Role of PGF2α in luteolysis based on inhibition of PGF2α synthesis in the mare

The effects of inhibition of PGF2α synthesis on luteolysis in mares and on the incidence of prolonged luteal activity were studied in controls and in a group treated with flunixin meglumine (FM), a PGF2α inhibitor (n = 6/group). The FM was given every 8 hours (1.0 mg/kg) on each of Days 14.0 to 16.7. Concentration (pg/mL) of PGF2α metabolite averaged over 8 hours of hourly blood sampling at the beginning of each day, was lower in the FM group than in the controls on Day 14 after ovulation (6.7 ± 1.3 vs. 13.8 ± 2.9, P < 0.05), Day 15 (15.0 ± 3.9 vs. 35.2 ± 10.4, P < 0.10), and Day 16 (21.9 ± 5.7 vs. 54.7 ± 11.4, P < 0.03). Concentration (ng/mL) of progesterone (P4) was greater in the FM group than in the controls on Day 14 (10.1 ± 0.9 vs. 7.7 ± 0.9, P < 0.08), Day 15 (9.2 ± 1.0 vs. 4.3 ± 1.0, P < 0.008), and Day 16 (5.6 ± 1.6 vs. 1.2 ± 0.4, P < 0.02). The interval from ovulation to the beginning of a decrease in P4 and to the end of luteolysis (P4 < 1 ng/mL) was each delayed (P < 0.03) by ∼1 day in the FM group. Intervals involving the luteal phase were long (statistical outliers, P < 0.05) in two mares in the FM group, indicating prolonged luteal activity. Results supported the hypotheses that (1) inhibition of PGF2α synthesis interferes with luteolysis in mares and (2) inhibition of PGF2α at the expected time of luteolysis may lead to prolonged luteal activity.     

Effect of uterine luminal perfusion of PGF2α and PGE2 on uterine vasomotor response and PGF2α output in cyclic cattle

Six cyclic Holstein dairy cows were anesthetized on days 12–14 post-oestrus. Reproductive tract was exposed by midventral incision, and the ovarian (utero-ovarian) vein and facial artery cannulated. Oviduct was ligated, and a catheter (affluent) introduced into the tip of the uterine horn. The uterine horn was ligated above the uterine body, a second catheter (effluent) introduced into the uterine lumen, and an electromagnetic blood flow transducer placed around the uterine artery. On the day following surgery, the uterine horn was infused constantly for 9 h with PGF_2α dissolved in PBS (0.7 ml/min, 177 ng/ml). During periods 1 and 3 (first 3 h and last 3 h, respectively) only PGF_2α was perfused; during period 2 (between 3 h and 6 h) 101tgμg/ml of PGE₂ were added to the perfusate together with PGF_2α. Uterine venous and peripheral blood samples were collected simultaneously every 15 min, and uterine blood flow recorded continuously. Least-square means for PGF measured in uterine venous drainage for periods 1, 2 and 3 were 315 ± 26, 557 ± 24 and 511 ± 26 pg/ml, respectively (P < 0.05). Uterine blood flow values were 52 ± 5, 67 ± 4 and 61 ± 4 ml/min for periods 1, 2 and 3 (P < 0.08), respectively.Results do not support the hypothesis that the antiluteolytic effect of PGE₂ is associated with a suppression of uterine PGF_2α release into the circulation. Greater release of PGF to the circulation in period 2 (addition of PGE₂) is probably the result of the vasodilatory effect of PGE₂ on uterine endometrial vasculature.     

Direct effect of PGF2α pulses on PRL pulses, based on inhibition of PRL or PGF2α secretion in heifers

The relationships between PRL and PGF_2α and their effect on luteolysis were studied. Heifers were treated with a dopamine-receptor agonist (bromocriptine; Bc) and a Cox-1 and -2 inhibitor (flunixin meglumine [FM]) to inhibit PRL and PGF_2α, respectively. The Bc was given (Hour 0) when ongoing luteolysis was indicated by a 12.5% reduction in CL area (cm²) from the area on Day 14 postovulation, and FM was given at Hours 0, 4, and 8. Blood samples were collected every 8-h beginning on Day 14 until Hour 48 and hourly for Hours 0 to 12. Three groups of heifers in ongoing luteolysis were used: control (n = 7), Bc (n = 7), and FM (n = 4). Treatment with Bc decreased (P < 0.003) the PRL concentrations averaged over Hours 1 to 12. During the greatest decrease in PRL (Hours 2-6), LH concentrations were increased. Progesterone concentrations averaged over hours were greater (P < 0.05) in the Bc group than in the controls. In the FM group, no PGFM pulses were detected, and PRL concentrations were reduced. Concentrations of PGFM were not reduced in the Bc group, despite the reduction in PRL. Results supported the hypothesis that a decrease (12.5%) in CL area (cm²) is more efficient in targeting ongoing luteolysis (63%) than using any day from Days 14 to ≥19 (efficiency/day, 10-24%). The hypothesis that PRL has a role in luteolysis was supported but was confounded by the known positive effect of LH on progesterone. The hypothesis was supported that the synchrony of PGFM and PRL pulses represents a positive effect of PGF_2α on PRL, rather than an effect of PRL on PGF_2α.     

The use of PGF2α as ovulatory stimulus for timed artificial insemination in cattle

The objective of this study was to evaluate the effect of a PGF2α-analogue (PGF) on ovulation and pregnancy rates after timed artificial insemination (TAI) in cattle. In experiment 1, crossbred dual-purpose heifers, in a crossover design (3 × 3), were given an intravaginal progesterone-releasing insert (controlled internal drug release [CIDR]) plus 1 mg estradiol benzoate (EB) intramuscularly (im) and 250 μg of a PGF-analogue im on Day 0. The CIDR inserts were removed 5 days after follicular wave emergence, and the heifers were randomly divided into three treatment groups to receive the following treatments: (1) 1 mg of EB im (EB group, n = 13); (2) 500 μg of PGF im (PG group, n = 13); or (3) saline (control group, n = 13), 24 hours after CIDR removal. Ovulation occurred earlier in EB (69.81 ± 3.23 hours) and PG groups (73.09 ± 3.23 hours) compared with control (83.07 ± 4.6 hours; P = 0.01) after CIDR removal. In experiment 2, pubertal beef heifers (n = 444), 12 to 14 months of age were used. On Day 0, the heifers were given a CIDR insert plus 2 mg EB im. On Day 9, the CIDR was removed and the heifers were given 500 μg of PGF im. Heifers were randomly assigned into one of three treatment groups: (1) 1 mg of EB (EB group; n = 145); (2) 500 μg of PGF (PG group; n = 149), both 24 hours after CIDR removal; or (3) 600 μg of estradiol cypionate (ECP group; n = 150) at CIDR removal. Timed artificial insemination occurred 48 hours after CIDR removal in the ECP group and 54 hours in the PG and EB groups. The percentage of heifers ovulating was higher in the PG group compared with the other groups (P = 0.08). However, the pregnancy rates did not differ among groups (47.6%, 45%, and 46.6%, for EB, PG, and ECP, respectively; P = 0.9). In experiment 3, 224 lactating beef cows, 40 to 50 days postpartum with 2.5 to 3.5 of body condition score were treated similarly as described in experiment 2, except for the ECP group, which was excluded. The treatments were as follows: 1 mg EB (EB group; n = 117) or 500 μg PGF (PG group; n = 107), 24 hours after CIDR removal. The calves were temporarily separated from their dams from Days 9 to 11. No difference was detected on the pregnancy rate between the EB and PG groups (58.1% vs. 47.6%, respectively; P = 0.11). Taken together, the combined results suggested that PGF2α could be successfully used to induce and synchronize ovulation in cattle undergoing TAI, with similar pregnancy rates when compared with other ovulatory stimuli (ECP and EB).     

Abortion after PGF2α in heifers with multiple pregnancies following superovulation with FSH and PGF2α

Multiple ovulations were induced with follicle stimulating hormone and estrus was synchronized with prostaglandin F_2α (PGF_2α) in 23 Holstein heifers. In 19 heifers which responded to the treatments, an average of 1.8 corpora lutea were formed after the induced estrus and 6 of 19 heifers conceived (total of ten fetuses at 39 days gestation) to artificial insemination at 60 and 84 hr after the PGF_2α injection. Injection of 33 mg PGF_2α Tham salt into the six pregnant heifers on day 40 of gestation caused abortion between 54 and 66 hr after treatment in all heifers.     

Concentrations of circulating hormones during the interval between pulses of a PGF2α metabolite in mares and heifers

The temporal relationship of several hormones to a metabolite of prostaglandin F2α (PGFM) was studied in mares and heifers from the beginning of the first PGFM pulse during luteolysis to the end of the second pulse. Mares (n=7) were selected with a 9-h interval between the peaks of the two pulses. In mares, estradiol-17β (estradiol) increased (P<0.05) within each PGFM pulse and plateaued for a mean of 6h between the pulses, resulting in a stepwise estradiol increase. Progesterone decreased linearly (P<0.0001) throughout the intra-pulse and inter-pulse intervals of PGFM. In heifers (n=6), inter-pulse intervals were variable, and therefore Hours 1-4 of the first pulse (Hour 0=PGFM peak) and Hours -4 to -1 of the second pulse were used to represent the mean 8-h interval between peaks of the two pulses. Estradiol increased (P<0.05) during the ascending portion of each PGFM pulse and then decreased (P<0.05) beginning at Hour -1 of the first PGFM pulse and Hour 0 of the second pulse. The 1-h delay during the second pulse was accompanied by an apparent increase in PRL. A transient decrease in estradiol occurred in individuals between PGFM pulses at a mean of 5h after the first PGFM peak, concomitant with a transient LH increase (P<0.05). Results indicated that estradiol plateaued in mares and fluctuated in heifers during the interval between PGFM pulses. Heifers also showed temporal relationships between estradiol and LH and apparently between estradiol and PRL.     

Temporal relationships of a pulse of prolactin (PRL) to a pulse of a metabolite of PGF2α in mares

Hourly blood samples were collected from 10 mares during 24 h of each of the preluteolytic, luteolytic, and postluteolytic periods. The autocorrelation function of the R program was used to detect pulse rhythmicity, and the intra-assay CV was used to locate and characterize pulses of prolactin (PRL) and a metabolite of prostaglandin F2α (PGFM). Rhythmicity of PRL and PGFM concentrations was detected in 67% and 89% of mares, respectively. Combined for the three periods (no difference among periods), the PRL pulses were 5.2 ± 0.4 h (mean ± SEM) at the base, 7.5 ± 1.5 h between nadirs of adjacent pulses, and 12.3 ± 1.5 h from peak to peak. The peaks of PRL pulses were greater (P < 0.05) during the luteolytic period (46 ± 14 ng/mL) and postluteolytic period (52 ± 15 ng/mL) than during the preluteolytic period (17 ± 3 ng/mL). Concentrations of PRL during hours of a PGFM pulse were different (P < 0.003) within the luteolytic period and postluteolytic period and were greatest at the PGFM peak; PRL concentrations during a PGFM pulse were not different during the preluteolytic period. The frequency of the peak of PRL and PGFM pulses occurring at the same hour (synchrony) was greater for the luteolytic period (65%, P < 0.01) and postluteolytic period (50%, P < 0.001) than for the preluteolytic period (17%). This is the first report in mares on characterization and rhythmicity of PRL pulses, synchrony between PRL and PGFM pulses, and greater PRL activity during the luteolytic and postluteolytic periods than during the preluteolytic period.     

Ovarian and PGF2α responses to stimulation of endogenous PRL pulses during the estrous cycle in mares

The effects of a PRL-stimulating substance (sulpiride) on PRL and PGF2α secretion and on luteal and ovarian follicular dynamics were studied during the estrous cycle in mares. A control group (n = 9) and a sulpiride group (Sp; n = 10) were used. Sulpiride (25 mg) was given every 8 h from Day 13 postovulation to the next ovulation. Repeated sulpiride treatment did not appear to maintain PRL concentrations at 12-h intervals beyond Day 14. Therefore, the hypothesis that a long-term increase in PRL altered luteal and follicular end points was not testable. Hourly samples were collected from the hour of a treatment (Hour 0) to Hour 8 on Day 14. Concentrations of PRL increased to maximum at Hour 4 in the Sp group. The PRL pulses were more prominent (P < 0.008) in the sulpiride group (peak, 19.4 ± 1.9 ng/mL; mean ± SEM) than in the controls (11.5 ± 1.8 ng/mL). Concentrations of a metabolite of PGF2α (PGFM), number, and characteristics of PGFM pulses, and concentrations of progesterone during Hours 0 to 8 were not affected by the increased PRL. A novel observation was that the peak of a PRL pulse occurred at the same hour or 1 h later than the peak of a PGFM pulse in 8 of 8 PGFM pulses in the controls and in 6 of 10 pulses in the Sp group (P < 0.04), indicating that sulpiride interfered with the synchrony between PGFM and PRL pulses. The hypothesis that sulpiride treatment during the equine estrous cycle increases concentrations of PRL and the prominence of PRL pulses was supported.     

Combination of the ram effect with PGF2α estrous synchronization treatments in ewes during the breeding season

The role of the ram effect on the reproductive performance of ewes that have initiated estrous cycles following lambing in combination with synchronization of estrus using PGF(2α) was examined. A total of 1264 Corriedale × Merino ewes in the breeding season (March-April) were allocated to one of three treatments. The control group (PG2) of ewes (n=415) were in permanent direct contact with vasectomized rams throughout the experiment from 60 d prior to the administration of the first luteolytic dose of PGF(2α) which was followed by a second dose 13 d later (Day 0 of the experiment). Ewes assigned to the other two treatments remained isolated from rams until Day 0. In the second treatment, ewes (PG2RE; n=445) were administered PGF(2α) in the same manner and were joined with vasectomized rams at Day 0. Ewes allocated to the third treatment (PGRE; n=404) did not receive the second dose of PGF(2α) but were introduced to vasectomized rams on Day 0. Sexual receptivity, as indicated by tail-head marking, was recorded until d 11. More PG2RE ewes (407/445; 92%) were observed in estrus by Day 11 than occurred for PG2 ewes (353/415; 85%; P=0.003). The accumulated frequency of PG2RE ewes in estrus was greater than for PG2 ewes for each period from Day 3 (P<0.001) to Day 11 (P<0.01). The onset of estrus was earlier in PG2RE ewes (2.98±0.07 d) than for PG2 ewes (3.31±0.07 d; P<0.0001). In contrast, the total frequency of PGRE ewes observed in estrus by Day 11 (356/404; 88%) was similar to that observed for PG2 ewes. However, the trajectory of the accumulated frequency of the incidence of estrus was less for the PGRE ewes initially, particularly during the period of Days 3-6 of observation (P<0.0001). Consequently, onset of estrus was earlier in PG2 ewes (3.31±0.07 d) than for PGRE ewes (5.30±0.11 d; P<0.0001). It was concluded that the introduction of vasectomized rams simultaneously with the second administration of PGF(2α) advanced the onset of estrus and increased the number of ewes that responded. The introduction of rams 13 d after a single dose of PGF(2α) did not substitute for the second administration of PGF(2α).     

Effects of estriol on PGF2α output by cultures of human endometrium and endometrial cells

We have shown that the rate of release of PGF_2α by monolayer cultures of epithelial cells from proliferative endometrium is markedly elevated by addition of estradiol to the medium. In cultures maintained in HAM F-10 medium containing charcoal stripped calf serum, estradiol (10⁻⁸M) increased the levels of PGF_2α several fold during the second and third days in culture. Similar responses were obtained with estradiol at 10⁻¹⁰M concentration.When this system was used to compare the effects of estradiol and estriol at equal concentrations (10⁻⁸M), similar elevation (10–16-fold) of PGF_2α levels were noted during 3 consecutive days in culture. When cultures of epithelial cells derived from secretory endometrium were used for these tests, estriol was as effective as than estradiol in elevating PGF_2α levels in the medium.When the effects of estradiol and estriol were compared using fragments of secretory endometrium in organ culture, the increases in PGF_2α levels noted in the medium were about equal (2- to 10-fold) for the two estrogens at the same concentration (10⁻⁹−10⁻⁸M).Exposure of the tissue to either estradiol or estriol for only 1 h resulted in increases in PGF_2α output for the following 3 days.These results clearly show that estriol is as effective as estradiol in stimulating PGF_2α output by human endometrial tissue.     

Urinary 6-keto PGF1α and PGE2 in two kidney-one clip hypertension in the rat

The 24 hour urinary excretion of 6-keto PGF_1α and PGE₂ was compared in 2 kidney-1 clip rats developing hypertension within 12 weeks of renal artery clipping with rats remaining normotensive over this period. Although systolic blood pressure was markedly elevated in the hypertensive (210 ± 5.1 mm Hg), in contrast with the normotensive (141 ± 1.9 mm Hg) group, urinary levels of 6-keto PGF_1α (26.1 ± 3.4 and 22.1 ± 2.7 ng/24h, respectively) and PGE₂ (52.8 ± 28 and 53.3 ± 10.8 ng/24h) were not significantly different. Treating the 2 kidney-1 clip normotensive group with indomethacin (3.0 mg/kg, by intraperitoneal injection) twice-weekly for 3 weeks reduced 6-keto PGF_1α excretion from 22.1 ± 2.7 to 8.4 ± 2.2 ng/24h (P < 0.002) and PGE₂ from 53.3 ± 10.8 to 8.7 ± 1.8 ng/24h (P < 0.002) but did not change blood pressure when compared with a similar group given buffer vehicle only. These findings do not support a role for renal prostaglandins in 2 kidney-1 clip hypertension in the rat.     

Effect of early postpartum PGF2α treatment on reproductive performance in dairy cows with calving and puerperal traits

The objective of this study was to evaluate the effects of early postpartum PGF two alpha treatment on reproductive performance in dairy cows with calving and puerperal traits. A total of 363 Holstein cows (128 primiparous and 235 multiparous) were selected based on the presence of at least one of calving and puerperal traits (dystocia, retained placenta, twin, abortion, and postpartum uterine infections) and were assigned to two groups (treatment and control) irrespective of presence or absence of luteal tissue. Cows in the treatment group were treated twice with 25 mg dinoprost 8 h apart on day 20 postpartum, and for the control group saline placebo was administered. As it was speculated that the timing of a second dose would mimic the release of endogenous PGF2α from the uterus, our hypothesis was that two doses of PGF2α 8 h apart may increase the duration of elevated plasma prostaglandin F2α metabolite concentration in these cows. Recorded reproductive variables included days to first estrus, days to first AI, first service conception rate, pregnancy by 150 days in milk, service per conception, open days, and the percentage of repeat breeder animals. The data were analyzed using SPSS (Version 15) (IBM North America, New York, NY, USA) and Minitab (Version 14) (Minitab, State College, PA, USA). Although early postpartum PGF2α treatment had no effect on days to first estrus (36.7 days vs. 34.9 days, P = 0.056) and days to first AI (70.5 days vs. 72.2 days, P = 0.537), it increased first service conception rate (47.1% vs. 27.6%, P < 0.001); and this was more remarkable in primiparous cows (64.7% vs. 25%, P < 0.001). PGF2α treatment reduced the mean service per conception (1.92 vs. 2.72, P < 0.001) and the mean open days (112 days vs. 144 days, P < 0.001), and increased pregnancy by 150 days in milk (DIM) (80% vs. 66%, P = 0.004). The prevalence of repeat breeder syndrome in cows with calving and puerperal traits was reduced by PGF2α treatment (10% vs. 29.8%, P < 0.001). In conclusion, treatment of cows with calving and puerperal traits twice with a luteolytic dose of PGF2α 8 h apart on Day 20 postpartum improved reproductive performance and reduced the prevalence of repeat breeder syndrome.     

Determination of 15-keto-13,14-dihydro-metabolites of PGE2 and PGF2α in plasma using high performance liquid chromatography and gas chromatography-mass spectrometry

A method is described for the measurement of 15-keto-13,14-dihydrometabolites of PGE₂ and PGF_2α in peripheral human plasma. This involves purification by high performance liquid chromatography followed by determination of levels by combined gas chromatography-mass spectrometry using tetradeuterated analogs of the metabolites as internal standards. The levels of these metabolites in plasma are considered to be a more reasonable index of the entry of PGE₂ and PGF_2α into peripheral blood than are the levels of the corresponding primary prostaglandins. The endogenous levels of 15-keto-13,14-dihydro-PGE₂ and 15-keto-13,14-dihydro-PGF_2α found in peripheral plasma are 33 ± 10 pg/ml (SD; n=6) and 40 ± 16 pg/ml (SD; n=6), respectively.     

Effect of the first GnRH and two doses of PGF2α in a 5-day progesterone-based CO-Synch protocol on heifer pregnancy

The objectives were (1) to determine the effects of gonadorelin hydrochloride (GnRH) injection at controlled internal drug release (CIDR) insertion on Day 0 and the number of PGF2α doses at CIDR removal on Day 5 in a 5-day CO-Synch + CIDR program on pregnancy rate (PR) to artificial insemination (AI) in heifers; (2) to examine how the effect of systemic concentration of progesterone and size of follicles influenced treatment outcome. Angus cross beef heifers (n = 1018) at eight locations and Holstein dairy heifers (n = 1137) at 15 locations were included in this study. On Day 0, heifers were body condition scored (BCS), and received a CIDR. Within farms, heifers were randomly divided into two groups: at the time of CIDR insertion, the GnRH group received 100 μg of GnRH and No-GnRH group received none. On Day 5, all heifers received 25 mg of PGF2α at the time of CIDR insert removal. The GnRH and No-GnRH groups were further divided into 1PGF and 2PGF groups. The heifers in 2PGF group received a second dose of PGF2α 6 hours after the administration of the first dose. Beef heifers underwent AI at 56 hours and dairy heifers at 72 hours after CIDR removal and received 100 μg of GnRH at the time of AI. Pregnancy was determined approximately at 35 and/or 70 days after AI. Controlling for herd effect (P < 0.06), the treatments had significant effect on AI pregnancy in beef heifers (P = 0.03). The AI-PRs were 50.3%, 50.2%, 59.7%, and 58.3% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PRs were ranged from 50% to 62.4% between herds. Controlling for herd effects (P < 0.01) and for BCS (P < 0.05), the AI pregnancy was not different among the treatment groups in dairy heifers (P > 0.05). The AI-PRs were 51.2%, 51.9%, 53.9%, and 54.5% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PR varied among locations from 48.3% to 75.0%. The AI-PR was 43.5%, 50.4%, and 64.2% for 2.5 or less, 2.75 to 3.5, and greater than 3.5 BCS categories. Numerically higher AI-PRs were observed in beef and dairy heifers that exhibited high progesterone concentrations at the time of CIDR insertion (>1 ng/mL, with a CL). In addition, numerically higher AI-PRs were also observed in heifers receiving CIDR + GnRH with both high and low progesterone concentration (<1 ng/mL) initially compared with heifers receiving a CIDR only with low progesterone. In dairy heifers, there were no differences in the pregnancy loss between 35 and 70 days post-AI among the treatment groups (P > 0.1). In conclusion, GnRH administration at the time of CIDR insertion is advantageous in beef heifers, but not in dairy heifers, to improve AI-PR in the 5-day CIDR + CO-Synch protocol. In addition, in this study, both dairy heifers that received either one or two PGF2α doses at CIDR removal resulted in similar AI-PR in this study regardless of whether they received GnRH at CIDR insertion.     

Specific in vitro phosphorylation of plant eIF2α by eukaryotic eIF2α kinases

Phosphorylation of the subunit of eukaryotic initiation factor 2 (eIF2) is known to be an important translational control mechanism in all eukaryotes with the major exception of plants. Regulation of mammalian and yeast eIF2 activity is directly governed by specific phosphorylation on Ser-51. We now demonstrate that recombinant wheat wild-type (51S) but not mutant 51-Ala (51A) protein is phosphorylated by human PKR and yeast GCN2, which are defined eIF2 kinases. Further, only wheat wild-type eIF2 is a substrate for plant-encoded, double-stranded RNA-dependent kinase (pPKR) activity. Plant PKR and GCN2 phosphorylate recombinant yeast eIF2 51S but not the 51A mutant demonstrating that pPKR has recognition site capability similar to established eIF2 kinases. A truncated version of wild-type wheat eIF2 containing 51S but not the KGYID motif is not phosphorylated by either hPKR or pPKR suggesting that this putative eIF2 kinase docking domain is essential for phosphorylation. Taken together, these results demonstrate the homology among eukaryotic eIF2 species and eIF2 kinases and support the presence of a plant eIF2 phosphorylation pathway.     

Detection of estrous behavior in buffalo heifers by radiotelemetry following PGF2α administration during the early or late luteal phase

This study examined the usefulness of radiotelemetry for estrous detection in buffalo heifers and the impact of prostaglandin F_2α (PGF_2α) administration during the early or late luteal phase on estrous behavior and ovulatory follicle variables. Induction of estrus with PGF_2α at a random stage of the estrous cycle was followed by the arbitrary division of heifers into groups receiving a second dose of PGF_2α during either the early (n = 33) or late (n = 17) luteal phase (6–9 or 11–14 days after estrus, respectively) for the induction of synchronized estrus. The electronic detection of synchronized estrus by radiotelemetry was confirmed using ultrasonography every 6 h until ovulation. Radiotelemetry was 90% efficient and 100% accurate for estrous detection. Intervals between the PGF_2α dose and the beginning of synchronized estrus (40.7 ± 10.9 vs. 56.7 ± 12.8 h) or ovulation (70.0 ± 11.3 vs. 85.6 ± 12.5 h) were shorter (P < 0.05) for heifers receiving PGF_2α during the early luteal phase. PGF_2α administration during the early or late luteal phase produced similar (P > 0.05) results for the duration of estrus, the intervals from the beginning or end of estrus to ovulation, the number and duration of mounts per estrus, the duration of mounts, the diameter of the ovulatory follicle and the luteal profile on day 5 after estrus. In conclusion, radiotelemetry was a suitable tool for the efficient and accurate detection of estrus in buffalo heifers. Treatment with PGF_2α during the early luteal phase had a shorter interval to synchronized estrus and ovulation; however, estrous behavior, ovulatory follicle dynamics and subsequent luteal activity were similar following PGF_2α administration during the early or late luteal phase.