PGF2α Administration Research Articles

Ovarian and endocrine responses to prostaglandin F2α (PGF2α) given at the expected time of the endogenous FSH peak at mid-cycle in ewes

In the ewe, a rise in circulating concentrations of FSH preceding follicular wave emergence begins in the presence of growing follicles from a previous wave. We hypothesized that prostaglandin F2α (PGF2α) given at the time of an endogenous FSH peak in cyclic ewes would result in synchronous ovulation of follicles from two consecutive waves, increasing ovulation rate. Twelve Western White Face (WWF) ewes received a single i.m. injection of PGF2α (15mg/ewe) at the expected time of a peak in FSH secretion, from Days 9 to 12 after ovulation. The mean ovulation rate after PGF2α treatment (2.3±0.3) did not differ (P>0.05) from the pre-treatment ovulation rate (1.7±0.1). Five ewes ovulated follicles from follicular waves emerging before and after PGF2α injection (3.0±0.6ovulations/ewe) and seven ewes ovulated follicles only from a wave(s) emerging before PGF2α treatment (2.0±0.3ovulations/ewe; P>0.05). The mean interval from PGF2α to emergence of the next follicular wave (1.0±0.4 and 4.0±0.0d, respectively; P<0.001) and the interval from PGF2α treatment to the next FSH peak (0 and 3.5±0.4d, respectively; P<0.05) differed between the two groups. Six ewes ovulated after the onset of behavioral estrus, with a mean ovulation rate of 1.7±0.2, and six ewes ovulated both before and after the onset of estrus (3.0±0.5ovulations/ewe; P<0.05). None of the ovulations that occurred before estrus resulted in corpora lutea (CL) with a full life span. At 24h before ovulation, follicles ovulating before or after the onset of estrus differed in size (4.1±0.3 or 5.5±0.4mm, respectively; P<0.05) and had distinctive echotextural characteristics. In conclusion, the administration of PGF2α at the expected time of an FSH peak at mid-cycle in ewes may alter the endogenous rhythm of FSH secretion and was not consistently followed by ovulation of follicles from two follicular waves. In non-prolific WWF ewes, PGF2α-induced luteolysis disrupted the normal distribution of the source of ovulatory follicles and may be associated with untimely follicular rupture and luteal inadequacy.

Replacement of the First GnRH Administration in the Ovsynch Protocol by Selecting Cows According to the Stage of Follicular Development

The aim of the study was to replace the first GnRH in the Ovsynch protocol by selecting cows bearing corpus luteum as well as follicles in a defined stage of development at PGF2α administration. Additionally, various terms of GnRH administration after PGF2α were tested. Seventy five non-pregnant cows bearing corpus luteum were divided into groups according to the phase of follicular development on D 0 (day of PGF2α administration)-growth (GR, follicles 3.0-7.9 mm in diameter), early dominance (ED, dominant follicle 8.0-14.9 mm) and late dominance (LD, dominant follicle 15.0-23.0 mm). In addition, the cows were divided into groups according to the terms of GnRH administration (24, 48 or 72 h after PGF2α). In this way, groups GR 48 (n = 5), GR 72 (n = 6), ED 24 (n = 10), ED 48 (n = 12), ED 72 (n = 12), LD 24 (n = 10), LD 48 (n = 10) and LD 72 (n = 10) were established. Growth of ovulatory follicle, term of ovulation, insemination and conception rates as well as relation of the size of preovulatory follicle (day of ovulation) to the size of following corpus luteum (day 14) were evaluated. The highest level of synchronization of ovulation (100% on D 3) as well as conception rate (50%) was achieved in group ED 48. This protocol gives an opportunity of timing artificial insemination to 18-24 hours after GnRH administration, as ovulation occurs with a high probability within 24 - 48 hours after GnRH administration.

A cooperative action of endothelin-1 with prostaglandin F 2α on luteal function in the cow

Prostaglandin F 2α (PGF 2α) is the primary luteolysin in the cow, and luteal endothelin-1 (ET-1) interacts with PGF 2α during the process of luteolysis. In contrast, a developing corpus luteum (CL) is refractory to exogenous administration of PGF 2α. Thus, the present study was aimed to investigate the functional relationship between ET-1 and PGF 2α in the mid-CL (PGF 2α-sensitive) and early-CL (PGF 2α-refractory). In the mid-CL model, cows ( n = 6/treatment) were assigned to receive one of five types of treatments on day 10 of the estrous cycle: (1) an injection of saline; control, (2) a 500 μg of PGF 2α analogue (sufficient dose to induce luteolytis); full-PG, (3) an intraluteal injection of 0.25 mg ET-1; ET-1, (4) a 125 μg of PGF 2α (insufficient dose to induce luteolytis); 1/4PG or (5) an intraluteal injection of 0.25 mg ET-1 after administration of a insufficient dose of PGF 2α analogue; 1/4PG/ET. In the early-CL model, cows were assigned to receive one of two types of treatments on day 5 of the estrous cycle: (1) a sufficient dose of PGF 2α analogue; PG ( n = 5) or (2) an intraluteal injection ET-1 after a sufficient dose of PGF 2α; PG/ET ( n = 7). In the mid-CL model, 1/4PG/ET resulted in a rapid reduction of progesterone (P) concentrations similar to that in full-PG from the next day. However, the levels of P in 1/4PG/ET (1.5–2.5 ng/ml) kept significantly higher than that in full-PG (<0.5 ng/ml). ET-1 or 1/4PG did not decrease plasma P concentrations (4–6 ng/ml). The plasma ET-1 levels increased with the full-PG administration. In the early-CL model, both treatments had no effect on plasma P increase and ET-1 levels. The overall results indicate that the intraluteal ET-1 injection after administration of insufficient dose of PGF 2α induces the depression of P secretion in vivo during the mid luteal phase in the cow, supporting the concept that ET-1 is one of a local mediator of functional luteolysis in the cow. The result further indicates that the early-CL is not only PG-refractory but also ET-1-refractory.

Comparison of synchronization of ovulation with timed insemination and exogenous progesterone as therapeutic strategies for ovarian cysts in lactating dairy cows

The objective of this study was to compare the effectiveness of the Ovsynch and controlled internal drug releasing (CIDR) protocols under commercial conditions for the treatment of cystic ovarian disease in dairy cattle. A total of 401 lactating dairy cows with ovarian cysts were alternatively allocated to two treatment groups on the day of diagnosis. Cows in the Ovsynch group were treated with GnRH on Day 0, PGF2α on Day 7, GnRH on Day 9, with timed insemination 16–20 h later. Cows in the CIDR group were treated with a CIDR insert on Day 0 for 7 days; on Day 7, the CIDR was removed, and cows were treated with PGF2α. All cows in the CIDR group were observed for estrus and cows exhibiting estrus within 7 days following removal of the CIDR and PGF2α administration were inseminated. The outcomes of interest for this experiment were the likelihood to be inseminated, return to cyclicity (determined by a CL on Day 21), conception and pregnancy rates. Data for these variables were analyzed using logistic regression. The percentage of cows inseminated in the Ovsynch and CIDR groups were 82 and 44%, respectively. Cows in the Ovsynch group were 5.8 times more likely to be inseminated than cows in the CIDR group. Cows with a low BCS were 0.48 times less likely to be inseminated than cows with a high BCS. The percentage of cows with a CL on Day 21 for the Ovsynch and CIDR groups was 83 and 79%, respectively ( P > 0.05). Cows with a low BCS were 0.49 times less likely to have CL on Day 21 than cows with a high BCS. Conception and pregnancy rates for cows in the Ovsynch group were 18.3 and 14.4%, respectively. Conception and pregnancy rates for cows in the CIDR group were 23.1 and 9.5%, respectively. There was no significant differences between conception or pregnancy rates in cows in both groups. Primiparous cows were 2.6 times more likely to conceive than multiparous cows. In conclusion, the results of this study suggested that fertility was not different between cows with ovarian cysts treated with either the Ovsynch or the CIDR protocols in this dairy herd. In addition, primiparous cows had an increased likelihood for conception compared to multiparous cows, and cows with a low BCS were less likely to be inseminated or have a CL on Day 21, regardless of treatment.

Effect of repeated administration of PGF2α in the early post partum period on the prevalence of clinical endometritis and probability of pregnancy at first insemination in lactating dairy cows

Two experiments were performed to determine the effects of repeated administration of PGF2α in the immediate post partum period on the prevalence of clinical endometritis at 22 and 58 days post partum, and the probability of pregnancy at first insemination, in post partum dairy cows. In Experiment 1, 228 cows on day 7 post partum were used. Cows in Group 1 ( n = 114) were treated twice with PGF2α (25 mg, im) 8 h apart on days 7 and 14 post partum, and only once on days 22 and 35 post partum. Cows in Group 2 ( n = 114) served as untreated controls. Vaginoscopy and transrectal palpation of the genital tract were done on days 22 and 58 post partum. Cows in both groups were inseminated at estrus after a voluntary waiting period of 100 days. Pregnancy was determined by transrectal palpation between 45 and 50 days after insemination. Repeated administration of PGF2α in the immediate post partum period did not reduce the prevalence of clinical endometritis on days 22 or 58 post partum (65 versus 62% on day 22 and 28.3 versus 35.2% on day 58 in Groups 1 and 2, respectively). There was no significant difference in the probability of pregnancy at first insemination between cows in both groups. In Experiment 2, 418 cows on day 7 post partum were used. Cows in Group 1 ( n = 209) were treated twice with PGF2α (25 mg, im) 8 h apart on days 7 and 14 post partum, and only once on days 22 and 35 post partum. Cows in Group 2 ( n = 209) served as untreated controls. Cows in both groups were subjected to the Presynch and Ovsynch protocols on days 49 and 75 post partum, respectively. Pregnancy was determined by transrectal ultrasonography between days 29 and 32 after timed insemination. There was no significant difference in the probability of pregnancy at first insemination between cows in both groups. In conclusion, repeated administration of PGF2α to cows in this herd had no effect on the prevalence of clinical endometritis at 22 and 58 days post partum, and that there was no effect on the probability of pregnancy after insemination at estrus among cows with a voluntary waiting period of >100 days, or at timed AI at 85 days in milk when Presynch was employed.

Estrous Response and Fertility in Postpartum Suckled Female Yaks (Bos grunniens) Treated with an Intravaginal Device Containing Progesterone (CIDR), Pregnant Mares` Serum Gonadotrophin and Prostaglandin Analogue

The efficiency of a short-term treatment with an intravaginal device containing progesterone (CIDR) combined with pregnant mares' serum gonadotrophin (PMSG) and prostaglandin analogue (PGF2α) was evaluated for the induction of estrus, initiation of cyclic activity, and fertility in postpartum suckled yak cows. Seventy-five postpartum suckled yak cows were assigned to three treatments: (1) insertion of a CIDR intravaginal progesterone (1.9 g) (day 0), an administration of PGF2α (0.2 mg i.m.) on day 6 and PMSG (1,000 IU i.m.) at the time of CIDR withdrawal on day 7 (CPP group, n=28); (2) an administration of PGF2α (0.2 mg i.m.) on day 6 and PMSG (1,000 IU i.m.) on day 7 (PP group, n=21); (3) untreated animals served as the control (CG group, n=26). Seven yak bulls were placed in pastures with the cows for natural mating. Estrus rate in the CPP group (28/28) was higher (p<0.01) than in the PP group (6/21) and in the CG group (0/26) within 96 h after the end of treatment. The first service conception rate in the CPP group (21/28) was higher (p<0.01) compared with in the PP group (2/9) as judged by serum P4 concentration ≥2.35 ng/ml on day 21 after breeding. It is concluded that a short-term progesterone treatment combined with PMSG and prostaglandin increased the proportion of yak cows that exhibited behavioral estrus with more synchronized estrus response and satisfactory conception rate in postpartum suckled yak cows. (Asian-Aust. J. Anim. Sci. 2005. Vol 18, No. 4 : 470-474)

Nutzung einer terminorientierten Besamung beim Rind auf der Grundlage einer Prostaglandin – GnRH-Behandlung

Abstract. Title of the paper: Practical application of timed artificial insemination in cattle using a GnRH and Prostaglandin treatment Three experiments were conducted to establish a regime of oestrous synchronization and artificial insemination at a predetermined time in dairy cattle. In experiment 1, dairy heifers (n = 43) were synchronized by administering PGF2α on day 5, 8, 11 or 14 and the LH surge was recorded. Release of the LH surge ranged from 57.0 ± 8.6 h to 76.3 ± 10.0 h depending upon the day of induced luteolysis. The release of LH was followed by ovulations. The day of PGF2α administration did not affect the interval from LH peak to ovulation. In experiment 2, heifers (n = 30) were synchronized on days 8, 11 or 14 of the oestrous cycle. Animals received an injection of GnRH 65 h after induction of luteolysis. Uniform intervals from PGF2α application to LH surge were observed in animals given PGF2α on day 11 and 14. Variation for this parameter decreased also in the group of animals where luteolysis was induced on day 8. There were no significant differences due to treatment in the mean interval from LH-peak to ovulation. In experiment 3, fixed time insemination was tested on the basis of data from Experiments 1 and 2. Synchronized heifers and high yielding cows received GnRH 65 hours after PGF2α administererd between d 8 and 14 of the oestrous cycle. Artificial insemination was carried out 13 h after GnRH application. Pregnancy rates show, that fixed time artificial insemination, independent of the recorded onset of estrus can result in high pregnancy rates. Pregnancy rates in animals at different locations were higher after induction of ovulation and timed artificial insemination (79.0, 76.0 and 47.1, 53.3 %) than in control groups with insemination after detected estrus (69.8, 63.2 and 38.6, 45.0 %).

Changes in bovine luteal progesterone metabolism in response to exogenous prostaglandin F 2α

An experiment was conducted to determine the effect of prostaglandin F 2α (PGF 2α) on luteal synthesis of progesterone (P 4) and related progestins. Sixteen beef heifers were assigned in equal numbers to four groups in a 2 × 2 factorial arrangement of treatments. The experiment consisted of two levels of PGF 2α analog (0 and 500 μg) 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 PGF 2α (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 P 4 by use of radioimmunoassay. Luteal tissue was analyzed by gas chromatography/mass spectrometry for P 4, 20β-hydroxyprogesterone, pregnenolone, and allopregnanolone (3β-hydroxy-5α-pregnan-20-one). Treatment with PGF 2α reduced serum concentrations of P 4 as early as 1 h after injection ( P < 0.005) and steroid levels remained low over 24 h. Similarly, administration of PGF 2α caused a decline in luteal P 4 ( P < 0.005), 20β-hydroxyprogesterone ( P < 0.10), and pregnenolone ( P < 0.05). In contrast, treatment with PGF 2α caused an increase in luteal allopregnanolone over time (time × treatment interaction; P < 0.05). These data are interpreted to suggest that PGF 2α promotes conversion of P 4 to the metabolite allopregnanolone.

Prostaglandin F2$alpha;-induced estrus in ewes exhibiting estrous cycles of different duration

Effects of prostaglandin F2α (PGF2α), administered during the mid-luteal phase of the estrous cycle, were examined in ewes exhibiting estrous cycles classified as short (≤16.5 days, short-cycle ewes, n=10) or long (≥18 days, long-cycle ewes, n=9) based on the durations of two estrous cycles (cycles −2 and −1) before treatment. The ewes received (i.m.) 20 mg of PGF2α on day 10 of the third estrous cycle (cycle 0) followed, 36 h later, by 25 μg of gonadotropin releasing hormone (GnRH) to time the events of ovulation. Duration of subsequent estrous cycles +1 and +2 were recorded, and then the ewes were treated with the same combination of PGF2α and GnRH beginning on day 10 of estrous cycle +3. Ovaries were recovered 6 h after GnRH administration to assess development of pre-ovulatory follicles. The proportion of ewes that exhibited estrus after PGF2α and GnRH treatment on cycle 0 was not different (P>0.05) between short- and long-cycle ewes. Onset of estrus occurred sooner (P<0.05) after PGF2α injection in short-cycle ewes than in long-cycle ewes (1.9±0.1 days and 2.3±0.1 days, duration of cycle 0 was 11.9 and 12.3 days, respectively). Duration of estrous cycle +1 was 1.2 days longer (P<0.01) than cycle −1 in short-cycle ewes. However, duration of estrous cycle +1 did not change (P>0.05) after PGF2α and GnRH administration in ewes having long cycles. Pre-ovulatory follicles did not differ (P>0.05) in numbers, diameter, layers of granulosa cells nor concentrations of progesterone and estradiol-17β in follicular fluid between short- and long-cycle ewes after PGF2α and GnRH treatment. In conclusion, ewes having short or long estrous cycles responded differently to PGF2α and GnRH treatment with respect to the interval to onset of estrus and duration of the subsequent estrous cycle.

Prostaglandin F 2α-induced estrus in ewes exhibiting estrous cycles of different duration

Effects of prostaglandin F 2α (PGF 2α), administered during the mid-luteal phase of the estrous cycle, were examined in ewes exhibiting estrous cycles classified as short (≤16.5 days, short-cycle ewes, n=10) or long (≥18 days, long-cycle ewes, n=9) based on the durations of two estrous cycles (cycles −2 and −1) before treatment. The ewes received (i.m.) 20 mg of PGF 2α on day 10 of the third estrous cycle (cycle 0) followed, 36 h later, by 25 μg of gonadotropin releasing hormone (GnRH) to time the events of ovulation. Duration of subsequent estrous cycles +1 and +2 were recorded, and then the ewes were treated with the same combination of PGF 2α and GnRH beginning on day 10 of estrous cycle +3. Ovaries were recovered 6 h after GnRH administration to assess development of pre-ovulatory follicles. The proportion of ewes that exhibited estrus after PGF 2α and GnRH treatment on cycle 0 was not different ( P>0.05) between short- and long-cycle ewes. Onset of estrus occurred sooner ( P<0.05) after PGF 2α injection in short-cycle ewes than in long-cycle ewes (1.9±0.1 days and 2.3±0.1 days, duration of cycle 0 was 11.9 and 12.3 days, respectively). Duration of estrous cycle +1 was 1.2 days longer ( P<0.01) than cycle −1 in short-cycle ewes. However, duration of estrous cycle +1 did not change ( P>0.05) after PGF 2α and GnRH administration in ewes having long cycles. Pre-ovulatory follicles did not differ ( P>0.05) in numbers, diameter, layers of granulosa cells nor concentrations of progesterone and estradiol-17β in follicular fluid between short- and long-cycle ewes after PGF 2α and GnRH treatment. In conclusion, ewes having short or long estrous cycles responded differently to PGF 2α and GnRH treatment with respect to the interval to onset of estrus and duration of the subsequent estrous cycle.

Estrous cycle characteristics, luteal function, secretion of oxytocin (OT) and plasma concentrations of 15-keto-13,14-dihydro-PGF2α (PGF2α-metabolite) after administration of low doses of prostaglandin F2α (PGF2α) in pony mares

In the present study, the kinetics of the prostaglandin F2α (PGF2α)-metabolite 15-keto-13,14-dihydro-PGF2α after a single intramuscular application of various doses of the natural PGF2α dinoprost at Day 7 of the cycle in the mare were investigated. Effects of low doses on estrous cycle length and life span of corpus luteum were examined, because release of PGF2α is still under discussion to have detrimental influence on success rates of transcervical transfer of equine embryos. Eight Shetland pony mares were each randomly assigned to each of four treatments: (a) 0.8 mg/100 kg (group T1), (b) 0.4 mg/100 kg (group T2), (c) 0.2 mg/100 kg BM dinoprost i.m. (group T3), and (d) 1 ml physiological saline i.m. (group CO). Treatments were administered as single doses on Day 7 of the estrous cycle. Administration of dinoprost caused dose-dependent rises of plasma concentrations of PGF2α-metabolite, although values of individual mares showed great variation within groups. Prostaglandin treatments resulted in a distinct decrease of plasma progesterone concentrations to values between 1.6 and 7.9 ng/ml within 24 h. Treatment groups had significantly lower progesterone area under the curve (AUC: T1 942.8±175.9, T2 1050±181.2 and T3 1117.9±179.8 ng/ml/h) when compared with controls (CO 1601.9±227.6; t-test, P<0.05). There was a small, but significant negative correlation between AUC of progesterone and of PGF2α-metabolite ( R=−0.4; P<0.05). Administration of PGF2α caused secretion of oxytocin in three (T1, T2) and two (T3) mares out of eight ranging from 19.3 to 63.1 pg/ml. The AUC of oxytocin was positively correlated with AUC of PGF2α-metabolite ( R=0.4, P<0.05) and negatively correlated with AUC of progesterone ( R=−0.4, P<0.05). Administration of dinoprost yielded significantly shorter intervals from treatment to estrus and ovulation (values in parentheses), respectively, when compared with controls: T1 3.9±0.7 days (12.1±0.7 days), T2 4.5±0.6 (12.3±0.6), T3 4.9±0.5 (12.3±0.6), and CO 8.9±0.6 days (16.5±0.8 days) ( t-test, P<0.01) (Fig. 2). Different doses of PGF2α caused similar effects. Data suggest that progesterone concentrations at applications influence efficacy of treatments more than doses administered, as demonstrated by their high correlation with estrous cycle patterns. It is important to note that differences we achieved are gradual and that all mares responded to treatment by luteolysis and premature estrus, regardless of doses applied.

Timing of final GnRH of the Ovsynch protocol affects ovulatory follicle size, subsequent luteal function, and fertility in dairy cows

Synchronization of ovulation (Ovsynch) is an effective method for controlling time of first and subsequent AI in lactating dairy cows. However, validation of the original Ovsynch program did not include testing the optimal time to deliver the final treatment of GnRH. In Experiment 1, the effect of administering the final dose of GnRH on the same day as prostaglandin F 2α (PGF 2α) administration was tested. Lactating dairy cows ( n=218) were randomly assigned to receive either Ovsynch (OV; cows were given 100 μg GnRH, then 7 days later cows were administered 25 mg PGF 2α followed by a subsequent treatment of 100 μg GnRH 2 days after the PGF 2α) or the modified version of Ovsynch (MOV; cows were given 100 μg GnRH, then 7 days later cows were administered 25 mg PGF 2α followed immediately with 100 μg GnRH). In both treatment groups, AI took place 16 h after the final administration of GnRH. In Experiment 2, cows ( n=457) were randomly divided into four treatment groups that were administered GnRH 0, 12, 24 and 36 h following PGF 2α. The 36 h treatment group served as control. Pregnancy diagnoses were performed by palpation per rectum 36 days post-AI in Experiment 1 and by ultrasonography on Day 28 in Experiment 2. In Experiment 1, pregnancy rate/AI (PR/AI) was greater ( P<0.025) in OV versus MOV. In a subset ( n=85), percentage of cows with both synchronized ovulations and regressed CL following administration of PGF 2α were similar ( P>0.1) between OV and MOV, respectively. All cows that became pregnant in the MOV subset group showed regression of the CL in response to the PGF 2α. Diameter of the ovulatory follicle at the time of final GnRH administration was greater ( P<0.05) in OV versus MOV. In Experiment 2, the synchronization rate was once again similar among treatments ( P>0.28). There was a linear effect of treatment on follicle size ( P<0.05) and PR/AI ( P<0.0001) as time increased between administration of PGF 2α and GnRH, with the greatest PR/AI at 36 h. There was a trend for a greater percentage of cows with short luteal phases in the 0 h group ( P<0.10). In summary, delivering the final treatment of GnRH of the Ovsynch program at the same time as PGF 2α, or in the 24 h following PGF 2α, resulted in lower fertility compared to controls.

Conception rates of dairy cows following early not-pregnant diagnosis by ultrasonography and subsequent treatments with shortened Ovsynch protocol

Our objective was to determine the feasibility of prompt reinsemination of dairy cows when diagnosed not pregnant 27–29 days after first-service timed AI (TAI). We assumed that a first-wave dominant follicle was present at that time that would ovulate in response to GnRH once precocious luteal regression was induced after administration of PGF 2α. Cows that had not been detected in estrus and reinseminated by Days 27–29 after a first-service TAI were diagnosed not pregnant by ultrasonography. Nonpregnant cows from three herds were assigned randomly to receive either no further treatment until reinsemination (controls; n=189); 25 mg i.m. of PGF 2α and then reinsemination according to detected estrus (81 of 108) or at 72–80 h after PGF 2α treatment (PGF) in the absence of estrus (27 of 108); or 25 mg i.m. of PGF 2α followed by 100 μg i.m. of GnRH 48 h later (PGF+GnRH) and then reinsemination after detection of estrus (9 of 160) or at 16–20 h after GnRH (151 of 160). Blood samples were collected at the time of the not-pregnant diagnosis and again 48 h later. Concentrations of progesterone before treatment with PGF 2α were elevated (<1 ng/ml) in 61% of the cows when PGF 2α was administered and 81% of the cows given PGF 2α had low (<1 ng/ml) concentrations of progesterone 48 h after PGF 2α. Treated cows were re-inseminated earlier ( P<0.01; 31±1 days) after first-service TAI than controls (55±1 days). Conception rates after treatment were not different among treatments: PGF (22%), PGF+GnRH (23%), and control (23%). Average intervals from calving to conception were 22–23 days less ( P<0.001) in treated cows than in controls. We concluded that treating nonpregnant cows with PGF 2α on Days 27–29 after insemination produced acceptable conception rates when inseminations were made after detected estrus or when TAI was used after GnRH treatment. Further, both treatments reduced days between first-service TAI and second inseminations, and days from calving to conception.

Ovulation rate after GnRH or PGF 2α administration in early postpartum dairy cows

The objectives of this study evaluating induction of ovulation in early postpartum dairy cows were to: compare two methods of GnRH (100 mcg) administration (i.m. route and s.c. implant), and determine if prostaglandin F 2α (PGF) causes release of LH or ovulation similar to that reported for GnRH. In trial #1, serum LH peaked at 2 h after i.m. administration of GnRH and was declining at 4 h. The s.c. GnRH implant also caused an elevation in serum LH at 2 and 4 h after treatment, with LH declining at 6 h. Serum LH was unchanged in control cows. Experimental treatment caused ovulation in 4 of 14 GnRH i.m. treated cows, 4 of 12 GnRH implanted cows and 0 of 13 control cows. Parity had no effect on LH response but did affect resulting ovulation rate as multiparous cows were more likely to ovulate than were primiparous cows in response to either GnRH treatment. All cows that ovulated had a follicle larger than 12 mm at the time of treatment. In trial #2, serum LH increased as before after i.m. administration of GnRH, however, serum LH was unchanged in cows treated with PGF or saline. Gonadotropin releasing hormone caused more cows to ovulate than did PGF or saline treatments, and GnRH shortened the interval from treatment to the onset of CL function over the PGF treatment; 13.9±2.6, 28.2±4.1 and 22.3±4.1 days for GnRH, PGF and saline, respectively. In summary, there was no difference in the ability of s.c. implantation and i.m. administration of GnRH to cause ovulation. Prostaglandin F 2α did not cause release of LH or ovulation. In 22 early postpartum dairy cows treated with 100 mcg GnRH i.m. in these two trials, nearly all cows (95%) responded with a release of LH but only 45% (10/22) responded with an ovulation and subsequent formation of a CL.

Effect of local interaction of reactive oxygen species with prostaglandin F 2α on the release of progesterone in ovine corpora lutea in vivo

Prostaglandin (PG) F 2α is implicated in the process of luteal regression in many species, and has been shown to increase the generation of reactive oxygen species. In this study, the role of reactive oxygen species in the local regulatory mechanisms of functional luteolysis in the ewe was examined. In Experiment 1, we studied local effects of hydrogen peroxide (H 2O 2) and its interaction with PGF 2α on P secretion in ovine corpus luteum (CL) in vivo. For this purpose, a microdialysis system (MDS) was used, where only the cells surrounding the capillary membrane in the microenvironment of the CL are exposed to these factors, and the P secretory ability of the CL is maintained as if intact. The study used a multiple CL model to implant the MDS, enabling us to examine in parallel several experimental infusions into the MDS implanted in different CLs (one MDS line per CL) developed after superovulation in one ewe. On Day 8 after GnRH treatment, the MDS were implanted into multiple CL in both ovaries of six ewes. A 4-h infusion with PGF 2α (10 −6 M) at 8–12 h slightly increased P release during infusion, while a 4-h infusion with H 2O 2 (10 −3 M) at 20–24 h decreased P release at 27–38 h. A pre-infusion with PGF 2α for 4 h at 8–12 h, followed by infusion of H 2O 2 at 20–24 h rapidly decreased the P release at 20–40 h ( P<0.05); this decrease occurred 7 h earlier than in the CL treated with H 2O 2 alone. In Experiment 2, by utilizing the MDS we also applied free radical scavengers to examine their possible weakening effect on the inhibition of P secretion in the microenvironment within the regressing CL induced by PGF 2α treatment. On Day 8 after estrus, the MDS were implanted into the CL (single CL model, two MDS lines per CL). Infusion of free radical scavengers, superoxide dismutase ( SOD; 50 mg/ ml)+ catalase (CAT; 10 mg/ml), at 0–28 h first increased P release until 12 h ( P<0.05), and consequently delayed the decrease in P release until 30 h after administration of PGF 2α i.m. ( P<0.05). The present results support the concept that the leading pathway from PGF 2α induces an increase of reactive oxygen species in luteolysis in the ewe.

Treatment with prostaglandin F 2α increases expression of prostaglandin synthase-2 in the rat corpus luteum

Recent studies indicate that the corpus luteum (CL) may be a source of prostaglandin F 2α (PGF 2α) for regression. We investigated expression of mRNA and protein for prostaglandin G/H synthase (PGHS) in the CL of immature superovulated rats following administration of PGF 2α. We observed an increase in mRNA for PGHS-2, the induced isoform, at 1 h and protein at 8 and 24 h after treatment. One hour after PGF 2α, there was also a progressive decrease in plasma progesterone concentration. There were no changes, however, in expression of PGHS-1, the constitutive isoform, over the 24 h sampling period. These results indicate that PGHS-2 increases following PGF 2α treatment and that expression of this enzyme in the rat CL may contribute to the luteolytic mechanism.

The Effect of Treatment of Clinical Endometritis on Reproductive Performance in Dairy Cows

The objective of this field trial was to compare the effect of intrauterine (i.u.) antibiotic or intramuscular (i.m.) prostaglandin F2α (PGF2α) on time to pregnancy in dairy cows diagnosed with clinical endometritis between 20 and 33 days in milk (DIM). The case definition of endometritis was the presence of purulent uterine discharge or cervical diameter >7.5cm, or the presence of muco-purulent discharge after 26 DIM. There were 316 cows with endometritis from 27 farms assigned randomly within herd to receive 500mg of cephapirin benzathine intrauterine (i.u.), 500μg of cloprostenol i.m., or no treatment. The rate of resolution of clinical signs 14 d after treatment was 77% and was not affected by treatment. Reproductive performance was monitored for a minimum of 7 mo after treatment. Survival analysis (multivariable proportional hazards regression) was used to measure the effect of treatment on time to pregnancy. There was no benefit of treatment of endometritis before 4 wk postpartum. Administration of PGF2α between 20 and 26 DIM to cows with endometritis that did not have a palpable corpus luteum was associated with a significant reduction in pregnancy rate. Between 27 and 33 DIM, cows with endometritis treated with cephapirin i.u. had a significantly shorter time to pregnancy than untreated cows (hazard ratio=1.63). In this time period, there was no difference in pregnancy rate between PGF2α and untreated cows, but the difference in pregnancy rate between cows treated with cephapirin i.u. and with PGF2α was not statistically significant. Treatment of postpartum endometritis should be reserved for cases diagnosed after 26 DIM, based on criteria that are associated with subsequent pregnancy rate.

Ultrasound and endocrine evaluation of the ovarian response to PGF 2α given at different stages of the luteal phase in ewes

The purpose of this study was to evaluate the ovarian response of ewes to two treatments with PGF 2α using transrectal ovarian ultrasonography and hormone measurements. Fifteen milligrams of PGF 2α was given to six cyclic Western White Face (WWF) ewes early in the estrous cycle (Days 4 to 7) and to six late in the cycle (Days 10 to 12 after ovulation), and a second treatment was given 9 days after the first. Ultrasound scanning and blood sampling started 7 days prior to the first PGF 2α treatment and ended 10 days (scanning) or 19 days (blood sampling) after the second PGF 2α treatment, for both groups of ewes. Mean ovulation rate (2.6±0.7) did not differ significantly between the ewes first treated early or late in the cycle, or after the first or second treatments with PGF 2α. The time from treatment to ovulation was longer in ewes first treated early (4.0±0.3 days) compared to late (2.8±0.4 days) in the cycle ( P<0.05). Both the number of ovulations (range: 0–7) and time from treatment to ovulation (range: 1–9 days) were highly variable. This variability appeared to be due to the extension of the life span of ovulating follicles that emerged prior to PGF 2α administration and also ovulation of some follicles that emerged after treatment. When results for first and second treatments were pooled, the total number of follicles ≥5 mm in diameter on the day of treatment that failed to ovulate in response to PGF 2α was higher in ewes first treated early (0.8±0.2/ewe) compared to late (0.3±0.2/ewe) in the cycle ( P<0.05). The proportion of detected luteal structures relative to the number of ovulations was lower in ewes first treated early compared to late in the cycle (60 and 86%, respectively; P<0.05). Disruption of ovulatory follicle dynamics and normal luteogenesis, and variability in the timing of ovulation after PGF 2α treatments could all contribute to poor or variable fertility when prostaglandins are used for estrus synchronization.

Postovulatory effect of repeated administration of prostaglandin F 2α on the endocrine status, ova transport, binding of accessory spermatozoa to the zona pellucida and embryo development of recently ovulated sows

We investigated the postovulatory effect of repeated administration of prostaglandin F 2α (PGF 2α) on the endocrine status, ova transport, binding of accessory spermatozoa to the zona pellucida (ZP) and embryo development of recently ovulated sows. We used altogether 10 Swedish crossbred (Landrace×Yorkshire) multiparous sows. The treatment group (P-group) was administered 1 mg of PGF 2α intravenously every 6 h via an indwelling jugular cannula, commencing 4–8 h after ovulation was detected in the second estrus after weaning. All sows were inseminated once and blood was sampled until the end of the experimental period. After slaughter, we immediately recovered the reproductive tracts and divided them into three equal isthmic segments (IST1, IST2 and IST3) and a third of the uterine horn from the utero-tubal-junction (UTJ), and we flushed each one with PBS for ova recovery. We immediately stained the ova and examined them under epi-fluorescence illumination. We found the highest proportion of ova in the P-group in IST1 (41.5%), while we found the highest proportion in the C-group in the uterus (40.7%). A total of 68.7% of ova in the P-group had more than 50 accessory spermatozoa attached to the ZP, compared with 36.7% in the C-group sows. A total of 77% of ova had more than three blastomeres in the P-group, compared with 73% in the C-group. PGF 2α metabolite and cortisol levels were elevated ( P<0.05) following every PGF 2α administration. Despite peaks, we saw no changes ( P>0.05) in progesterone levels between the P-group and the C-group. We saw no differences ( P>0.05) in estradiol-17β levels between the P-group and the C-group. We concluded that PGF 2α stimulates the hypothalamus–pituitary–adrenal axis, as evidenced by the elevation of cortisol and progesterone but not estradiol-17β. Furthermore, repeated PGF 2α administration might be associated with a delayed ova transport and an increased number of accessory spermatozoa bound to the ZP. However, the effect of PGF 2α on embryo development is unclear.

Oestrus Synchronization by PGF2α and GnRH in Intervals according to Stage of Follicular Development at Time of Initial Treatment in Cows

DoleIel R. , S. âech, J. Zajic, V. Havliaek: Oestrus Synchronization by PGF2α and GnRH in Intervals according to Stage of Follicular Development at Time of Initial Treatment in Cows. Acta Vet. Brno 2002, 71: 101-108. The objective of this study was to evaluate the efficiency of oestrus/ovulation synchronization using PGF 2α and GnRH at intervals according to the sizes of ovarian follicles at the time of initial treatment. Oestrus synchronization was performed in 65 cows from 3 commercial dairy farms. Synthetic analogue of PGF 2α cloprostenol was administered in cows bearing corpus luteum between days 50 to 100 post partum. The cows were divided into 3 groups according to diameters of ovarian follicles in ultrasonographical image: Group 1 – small follicles ( 3-7 mm, n = 10), Group 2 – small and medium follicles (3–7 and 8–14 mm, n = 35) and Group 3 – small, medium and large follicles (3-7 mm, 8-14 mm and 15–23 mm, n = 20). GnRH was administered 72 hours (Group 1), 48 h (Group 2) and 24 h (Group 3) after PGF 2α . Ultrasonographical examinations of ovarian structures were performed on days 0 (day of PGF2α administration) 2, 4, 6, and 12. Blood samples for progesterone determination by RIA were obtained in 50 cows (10 cows in Group 1, 25 cows in Group 2 and 15 cows in Group 3) on days 0 and 12. Detection of oestrus was performed twice daily and cows in oestrus were inseminated. Term of oestrus and ovulation, progesterone concentration and conception rate were evaluated. Oestrus was detected and insemination was performed in 8 of 10 (80%), 33 of 35 (94%) and 12 of 20 (60%) cows in experimental Groups 1, 2 and 3, respectively, within 5 days after PGF 2α administration. Ovulation occurred in all inseminated cows in Groups 1 and 2 within 2 days after insemination. In spite of oestrus occurring and insemination being performed only in 12 cows in Group 3 ovulation occurred in 15 cows in this Group within 5 days after PGF 2α . Corpora lutea were found in all ovulated cows (except 1 cow in Group 2) on day 12. Conception rates in inseminated cows were 50%, 64% and 42% in Groups 1, 2, and 3, respectively. The highest efficiency of oestrus synchronization was found in Group 2 in which oestrus occurred in 29 of 35 (83%) observed cows on day 3 after PGF2α and conception rate was 66% in these cows. PGF 2α , GnRH, corpus luteum, follicle diameter, oestrus, ovulation, conception rate