Possibility of reducing the luteolytic dose of cloprostenol in cyclic dairy cows

The administration of cloprostenol by intravulvosubmucous (i.v.s.m.) injection at 1 2 and 1 4 of the dose usually given by intramuscular (i.m.) injection, was tested in dairy cows for luteolysis and estrus synchronization. The i.m. injection was used in ten adult cows at the usual dose of 500 mug/animal. Eleven adult cows and 11 heifers were treated i.v.s.m. with a dose equivalent to 250 mug/animal and 125 mug/animal, respectively. Two injections of cloprostenol were administered 11 days apart to the cows not detected in oestrus after a single injection. Forty-three out of the total 46 animals were detected to be in dioestrus at the time of at least one of the injections, as reflected by the plasma progesterone concentrations at the time of treatments. Three out of the 43 animals injected during dioestrus were refractory to the luteolytic effect of cloprostenol; this appeared to be independent of the dosage and the route of administration (refractory cows were: one adult cow treated i.m. and two treated i.v.s.m. with 125 mug of cloprostenol). The mean time interval from injection to the onset of heat was 82.8 hours with a confidence limit for 95% of probability between 67.9 hours and 92.7 hours. The difference between treatments is not significant. The results suggest that in heifers and adult cows cloprostenol can be given i.v.s.m. route at a reduced dose of 1 4 of the usual 500 mug i.m. dosage without affecting the luteolytic effect of the drug or fertility.     

Cloprostenol-induced luteolysis in the marmoset monkey (Callithrix jacchus)

A single intramuscular injection of 0.5 micrograms cloprostenol was not luteolytic on Day 6 or 7 of the ovarian cycle (N = 3), but was luteolytic in some animals (3/5) on Day 8 and 9 and luteolytic in all 23 animals treated between Days 10 and 17 of the ovarian cycle, and in 7 animals treated between Days 19 and 43 of pregnancy. Luteal function was monitored by measurement of progesterone in peripheral blood using a simple and rapid non-extraction assay. There was a dramatic fall in peripheral blood progesterone to less than 10 ng/ml within 24 h of cloprostenol injection; progesterone remained at this low level until the day after post-treatment ovulation. The interval from cloprostenol injection to ovulation in animals treated between Days 8 and 17 was 10.7 +/- 0.3 days. A similar interval was found in pregnant animals. Embryos recovered from the uterus after cloprostenol treatment were morphologically normal (23/24).     

Double bond isomers of cloprostenol

The syntheses of five compounds isomeric with the potent luteolytic agent cloprostenol are described. These are the trans-delta 5, cis and trans-delta 4, cis-delta 6 (methyl ester) and cis-delta 13 analogues. The cis-delta 4 isomer is as potent as cloprostenol as a luteolytic agent in hamsters but the others are markedly less so.     

Estrus induction with prostaglandin F2alpha, cloprostenol or fenprostalene during the normal estrous cycle, superovulation and after embryo collection

Holstein heifers used as embryo donors were treated with three luteolytic agents (PGF2alpha, cloprostenol, fenprostalene) during the normal estrous cycle, superovulation or after embryo collection to determine the interval from treatment to estrus. A similar return-to-estrus interval was observed for each luteolytic agent among the three groups of heifers. Nevertheless, after embryo collection, fenprostalene had a tendency to induce the longest delays (p = 0.08). This tendency is supported by a higher proportion of delayed luteolysis and more heifers showing estrus later than 11 d post treatment. Also, during normal estrous cycles, 5/10 and 0/8 fenprostalene- and cloprostenol-treated heifers, respectively, showed progesterone concentrations higher than 1 ng/mL 48 h after treatment. Regardless of the luteolytic agent used, estrus was induced earlier (P < 0.005) during superovulation than when heifers were treated between Days 9 to 16 of the normal estrous cycle or after embryo collection. However, the return-to-estrus interval was similar between heifers treated during superovulation and those treated between Days 6 to 8 of the normal estrous cycle. After embryo collection, intervals before the return to estrus increased with the number of Corpora lutea (CL) palpated except in the nonresponding group (0 to 1 CL), which returned to estrus later than the low responding group (2 to 4 CL).     

Double bond isomers of cloprostenol

The syntheses of five compounds isomeric with the potent luteolytic agent cloprostenol are described. These are the -Δ⁵, and -Δ⁴, -Δ⁶ (methyl ester) and -Δ¹³ analogues. The -Δ⁴ isomer is as potent as cloprostenol as a luteolytic agent in hamsters but the others are markedly less so.     

Prostaglandin f(2alpha) induces distinct physiological responses in porcine corpora lutea after acquisition of luteolytic capacity

This study examines differences in intracellular responses to cloprostenol, a prostaglandin (PG)F(2alpha) analog, in porcine corpora lutea (CL) before (Day 9 of estrous cycle) and after (Day 17 of pseudopregnancy) acquisition of luteolytic capacity. Pigs on Day 9 or Day 17 were treated with saline or 500 microgram cloprostenol, and CL were collected 10 h (experiment I) or 0.5 h (experiment III) after treatment. Some CL were cut into small pieces and cultured to measure progesterone and PGF(2alpha) secretion. In experiment I, progesterone remained high and PGF(2alpha) low in luteal incubations from either Day 9 or Day 17 saline-treated pigs. Cloprostenol increased PGF(2alpha) production 465% and decreased progesterone production 87% only from Day 17 luteal tissue. Cloprostenol induced prostaglandin G/H synthase (PGHS)-2 mRNA (0.5 h) and protein (10 h) in both groups. In cell culture, cloprostenol or phorbol 12, 13-didecanoate (PDD) (protein kinase C activator), induced PGHS-2 mRNA in luteal cells from both groups. However, acute cloprostenol treatment (10 min) decreased progesterone production and increased PGF(2alpha) production only from Day 17 luteal cells. Thus, PGF(2alpha) production is induced by cloprostenol in porcine CL with luteolytic capacity (Day 17) but not in CL without luteolytic capacity (Day 9). However, this change in PGF(2alpha) production is not explained by a difference in induction of PGHS-2 mRNA or protein.     

Hormone-induced luteolysis on physiologically persisting corpora lutea in Eurasian and Iberian lynx (Lynx lynx and Lynx pardinus)

The Iberian lynx (Lynx pardinus) is the most critically endangered felid. A high reproductive success within the Iberian Lynx Conservation Breeding Program is crucial to maintaining the goal of reintroducing captive born offspring to the wild and thus increasing the population. Lynx follow a unique reproductive strategy with a monoestrous cycle and persisting CLs over many years. These persistent CLs constantly produce progesterone (on average 5 ng/mL) and are hypothesized to hinder a polyestrous cyclicity in lynx. The aim of this study was to evaluate whether artificial luteolysis can be achieved with common luteolytic drugs and if luteolysis would induce a second estrus naturally. We observed a functional regression of lynx CLs after artificial luteolysis with 2.5 μg/kg body weight PGF2α analogue (cloprostenol) administered three times every 16 hours. We could see a similar effect when combining cloprostenol with other drugs like an anti-gestagen (aglepristone) or a dopamin-agonist (prolactin-inhibitor, cabergolin) or by prolonging the cloprostenol administration to a total of 5 days. However, the sample size was too small to draw conclusions about which protocol is superior or if combining different drugs would result in a positive synergism. Neither structural regression of CLs nor subsequent spontaneous estrus induction was induced with any of these treatments. We suggest that a dose of 2.5 μg/kg body weight cloprostenol administered once daily over 3 to 5 days is sufficient for functional luteolysis in lynx. The next step would be to compare the success of estrus induction with or without the preceding artificial luteolysis.     

Effects of an LHRH antagonist on gonadotrophin and oestradiol secretion, follicular development, oestrus and ovulation in Holstein heifers

Mature cyclic Holstein heifers were given a luteolytic dose of cloprostenol followed by two i.v. injections, 12 h apart, of various doses of [Ac-D-Nal1, D-p-Cl-Phe2, D-Trp3, D-Arg6, D-Ala10]-LHRH, beginning either at the time of first observation of behavioural oestrus, or 48 h after the cloprostenol injection. When treatment began at the first observation of oestrus, the time of ovulation, as determined by ultrasonic echography, was significantly delayed by total doses of 0.8 mg or more of the antagonist. When given at 48 and 60 h after cloprostenol injection, a total dose of 1.5 mg of the antagonist significantly delayed the growth of the ovulating follicle, the onset of oestrus, the preovulatory surges of oestradiol, LH and FSH, and ovulation. It is concluded that the LHRH antagonist can effectively suppress endogenous LH secretion and may therefore be useful in the study of follicular development, ovulation, and other events in the oestrous cycle of the cow.     

Failure of the LH-releasing hormone agonist, deslorelin, to prevent development of a persistent follicle in heifers synchronized with norgestomet

The use of exogenous progestagens for estrus synchronization in cattle can result in a persistent dominant follicle which is associated with reduced fertility. We examined whether the LHRH agonist, deslorelin, would prevent the formation of a persistent follicle in heifers synchronized with norgestomet. The estrous cycles of heifers were synchronized with cloprostenol, and on Day 7 of the ensuing cycle the heifers received one of the following treatments for 10 d: Group C (n = 5), untreated control; Group N (n = 6), injection of a luteolytic dose of cloprostenol on Days 7 and 8 and implant of norgestomet from Day 7 to Day 17 (i.e. typical 10-day norgestomet implant period); Group D (n = 6), injection of cloprostenol on Days 7 and 8 and implants of deslorelin from Day 7 to Day 17; Group ND (n = 6), injections of cloprostenol and both norgestomet and deslorelin implants as above. Follicle growth was monitored using ultrasonography. Group-N heifers showed continued follicle growth and had larger follicles on Day 17 of the cycle than Group-C heifers (16.8 +/- 1.6 and 10.4 +/- 1.6 mm). Follicle growth for Group-D and ND heifers was similar and variable, and seemed to depend on follicle status at the initiation of treatment. Heifers with follicles of 5 to 10 mm (n = 9) in diameter either showed no follicle growth (2 9 ) or developed large follicles (7 9 ), while heifers with follicles approximately 12 mm (n = 3) in diameter showed follicle atresia with no further significant growth. On Day 17, size of the largest follicle was similar for Group-ND (14.3 +/- 2.9) and Group-D (16.8 +/- 1.6) heifers. Heifers in Group N showed estrous behavior 1.8 +/- 0.2 d after treatment, whereas heifers in Groups D and ND did not show estrus for 2 to 4 wk. The results show that combined treatment with progestagen and an LHRH agonist does not consistently prevent the development of a persistent dominant follicle and that return to estrus can be delayed after treatment with an LHRH agonist.     

Short synchronization system for estrus cycles in dairy heifers: a preliminary report

In previous studies we demonstrated that the administration of a luteolytic dose of cloprostenol to dairy cows in luteal phase, followed by hCG plus estradiol benzoate (EB) 12 h later, led to successful timed AI 48 h after the initiation of treatment. This article reports two consecutive studies. In Study 1 we determined the pregnancy rate of dairy heifers in luteal phase (established by palpation per rectum) treated with cloprostenol followed by 250 IU of hCG plus 1 mg of EB 12 h later, and inseminated 48 h after cloprostenol injection. Study 2 was designed to evaluate the efficiency this synchronization protocol, irrespective of the estrus stage of the animals. In Study 1, 1272 Friesian heifers aged 14 to 16 months with a palpable corpus luteum received 500 mcg cloprostenol. Heifers were then synchronized either according to the hCG plus EB protocol (hCG-EB, n=637), or by a second dose of cloprostenol 11 d later (PG, n=636). Animals in this last group served as controls and were inseminated 72 and 96 h after the second cloprostenol injection. The pregnancy rate was significantly higher (P<0.0001) in the hCG-EB group (59.5%, 379/637) than in PG (44.8%, 285/636). In Study 2, 135 contemporary heifers (with no corresponding information on estrus stage) were subjected to the same protocol as those in the hCG-EB group of Study 1. These animals were classified in retrospect according to estrus stage established by plasma progesterone concentration. Pregnancy rates were 66.7% (24/36), 51% (25/49) and 58% (29/50) for animals in the follicular, early/late luteal, and mid-luteal phase, respectively. The total pregnancy rate was 57.8% (78/135). These findings indicate an improved pregnancy rate for heifers subjected to single insemination after cloprostenol/hCG/EB synchronization, compared to double insemination after synchronization by 2 cloprostenol injections 11 d apart. The cloprostenol/hCG/EB protocol did result in acceptable pregnancy rates after timed AI of dairy heifers regardless of their estrus cycle phase.     

Effects of dose and route of administration of cloprostenol on luteolysis,estrus and ovulation in beef heifers

Four experiments were conducted (with crossbred beef heifers) to determine the effects of dose and route of administration of cloprostenol on luteolysis, estrus and ovulation. In Experiment 1, 19 heifers with a CL > or = 17 mm in diameter were randomly allocated to receive cloprostenol as follows: 100 microg s.c., 250 microg s.c., or 500 microg i.m. Heifers given 100 microg s.c. had a longer (P<0.03) interval (120.0 h+/-10.7 h; mean+/-S.E.M.) from treatment to ovulation than those given either 250 microg s.c. or 500 microg i.m. (92.0 h+/-7.4 h and 84.0 h+/-8.2 h, respectively). In Experiment 2, 28 heifers were given porcine LH (pLH), followed in 7 days by cloprostenol (same doses and routes as in Experiment 1), and a second dose of pLH 48 h after cloprostenol. Luteolysis occurred in all heifers, and no difference was detected among treatment groups in the interval from cloprostenol treatment to ovulation (mean, 101 h; P<0.9). In Experiment 3, 38 heifers at random stages of the estrous cycle (but with plasma progesterone concentrations > or =1.0 ng/ml) received 500 or 125 microg cloprostenol by either i.m. or s.c. injection (2/2 factorial design). There was no difference (P<0.4) among groups in the proportions of heifers that were detected in estrus or that ovulated. However, the interval from cloprostenol treatment to estrus was shorter (P<0.02) in the group that received 500 microg i.m. (58.5h) than in the other three groups (500 microg s.c., 75.0 h; 125 microg i.m., 78.0 h; and 125 microg s.c., 82.3h). In Experiment 4, 36 heifers were treated (as in Experiment 3) on Day 7 after ovulation. The proportions of heifers detected in estrus and ovulating after 125 microg s.c. (33 and 44%, respectively) or 125 microg i.m. (55 and 55%) were lower (P<0.05) than in those that received 500 microg s.c. (100 and 100%), but not different from those receiving 500 microg i.m. (78 and 89%, respectively). Overall, ovulation was detected in 9/18 heifers given 125 microg and 17/18 heifers given 500 microg of cloprostenol, on Day 7 (P<0.01) and was detected in 17/20 heifers given 125 microg and 18/18 heifers given 500 microg of cloprostenol, at random stages of the estrous cycle (P>0.05). Although there was no significant difference in luteolytic efficacy between i.m. and s.c. injections of the recommended dose (500 microg) of cloprostenol, variability in responsiveness to a reduced dose depended upon CL sensitivity, therefore, reduced doses cannot be recommended for routine use.     

Effect of administering oxytocin or cloprostenol in the periovulatory period on pregnancy outcome and luteal function in mares

Mares (n = 37) were treated from 4h after breeding through 2 days post-ovulation with oxytocin or cloprostenol. Oxytocin (20 units i.m.) was administered every 6 h and cloprostenol (250 mcg i.m.) daily. Luteal function was impaired for several days following treatment, however, lower progesterone levels among cloprostenol treated mares in this study did not result in decreased pregnancies. Pregnancy outcome at 15 days post-ovulation was not different between the oxytocin (13/18) and cloprostenol (13/19) treatment groups, respectively (P = 0.80). The results of this study indicate cloprostenol can be used to treat post-breeding mares through the second day following ovulation without decreasing pregnancy outcome.     

Effects of a synthetic prostaglandin analogue, cloprostenol, on the corpus luteum of the guinea pig

The effects of a synthetic prostaglandin analogue, cloprostenol, on luteal function in a guinea pig were studied. At a dose of 250μg, cloprostenol administered I-P on day 9 of the oestrous cycle caused a reduction in the length of the oestrous cycle from 17.4±s.d. 0.9 to 14.5±1.1 days (p<0.01). Lower doses were ineffective, and post-treatment cycles were not different in length from pre-treatment cycles. Cloprostenol also caused a dose-dependent reduction in luteal weight, which fell from 3.52±0.82 to 1.82±0.4mg (<0.01) 48 h after administation of a 250μg dose on day 9. Plasma progesterone, measured by radioimmunoassay, was reduced from 4.67±0.59 to 2.69±0.66 ng ml⁻¹(p<0.01) 48 h after administration of 250μg cloprostenol on day 9. 250μg cloprostenol also reduced blood flow per corpus luteum, measured by ⁸⁵Sr-labelled 15μm microspheres, both at 3 h (20.20±10.36 to 9.40±4.2μ1 min⁻¹; p0.05) and at 48 h 18.47±8.27 to 5.23±1.90μl min⁻¹; p<0.01) after administration on day 9. No adverse side-effects were observed at any dose level of cloprostenol used. It was concluded that cloprostenol is a useful experimental luteolysin in the guinea pig.     

Involvement of endothelin-1 and its receptors in PGF2alpha-induced luteolysis in the rat

The possible mediatory role of endothelin-1 (ET-1) in prostaglandin F(2alpha) (PGF(2alpha))-induced luteolysis in the rat was examined. The effect of PGF(2alpha) was tested on day 9 of pregnancy either in vivo, by injecting cloprostenol, an analog of PGF(2alpha) or in vitro, in isolated intact corpora lutea incubated with PGF(2alpha). Luteolysis was confirmed by progesterone determination in the peripheral blood serum or in the culture medium, respectively. Administration of cloprostenol (.0025 mg/rat) induced within 1 hr, a significant fall (from 56.8 to 27.6 ng/ml, P < 0.0001) in serum progesterone concentrations that was associated with an increased expression of the mRNA to ET-1 and its protein product in rat luteal tissue. Elevated level of ET-1 were also determined at the spontaneous regression of the CL, upon parturition. Expression of the ET receptors, ETA and ETB was not affected by cloprostenol. On the other hand, this PGF(2alpha) analog induced expression of luteal VEGF mRNA. In vitro experiments demonstrate that the LH (100 ng/ml)-induced increase in luteal progesterone secretion was reduced by PGF(2alpha) (1 microg/ml). The inhibitory effect of PGF(2alpha) was reversed by BQ123 (10(- 7) M), that is a selective ETA receptor antagonist. We conclude that the PGF(2alpha)-induced elevation in luteal expression of ET-1 combined with the reversal of its luteolytic effect by an ETA receptor antagonist suggest that ET-1 may take part in the PGF(2alpha)-induced luteolysis in the rat.     

Effects of cloprostenol sodium and clenbuterol HCl on reproductive performance in postpartum anestrous cows

Two experiments were conducted to study effects of cloprostenol sodium (cloprostenol) and clenbuterol HCl (clenbuterol) during postpartum anestrus on subsequent reproductive performance in cows. In Experiment I, 96 cows received either 0.5 mg cloprostenol (PGF, n = 25), 364 mg clenbuterol (CLEN, n = 24), 0.5 mg cloprostenol and 364 mg clenbuterol (CLEN+PGF, n = 21) or no treatment (Control, n = 26) on Day 20 post partum. Treatments failed to influence postpartum interval, pregnancy rate or the incidence of short estrous cycles preceding the first normal estrous cycle. In Experiment II, anestrous cows were administered cloprostenol (0.5 mg) on either Day 20 (PGF20, n = 27) or Day 35 post partum (PGF35, n = 25), or served as untreated controls (Control, n = 26). Neither postpartum interval nor pregnancy rate were affected by cloprostenol treatment. In conclusion, treatment of postpartum cows with PGF did not alter the resumption of normal estrous cycles following parturition.     

Expression of mRNA encoding insulin-like growth factor binding protein-2 (IGFBP-2) during induced and natural regression of equine corpora lutea

The insulin-like growth factors, IGF-I and -II, have been shown to play a key role in luteal function in some species. The IGF binding proteins, IGFBP-2 and -3, have been shown to inhibit binding of IGF-I and -II to bovine luteal cells and decrease progesterone production. We have recently shown that equine follicles have the genetic capacity to produce IGFBP-2, and that levels decrease in healthy preovulatory follicles. In the present study expression of mRNAs encoding IGFBP-2, as well as the rate-limiting steroidogenic enzyme, P450scc, were studied in equine corpora lutea to investigate whether IGFBP-2 might be involved in luteolysis. Corpora lutea were collected from mares in mid-luteal phase (day 10), at early regression (day 14), late regression (day 17), and 12 and 36 h after intramuscular administration of the PGF(2alpha) analogue, cloprostenol (0.5 microg/kg). During early natural regression, and 12 h after administration of cloprostenol on day 10, steady state levels of mRNAs encoding P450scc had decreased significantly compared with day 10 of dioestrus (P < 0.001). Levels of mRNA encoding IGFBP-2 increased significantly between mid-diestrus and early (P < 0.01) and late (P < 0.001) regression, and 36 h after cloprostenol administration (P < 0.001). We conclude that the genetic capacity for increased IGFBP-2 production in the early stages of natural luteolysis in the mare may act to sequester IGF-I in the CL, assisting in inhibition of progesterone production. However the delay in increase in mRNA encoding IGFBP-2 after cloprostenol administration, combined with the sharp fall in expression of P450scc mRNA, suggests that the luteolytic action of a pharmacological dose of cloprostenol may not be mediated via IGFBP-2 in the mare.     

Reproductive performance of dairy cows following treatment with fenprostalene, dinoprost, or cloprostenol between 24 and 31 Days post partum: a field trial

Three hundred and one Holstein cows (n=301), calving at a commercial free-stall dairy farm, were randomly assigned to 1 of 3 prostaglandin treatment groups or a placebo group. The placebos were packaged 3 ways to mimic the 3 commercial prostaglandin preparations. Group 1 received 1 mg fenprostalene and 1.6 mg oxytetracycline; Group 2 received the fenprostalene placebo (2 ml polyethylene glycol and 1.6 mg oxytetracycline); while Group 3 was given 25 mg dinoprost. Group 4, the dinoprost placebo received 5 ml saline; Group 5 received 500 ug cloprostenol; and Group 6 the cloprostenol placebo received 2 ml saline. The treatments were administered between Days 24 and 31 post partum. Double blind techniques were used in administering treatments and in assessing the response to treatment. There were no significant differences among treatment groups with respect to incidence of retained fetal membranes, endometritis, pyometra, anestrus, number of services per pregnancy, calving-to-first estrus interval, services per conception, number of prostaglandin treatments other than those administered between Days 24 and 31 post partum, the percentage culled for reproductive reasons and all factors combined. Cows receiving fenprostalene, dinoprost or cloprostenol had a decreased calving-to-conception interval compared with that of the controls (P = 0.05). It is concluded that, in the herd studied, treatment with any of the 3 commercially available prostaglandin products between Days 24 and 31 post partum was beneficial for reproductive performance.     

Reproductive performance of lactating dairy cows treated with cloprostenol, hcg and estradiol benzoate for synchronization of estrus followed by timed AI

In previous studies, we demonstrated that the administration of a luteolytic dose of cloprostenol, followed by 750 IU hCG plus 3 mg estradiol benzoate (EB) 12 h later, synchronized estrus in cows in the luteal phase. Most cows were ready for service 48 h after the beginning of treatment. The objectives of this study were to evaluate the reproductive performance of lactating dairy cows treated with this method of estrus synchronization and to determine the effect of decreasing the hCG-EB dose on synchronization and pregnancy rates after timed AI. Data were obtained from cows first inseminated within an interval of 45 to 70 d postpartum. A total of 2,472 lactating dairy cows in their first to second lactation period were assigned to 4 groups. Cows estimated to be in the luteal phase by rectal palpation were treated with 500 mcg, im, of cloprostenol and assigned to 1 of 3 groups to be intramuscularly injected with hCG-EB 12 h later at the following doses: Group 1 (n=626), 250 IU of hCG and 1 mg of EB; Group 2 (n=592), 500 IU of hCG and 2 mg of EB; and Group 3 (n=664), 750 IU of hCG and 3 mg of EB. Cows displaying natural estrus were inseminated to serve as controls (n=590). The synchronized cows were inseminated 48 h after cloprostenol injection, and control animals visually determined to be in natural estrus during the morning or afternoon were inseminated the following morning. Pregnancy diagnosis was performed by rectal palpation at 34 to 40 d postinsemination. All synchronized cows showed estrous activity within 24 to 36 h after cloprostenol treatment and were considered to be ready for service 48 h after this treatment. There was a significant effect of treatment on the pregnancy rate, either to first AI or to 2 rounds of AI. The pregnancy rate in response to first or second rounds of AI was similar to control rates for cows in Groups 1 and 2, and lower than control rates in Group 3. Cows in Group 1 showed a higher pregnancy rate to first AI than those in Group 3 (P<0.0001), and a higher pregnancy rate to second AI rounds than cows in Groups 2 (P<0.02) and 3 (P<0.0001). The number of cows returning to estrus was unaffected by treatment. However, treatment significantly decreased (P<0.01) the time of return to estrus as the hCG-EB dose increased. These findings indicate that the lowest dose of hCG-EB treatment tested gave the overall best pregnancy results among the treated groups. Furthermore, the synchronization protocol used in this experiment allows effective AI management of lactating dairy cows without the need for estrus detection.     

Rates of luteolysis and pregnancy in dairy cows after treatment with cloprostenol or dinoprost

Our objective was to determine whether rates of luteolysis or pregnancy differed in lactating dairy cows of known progesterone status and either known or unknown luteal status after either cloprostenol or dinoprost was injected as part of a timed-insemination program. In Experiment 1, 2358 lactating dairy cows in six herds were given two injections of PGF_2α 14 d apart (Presynch), with the second injection given 12 to 14 d before the onset of a timed AI protocol (Ovsynch). Cows (n = 1094) were inseminated when detected in estrus after the Presynch PGF_2α injections. Cows not inseminated (n = 1264) were enrolled in the Ovsynch protocol and assigned randomly to be treated with either cloprostenol or dinoprost as part of the timed-AI protocol. In cows having pretreatment concentrations of progesterone ≥ 1 ng/mL and potentially having a functional corpus luteum (CL) responsive to cloprostenol (n = 558) or dinoprost (n = 519), dinoprost increased (P < 0.05) luteal regression from 86.6 to 91.3%. Despite a significant increase in luteolysis, pregnancies per AI did not differ between luteolytic agents (dinoprost = 37.8% and cloprostenol = 36.7%). Fertility was improved in cows of both treatments having reduced concentrations of progesterone at 72 h and in cows showing signs of estrus. In Experiment 2, an ovulation-resynchronization program was initiated with GnRH or saline in 427 previously inseminated lactating dairy cows of unknown pregnancy status in one herd. Seven days later, pregnancy was diagnosed and nonpregnant cows were blocked by number of CL and assigned randomly to be treated with cloprostenol or dinoprost. Compared with cloprostenol, dinoprost increased (P < 0.05) luteal regression from 69.1 to 78.5%, regardless of the number of CL present or the total luteal volume per cow. Pregnancies per AI did not differ between dinoprost (32.8%) and cloprostenol (31.3%). Although dinoprost was more effective than cloprostenol at inducing luteolysis in lactating dairy cows exposed to an Ovsynch or ovulation-resynchronization protocol, resulting fertility did not differ between products.     

Pulsatile secretion of gonadotrophins, ovarian steroids and ovarian oxytocin during prostaglandin-induced regression of the corpus luteum in the cow

A luteolytic dose (500 micrograms) of cloprostenol was given on Day 12 of the oestrous cycle to 5 heifers. Blood samples were collected simultaneously from the caudal vena cava and jugular vein at 5-20-min intervals from -6 to 0 (control period), 0 to 12 and 24 to 36 h after PG injection. Pulses of LH were secreted concomitantly with pulses of FSH during all sampling periods. However, during the control period separate FSH pulses were detected resulting in a shorter (P less than 0.01) interpulse interval for FSH than LH (93 versus 248 min). LH and FSH pulse frequencies increased (P less than 0.01) beginning 1-3 h after PG to interpulse intervals of 59 and 63 min, respectively, and continued to be maintained 24-36 h after PG. Concomitantly there was a 2-3-fold increase (P less than 0.01) in basal concentrations and pulse amplitude for LH (but not FSH). FSH basal concentrations and pulse amplitudes decreased (P less than 0.05) in 3 heifers 24-36 h after PG. Pulsatile secretion of oestradiol was observed at frequencies similar to LH during the periods 4-12 h (3 heifers) and 24-36 h (2 heifers) after PG, respectively, resulting in higher (P less than 0.05) mean oestradiol concentrations. Progesterone concentrations in the vena cava increased (P less than 0.01) 5-10 min after PG but decreased (P less than 0.01) 67% by 20 min after PG. This decrease was followed by a rise (P less than 0.05) beginning 2-3 h after PG and lasting for an average of 3.3 h.(ABSTRACT TRUNCATED AT 400 WORDS)