Megestrol acetate for estrus postponement in the bitch.

Megestrol acetate was given orally to 389 bitches in early proestrus, at a dosage of 2.2 mg/kg (1 mg/lb) per day for 8 days. Estrus was suppressed in 357 (92%) of the bitches. Additionally, 119 bitches in anestrus were given the drug at the rate of 0.55 mg/kg (0.25 mg/lb) per day for 32 days. Estrus was suppressed in 115 (98%) of these bitches. Adverse effects were minimal. Pyometra developed in 3 (0.8%) of the 389 bitches treated in early proestrus. The drug also was given to 19 bitches at the rate of 0.55 mg/kg/day for 32 days, regardless of the stage ofting at the 1st posttreatment estrus and 4 after mating at the 2nd posttreatment estrus. Litter size, success in rearing pups, and sex ratios were not significantly different from these factors in 53 litters from untreated bitches.     

Changes in luteinizing hormone pulse frequency and prolactin levels in bitches in response to estrus induction by cabergoline-its cases where it is delayed to induce estrus

The effect of estrus induction by cabergoline on gonadotropin and steroid hormone responses was examined in anestrous bitches. Eleven beagles were used in the study; seven were included in the estrus induction group and four were included in the spontaneous estrus group. Cabergoline was orally administered to the estrus induction group at 5 µg/kg once daily for four weeks, or until hemorrhagic discharge was detected. The inter-estrus interval in the estrus induction group was significantly shorter than the previous estrus interval. Bitches that showed proestrus within four weeks of treatment showed increased luteinizing hormone (LH) pulse frequency and, subsequently, increased estradiol (E₂) levels. Prolactin (PRL) levels declined promptly after treatment, except in one bitch that did not show proestrus during the cabergoline treatment period. There was a significant correlation between the time to proestrus induction and the reduction in PRL levels. A positive correlation was found between the LH levels two weeks after cabergoline administration and PRL reduction. This study demonstrates that an abrupt reduction in PRL is likely to be important for initiation of estrus in bitches. A reduction in PRL indirectly leads to an increase in LH pulse frequency, which regulates follicular development in bitches. However, if the period from the end of the previous estrus to the cabergoline treatment is short, it may take some time to show proestrus without increasing E₂ levels, even if the LH level increases after cabergoline administration.     

Efficacy and toxicity of tamoxifen citrate for prevention and termination of pregnancy in bitches

Five groups of bitches were given tamoxifen citrate (1 mg/kg of body weight) orally twice daily for 10 days. Drug administration commenced during late proestrus, day 4 of estrus, day 2 of diestrus, day 15 of diestrus, or day 30 of diestrus (n = 4/group). Nineteen of the bitches accepted natural mating by 1 or more of 3 stud dogs of known fertility (1 bitch did not). Twenty days after cessation of drug administration, ovarian, uterine, and hepatic specimens were obtained from each bitch in 4 of the groups. Pregnancy proceeded to natural termination in bitches of the remaining group (diestrous day 30). Pregnancy was not detected in any bitch of the proestrus, estrous, or early diestrous groups. Of 4 bitches of each of the remaining groups (diestrous day 15 and diestrous day 30), 2 aborted fetuses and/or resorbed placental remnants; the other 2 bitches in each of these groups had normal-appearing fetuses (diestrous day-15 group) or clinically normal pups (diestrous day-30 group). Of the 20 bitches given tamoxifen citrate, 5 developed endometritis with or without pyometra, and 4 of these had ovarian cysts. Although tamoxifen citrate is effective for preventing or terminating pregnancy in the bitch, the regimen used in the study reported here was associated with high frequency of pathologic changes in the reproductive tract.     

Induction of estrus and ovulation in the bitch, using exogenous gonadotropins

The capability of pregnant mare serum (PMS) and human chorionic gonadotropin (HCG) to induce estrus and ovulation was tested in mature, anestrous bitches. The PMS was given for 10 consecutive days in 1 of 3 regimens: 500 IU/day (experiment 1), 250 IU/day (experiment 2), or 20 IU/kg/day (experiment 3). The HCG was given as a single 500-IU dose on experimental day 10. Controls were given saline solution. Vaginal smears were collected on days 1, 3, 5, 7, 9, and 12 by jugular venipuncture, and the plasma was assayed for progesterone concentration by radioimmunoassay. On day 13, the bitches were euthanatized, ova were flushed from the uterine tubes (oviducts), and the ovaries were collected and prepared for microscopic examination. Fourteen of 25 bitches treated with PMS and HCG showed estrus and ovulated. Proestrus (vaginal bleeding) commenced between experimental days 7 and 10. Estrus commenced on day 9 or 10. Progesterone increased from approximately 1 ng/ml on day 1 to more than 6 ng/ml on day 12. Numbers of ovulation sites on both ovaries were 4.7 +/- 1.1 and 4.6 +/- 0.5 (mean +/- SEM) in those given the daily doses of 500 and 250 IU of PMS and 9.8 +/- 1.5 in experiment 3 bitches. Eleven hormone-treated dogs and 7 saline-treated dogs did not show any detectable response. Neither cystic nor unovulated, luteinized follicles appeared on the ovaries.     

Uterine motility during the estrous cycle: studies in healthy bitches

Natural and drug-induced uterine motilities (UM) were recorded via uterine-implanted catheter-tip pressure transducers in 5 bitches during proestrus and estrus and in 6 bitches during early (30 days) and late (60 days) diestrus. The UM was monitored in unanesthetized bitches for 2 days after the estrous-cycle stage had been determined by vaginal cytologic findings. Natural UM, expressed as Alexandria units (pressure X frequency X duration of contractions), was greatest during estrus, moderate during proestrus, and appreciably decreased or lacking during early and late diestrus. During proestrus and estrus, prostaglandin F2 alpha (5 micrograms/kg of body weight, IV) induced intrauterine pressures of 107 and 115 mm of Hg, respectively, and oxytocin (0.05 USP units/kg, IV) induced pressures of 106 and 116 mm of Hg, respectively. In contrast, the intrauterine pressure values induced by prostaglandin F2 alpha given IV during early and late diestrus were 61 and 58 mm of Hg, respectively, and for oxytocin, were 61 and 51 mm of Hg, respectively. Prostaglandin F2 alpha given IM (50 micrograms/kg) also induced a greater intrauterine pressure during proestrus and estrus than during diestrus. We concluded that in the bitch, natural and drug-induced UM are decreased during early and late diestrus.     

Use of pulsatile intravenous administration of gonadotropin-releasing hormone to induce fertile estrus in bitches

The pulsatile IV administration of gonadotropin-releasing hormone (GnRH) was evaluated as a method to induce fertile estrus in 8 anestrous Beagle bitches. Bitches received 1.25 micrograms of GnRH every 90 minutes for 11 to 13 days. Gonadotropin-releasing hormone was delivered by use of an automatic pump. Reproductive history was known for all bitches, 4 of which, on the basis of 3 or 4 preceding cycles, had an interestrous interval of 219 +/- 14 days (mean +/- SEM). Estrus induction was attempted during early anestrus in 6 bitches (ie, 148 +/- 10 days since the preceding estrus) and late anestrus in 1 bitch (ie, 260 days since the preceding estrus); another bitch had not had an estrous cycle for nearly 2 years before GnRH administration. Signs of estrus were seen within 16 days after the start of GnRH administration in the bitches with regular estrous cycles (group 1, n = 7), and within 23 days in the bitch (group 2) with prolonged anestrus. All bitches were bred, and 7 of 8 (87.5%) became pregnant, with a mean litter size of 4.5 +/- 0.75. A normal hormonal response pattern was observed in group-1 bitches--a peak increase in plasma estrogen concentration of 22.3 +/- 2 pg/ml immediately before the onset of estrus. Peak plasma progesterone concentration (17.3 +/- 3 ng/ml) was observed 1 to 14 days after the onset of diestrus in the group-1 bitches that ovulated, and adequate plasma progesterone concentration was maintained throughout gestation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Concentration of receptors for estradiol and progesterone in canine endometrium during estrus and diestrus

Receptors for estrogen and progesterone were measured in cytosols prepared from specimens of canine endometrium obtained at late proestrus, day 4 of estrus, day 2 of diestrus, and at 10 day intervals from days 10 through 80 of diestrus. Twenty nine adult bitches were used, with 2 to 4 dogs used at each time point. Concentrations of estradiol receptors measured in endometrial cytosols from late proestrus through day 10 of diestrus were similar (mean +/- SEM: 9.9 +/- 2.2, 10.5 +/- 1.2, 16.3 +/- 1.6, and 16.2 +/- 2.9 pmol/g of tissue at proestrus, day 4 of estrus, days 2 and 10 of diestrus, respectively). As serum concentrations of progesterone increased during early diestrus, the concentration of estradiol receptors decreased and were significantly (P less than 0.05) lower on days 30 (4.9 +/- 1.3 pmol/g of tissue) and 40 (3.7 +/- 0.6 pmol/g of tissue) of diestrus. After day 40 of diestrus, when serum concentrations of progesterone were approaching basal concentrations, the concentration of estradiol receptors increased and remained significantly (P less than 0.05) higher from days 60 to 80 of diestrus (day 60, 13.4 +/- 2.9; day 70, 15.7 +/- 1.7; day 80, 19.8 +/- 2.4 pmol/g of tissue). As observed for estrogen receptors, the concentration of endometrial receptors for progesterone also gradually increased from late proestrus (4.9 +/- 1.3 pmol/g of tissue) to day 2 of diestrus (6.4 +/- 0.3 pmol/g of tissue).(ABSTRACT TRUNCATED AT 250 WORDS)     

Concentrations of testosterone in canine serum during late anestrus, proestrus, estrus, and early diestrus

Serum testosterone concentrations in samples collected daily from 6 bitches for at least 60 days before the onset of diestrus were determined by radioimmunoassay. Mean serum concentrations (+/- SEM) of testosterone ranged from 31 +/- 11 to 141 +/- 63 pg/ml during late anestrus. Mean testosterone concentrations during proestrus ranged from 106 +/- 29 to 239 +/- 113 pg/ml, with the highest concentration (526 +/- 225 pg/ml) occurring the day of the preovulatory surge of luteinizing hormone. Although the ovaries may be sites of production during late anestrus, proestrus, estrus, and early diestrus, further investigation is necessary to determine whether testosterone has an important physiologic or endocrinologic function in the bitch (ie, sexual behavior, vaginal hypertrophy, and luteinizing hormone surge).     

乏情母犬用溴隐亭处理后的发情表现与血清中孕酮和雌二醇水平变化

选择 3只年龄为 3岁处于乏情期的苏北红犬和 6只 1～ 2岁未发情的罗威纳犬 ,用溴隐亭处理后有 4只母犬发情 ,1只母犬受孕而后流产。分析犬血清中雌二醇和孕酮水平 ,发情受孕犬雌二醇和孕酮分泌呈现规律性变化趋势 ;发情未受孕犬在雌二醇分泌峰出现后孕酮分泌不稳定 ;而未发情犬雌二醇和孕酮没有变化。结果表明 ,溴隐亭能够有效地缩短母犬的乏情期 ,溴隐亭处理后不同生理状态母犬反应差异较大 ,发过情的母犬作用明显 ,对从未发过情的母犬效果较差     

Efficacy and toxicity of estrogens commonly used to terminate canine pregnancy

Three groups of bitches were treated with diethylstilbestrol (75 micrograms/kg) orally for 7 days (n = 12), estradiol cypionate intramuscularly once (22 micrograms/kg; n = 12), or estradiol cypionate intramuscularly once (44 micrograms/kg; n = 12). Treatments commenced during late proestrus (n = 4/group), the fourth day of behavioral estrus (n = 4/group), or the second day of diestrus (n = 4/group). All bitches were bred on alternate days throughout estrus to stud dogs of known fertility. Ovariohysterectomies were performed on day 25 of diestrus to diagnose pregnancy and to assess any pathologic changes in the uterus. Eleven bitches treated with diethylstilbestrol, 6 bitches treated with the low dosage of estradiol cypionate, and 4 bitches receiving the high dosage of estradiol cypionate were pregnant at the time of surgery. Ten of the bitches treated with estrogens during proestrus, 6 treated during estrus, and 4 treated during diestrus were pregnant. The serum concentration of progesterone in 2 bitches treated with the high dosage of estradiol cypionate decreased to less than 2 ng/ml by day 25 of diestrus, suggesting premature luteal regression. Diethylstilbestrol appeared to have little efficacy in terminating pregnancy. Estradiol cypionate appeared to have greater efficacy when administered during estrus or early diestrus; however, pyometra developed in 2 bitches treated with this estrogen during diestrus.     

Shortening of interestrous intervals with cabergoline in bitches: a clinical trial

Two consecutive interestrous intervals (n=46) were recorded in 23 bitches of different breeds. At varying times after day 100 from the onset of the second proestrus, cabergoline (5 microg/kg per os q 24 hours) was administered from early (n=11), mid- (n=10), and late (n=2) anestrus until 2 days after the beginning of the following proestrus. Interestrous intervals (IEI) were significantly shorter in the cabergoline-treated time periods when compared to the nontreated IEI (184+/-4.5 days versus 239+/-4.5 days; P<0.01). The mean number of days of cabergoline treatment until the onset of proestrus was 21.4+/-2.9 (least square means and standard error of the mean [LSM+/-SEM]). Mean cabergoline treatment durations beginning in early, mid-, and late anestrus were 27.4+/-3.7, 17.6+/-3.8, and 5+/-3 days (LSM+/-SEM), respectively. A significant correlation was found between the stage of anestrus in which the treatments began and the duration of the treatments required to induce estrus (0.51, P=0.01).     

产后无发情和亚发情母牦牛激素诱导发情试验

选择怀孕母牦牛84头,在生产前后1个月进行补饲,其中40头在产后当年发情季节进行激素诱导发情试验,44头作对照;另选择60头自然生产的产后母牦牛在发情季节进行单纯的激素诱导发情试验,60头作对照.激素诱导发情方法是0 d注射氯前列烯醇0.2 mg,7 d后注射促黄体素释放激素A3 25 μg,连续3 d;在0和7 d进行直肠检查和血样采取,血样进行孕酮测定;测定处理时母牦牛卵巢状态,观察母牦牛发情配种受孕情况.结果显示,通过直肠检查和血浆孕酮测定,发现无发情状态的产后母牦牛占产后牦牛的63.33%和65%,亚发情的产后母牦牛占产后牦牛的36.67%和35%.采用氯前列烯醇和促性腺激素释放激素处理方案进行诱导发情,26.67%的产后母牦牛在处理后出现了发情;对怀孕母牦牛在围产期进行补饲,产后母牦牛在发情季节采用氯前列烯醇和促性腺激素释放激素诱导发情,有45.45%的产后母牦牛恢复了发情,而只补饲不进行激素诱导发情的母牦牛只有20%的母牦牛出现了发情;通过孕酮测定发现2组中激素诱导发情成功的母牦牛中,有68.18%和72%是处于亚发情状态的母牦牛.结果表明,氯前列烯醇和促性腺激素释放激素进行诱导发情的处理方案适合于产后亚发情状态的母牦牛.     

Comparison of estrus induction and subsequent fertility with two different intravaginal devices in ewes during the non-breeding season

Two experiments were conducted to compare the effect of estrus induction by controlled internal drug release (CIDR) and intravaginal cream containing 500 mg progesterone (P cream) in ewes during the non-breeding season. In the first experiment, twenty-four ewes were randomly grouped for two treatments with the different intravaginal devices for 12 days: Group A was the CIDR group and Group B was the P cream group. Blood was collected from all treated ewes, and progesterone (P(4)), estradiol 17-beta (E(2)) and luteinizing hormone (LH) concentrations were measured by enzyme immunoassay. In the second experiment, the conception rates from natural mating, estrus-detected AI (inseminated 12 h after estrus detection), or fixed-time AI (inseminated 42 h after removal of an intravaginal device) in 127 ewes treated with CIDR or P cream were compared. In Experiment 1, the rate of estrus induction and the time of estrus onset after device removal were 91.7% and 36.3 +/- 15.7 h in Group A, and 100% and 35.0 +/- 12.6 h in Group B, respectively. There were no significant differences between the devices. The mean plasma P(4) concentration in Group B was significantly (P < 0.01) lower than Group A between day -9 and day -1 (Day 0: the day of device removal). However, no significant differences were found in the mean E(2) concentrations of the two groups after treatment. The mean time of estrus onset in ewes with an observed LH surge and the time of LH surge after treatment were 23.3 +/- 8.7 h and 30.3 +/- 5.0 h for Group A and 27.6 +/- 6.5 and 26.3 +/- 8.0 h for Group B, respectively, and there were no significant differences. However, a significant difference (P < 0.05) was found in the mean time from the time of estrus onset to LH surge between Group A (6.4 +/- 6.7 h) and Group B (-1.3 +/- 4.1 h). In Experiment 2, the conception rates for natural mating, estrus-detected AI, and fixed-time AI were 55.0, 29.4, and 25.0% for Group A and 40.7, 25.0, and 42.1% for Group B, respectively, and there were no significant differences. These results suggest that the effect of induction of estrus and ovulation and the rate of conception after treatment were comparable to CIDR even though the plasma P(4) concentration of the P cream method tended to be low during the insertion period.     

Recovery and light microscopic evaluation of follicular oocytes of swine and relationship between the degeneration rate of oocytes and the estrus phase

Cumulus-oocyte complexes were recovered from 25 gilts by aspiration of follicular fluid or cutting of follicles from all Graafian follicles of greater than or equal to 3 mm in diameter during diestrus, proestrus or estrus. In 5 gilts the oocytes were collected post ovulation by flushing of oviducts. The recovery rate of follicular oocytes differed between 75.5% during the late diestrus (days 13-17) and 43.5% during the proestrus (days 18-21). During the proestrus and on day 1 of the estrus the recovery of oocytes was more difficult as a result of the higher viscosity of follicular fluid and the mucification of cumulus-oocyte complexes. The degeneration rate of oocytes was high during the diestrus with a peak at the time of regression of corpora lutea. From diestrus to the estrus the degeneration rate decreased. Following degeneration rates were found in the oocytes during the cycle: days 7-12: 38.8%, days 13-17: 50.0%, days 18-21: 29.6%, day 1 of the estrus: 10.8%, day 2 of the estrus ante ovulation: 11.8%, day 2 of the estrus post ovulation: 6.2%. Signs of degeneration were: Loss of cumulus cells (during diestrus and proestrus), damaged zona pellucida, enlargement of perivitelline space, deformation of oocyte, alteration of structure of the ooplasm, diameter of vitellus less than 100 microns. It was concluded that the selection of dominant follicles takes place in pigs during a long time of the cycle, especially during the diestrus. There were not any indications of a 2-wave hypothesis of follicular growth during the cycle in pig.     

Parenteral use of medroxyprogesterone acetate as an antifertility agent in the bitch

10 kg unbred Beagle and mongrel bitches were used in each of 4 experiments (exp). 6 alpha-methyl-17 alpha-acetoxyprogesterone (MAP or medroxyprogesterone acetate) was prepared as a sterile aqueous suspension (50 mg/ml) and was used in exps 1, 2 and 3. Tritiated MAP was used in exp 4. In exp 1, 7 bitches were given 500 mg and 7 were given 50 mg subcutaneously (sc). 6 controls were used. In exp 2, 50, 100 or 250 mg were given sc, intramuscular (im) or intraperitoneal (ip) to 4 dogs at each dose level and route of administration. In exp 3, 12.5 or 25 mg was given either sc or im in 4 groups of 8 bitches each. In exp 4, a single 50 mg mixture of MAP and tritiated MAP was given to each of 3 dogs: 1 sc, 1 im, and 1 ip. Results of exp 1 showed those on 500 mg had first posttreatment estrus an average of 504 days (range of 247-730) after injection. Those on 50 mg averaged 329 days (range of 205-429). Breeding resulted in 6 live pups/litter for the controls 5.2 for those on 50 mg, and 4 for those on 500 mg. In exp 2, results showed prolonged cycling in those injected sc (295 days to estrus), while those injected im reached estrous in 225 days and those injected ip in 148 days. In exp 3, 3 on 25 mg sc had a 6 month estrous delay while 4 did when injected im. 3 of 16 given 12.5 mg sc and im had a 6 month delay in cycling. Exp 4 showed ip treated dogs had estrus 148 days after treatment, 225 days for im, and 295 days for sc. Ip treated dogs whelped 5 pups; im 7 pups; and sc, 5 pups. 7 months lapsed before nearly all of the 50 mg sc administered dose was excreted. An additional 2.5 months lapsed before estrus occurred in this dog.     

Temporal sequence of events in the estrous cycle of the bitch.

Serum concentrations of luteinizing hormone (LH), estradiol-17 beta, and progesteron were compared with the onset of diestrus in Beagle bitches. The LH peak occurred 8.0 (standard error (SE), 0.3) days before the onset of diestrus. Vaginal cytologic characteristics during proestrus were studied, and vaginal cornification was complete 12.1 (SE,0.2) days before the onset of diestrus. A time sequence of hormonal, vaginal cytologic, and developmental events was outlined during proestrus, estrus, and early diestrus.     

Synchronization of estrus in dairy goats given norgestomet and estradiol valerate at various stages of the estrous cycle.

Dairy goats were given subcutaneous implants with 3 mg of norgestomet (NOR) and IM injections of 0.625 mg of estradiol valerate and 0.375 mg of norgestomet on day 0 of the estrous cycle (estrus; NOR 0, n = 18), on postestrus day 4 (NOR 4, n = 18), or on postestrus day 11 (NOR 11, n = 15). Ear implants were removed after 9 days. Mean (+/- SE) hours from removal of ear implants to onset of estrus and proportion of goats responding were 36 +/- 3.8 and 83%, 33 +/- 4.0 and 61%, and 36 +/- 2.7 and 93% for groups NOR 0, NOR 4, and NOR 11, respectively. There were no significant differences between treatment groups in time to onset of estrus. The percentage of goats in group NOR 11 that had signs of estrus was significantly greater than the percentage of goats in group NOR 4. Of the goats in groups NOR 0, NOR 4, and NOR 11 that had signs of estrus, 53, 55, and 86%, respectively, had onset of behavioral estrus between 24 and 48 hours after implant removal. All goats that had signs of estrus had onset of behavioral estrus between 12 and 72 hours after implant removal. Mean (+/- SE) hours from removal of ear implants to time of peak concentrations of luteinizing hormone (LH) were 49 +/- 4.1, 49 +/- 3.8, and 49 +/- 4.0 for groups NOR 0, NOR 4, NOR 11, respectively (not different). The percentage of goats in group NOR 11 that had LH peaks was significantly greater than the percentage of goats in group NOR 4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Response of gilts with delayed puberty to pregnant mare serum gonadotropin or estrogen

The effect of pregnant mare serum gonadotropin (PMSG) or estradiol cyclopentylpropionate (EC) on the induction of estrus, duration of estrus, and serum progesterone concentration after estrus was evaluated in 8 gilts with delayed puberty. Four gilts were given 500 IU of PMSG IM and 4 were given 2 mg of EC, IM. The inactive status of the ovaries at the time of treatment was verified by serum progesterone values of less than 0.5 ng/ml in serial samples collected before treatment. The 4 EC-treated gilts came into estrus at a mean of 3.5 days after treatment, but 1 of the gilts did not form corpora lutea. Three PMSG-treated gilts came into estrus at a mean of 4.0 days after treatment. The remaining PMSG-treated gilt remained anestrus and did not form corpora lutea. The mean duration of estrus in EC-treated gilts was 5.25 days compared with 2.0 days for PMSG-treated gilts (P less than 0.05). Serum progesterone concentrations were higher in PMSG-treated gilts than in EC-treated gilts at 8, 11, and 17 days after treatment (P less than 0.05).     

Resynchronization of estrus in beef cattle: ovarian function, estrus and fertility following progestin treatment and treatments to synchronize ovarian follicular development and estrus

The objective was to optimize rebreeding of nonpregnant, previously inseminated beef cattle. In Experiment 1, 43 cows received a used intravaginal progesterone-releasing insert (IVPRI; Days 0-7) 12.3 d after ovulation and received concurrently no treatment, 100 microg gonadotropin releasing hormone (GnRH), 1 mg estradiol cypionate (ECP), or 150 mg progesterone. Emergence of a new ovarian follicular wave was most synchronous (P < 0.0001) in the GnRH group. In Experiment 2, 675 heifers were given GnRH or no treatment on Day 0, fed melengestrol acetate (MGA; 0.5 mg/head/d) from Days 0-5 (Day 0 = 13-14 d after timed insemination; TAI), given 0.5 mg ECP or nothing on Day 7, and reinseminated 6-12 h after onset of estrus. Estrus was more synchronous (P < 0.05) in heifers given GnRH versus no treatment on Day 0. In Experiment 3, 317 TAI heifers were resynchronized with either MGA or a used IVPRI with or without ECP on Day 7; estrus was more synchronous (P < 0.05) and pregnancy rates were higher (54.1% versus 39.2%, P < 0.05) in heifers given a used IVPRI than those fed MGA. For resynchronization of heifers, pregnancy rates were not significantly improved with GnRH treatment, but were higher with a used IVPRI than with MGA.