Effects of intravulvo-submucosal cloprostenol injections on hormonal profiles and fertility in subestrous cattle

Eighty-two subestrous cattle were treated with different doses of cloprostenol through intramuscular (i.m.) and intravulvo-submucosal (i.v.s.m.) injections to study hormonal profile and fertility. The study was divided into two experiments. In Experiment I, 13 cows were treated with one of three doses of cloprostenol (500 mug i.m., 125 and 62.5 mug i.v.s.m.) to measure response of progesterone (P(4)) and estradiol (E(2)). P(4) decreased abruptly and E(2) levels increased from basal levels following injections of the two larger doses of cloprostenol. P(4) decreased to<5 nmol/l approximately 72 h after treatment. E(2) levels increased to >300 pmol/l 24 h after cloprostenol injections except in cows treated with 62.5 mug dose. Close agreement was observed between P(4) profiles and clinical findings following 500 and 125 mug of cloprostenol treatment. In Experiment II, 69 subestrous cows were treated with either 500 mug i.m. or 250, 125 or 62.5 mug i.v.s.m. doses of cloprostenol. The percent of cows in estrus 96 h following treatment were 60, 80, 67.8 and 18%, respectively. A total of 29 cows were artificially inseminated and 41.3% conceived. We concluded that i.v.s.m. injections of cloprostenol at the dosage of 125 mug and above causes luteolysis, induces estrus and establishes fertility in subestrous cattle. The method is economical but time consuming when compared to the intramuscular route.     

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.     

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.     

The effects of buck teasing on synchronization of estrus in goats after intravulvo-submucosal administration of cloprostenol

A study was conducted on 35 East African shorthorned female goats to determine if a combination of buck teasing and low doses of a prostaglandin (PGF(2) alpha) analogue, cloprostenol, given intravulvo-submucosally (i.v.s.m.) would be suitable for synchronization of estrus. Goats were allotted, with the onset of estrus, to seven groups (n = 5 goats per group). Five of the seven groups received varying doses of cloprostenol: Group 1 (125 mug cloprostenol i.m. per goat); Group 2 (62.5 mug cloprostenol i.v.s.m. per goat); Group 3 (62.5 mug cloprostenol i.v.s.m. per goat plus buck teasing); Group 4 (31.25 mug cloprostenol i.v.s.m. per goat); Group 5 (31.25 mug cloprostenol i.v.s.m. per goat plus buck teasing); Group 6 (buck teasing); Group 7, (2 ml physiological saline i.v.s.m. per goat, control group). Plasma progesterone concentration was measured on day of treatment and for 6 d thereafter. All goats in groups 1, 2, 3 and 5 exhibited estrus within 68 h. Thus, the number of goats receiving low doses of PG-cloprostenol intravulvo-submucosally observed in estrus increased (P < 0.05) with exposure to bucks. Exhibition of behavioral signs of estrus was maximal between 2 and 20 h after onset of signs of estrus. The exposure of females to males prior to intrauterine penetration was an advantage because copious mucus eased penetration.     

Control of estrus in dairy cows with a synthetic analogue of prostaglandin F2 alpha

Trials were carried out on 1184 dairy cows calved at least six weeks before treatment and 255 heifers to determine effectiveness of the prostaglandin analogue, cloprostenol to control estrus. In trial 1, following two injections of cloprostenol given 12 days apart, there was no difference in calving rate following AI either at 72 and 96 hr after treatment (71 163 ) or at a detected estrus (53 118 ) compared to control cows bred at estrus (54 110 ). In trial 2, treated cows were injected once after 5 to 7 days of estrous detection and AI. The calving rate following AI either at 72 and 96 hr after cloprostenol (46 100 ) or at a detected estrus (39 71 ) was similar to that in control cows bred at estrus (45 86 ). In trial 3, cows were bred at a detected estrus after the first cloprostenol injection. Twelve days after this injection, cows not bred were given a second injection and bred 72 and 96 hr later. The calving rate in treated cows bred at estrus after the first injection (66 138 ) was similar to calving rate in controls (55 95 ). However, calving rate in cows given a second injection and bred 72 and 96 hr later was significantly (P angle 0.05) lower (30 98 ). Similar results were obtained in heifers, except calving rate in trial 3 after the second cloprostenol injection was not reduced.     

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.     

Plasma concentrations of gonadotrophins, preovulatory follicular development and luteal function associated with bovine follicular fluid-induced delay of oestrus in heifers

In Exp. 1, injections of 10 ml bovine follicular fluid (bFF, i.v. or s.c.), given twice daily for 3 days after injection of a luteolytic dose of PGF-2 alpha, delayed the onset of oestrus in 3 of 6 heifers to 8 or 9 days after PGF-2 alpha, as compared with 2 or 3 days after PGF-2 alpha in control heifers. Mean plasma concentrations of FSH and LH during the injection period were not different from those in saline-injected heifers. In Exp. 2, i.v. injections of 20 ml bFF twice daily for 3 days uniformly delayed oestrus to 8 days after PGF-2 alpha (N = 4) and injections of 20 ml bFF i.v. every 6 h for 24h on the day of PGF-2 alpha injection delayed oestrus to 5.0 +/- 0.6 days after PGF-2 alpha as compared with 2.8 +/- 0.3 days for control heifers. In both treatment groups, plasma concentrations of FSH were suppressed during the injection period and increased transiently after treatment, but plasma concentrations of LH during the injection period were not different from those of control heifers. Plasma levels of oestradiol in heifers given bFF remained basal for 2 or 3 days after treatment, then increased several days before the delayed oestrus, in a manner similar to that in control heifers, and elicited normal preovulatory surges of LH and FSH. Plasma concentrations of progesterone and the length of the next oestrous cycle were normal, indicating formation of functional corpora lutea. Therefore, bFF treatments appear to delay oestrus by selectively suppressing plasma FSH, without affecting LH, and delaying the development of the preovulatory follicle. These results suggest that FSH may be critical to support the growth and development of the preovulatory follicle after luteolysis in cows.     

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.     

Effects of GnRH on superovulated cattle

Gonadotropin releasing hormone (GnRH) was given to 109 cows and heifers during the course of 224 superovulations. Follicle stimulating hormone (FSH) was administered twice daily (5 or 6 mg) for 3.5 to 4 days beginning on any of Days 9 to 14 of the estrous cycle; prostaglandin (45 mg PGF(2)alpha or 750 ug cloprostenol) was given in a split dose on the fourth day. Donor cows and heifers were placed into four groups according to previous superovulation treatments, which consisted of one to three treatments or of no previous treatment. Every other cow or heifer within each of the four subgroups was treated with GnRH (200 mug i.m.) at standing estrus. Only donors that exhibited estrus within 32 to 72 h after the first prostaglandin treatment were used in the study. Animals were inseminated artificially 12 and 24 h after standing estrus was first observed. No differences were noted in the number of ovulations, total ova or transferable embryos recovered from the GnRH or control groups; however, two interactions were detected. Cows given GnRH had fewer palpable corpora lutea than control cows (P < 0.05), but this difference was not seen in heifers. The second interaction was that GnRH seemed to depress ovulation rate in donors not previously superovulated, but this effect was not observed with subsequent superovulations. Cows yielded more total ova than heifers (P < 0.01). There was no difference in return to estrus between GnRH and control groups after a second prostaglandin treatment at the time of embryo recovery. Most donors within each group resumed cycling between 5 and 12 d after embryo recovery.     

Influence of repeated low doses of gonadotrop in releasing hormone on postpartum interval and serum luteinizing hormone in Brahman cross cows

Two experiments were conducted to examine the effects of repeated low-dose injections of gonadotropin releasing hormone (GnRH) 30 to 40 d post partum on reproductive characteristics in multiparous suckled Brahman cross cows. In Experiment I, 39 cows were injected (i.v.) with GnRH (5 mug/injection) at 2-h intervals for either 0 (control), 6, 12, or 24 h at 30 to 37 d post partum. GnRH injections for short periods (6h) increased the number of cows exibiting estrus within 45 d of treatment, but cows injected for 24 h failed to exhibit estrus during this period. The period from treatment to first estrus was shorter in the 6-h GnRH group compared to the control group. Injections for 6h significantly (P < 0.05) increased in serum luteinizing hormone (LH) concentrations 1 d after GnRH treatment. In Experiment II we examined the effect of i.v. GnRH injections (5 mug/injection at 2-h intervals) for 6h in a larger group of cows (n = 70). The days from treatment to first estrus were reduced (P < 0.05) in GnRH-treated cows; however, first-service conception rates were significantly lower (P < 0.01) in treated compared to control cows (46.4 and 80.0%, respectively). The results led us to believe that GnRH injections for short periods reduce postpartum interval to first estrus, but fertility at first estrus is lowered.     

Synchronization of ovulation in dairy cows using PGF2alpha and GnRH

This paper reports a new method for synchronizing the time of ovulation in cattle using GnRH and PGF(2alpha). In Experiments 1 and 2, lactating dairy cows (n=20) ranging from 36 to 280 d postpartum and dairy heifers (n=24) 14 to 16 mo old were treated with an intramuscular injection of 100 mug GnRH at a random stage of the estrous cycle. Seven d later the cattle received PGF(2alpha) to regress corpora lutea (CL). Lactating cows and heifers received a second injection of 100 mug GnRH 48 and 24 h later, respectively. Lactating cows were artificially inseminated 24 h after the second GnRH injection. Ovarian morphology was monitored daily by trans-rectal ultrasonography from 5 d prior to treatment until ovulation. In Experiment 3, the flexibility in the timing of hormonal injections with this synchronization protocol was evaluated by randomly assigning 66 lactating dairy cows to 3 different treatment groups. Lactating cows received the injection of PGF(2alpha) 48 (Group 1), 24 (Group 2), and 0 h (Group 3) prior to the second injection of GnRH, which was administered at the same time in each group to ensure the second injection of GnRH was given when follicles were at a similar stage of growth. In Experiments 1 and 2, the first injection of GnRH caused ovulation and formation of a new or accessory CL in 18 20 cows and 13 24 heifers. In addition, this injection of GnRH initiated or was coincident with initiation of a new follicular wave in 20 20 lactating cows and 18 24 heifers. Corpora lutea regressed after PGF(2alpha) in 20 20 cows and in 18 24 heifers. All cows and 18 24 heifers ovulated a newly formed dominant follicle between 24 and 32 h after the second injection of GnRH. Ten of 20 cows conceived to the timed artificial insemination. In Experiment 3, the conception rate in Groups 1 and 2 were greater than in Group 3, (55 and 46 % vs 11%, respectively). In summary, this protocol could have a major impact on managing reproduction in lactating dairy cows, because it allows for AI to occur at a known time of ovulation and eliminates the need for detection of estrus.     

Single appointment insemination for heifers after prostaglandin or progestin synchronization of estrus

Pregnancy rates to a single appointment insemination were compared in seven groups of beef or dairy heifers following estrus synchronization with the prostaglandin F(2a) product, cloprostenol, versus the progestín product, Syncro-Mate-B. For cloprostenol synchronization, two injections of cloprostenol were given 11 d apart, with insemination occurring at 61+/-1 h after the second injection. The Syncro-Mate-B treatment consisted of a norgestomet/estradiol injection and a norgestomet implant on Day 0, followed by insemination at 49+/-1 h after implant removal on Day 9. Treatments were coordinated so all heifers in each group were housed together at the time of and for 48 h before a common insemination time so that the treatment received by individual heifers was not known. Overall pregnancy rates did not differ between treatment groups: 42% for 111 heifers treated with cloprostenol and 38% for 108 heifers treated with Syncro-Mate-B. Four blood samples per heifer taken during each replicate showed that two groups (n = 67) had many noncyclic heifers, while five groups (n = 152) had very few. Differences in pregnancy rates between these categories existed for both estrus synchronization methods, 18 versus 53% for cloprostenol and 21 versus 45% for Syncro-Mate-B. Thus the two methods were equally effective for cyclic heifers and equally ineffective for noncyclic heifers.     

Induction of parturition, progesterone secretion, and delivery of placenta in beef heifers given relaxin with cloprostenol or dexamethasone

Sixty primiparous beef heifers from a crossbreeding study were used to examine the effects of inducing parturition with relaxin (3,000 U/mg) combined with cloprostenol (500 micrograms, i.m., n = 30) or dexamethasone (20 mg, i.m., n = 30) at Day 273, 10 +/- 1 days before expected parturition (Day 283). Heifers were assigned at random within cloprostenol and dexamethasone groups to receive relaxin (1 mg, n = 5/treatment), i.m. or in the cervical os (OS), at 0 h (the same time as cloprostenol and dexamethasone) or 24 h later. Eleven and six first-calving heifers and sixteen and nine second-calving cows also received cloprostenol + relaxin and cloprostenol + phosphate-buffered saline, respectively. Radioimmunoassay of daily plasma samples indicated an abrupt decrease in progesterone with time (p less than 0.001), from 7.5 +/- 0.50 to 1.0 +/- 0.30 ng/ml (mean +/- SE) within 48 h for all groups. The mean rate of progesterone decrease (ng/ml in 24 h) was accelerated (p less than 0.01) in relaxin-treated heifers (5.3 +/- 0.36), in contrast to dexamethasone- and cloprostenol-treated control heifers (2.8 +/- 0.40). Relaxin combined with cloprostenol or dexamethasone shortened the calving period in these heifers by reducing the interval between treatment and calving (33 vs. 56 h; p less than 0.01). The incidence and duration of retained placenta were reduced by 22 vs. 75% and 14 vs. 34 h for relaxin combined with cloprostenol or dexamethasone as compared with cloprostenol- or dexamethasone-treated controls, respectively (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of estrus in cows by a new analogue of PGF2α(alfaprostol)

A new analogue of PGFα, alfaprostol, was used to induce estrus in normally cycling and anestrous cows.Five groups of six animals were treated with single injections of different doses of the drug (4, 5, 6, 7 or 8 mg/animal) on day 10–11 of the estrous cycle. Six cows in anestrus, with palpable corpora lutea, were treated i.m. with 8 mg/animal. The luteolytic properties of alfaprostol were assessed by measuring milk progesterone by RIA for 96 h after treatment and by checking for the subsequent signs of estrus. The dose of 4 mg caused a slight fall in progesterone but did not induce heat; the 5 and 6 mg doses induced estrus in animals and the 7 mg dose was effective in animals. The 8 mg dose produced a sharp reduction in milk progesterone within 24 h, followed by estrus in both the normally cycling and the anestrous groups in animals. No clinical signs of drug intolerance were seen. The present results show that alfaprostol might be of great use for both cycle synchronization in normally cycling cows and for treatment of anestrus caused by a persistent corpus luteum.     

Observations on the use of human chorionic gonadotrophin (HCG) during the post-insemination period on conception rates in synchronized beef cows with sub-optimum reproductive performances

Oestrus was synchronized in 46 Afrikaner and Mashona beef cows by two injections of cloprostenol 11 days apart. All cows had a history of sub-optimum reproductive performance. Cows were inseminated up to three times after the second cloprostenol injection on the basis of observed oestrus and changes in the conductivity of cervical mucus. Half the cows received daily injections of 1000 i.u. HcG from days four to 19 after their last insemination; the other half received daily injections of 2 ml saline over the same period. Concentrations of progesterone in plasma was determined from samples taken on days 6, 8 and 22 after the last insemination. Treatment did not significantly affect conception rate and overall conception rate was 39 per cent. On day 8 after insemination none of the 8 cows that had progesterone levels of less than 1 ng/ml were pregnant when examined at day 70. Mean progesterone concentrations were not significantly different between treated and control cows on days 6 and 8, but were significantly higher (P<0,05) in treated cows by day 22. The practical significance of using HcG to stimulate luteal function in the early post-inseminaion period is discussed.     

Synchronization of estrus and fertility in beef cattle with two injections of buserelin and prostaglandin

Postpartum beef cows and heifers in Group 1 received 8 mug of buserelin on Day 0 (the beginning of the experiment) and 500 mug of cloprostenol (PGF) on Day 6 (GnRH I, n = 54). In Group 2 (GnRH II, n = 54), the females were injected with buserelin on Day 0 (8 mug) and Day 3 (4 mug), and PGF on Day 6 and Day 9 for females not detected in estrus previously. Animals were bred by AI 12 hours after the onset of estrus. Blood samples were collected on Day -11 and Day 0 to assess cyclicity and on Day 3 and Days 6 to 12 to examine luteal activity. Progesterone levels did not differ between the 2 groups between Days 0 to 9. In both groups, the proportion of spontaneous estruses from Days 0 to 6 was reduced. Precision of estrus was higher (P < 0.005) in the GnRH II group than in the GnRH I group of cows that were detected in estrus between Days 6 and 9. The synchronization rate, interval to estrus, pregnancy and conception rates were similar in GnRH I and GnRH II groups. The conception rate and interval to estrus were similar in cyclic and acyclic cows. Increasing the number of buserelin injections enhanced the precision of estrus, but not the conception rate, without any detrimental effect on luteal activity and induced more estruses in postpartum acyclic beef cattle.     

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).     

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.     

Timing of the onset and duration of ovulation in superovulated beef heifers

Thirty-two beef heifers were induced to superovulate by the administration of follicle stimulating hormone-porcine (FSH-P). All heifers received 32 mg FSH-P (total dose) which was injected twice daily in decreasing amounts for 4 d commencing on Days 8 to 10 of the estrous cycle. Cloprostenol was administered at 60 and 72 h after the first injection of FSH-P. Heifers were observed for estrus every 6 h and were slaughtered at known times between 48 to 100 h after the first cloprostenol treatment. The populations of ovulated and nonovulated follicles in the ovaries were quantified immediately after slaughter. Blood samples were taken at 2-h intervals from six heifers from 24 h after cloprostenol treatment until slaughter and the plasma was assayed for luteinizing hormone (LH) concentrations. The interval from cloprostenol injection to the onset of estrus was 41.3 +/- 1.25 h (n = 20). The interval from cloprostenol injection to the preovulatory peak of LH was 43.3 +/- 1.69 h (n = 6). No ovulations were observed in animals slaughtered prior to 64.5 h after cloprostenol (n = 12). After 64.5 h, ovulation had commenced in all animals except in one animal slaughtered at 65.5 h. The ovulation rate varied from 4 to 50 ovulations. Approximately 80% of large follicles (> 10 mm diameter) had ovulated within 12 h of the onset of ovulation. Onset of ovulation was followed by a dramatic decrease in the number of large follicles (> 10 mm) and an increase in the number of small follicles (相似文献   

Effects of cloprostenol, human chorionic gonadotropin and estradiol benzoate treatment on estrus synchronization in dairy cows

Two consecutive experiments were conducted. In Experiment 1, 24 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received intramuscularly (i.m.) 500 mcg of cloprostenol, 1250 IU of human chorionic gonadotropin (hCG) and 5 mg of estradiol benzoate 12 h after cloprostenol treatment. Cows in Group II received 750 IU i.m. of hCG and 3 mg of estradiol benzoate 12 h after cloprostenol treatment. Treatment was given on Day 16 after estrus in both groups. All animals showed estrus within 24 to 48 h after cloprostenol treatment. The average interval from cloprostenol injection to the onset of estrus was not influenced by treatments. Four cows in Group I failed to ovulate and became cystic. In Experiment 2, 71 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received 500 mcg i.m. of cloprostenol after corpus luteum detection by palpation per rectum. Cows in Group II received 500 mcg of cloprostenol plus 750 IU of hCG and 3 mg of estradiol benzoate 12 h after. When estrus ready for service was confirmed by rectal examination, cows were inseminated. The percentage of cows ready for service tended to be lower (P < 0.06) between cows in Group I (88%) and those in Group II (100%). The average interval from cloprostenol treatment to service was longest (P < 0.001) in Group I (78.7 h +/- 14.9, X +/- SD) vs Group II (48 h +/- 2.9). The degree of readiness for service synchrony was lowest (P < 0.001) in Group I (59.3%) vs Group II (94.2%). The pregnancy rates of cows synchronized or treated were not altered by hCG-estradiol benzoate treatment (P > 0.25). These results suggest that in dairy cows treated with cloprostenol following palpation per rectum of a corpus luteum and then with 750 IU of hCG and 3 mg of estradiol benzoate 12 h later, a single fixed-time insemination at 48 h after cloprostenol treatment should be performed.