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PubMed2002

Synchronization of estrus in virgin beef heifers using melengestrol acetate and PGF2alpha: an efficacy comparison of cloprostenol and dinoprost tromethamine.

This study compared the efficacy of two sources of PGF2alpha on the reproductive performance of virgin beef heifers, after synchronization of estrus using melengestrol acetate (MGA) and PGF2alpha. Angus-based heifers (n = 1002) in five herds were fed 0.5 mg per head per day of MGA for 14 days. Nineteen days after the last day of MGA feeding, heifers were randomly assigned to receive (i.m.) either 0.5 mg cloprostenol (n = 504; Estrumate, E) or 25 mg dinoprost tromethamine (n = 498; Lutalyse, L) as a source of exogenous PGF2alpha. Heifers were observed twice daily for 5 days for signs of estrus and artificially inseminated 8-12 h later, except in herd A, wherein animals not detected in estrus by 80 h after PGF2alpha were mass-mated and no longer monitored for signs of estrus. Estrumate and Lutalyse were equally (P > 0.1) effective among all response variables evaluated, including estrus response (E, 89% and L, 86%), conception rate (E, 67% and L, 67%), and synchronized pregnancy rate (E, 61% and L, 57%). Synchrony of estrus was not affected (P > 0.1) by PGF2alpha source, and peak estrus response occurred 60 h post-PGF for both treatments. Conception rate to timed insemination was not different (P > 0.1) among Estrumate- and Lutalyse-treated heifers within herd A (14%, 4/28 and 7%, 2/29, respectively). Herd had a significant (P < 0.05) effect on all indicators of reproductive performance. Conception rates within herds A and D were influenced by technician (P < 0.05), however, this effect was balanced across treatments and no treatment by technician interaction was detected. In conclusion, when administered 19 days after a 14-day MGA feeding period, cloprostenol and dinoprost tromethamine are equally efficacious for synchronous induction of a fertile estrus in virgin beef heifers.

Animals↗
PubMed2004

Synchronization of estrus in postpartum beef cows and virgin heifers using combinations of melengestrol acetate, GnRH, and PGF2alpha.

The efficacy of various combinations of melengestrol acetate (MGA), GnRH, and PGF2alpha for the synchronization of estrus in Angus-based beef cattle was compared. Hormones were administered as follows: MGA, 0.5 mg x animal(-1) x d(-1) mixed in a grain carrier; GnRH, 100 microg i.m.; PGF2alpha, 25 mg i.m. In Exp. 1, 2, and 3, cows were randomly assigned to treatments by parity and interval postpartum. The detection of estrus and AI were conducted from d -2 until 72 to 96 h after PGF2alpha, at which time cows not detected to be in estrus received GnRH and fixed-time AI (TAI). Data were analyzed separately for primiparous and multiparous cows. In Exp. 1, cows (n = 799) at three locations received GnRH on d -7 and PGF2alpha on d 0 and either no further treatment (GnRH-PGF) or short-term MGA from d -6 through d -1 (STMGA). Among multiparous cows, conception rate at TAI was greater (P < 0.05) for STMGA (41%, 47/115) than for GnRH-PGF treated cows (26%, 24/92). Across herds and parity, synchronized AI pregnancy rate (SPR) was not affected (P > 0.10) by treatment (GnRH-PGF vs. STMGA; 54%, 210/389 vs. 57%, 228/402). In Exp. 2, cows (n = 484) at three locations received either STMGA or long-term MGA from d -32 through d -19, GnRH on d -7, and PGF2alpha on d 0 (LTMGA). Among primiparous cows, SPR was greater (P < 0.01) in LTMGA (65%, 55/85) than STMGA-treated cows (46%, 40/87). Treatment had no effect (P > 0.10) on SPR among multiparous cows (STMGA vs. LTMGA; 59%, 92/155 vs. 64%, 101/157). In Exp. 3, cows (n = 838) at four locations received the LTMGA treatment and either no further treatment or an additional period of MGA exposure from d -6 through d -1 (L&STMGA). Among primiparous cows, SPR tended to be influenced (P < 0.10) by the herd x treatment interaction and was greater (P < 0.01) among L&STMGA (86%, 19/22) than LTMGA-treated cows (56%, 14/25) at a single location. Among multiparous cows, SPR was lower (P < 0.05) in L&STMGA (46%, 165/358) than LTMGA-treated cows (55%, 184/336). In Exp. 4, Angus heifers (n = 155) received either STMGA or 14 d of MGA (d -32 through d -19) and PGF2alpha on d 0 (MGA-PGF). The detection of estrus and AI were conducted from d -2 to d 6. Interval to estrus was greater (P < 0.05) and estrous response was lower (P < 0.05) in STMGA than MGA-PGF-treated heifers. In conclusion, primiparous cows responded more favorably to longer-duration MGA treatments than did multiparous cows. All protocols achieved sufficient SPR to justify their use for improved reproductive management of postpartum beef cows.

Animals↗
PubMed1983

[Results of impregnating cows and heifers on consolidated farms and the methods for synchronizing their estrus].

Studied were the conception rate, milk productivity, calving period, and age at first conception with 3265 cows of 12 herds and 3 breed groups--Bulgarian Red Cattle (BRC), Holstein-Friesian Cattle (HFC), and HFC X BRC. The effect was followed up of the enzyme preparations Cytochrome 'C' and Beta-glucuronidase on the conception rate of cows. Tested was the action of prostaglandin F2 alpha and its analogues Equimate, Luteolysine, and Panazelen on the synchronization of the estrus and the conception. It was found that there was a considerable delay in the calving of the heifers (29 months). The calving period of the cows was prolonged and ranged in days from 369.17 +/- 3.17 up to 381.26 +/- 8.61 for BRC, 378.09 +/- 3.56 to 393.21 +/- 14.85--for HFC, and 339.75 +/- 6.56 to 390.42 +/- 3.51--for HFC X BRC. The use of Beta-glucuronidase and Cytochrome 'C' in the artificial insemination of the cows with deep-frozen semen raised the conception rate at first insemination by about 8-10 per cent.

Animals↗
PubMed1988

Effect of estrous cycle stage at Syncro-Mate B treatment on conception and time to estrus in cattle.

Two trials involving 85 heifers and 67 cows were conducted to determine the effect of estrous cycle stage at the time of Syncro-Mate-B((R)) (SMB) treatment on interval to estrus following implant removal and on conception rate at the synchronized estrus. In Trial 1, 57 beef and 28 dairy heifers were treated with SMB on each representative day of a 22-d estrous cycle (estrus = Day 0). Beef heifers were artificially inseminated approximately 48 h after implant removal, whereas dairy heifers were inseminated 0 to 12 h after detection of estrus. Inseminations were scored by the inseminator according to their difficulty. Interval to the onset of estrus was not different between heifers treated early (</= Day 11) in the estrous cycle (31.3 +/- 7.4 h) and heifers treated late (> Day 11) in the cycle (35.2 +/- 7.2 h). Conception rate at the synchronized estrus was slightly higher in early-cycle heifers (22 47 = 47% ) compared to late-cycle heifers (14 38 = 37% , P = 0.2). Heifers that were difficult to inseminate had lower (P < 0.01) conception rates (2 11 = 18% ) at the synchronized estrus than heifers considered normal (21 51 = 41% ) or easier than normal to inseminate (13 23 = 57% ). In Trial 2, of the 131 beef cows synchronized, 67 that were estimated to be either early or late in the estrous cycle by progesterone analysis were utilized. Cows were treated with SMB and inseminated without regard to estrus 48-h after implant removal. Inseminations were scored as in Trial 1. Calves were separated from cows from the time of implant removal to insemination. Conception rate was higher (P < 0.05) in cows treated with SMB early (</= Day 11) in the estrous cycle (20 32 = 62.5% ) compared to cows treated late (> Day 11, 16 35 = 46% ). Cows that were difficult to inseminate had a lower (P < 0.01) conception rate (0 8 = 0% ) than cows that were normal (43 94 = 46% ) or easier than normal to inseminate (13 29 = 45% ).

Journal Article↗
PubMed2005

Induction and synchronization of estrus in dogs.

Indications for estrus induction in the bitch include missed breeding opportunities or conception failure, the treatment of primary or secondary anestrus and synchronization of ovulation for embryo transfer programs. Reported methods for canine estrus induction include the use of synthetic estrogens (diethylstilbesterol), dopamine agonists (bromocryptine and cabergoline), GnRH agonists (lutrelin, buserelin, fertirelin, deslorelin, and leuprolide) and exogenous gonadotropins (luteinizing hormone, follicle stimulating hormone, human chorionic gonadotropin, pregnant mare serum gonadotropin, and human menopausal gonadotropin). These methods vary widely in efficacy of inducing estrus, as well as in the fertility of the induced estrus. The applicability of some of these methods for clinical practice is questionable. This review will summarize published reports on estrus induction and synchronization in bitches and summarize preliminary results using a long-acting injectable preparation of deslorelin.

Animals↗
PubMed1977

[Selection for fertility under gestagen synchronization of estrus in mice].

The results of selection of mice for the selection index, with the use of gestagenic synchronization of oestrus for 12 generations, allows to affirm that: The synchronization effect decreases with successive generations, which is connected with the existence of a negative correlation between the synchronizability and fertility. The selection effect in the control population was higher than that in experimental one, subjected to oestrus synchronization. It can be supposed that gestagen dimishes the correlation between the genotype and the phenotype, thus decreasing the selection efficiency in the experimental population. A similar tendency was found for the number of implantations and litter size at the age of 1, 10 and 21 days after birth.

Animals↗
PubMed1990

Pregnancy rate of dairy cows following synchronization of estrus with cloprostenol, hCG and estradiol benzoate.

After assessment of luteal function by the milk progesterone test, oestrus was synchronized in 78 lactating Friesian cows with a luteolytic dose of cloprostenol which was followed by injection of hCG and estradiol benzoate 12 hours later. The cows were inseminated 48 hours after the injection of cloprostenol. Thirty-eight of the 78 cows became pregnant (48.7 per cent), compared with 59 of the 115 cows (51.3 percent) which were inseminated at natural oestrus. These results suggest that in dairy cows synchronized with cloprostenol, hCG and estradiol benzoate fertility is not altered.

Animals↗
PubMed1992

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 microg 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 microg) and Day 3 (4 microg), 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.

Journal Article↗
PubMed1992

Evaluation of a melengestrol acetate and prostaglandin F(2)alpha system for the synchronization of estrus in beef heifers.

This study was conducted to determine the efficacy of feeding melengestrol acetate (MGA) for 14 days and administering prostaglandin F(2)alpha (PGF) 17 days after MGA to synchronize or induce estrus in yearling beef heifers. The study involved 56 Angus (n = 19), Hereford (n = 15) and Simmental (n = 22) heifers that were assigned by breed and pubertal status to either MGA+PGF or to control groups. Heifers in the synchronized group were fed 0.5 mg MGA per head per day for 14 days from a grain carrier and were injected with 25 mg, i.m. PGF 17 days after the last daily feeding of MGA. Control heifers were fed from a grain carrier without MGA and were not treated with PGF. Heifers were classified as pubertal when concentrations of progesterono in the serum exceeded 1 ng/ml in 1 of 2 samples collected prior to the initiation of treatments. Blood samples were collected 7 days before and on the day that treatment with MGA or carrier began and 7 days before and on the day that PGF was administered. Progesterone concentrations in the serum were elevated ( > 1 ng/ml) in 61% (17 28 ) of the MGA+PGF-treated heifers and in 61% (17 28 ) of the control heifers prior to feeding MGA. However, concentrations of progesterone in the serum at the time PGF was administered differed (P<0.05) between MGA+PGF and control groups. Concentrations of progesterone in the serum exceeded 1 ng/ml in 100% (28 28 ) of the MGA+PGF-treated heifers and in 71% (20 28 ) of control heifers at the time PGF was administered (P<0.05). All heifers were inseminated 12 hours after the first detected estrus. Twenty-two of 28 (79%) of the MGA+PGF-treated heifers exhibited estrus within 6 days after PGF compared with 9 of 28 (32%) of control heifers (P<0.05). The conception rate at first service did not differ between MGA+PGF and control groups (64% and 67%, respectively). Synchronized pregnancy rates were higher (P<0.05) for MGA+PGF-treated heifers than for control heifers (14 28 , 50% vs 6 28 , 21%). Increased concentrations of progesterone in serum at the time PGF was administered and higher pregnancy rates during the synchronized period among MGA+PGF-treated heifers demonstrate the efficacy of this treatment for use in estrus synchronization. Moreover, this treatment may have a potential effect on inducing puberty in breeding age heifers.

Journal Article↗
PubMed2007

Luteinizing hormone release after administration of the gonadotropin-releasing hormone agonist Fertilan (goserelin) for synchronization of ovulation in pigs.

The generic GnRH agonist, Fertilan (goserelin), was tested for the ability to induce an LH surge and ovulation in estrus-synchronized gilts. Three experiments were performed to 1) examine the effect of various doses of Fertilan on secretion of LH in barrows, to select doses to investigate in gilts (Exp. 1); 2) determine doses of Fertilan that would induce a preovulatory-like rise of LH in gilts (Exp. 2); and 3) determine the time of ovulation after Fertilan treatment (Exp. 3). In Exp. 1, 10 barrows were injected on d 1, 4, 7, 10, and 13 with 10, 20, or 40 microg of Fertilan; 50 microg of Gonavet (depherelin; GnRH control) or saline (negative control); and sequential blood samples were collected for 480 min. There was a dose-dependent stimulation (P < 0.05) of LH release. Maximal plasma concentrations of LH (LH(MAX)) were 2.1 +/- 0.2, 4.1 +/- 0.3, 2.6 +/- 0.4, and 3.4 +/- 0.3 ng/mL after 10, 20, and 40 microg of Fertilan and 50 microg of Gonavet, respectively, and duration of release was 78 +/- 9, 177 +/- 12, 138 +/- 7, and 180 +/- 11 min, respectively. Fertilan doses of 10 and 20 microg were deemed to be the most suitable for testing in gilts. In Exp. 2, 12 gilts received (after estrus synchronization with Regumate and eCG) injections of 10 or 20 microg of Fertilan or 50 microg of Gonavet 80 h after eCG to stimulate a preovulatory-like LH surge and ovulation. An LH surge was induced in 3 of the 4 gilts in both of the Fertilan groups and in all of the Gonavet-treated gilts. Characteristics of induced release of LH did not differ among groups: LH(MAX), 5.0 +/- 0.9 vs. 4.6 +/- 1.8 vs. 6.6 +/- 1.1 ng/mL; duration, 11.7 +/- 2.0 vs. 12.3 +/- 2.2 vs. 14.3 +/- 0.5 h; interval from GnRH injection to LH(MAX), 4.0 +/- 2.0 vs. 6.7 +/- 1.3 vs. 5.8 +/- 1.6 h. In Exp. 3, estrus-synchronized gilts were injected with 20 microg of Fertilan (n = 8) or 50 microg of Gonavet (n = 4), and the time of ovulation was determined by repeated endoscopic examination. Time of ovulation ranged from 34 to 42 h postGnRH; however, ovulation occurred earlier in the Gonavet compared with the other groups (P < 0.05). Results of these experiments indicate that 1) barrows are an appropriate model for determining GnRH doses that can be effective in inducing a preovulatory-like LH surge in females; 2) the generic GnRH agonist Fertilan, at doses of 10 to 20 microg, can stimulate an LH surge in gilts, with subsequent ovulation; and 3) Fertilan at doses of 10 and 20 microg should be examined further for use in fixed-time insemination protocols.

Animals↗
PubMed1994

Comparison of two MGA-PGF2alpha systems for synchronization of estrus in beef heifers.

Yearling beef heifers (n=193) were used to evaluate reproductive performance attained with 2 MGA-PGF2alpha synchronization systems. These treatments were compared with an untreated control group. The 14-d MGA heifers were synchronized by feeding 0.5 mg MGA/h/d for 14 d. At 17 d after the last MGA feeding, these heifers were injected with PGF2alpha (25 mg, im). Heifers in the 7-d MGA treatment group were fed 0.5 mg MGA/h/d for 7 d and received a 25-mg, im injection of PGF2alpha on the last day of the MGA feeding period. Heifers in all 3 treatment groups were observed for estrus every 12 h for 7 d beginning 24 h after the PGF2alpha injection. Heifers observed in estrus during this 7-d period were artificially inseminated approximately 12 h after the onset of estrus. The percentages of heifers in estrus during the 7-d synchronized period were 75.4, 56.3 and 17.2% for the 14-d MGA, 7-d MGA and control groups, respectively. The estrous responses were significantly different in each treatment. The percentage of heifers in estrus during the peak 24-h period was higher (P<0.05) in heifers synchronized with the 14-d MGA system than in heifers synchronized with the 7-d MGA system (75.5 vs 50.0%). The synchronized conception rate of the 14-d MGA heifers was significantly higher (65.3%) than that of both the 7-d MGA (41.7%) and control (45.4%) heifers. Synchronized conception rates were similar (P=0.79) in the 7-d MGA and control treatments. Synchronized pregnancy rates were 55.2, 32.4 and 15.2% for the 14-d MGA, 7-d MGA and control groups, respectively. Both synchronization treatments resulted in significantly higher synchronized pregnancy rates compared with that of the controls. The synchronized pregnancy rate was higher (P<0.05) in the 14-d MGA group than it was in the 7-d MGA group. The mean day of conception within the breeding season was 11.5 and 9.3 d shorter in the 14-d MGA heifers than in the 7-d MGA and control heifers, respectively. Our results indicate that using the 14-d MGA system to synchronize estrus in beef heifers results in better reproductive performance than that attained in heifers synchronized with the 7-d MGA system or in control heifers.

Journal Article↗
PubMed1994

Acute progesterone administration regresses persistent dominant follicles and improves fertility of cattle in which estrus was synchronized with melengestrol acetate.

Experiments were conducted to determine whether acute progesterone administration would regress persistent follicles and improve fertility in heifers and postpartum cows fed melengestrol acetate (MGA). In Exp. 1, heifers (n = 13) were fed MGA for 11 d (1st d of MGA = d 1). Prostaglandin F2 alpha (PGF2 alpha) was administered to heifers on d 2 to regress the corpus luteum (CL). On d 9, heifers were randomly assigned to receive an injection of either 200 mg of progesterone (PROG) or no hormone (vehicle; VEH). Neither growth of the persistent follicle nor plasma estradiol concentrations were altered by administration of VEH, and the persistent follicle ovulated after cessation of MGA feeding. Administration of PROG regressed the persistent follicle, reduced (P < .05) systemic estradiol concentrations, and resulted in ovulation of a newly recruited follicle. In Exp. 2, heifers were fed MGA for 14 d and were administered either PROG (n = 30) or VEH (n = 31) on d 12. When the CL was absent on d 12, synchronization conception rate (SCR) and pregnancy rate (PR) were greater (P < .05) for heifers administered PROG than for those administered VEH. Neither SCR nor PR were different among treatments when the CL was present on d 12. In Exp. 3, cows (n = 49) were fed MGA for 14 d and were administered either PROG or VEH on d 12. In cows lacking a CL (n = 32), administration of PROG increased (P < .05) SCR, but not PR. We conclude that acute PROG administration induces turnover of persistent follicles and may increase fertility when estrus is synchronized with MGA.

Animals↗
PubMed2002

Synchronization of estrus in beef heifers using either melengesterol acetate (MGA)/prostaglandin or MGA/Select Synch.

The objective of this study was to evaluate synchronization, conception, and pregnancy rates of yearling beef heifers synchronized with either the Select Synch protocol preceded by 7 days of MGA feeding (MGA/Select Synch) or the traditional MGA/PGF protocol. Heifers in the MGA/Select Synch group (n = 402) were fed MGA (0.5 mg/day/head) for 7 days, received an injection of GnRH (100 microg) the day following the last MGA feeding and an injection of PGF (25 mg) 7 days after GnRH. Heifers in the MGA/PGF group (n = 394) received MGA (0.5 mg/day/head) for 14 days, followed by an injection of PGF (25 mg) 17 days later. Synchronization rates tended (P = 0.08) to be higher for the MGA/Select Synch (82%) compared to the MGA/PGF (77%)-treated heifers. Conception and pregnancy rates to AI were similar (P > 0.10), 57 and 46% for the MGA/Select Synch heifers and 61 and 47% for the MGA/PGF heifers, respectively. Mean estrous response (h) was earlier (P < 0.05) for the MGA/Select Synch versus MGA/PGF treatment, 56 versus 61 h post-PGF treatment, respectively. In summary, short-term (7 days) MGA feeding preceding the Select Synch protocol produced similar synchronization, conception, and pregnancy rates as the traditional MGA/PGF protocol.

Animals↗
PubMed1989

Time of ovulation in the South Australian Merino ewe following synchronization of estrus. 2. Efficacy of GnRH treatment and its relevance to insemination programs utilizing frozen-thawed semen.

In a study of the time of ovulation following synchronization of estrus in the ewe, the effect of time of treatment with GnRH (24 vs 36 h after pessary removal) and dosage (6.25 to 100 ug per ewe) were examined. All treatments synchronized the time of ovulation irrespective of when untreated ewes commenced to ovulate. As part of an evaluation of GnRH treatment in artificial insemination programs, an assessment was made of the quality of eggs obtained from control ewes and ewes treated with GnRH at either 24 or 36 h after pessary removal. Treatment at 24 h increased the number of retarded embryos (P < 0.01) and unfertilized ova (P < 0.01) collected per ewe, reduced the number of embryos collected per ewe (P < 0.01), and reduced (P < 0.05) the percentage of pregnant ewes compared with other groups. However, there were no differences between control ewes and ewes treated with GnRH at 36 h. GnRH treatment at 36 h was consequently examined as a means of improving conception rates following the intrauterine insemination of frozen-thawed semen. Insemination of GnRH-treated ewes 8 to 12 h before the median time of ovulation resulted in a nonsignificant increase (range 5.7 to 7.3%) in the percentage of ewes of mature age which became pregnant. Insemination 0 to 4 h before the median time of ovulation resulted in a nonsignificant decrease in the percentage of pregnant ewes. GnRH treatment did not influence the number of fetuses per ewe. Reasons for the failure of this treatment to significantly improve ewe fertility are discussed.

Journal Article↗
PubMed1980

Fertility of goats following synchronization of estrus with prostagland in F2alpha.

Thirty-four mixed breed cyclic does were randomly divided into two groups of 17 each. One group was synchronized for estrus using two i.m. injections of 8 mg PGF2alpha administered 11 days apart. The other group served as controls and was bred at the time of naturally occurring estrus. Both groups were bred by natural service. Ninety-four percent of the treated does came into estrus within a mean (+/- S.E.) of 53 +/- 3 hours after the second injection of 8 mg PGF2alpha. No differences (P > 0.10) in the first service conception rates based on radiography at mid-gestation were observed between the treated and control groups. It was concluded that the use of 8 mg injections of PGF2alpha 11 days apart had no detrimental effects on fertility of goats.

Journal Article↗
PubMed1995

Excretion of MPA in the milk of lactating ewes treated for synchronization of estrus.

Ten mature lactating ewes of the Chios island breed 3.5 +/- 0.5 (Mean +/- SEM) yr of age and weighing 51.9 +/- 1.6 kg (Mean +/- SEM) were synchronized for estrus with intravaginal sponges impregnated with 60 mg 6a-methyl-17-acetoxyprogesterone (MPA). The sponges remained in place for 14 d and 500 IU im PMSG were injected at their withdrawal. Daily milk samples (3 d pretreatment, 14 d on treatment, and 5 d posttreatment) were collected and analyzed by a double antibody RIA procedure for MPA. The concentration of MPA (Mean +/- SEM) in the milk increased to 5.05 +/- 0.11 ng/ml within the first day of sponge insertion, then declined and remained at a constant level (3.08 +/- 0.26 ng/ml) while the sponge was in place, eventually dropping to the background level (0.65 +/- 0.05 ng/ml) 24 h following sponge withdrawal. The curve for the quantity of MPA excreted in the milk was identical to that of MPA concentrations, showing significant differences among experimental days and among ewes. Finally, there was a significant relationship between milk production and MPA excretion into the milk (r = +0.581( * *)). It is concluded that only a very small percentage (0.08 +/- 0.01) of MPA contained in each sponge is excreted into the milk from the moment of sponge insertion until 5 d after its removal.

Journal Article↗
PubMed2006

Influence of reproductive stage at PRID insertion on synchronization of estrus and ovulation in mares.

In the present study, we investigated the effects of reproductive status, size of follicles and plasma progesterone concentrations of mares at PRID insertion on the efficacy of the treatment, estrous cycle patterns, plasma concentrations of progesterone and LH. The progesterone-releasing device (PRID) was administered intravaginally to 28 Haflinger mares for 11 days at different reproductive stages: anestrus (n=6), estrus (n=11) and diestrus (n=11). Plasma concentrations of progesterone at insertion (Day 1) of PRID differed among treatment groups (anestrus: 0.2-0.6 ng mL(-1), estrus: 0.2-0.5 and diestrus: 1.6-10.8 ng mL(-1); P<0.001). Total secretion of progesterone (area under curve (AUC)) during treatment period revealed highest values in diestrus (38.2+/-3.1 ng mL(-1)h(-1)) followed by estrus (25.1+/-2.7) and anestrus (21.0+/-0.4 ng mL(-1)h(-1); P<0.05). Progesterone area under curve (AUC) was positively correlated with initial progesterone concentrations (R=0.5; P<0.05), but it did not correlate with the interval from PRID removal to ovulation. Plasma concentrations of LH during treatment period, were significantly lower in anestrous mares (184.6+/-28.6 ng mL(-1)h(-1)) when compared to estrous and diestrous mares (349.7+/-53.3 and 370.5+/-40.3 ng mL(-1)h(-1); P<0.05). Follicular size at PRID insertion had no effects on the intervals from PRID removal to subsequent estrus and ovulation. Follicle diameters at removal of PRID were significantly correlated with the interval from coil removal to estrus (R=-0.55, P<0.05) and ovulation (R=-0.72, P<0.0004) in cyclic mares. In anestrus 0 of 6 (0%) mares, in estrus 5 of 11 (45.5%) and in diestrus 6 of 11 (54.5%) mares ovulated within a defined interval of 1 day before to 1 day after mean interval from PRID removal to ovulation. In cyclic mares, response to treatment was significantly higher when compared to anestrous mares: almost all mares responded with estrus and ovulation independent from the stage of the estrous cycle at the start of treatment. However, accuracy of synchronization was still unsatisfactory. In cyclic mares, the plasma progesterone concentrations at insertion of PRID seem to be more important for the efficacy of the treatment than the assignment to estrous cycle stages.

Administration, Intravaginal↗
PubMed2001

Reproductive responses to grazing endophyte-infected tall fescue by postpartum beef cows.

The objective was to determine pregnancy rate and stage of embryonic loss in response to grazing endophyte-free (E-; n = 20) or infected (E+; n = 30) tall fescue in postpartum beef cows with calves. Three weeks before estrus synchronization, cow-calf pairs were introduced to pastures (April 1999). Cows were synchronized and bred by AI after detected estrus for a period of 6 d and then by natural service for 62 d. Bulls were rotated weekly to minimize effects of fescue toxicosis on male fertility. Fetal development was monitored weekly between 30 and 60 d of pregnancy and at weaning using transrectal ultrasound. Respiration rate (52.0 +/- 1.4 vs 46.6 breaths/min; P < 0.02) and rectal temperature (39.6 +/- .09 vs 38.8 +/- .12 degrees C; P < 0.001) increased in E+ cows and serum concentrations of prolactin (7.2 vs 57.4 +/- 4.4 ng/mL; P < 0.001), total cholesterol (123.2 vs 149.6 +/- 3.6 mg/dL; P < 0.001), body condition (3.8 vs 5.2 +/- 0.15; P < 0.001; 1 = thin, 9 = fat) and adjusted weaning weight of calves (195.8 vs 210.8 +/- 4.5 kg; P < 0.02) were reduced compared to that of E- cows. Differences were not detected (E- vs E+) for estrus detection rate (84.9 +/- 10.6% vs 80.2 +/- 8.4%), pregnancy rate to synchronized estrus (41.7 +/- 11.8% vs 46.8 +/- 9.5%), overall pregnancy rate 30 d postbreeding (93.8 +/- 6.2% vs 93.5 +/- 5.1%), overall pregnancy rate at 60 d postbreeding (86.7 +/- 10.1% vs 81.2 +/- 8.3%), or serum concentrations of progesterone on day of PGF2alpha treatment (4.5 +/- 0.7 vs 4.5 +/- 0.8 ng/mL). Pregnancy losses that occurred between 30 and 60 d gestation were 6.0 (E-) vs 15.0 (E+) +/- 8.0% (P > 0.10) and occurred after environmental temperatures rose above 37.8 degrees C for three weeks. Total pregnancy losses that occurred by weaning (between 70 and 126 d of gestation) were 5.5 (E-) vs 17.6 (E+) +/- 8.0% (P > 0.10). Pregnancy rate and embryonic losses were not different between cows grazing E- and E+ tall fescue under these management conditions.

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