after luteal regression.     

Origin of plasma insulin-like growth factor-I (IGF-I) during estrus in goats

The objective of this study was to clarify the origin of the increase in plasma insulin-like growth factor-I (IGF-I) during estrus in goats. Focusing on the uterus, the effect of estradiol-17 beta (E2) on the secretion of IGF-I was examined using ovariectomized and hysterectomized animals. A single 5 microg/kg BW of E2 was injected intramuscularly into ovariectomized and hysterectomized goats for 3 consecutive days, and plasma IGF-I concentrations in the two groups were compared. The concentrations of IGF-I rose after the treatments in both groups. The concentrations were significantly higher from 3 to 8 days after the treatment than before the treatment in ovariectomized goats (P<0.05), and from 1 to 3 days after the treatment than before in hysterectomized goats (P<0.05). Thus higher concentrations of plasma IGF-I tended to last longer in ovariectomized than hysterectomized goats. The area under the IGF-I response curve for the 8-day period after the first injection of E2 tended to be greater in ovariectomized than in hysterectomized goats. The results show that E2 increases plasma IGF-I concentrations in goats, and suggest that E2-stimulated IGF-I in plasma may originate mainly from the uterus.     

Effect of the uterus on subnormal luteal function in anestrous beef cows

The effect of the uterus on luteal lifespan and pattern of secretion of progesterone following early weaning of calves from anestrous beef cows was studied. Calves were weaned from 15 anestrous beef cows 23 to 33 d postpartum, and cows were allotted to a control (sham surgery, n = 8) or a hysterectomy (n = 7) group, with surgery performed at weaning. Cows in the hysterectomy group were injected (im) with 25 mg prostaglandin F2 alpha (PGF2 alpha) approximately 20 d after first estrus (d 0). The interval from weaning to estrus was longer (P less than .05) for the hysterectomy group (10.4 +/- 1.6 d) than the control group (6.2 +/- .5 d). In the control group, the first estrous cycle (8.8 +/- .3 d) was shorter (P less than .01) than the second estrous cycle (20.2 +/- .5 d). Following first estrus in the hysterectomy group, cows were not detected in estrus until after injection of PGF2 alpha and did not return to estrus. From d 0 to 5, mean concentrations of plasma progesterone were similar (P greater than .05) between groups for both estrous cycles; after d 5 of estrous cycle 1, concentrations of plasma progesterone decreased in the control group. Within the hysterectomy group, the pattern of secretion of progesterone from d 0 to 16 was similar after the first and second estrus. Furthermore, there was no difference in the pattern of secretion of progesterone from d 0 to 16 between hysterectomy (first or second estrous cycles) and control (second estrous cycle) groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of feed restriction on reproductive and metabolic hormones in ewes

The goal of this study was to determine the effects of short-term feed withdrawal on reproductive and metabolic hormones during the luteal phase of the estrous cycle in mature ewes. Mature ewes observed in estrus were assigned randomly to control and fasted groups (n = 10 per group Trials 1 and 2). For Trials 1 and 2, control ewes had ad libitum access to feed, whereas fasted ewes were not fed from d 7 through 11 of their estrous cycle; on d 12, all ewes were treated with 10 mg of PGF2alpha, and fasted ewes were gvien ad libitum access to feed. For Trial 1, blood samples were collected daily through fasting and at 2-h intervals following PGF2alpha for 72 h. Serum concentrations of insulin (P < or = 0.002) and IGF-I (P < or = 0.01), but not GH (P > or = 0.60), were decreased during fasting compared with fed ewes. Serum concentrations of 29 (P = 0.02) and 34 kDa (P = 0.04) IGFBP were greater in fasted ewes at 96 h after initiation of fasting than in control ewes. Two control and four fasted ewes in Trial 1 did not exhibit a preovulatory surge release of LH by 72 h. Therefore, Trial 2 was conducted so that the timing of the LH surge could be predicted following the collection of blood samples at 2-h intervals for 112 h and then at 6-h intervals until 178 h following PGF2alpha administration and realimentation. The magnitude of the preovulatory LH surge in Trial 2 was decreased (P = 0.009) and delayed (P = 0.04), and serum concentrations of estradiol were diminished (P < or = 0.03) 12 h before the LH surge in fasted ewes. Ovulation rates were not influenced (P > or = 0.32) by fasting in Trials 1 and 2. Serum concentrations of progesterone in both Trials 1 and 2 were, however, greater (P < 0.001) in fasted than in control ewes. A third trial with ovariectomized ewes was conducted to determine whether the increased serum concentrations of progesterone observed in fasted ewes during Trials 1 and 2 were ovarian-derived. Ovariectomized ewes were implanted with progesterone-containing intravaginal implants and allotted to control (n = 5) or fasted (n = 5) treatment groups and fed as described for Trials 1 and 2. Similar to intact ewes, serum concentrations of progesterone were approximately twofold greater (P < 0.001) in fasted than in control implanted ovariectomized ewes. In summary, feed withdrawal for 5 d during the luteal phase of the estrous cycle increased serum concentrations of progesterone and evoked endocrine changes that could perturb the subsequent estrous cycle.     

Hormone secretion and characteristics of estrous cycles after treatment of heifers with human chorionic gonadotropin or prostaglandin F2 alpha during corpus luteum formation

Fertility in cattle is related positively to concentrations of progesterone in blood during the estrous cycle preceding insemination. This study determined whether treatment of heifers with prostaglandin F2 alpha (PGF2 alpha) or human chorionic gonadotropin (hCG) during d 2 to 4 of an estrous cycle affected progesterone during that cycle and whether hormone secretion during the cycle and onset of subsequent estrus were related to progesterone secretion. Nine Holstein heifers were assigned to an experiment designed as a triplicate Latin square, and each heifer received each of three treatments during three consecutive estrous cycles. Treatments were: saline (control, 1 ml) on d 2, 3 and 4 after estrus; hCG, 1000 IU on d 2, 3 and 4; and PGF2 alpha, 25 mg on d 3 with repeated doses 12 and 24 h later. Progesterone throughout the estrous cycle was higher in heifers given hCG than in those given saline. Progesterone during the first week of the cycle was lower in heifers given PGF2 alpha than those given saline, but means for these two groups were similar thereafter. Number of peaks of 15-keto,13,14-dihydro-PGF2 alpha (PGFM) during 24 h after onset of luteolysis was lower in heifers given hCG than in those given saline or PGF2 alpha. Patterns of secretion of luteinizing hormone and estradiol at subsequent estrus were not affected by treatment. Temporal relationships among hormone secretion and onset of estrus were unaffected by treatment.     

Effect of constant infusion of oxytocin on luteal lifespan and oxytocin-induced release of prostaglandin F2α in heifers

Two experiments were conducted to determine whether constant infusion of oxytocin would prolong the luteal phase and inhibit uterine prostaglandin F2 alpha (PGF2 alpha) secretion in heifers. In Experiment 1, twelve heifers, treated with saline (SAL) or oxytocin (OXY) via jugular cannulae infusions (INF) or osmotic minipumps (OMP), were allotted at estrus into four treatment groups (n = 3). Treatments were: SAL-INF, SAL-OMP, OXY-INF and OXY-OMP. Physiological saline or oxytocin was given from Days 10 to 23 (Day 0 = estrus) of the estrous cycle. Method of treatment (jugular cannula infusion or osmotic minipump) had no effect (P greater than 0.05) on estrous cycle length or pattern of secretion of progesterone; therefore, data were pooled. Estrous cycle lengths were extended (P less than 0.01) for heifers which received oxytocin (25.3 +/- 0.4 d) compared to saline (20.5 +/- 0.4 d). Luteolysis did not occur in oxytocin-treated heifers until after treatment ceased. Experiment 2 was designed and conducted identically to Experiment 1 with the addition of a "challenge" injection of oxytocin (100 IU oxytocin, i.v.) given on Day 16 of the estrous cycle. Treatment of heifers with oxytocin extended (P less than 0.05) estrous cycle length by an average of 3 d compared to heifers treated with saline. The "challenge" injection induced (P less than 0.05) secretion of PGF2 alpha (as measured by the stable PGF2 alpha metabolite, 15-keto-13,14-dihydro-PGF2 alpha) in saline-treated but not oxytocin-treated heifers. In both Experiment 1 and 2, serum concentrations of FSH were elevated (P less than 0.05) in oxytocin-treated heifers. No increase was observed for LH or prolactin. The rise in estradiol-17 beta at luteolysis was not affected (P greater than 0.10) by treatment. In summary, constant infusion of oxytocin extended luteal lifespan, prolonged secretion of progesterone, and inhibited oxytocin-induced secretion of PGF2 alpha. Constant infusion of oxytocin did not affect serum concentrations of estradiol-17 beta, LH or prolactin; however, serum concentrations of FSH were elevated during the oxytocin treatment period.     

Endogenous prostaglandin F2 alpha release induced by physiologic saline solution infusion in utero in the mare: effect of temperature, osmolarity, and pH

Thirty mares with normal estrous cycles were allotted equally to 5 groups and infused with 250 ml of saline (NaCl) solution in utero on the seventh day after ovulation to test the effects of temperature, osmolarity, or pH of the saline solution on prostaglandin F2 alpha (PGF2 alpha) release and luteolysis. Intrauterine infusion of phosphate-buffered saline solution failed to alter the duration of the luteal phase, compared with the control group. Similarly, increasing the temperature of phosphate-buffered saline solution to 42 C or increasing (600 mosm) or decreasing osmolarity (less than 10 mosm) did not change the duration of the luteal phase. Decreasing the pH of saline solution to 3 caused significant (P less than 0.0001) releases of PGF2 alpha from the uterus within the first hour after infusion, and the luteal phase was shortened to 8.8 +/- 1.0 days (mean +/- SEM; control, 15 +/- 1.2 days). The results of this study showed that pH is the main factor in eliciting PGF2 alpha release by intrauterine infusion of a saline solution, whereas increased temperature and osmolarity have no effect on the release of PGF2 alpha. The intrauterine infusion of sterile water or physiologic saline (NaCl) solution has been used to induce estrus in mares for the past 50 years. Many investigators have reported that intrauterine infusion of physiologic saline solution or water at body temperature (37 C) or warmer up to 45 C) causes most "anestrous" mares to return to estrus in 1 to 8 days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fish meal supplementation alters uterine prostaglandin F2alpha synthesis in beef heifers with low luteal-phase progesterone

The objective of the current study was to evaluate the effect of omega-3 fatty acids in fish meal on mitigating uterine PGF2alpha synthesis in heifers with low luteal-phase concentrations of progesterone. Animals were individually fed a corn silage-based diet supplemented with fish meal (5% of DMI; n = 12) or corn gluten meal (6% of DMI; n = 13). Estrous cycles were synchronized using PGF2alpha beginning on d 25 of supplementation. Random heifers from each supplement group (n = 6 fish meal, and n = 7 corn gluten meal) were given three additional i.m. injections of PGF2alpha (25 mg) at 12-h intervals beginning at 0600 on d 3 after estrus to induce formation of corpora lutea that secrete lower concentrations of progesterone. Jugular blood samples were collected daily commencing on d 1 and continuing through d 16 of the estrous cycle to determine serum progesterone concentrations. Oxytocin was administered i.v. (100 IU) to heifers on d 16 after estrus to stimulate uterine PGF2alpha synthesis. Before statistical analyses, heifers were sorted to either normal or low luteal-phase progesterone as determined from serum progesterone on d 9 of the estrous cycle. After sorting, treatment groups consisted of 1) normal luteal progesterone + fish meal (n = 6); 2) low luteal progesterone + fish meal (n = 6); 3) normal luteal progesterone + corn gluten meal (n = 6); and 4) low luteal progesterone + corn gluten meal (n = 7). Serum concentrations of the PGF2alpha metabolite following oxytocin stimulation tended (P = 0.09) to be greater in heifers with low luteal-phase progesterone compared with heifers with normal luteal-phase progesterone. Fish meal supplementation mitigated this response in heifers with low luteal-phase progesterone (P < 0.05), but had no effect on heifers with normal luteal-phase progesterone. In conclusion, the omega-3 fatty acids in fish meal seem to decrease uterine PGF2alpha synthesis in heifers with low luteal-phase serum concentrations of progesterone.     

Extending Interval from Seventeen to Nineteen Days in the Melengestrol Acetate - Prostaglandin Estrous Synchronization Program for Heifers

Two experiments were conducted to determine whether extending the interval between removal of melengestrol acetate (MGA) from feed and injection of prostaglandin F_2α (PGF) from 17 to 19 d would affect synchronization of estrus, conception, and pregnancy rates of beef heifers. In both experiments, heifers were fed MGA for 14 d, and PGF was given at either 17 or 19 d after cessation of MGA feeding. Heifers were observed for estrus and artificially inseminated for 5 d after PGF injection. In Exp. 1, 240 yearling heifers were randomly assigned to either a 17- or a 19-d treatment group according to estrous status and day of the estrous cycle. In Exp. 2, 1409 yearling heifers on a cooperating ranch were randomly assigned to the same two treatment groups without knowledge of estrous status. The PGF injection at 19 d (Exp. 1) caused a higher (P<0.05) percentage of heifers to exhibit estrus by 72 h after the injection compared with heifers receiving the injection at 17 d. A greater percentage (P<0.01) of heifers in the 19-d group were in the late luteal phase of the estrous cycle at the time of PGF injection compared with the heifers in the 17-d group, and pregnancy rates were higher for the heifers in the late luteal phase. In Exp. 2, heifers injected with PGF at 19 d after MGA had a greater (P<0.05) percentage in estrus (10%) during the 5-d breeding period, and had higher (P<0.05) pregnancy rates in 5 d (7.6%) and 50 d of breeding (5.5%), compared with heifers injected with PGF 17 d after withdrawal of MGA. These results indicate that the PGF injection given at 19 d after removal of MGA from the diet increases synchronized estrous response and results in higher pregnancy rates in heifers compared with the 17-d injection treatment.     

Effect of PGF2 alpha administration on the release of endogenous PGF2 alpha and oxytocin in indomethacin-treated goats

Repeated intramuscular injection of 1 mg prostaglandin F2 alpha (PGF2 alpha) during the luteal phase of the oestrous cycle of the goat hastened luteolysis and resulted in rapid increases in jugular concentrations of 13,14-dihydro-15-keto PGF2 alpha (PGFM), the primary metabolite of PGF2 alpha, and of oxytocin; similar injections of PGF2 alpha in indomethacin-treated goats had a reduced effect on PGFM and oxytocin concentrations, and failed to induce luteolysis. The same injections of PGF2 alpha were without effect on PGFM and oxytocin concentrations in ovariectomised goats. The results suggest that exogenous PGF2 alpha, or endogenous PGF2 alpha released at luteolysis, may induce the release of ovarian oxytocin in the goat.     

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)     

Induction of estrus by prostaglandin F2alpha administration in the vaginal vestibules of miniature pigs

Estrus induction is an important step in embryo production. It has been difficult to induce estrus in miniature pigs by intramascular (i.m.) injection of prostaglandin F2alpha (PGF2(2alpha)) in the early luteal stage of the estrous cycle. In the present study, we injected two different doses of PGF2(2alpha) i.m. and into the submucosa of the vaginal vestibule (i.ves.) of miniature pigs, and examined the effect of these treatments on estrus induction. Fifteen miniature pigs were divided into five experimental groups (control, saline injected i.m.; PGF2alpha treated, 1.0 or 1.5 mg of PGF2alpha injected twice i.m. or i.ves.), and the estrus length and concentrations of 17beta-estradiol (E2) and progesterone (P) in the blood were examined. Estrus length was significantly shortened by a large amount of PGF2alpha injected i.ves. In addition, the concentration of P in the blood significantly decreased after two injections of PGF2alpha (i.m. or i.ves.). These results suggest that in miniature pigs, administration of at least 3.0 mg of PGF2alpha is required for the induction of luteolysis and injection of PGF2alpha into the vaginal vestibule is a useful method of estrus induction.     

Changes in bovine luteal progesterone metabolism in response to exogenous prostaglandin F(2alpha)

An experiment was conducted to determine the effect of prostaglandin F2alpha (PGF2alpha) on luteal synthesis of progesterone (P4) and related progestins. Sixteen beef heifers were assigned in equal numbers to four groups in a 2x2 factorial arrangement of treatments. The experiment consisted of two levels of PGF2alpha analog (0 and 500 microg) and two levels of time (4 and 24 h after injection) of corpus luteum collection. All heifers were injected intravenously with saline (2 ml) or PGF2alpha (cloprostenol) on day 8 of the estrous cycle (estrus=day 0). Jugular blood was collected at 0, 1, 2, 3, 4 and 20, 21, 22, 23, and 24 h after injection. Resulting sera were analyzed for P4 by use of radioimmunoassay. Luteal tissue was analyzed by gas chromatography/mass spectrometry for P4, 20beta-hydroxyprogesterone, pregnenolone, and allopregnanolone (3beta-hydroxy-5alpha-pregnan-20-one). Treatment with PGF2alpha reduced serum concentrations of P4 as early as 1 h after injection (P<0.005) and steroid levels remained low over 24 h. Similarly, administration of PGF2alpha caused a decline in luteal P4 (P<0.005), 20beta-hydroxyprogesterone (P<0.10), and pregnenolone (P<0.05). In contrast, treatment with PGF(2alpha) caused an increase in luteal allopregnanolone over time (time x treatment interaction; P<0.05). These data are interpreted to suggest that PGF2alpha promotes conversion of P4 to the metabolite allopregnanolone.     

Ovsynch plus CIDR protocol for timed embryo transfer in suckled postpartum Japanese Black beef cows

We compared synchronization and pregnancy rates, and the increase in blood progesterone concentrations during luteal development, between (1) Ovsynch plus an intravaginal controlled internal drug release (CIDR) device protocol followed by timed embryo transfer (timed ET), and (2) a conventional estrus synchronization method using PGF(2 alpha) and ET in suckled postpartum Japanese Black beef cows. Cows in the PGF group (n=18) received a PGF(2 alpha) analogue when a CL was first palpated per rectum at 10-d intervals after 1 to 2 month postpartum. Cows (n=11), which showed estrus (Day 0) within 5 d of the PGF(2 alpha), and had a CL on Day 7, received ET. Cows in the Ovsynch+CIDR group (n=19) underwent the Ovsynch protocol plus a CIDR for 7 d (GnRH analogue and CIDR on Day-9, PGF(2alpha) analogue with CIDR removal on Day-2, and GnRH analogue on Day 0), with ET on Day 7. The ovulation synchronization (100%) and embryo transfer (100%) rates in the Ovsynch+CIDR group were greater (P<0.01) than the estrus synchronization (66.7%) and the embryo transfer (61.1%) rates in the PGF group. The postpartum interval at ET in the Ovsynch+CIDR group (62.5 +/- 2.5 d) was shorter (P<0.01) than in the PGF group (74.9 +/- 3.9 d). The pregnancy rate in the Ovsynch+CIDR group (57.9%) did not differ significantly from that in the PGF group (50.0%). Plasma progesterone concentrations were not significantly different in the two groups on Days 0, 1, 2, 5, 7, 14 and 21. In summary, higher synchronization and transfer rates, and shorter postpartum interval to ET, can be achieved with timed ET following the Ovsynch plus CIDR protocol than after estrus with the single PGF(2 alpha) treatment followed by ET in suckled postpartum recipient beef cows. Pregnancy rates were similar. Also, the increase in blood progesterone concentrations during luteal development following ovulation synchronized by the Ovsynch plus CIDR protocol was similar to that after estrus induced by the PGF(2 alpha) treatment.     

Estrous behavior and initiation of estrous cycles in postpartum Brahman-influenced cows after treatment with progesterone and prostaglandin F2alpha

Spring-calving, crossbred (1/4 to 3/8 Brahman) primiparous (n = 56) and multiparous (n = 102) beef cows were used to evaluate the effects of progesterone, delivered via a controlled internal drug-releasing (CIDR) device, and prostaglandin F(2alpha) (PGF(2alpha)) on estrous behavior, synchronization rate, initiation of estrous cycles, and pregnancy rate during a 2-yr period. To determine luteal activity, weekly blood samples were collected 3 wk before initiation of a 75-d breeding season. Treated cows received a CIDR for 7 d beginning on d -7 of the breeding season. On d 0, CIDR were removed, and cows receiving CIDR were administered PGF(2alpha); control cows received no treatment. Cows were exposed to bulls, and estrous activity was monitored using a radiotelemetry system for the first 30 d of the breeding season. Treatment with CIDR-PGF(2alpha) increased (P < 0.05) the number of mounts received (22.5 +/- 3.0 vs. 13.7 +/- 3.9 for CIDR-PGF(2alpha) vs. untreated control cows, respectively) but did not influence duration of estrus or quiescence between mounts. Number of mounts received and duration of estrus were greater (P < 0.05) in multiparous compared with primiparous cows. Synchronization of estrus was greater (P < 0.05) in cows treated with CIDR-PGF(2alpha) (56%) compared with control cows (13%) during the first 3 d of the breeding season. More (P < 0.05) anestrous cows treated with CIDR-PGF(2alpha) than anestrous control cows were in estrus during the first 3 d (59 vs. 12%) and 30 d (82 vs. 63%) of the breeding season. Treatment with CIDR-PGF(2alpha) decreased (P < 0.05) the interval to first estrus after treatment during the first 30 d of the breeding season compared with control cows (5.5 +/- 1.1 vs. 9.0 +/- 1.4 d). First service conception rate was greater (P < 0.05) in CIDR-PGF(2alpha)-treated cows compared with control cows. Cyclic cows at initiation of the breeding season had an increased (P < 0.05) 75-d pregnancy rate compared with anestrous cows, and the pregnancy rate tended (P = 0.10) to be greater in multiparous compared with primiparous cows. We conclude that treatment of Brahman-influenced cows with progesterone via a CIDR for 7 d, along with administration of PGF(2alpha) at CIDR removal, increases the number of mounts received, improves synchronization and first service conception rates, decreases the interval to first estrus after treatment, and may be effective at inducing estrous cycles in anestrous cows.     

Effect of termination of pregnancy or long-term progestogen exposure on subsequent estrous cycle length and concentration of progesterone in plasma of heifers

An experiment was conducted to determine whether short estrous cycles following abortion of heifers between 70 and 75 d of gestation are due to factors associated with the previous presence of a conceptus or long-term exposure of the uterus and(or) ovaries to a progestogen. Fifty crossbred heifers were randomly allotted at estrus (d 0) to five groups: control (n = 10), pregnant (Preg.; n = 14), progestogen (norgestomet) implant (Norg.; n = 9), progesterone-releasing intravaginal device (PRID; n = 9), or hysterectomy (Hyst.; n = 8). Control heifers were injected during the mid-luteal phase of an estrous cycle with 25 mg prostaglandin F2 alpha (PGF2 alpha) and length of the subsequent estrous cycle was determined. Beginning 6 to 8 d after estrus, heifers in the Norg. or PRID groups were given norgestomet ear implants or intravaginal coils, respectively, every 10 d for 70 d. Heifers were hysterectomized 5 to 8 d after estrus. Seventy to 75 d after conception, progestogen treatment or hysterectomy, heifers were injected (i.m.) with 25 mg PGF2 alpha and the last norgestomet ear implants or PRIDs were removed. Interval from PGF2 alpha injection to first estrus (means +/- SE) ranged from 2.5 +/- .2 to 4.4 +/- .7 d (P greater than .05). Length of the first estrous cycle means +/- SE) following PGF2 alpha-induced luteolysis or progestogen withdrawal was shorter (P less than .01) for the Preg. group (8.2 +/- .4 d) than for the control, Norg. and PRID groups (21.5 +/- .6 d; 19.3 +/- 1.4 d; and 18.2 +/- 1.3 d, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)