Reproductive performance of lactating dairy cows and heifers resynchronized for a second insemination with an intravaginal progesterone-releasing device for 7 or 8d with estradiol benzoate injected at the time of device insertion and 24h after removal

One aim of this study was to compare the reproductive performance of cows and heifers when resynchronizing returns to estrus for a second insemination by treating with an intravaginal progesterone-releasing device (IVD) for 7 or 8d when estradiol benzoate (EB) was administered at the start of treatment and again 24h after device removal. An additional aim was to document the pattern of onset and characteristics of estrus with each resynchrony treatment. Lactating cows in three herds were synchronized for a first estrus and AI by treatment with an IVD for 8d, starting on Day 0, cloprostenol (0.5 mg im) at device removal and EB at device insertion (2.0 mg im) and 24h after removal (1.0 mg im). Cows were resynchronized for a second estrus starting on Day 23 by reinsertion of IVDs for 7 (IVD-7-EB; n=449) or 8d (IVD-8-EB; n=445) with EB (1.0 mg im) administered at device insertion and 24h after removal. Cows were resynchronized for a third estrus by administration of EB (1.0 mg im) on Day 46, but subsequent treatments (no further treatment, reinsertion of CIDR or administration of EB on Day 55) varied among herds as part of separate studies. Maiden heifers (7-Day, n=68; 8-Day, n=69) were similarly treated as cows in a separate herd, but doses of EB were always 1.0 mg im at device insertion and 0.75 mg im 24h after removal. Heifers were not resynchronized for a third estrus. Cattle were inseminated on detection of estrus at each synchronized estrus. Cumulative pregnancy rates 4 week (66.0%, 276/418 versus 59.1%, 247/418) and 7 week (72.7%, 304/418 versus 67.7%, 283/418) after the start of AI were greater (P<0.05) in the IVD-7-EB cows compared to the IVD-8-EB cows, respectively; this was associated with a 9% increase in conception rates at the second estrus (P=0.051) in the IVD-7-EB cows. Treatment did not significantly affect reproductive performance in heifers. Characteristics of estrus measured with radiotelemetry did not differ significantly between the two treatment groups, but more cows were detected in estrus 36 h after removal of IVDs in the IVD-8-EB cows compared to the IVD-7-EB cows (P<0.05). We concluded that reproductive performance in resynchronized dairy cows but not heifers was greater following resynchronization of estrous cycles after AI with an IVD for 7 compared to 8d when EB was injected at the start of treatment and 24h after device removal.     

Hormonal induction of ovulation and artificial insemination in suckled beef cows under nutritional stress

The objective was to develop a program for inducing estrus (followed by insemination) of suckled beef cows under nutritional stress (poor body condition). A total of 123 cows, from 60 to 75 days postpartum, were classified according to their body condition score (BCS; range from 1 to 5, in increments of 0.5) and allocated into two groups. On Day 0 (without regard to stage of the estrous cycle), cows (n = 59) in the hormone induction (HI) treatment group were given an intravaginal device (IVD) containing 250 mg of medroxiprogesterone acetate (MAP) and an i.m. injection of 2.5 mg estradiol benzoate (EB). On Day 6, these cows were given 500 IU eCG i.m. and calves were weaned for 96 h. The IVD were removed on Day 7. Cows detected in estrus by 45 h after IVD removal were inseminated 12 h after standing estrus; cows not in estrus by 45 h after IVD removal received an i.m. injection of 100 microg gonadorelin (GnRH) and were inseminated 16-18 h later. In the control group (C), cows (n = 64) only had their calves weaned at Day 6 (for 96 h), with estrus detection and AI from Days 6 to 11. Overall, the BCS ranged from 2.0 to 3.0. In the treatment group, estrus and pregnancy rates in cows with BCS 2.0 (20 and 30%, respectively) was lower (P < 0.05) than those with BCS 3.0 (50 and 66.6%, respectively), but did not differ (P > 0.05) from BCS 2.5 (23.3 and 47.6%). In C group, only 2 of 66 cows were detected in estrus and bred (neither was pregnant). In conclusion, the program for induction of ovulation using MAP, EB, eCG and GnRH increased the pregnancy rate in beef cows in poor body condition, enabling AI to be done in a 63-h interval.     

Synchronization of estrus with PGF2 alpha administered 18 days after a progesterone treatment in lactating dairy cows

In a previous study we showed that estrus synchronization with 2 treatments of PGF2 alpha 13 d apart reduced conception rate at the synchronized estrus and that this reduction occurred mainly in cows in the early luteal phase at the second PGF2 alpha treatment. The objective of the present study was to determine the efficacy of a synchronization regimen in which PGF2 alpha was administered during the mid- to late-luteal phase to cows that had previously been synchronized with progesterone. Spring-calving cows from 6 dairy herds were used in this study. On Day -32 (Day 1 = the start of the breeding season), cows that had calved 2 or more weeks ago were randomly assigned to a synchronization (S, n = 732) or control (C, n = 731) group. Cows in Group S were treated with an intravaginal progesterone device (CIDR) for 12 d from Day -32 to Day -20, while those in Group C were left untreated. Similar percentages of cows in Group S (80.6%) and C (82.9%) had cycled by Day -7. The CIDR treatment synchronized the onset of estrus, resulting in 92.9% of cows in estrus being detected within 7 d after CIDR removal. Cows in Group S that had cycled by Day -7 were treated with PGF2 alpha (25 mg, i.m., Lutalyse) on Day -2. Cows in both groups that were anestrous on Day -7 were treated with a combination of progesterone and estradiol benzoate (EB) to induce estrus and ovulation (CIDR and a 10 mg EB capsule on Day -7, CIDR removal on Day -2, and injection of 1 mg EB 48 h after CIDR removal). The PGF2 alpha treatment synchronized the onset of estrus in 87.5% of the cows. Group S and C cows had similar conception rates to first (61.0 vs 58.3%) and second (58.4 vs 60.9%) AI; similar pregnancy rates over the AI period (82.8 vs 79.2%) and over the whole breeding season (91.9 vs 90.6%); and required a similar number of services per pregnancy to AI (1.7 vs 1.8). The interval from the start of the breeding season to conception for cows conceiving to AI or to combined AI and natural mating was shorter (P < 0.001) by 5.7 and 6.2 d, respectively, for the Group S cows. It is concluded that the treatment regimen tested in the present study achieved satisfactory estrus synchronization, had no detrimental effect on fertility at the synchronized estrus, and shortened the interval from start of the breeding season to conception.     

Follicular growth, estrus and pregnancy after fixed-time insemination in beef cows treated with intravaginal progesterone inserts and estradiol benzoate

An experiment was performed to compare the effects of 3 short-term treatments with progesterone and estradiol benzoate (EB) on follicular growth, synchrony of estrus and pregnancy rate after fixed-time insemination in lactating postpartum beef cows. In Treatment 1 (n = 46), each cow received a progesterone-containing intravaginal insert for 7 d with injection of EB (2 mg, i.m.) at the time of device insertion. In Treatment 2 (n = 46), the insert was used for only 5 d with injection of EB (2 mg, i.m.) at the time of insertion. Cows in Treatment 3 (n = 47) received an insert for 5 d with no EB at the time of insertion. Each cow in the 3 groups received PGF2 alpha (25 mg, i.m.) at the time of insert removal, followed by EB (1 mg, i.m.) 30 h later. The cows were then inseminated 28 to 30 h after treatment with EB (58 to 60 h after insert removal). Treatment with 2 mg EB terminated the growth of the largest ovarian follicle (> 5 mm in diameter) at device insertion in 16/16 and 14/15 cows in Treatments 1 and 2, respectively. Estrus was detected within an 8-h target period (48 to 56 h after insert removal) in 93, 87 and 81% of cows in Treatments 1, 2 and 3, respectively (P > 0.05). Pregnancy rates at 39 d post insemination were 60, 50 and 51% for Treatments 1, 2 and 3, respectively (P > 0.05). The pregnancy rates did not differ between cows that were anovulatory or those that had ovulated before the initiation of treatments (54%), or among cows that were 28 to 40, 41 to 60 or > 60 days post partum at insemination (43, 59 and 54%, respectively). Treatment with progesterone inserts for 5 or 7 d, PGF2 alpha at the time of insert removal and 1 mg EB 30 h later induced the high degree of synchrony of estrus and ovulation necessary for fixed-time insemination.     

Resynchrony of postpartum dairy cows previously treated for anestrus

Cows that are diagnosed as anestrus (defined as >3 weeks postpartum, not detected in estrus by 1 week before commencement of seasonal breeding and without a palpable corpus luteum) have a lower probability of being inseminated, a lower conception rate to insemination and hence a lower probability of pregnancy within the breeding period. A current progesterone (P) and estradiol benzoate (EB) treatment for anestrus results in an 85% insemination rate, but only 57% of cows not conceiving to that first insemination are subsequently detected in estrus 14-28 days later. Resynchrony after an initial anestrous treatment has been used to increase the probability that cows not conceiving to first insemination will subsequently be detected in estrus. Anestrous cows (n=971) were initially treated with an intravaginal P-releasing device for 6 days and given 1 mg EB 1 day after device removal (day of EB treatment=Day 0). Cows detected in estrus between Days 0 and 3 were assigned randomly to be treated with reinsertion of a used P-releasing device for 8 days (commencing on Day 15), with 0.5 mg EB at reinsertion and again 1 day after removal (EB-RS), treatment as for EB-RS group but with substitution of 250 microg GnRH for EB at device reinsertion (GnRH-RS), or left as untreated controls (no-RS). Resynchrony treatments increased the proportion of non-pregnant cows detected in estrus from Days 14 to 28 compared to no-RS (79.1, 69.8, and 55.1% for EB-RS, GnRH-RS, and no-RS, respectively; P<0.05). Fewer cows were pregnant by Days 28 and 56 following GnRH-RS than EB-RS and no-RS. The final pregnancy rate was higher following EB-RS treatment than no-RS or GnRH-RS treatment (95.0, 88.3, and 88.6%; P<0.05). In conclusion, EB-RS enhanced reproductive performance of anestrous cows compared to no-RS.     

Ovarian follicular development and hormone concentrations in inseminated dairy cows with resynchronized estrous cycles

The objective was to investigate ovarian follicular development and hormone concentrations in previously inseminated cows with estrous cycles resynchronized with various resynchronization treatments. Lactating dairy cows were treated with a previously used intravaginal progesterone releasing device (IVD) for 7d (EB+IVD 7+EB, n=15) or 8d (EB+IVD 8+EB, n=16), starting 13d (Day 13) after a first estrus (Day 0) and AI. Estradiol benzoate (EB; 1mgim) was given at device insertion and 24h after removal. Other cows were given the same treatment as the EB+IVD 8+EB cows, but were not treated with EB at IVD insertion (IVD 8+EB, n=11). There were no differences (P>0.05) between EB+IVD 7+EB and EB+IVD 8+EB treatments for follicle dynamics and plasma progesterone concentrations during treatment. Based on a comparison between the IVD 8+EB treated cows and the pooled results of the EB+IVD 7+EB and EB+IVD 8+EB treated cows, EB at device insertion increased the number of follicular waves between Days 13 and 20 (mean+/-S.E.M.; 2.3+/-0.14 vs 2.7+/-0.10, P=0.033), delayed emergence of follicles that were dominant or emerging on Day 20 (17.2+/-0.36 vs 14.1+/-0.65d, P<0.001), reduced diameters of dominant or emerging follicles on Day 20 (9.0+/-0.58 vs 12.7+/-0.59, P<0.001), and reduced plasma progesterone concentrations by 0.85+/-0.44ng/mL (P=0.059) during treatment. Furthermore, comparison of the IVD 8+EB to the EB+IVD 8+EB treated cows demonstrated that treatment with EB at device insertion also reduced the diameter of ovulatory follicles (14.2+/-0.58 vs 19.0+/-0.71mm, P=0.001), delayed emergence of ovulatory follicles (17.0+/-0.32 vs 13.5+/-1.26, P=0.020), and reduced the interval from emergence to ovulation (7.0+/-0.32 vs 10.5+/-1.26d, P=0.020). We concluded that administration of EB altered ovarian follicular dynamics and tended to reduce plasma progesterone concentrations during treatment with an IVD that was used to resynchronize estrous cycles. However, use of a 7-d compared to an 8-day treatment with an IVD did not significantly affect follicle dynamics nor plasma progesterone concentrations during treatment.     

Reproductive performance of lactating dairy cows treated with gonadotrophin-releasing hormone (GnRH) and/or prostaglandin F2a (PGF2a) for synchronization of estrus and ovulation

The objective of this study was to determine the reproductive performance of lactating dairy cows treated with GnRH and/or PGF2a for synchronization of estrus and ovulation. Between Days 43 and 57 post partum, a total of 374 dairy cows was divided into 4 groups. Cows in Group 1 (n = 62) were treated with 25 mg, i.m. PGF2a on Days 43 and 57; cows in Group 2 (n = 65) were not treated at this time; cows in Group 3 (n = 118) were treated with 100 ug, i.m. GnRH on Day 50, 25 mg, i.m. PGF2a on Day 57, 100 ug, i.m. GnRH on Day 59, and time-inseminated 16 h later; cows in Group 4 (n = 129) were treated with 25 mg, i.m. PGF2a once on Day 57. Cows in Groups 1 and 4 were inseminated at an induced estrus within 7 d after the last PGF2a treatment, and cows in Group 2 were inseminated at a noninduced estrus within a corresponding period of time. Conception rate, estrus detection rate and pregnancy rate were analyzed using logistic regression, and controlled for lactation number, body condition score and time of year. Days from calving to conception were analyzed using the GLM procedures of SAS, and the model included group, body condition score, lactation number, time of year, and their interactions. Cows in Group 3 had a significantly higher pregnancy rate than cows in Groups 1, 2 and 4. Orthogonal contrasts of mean days from calving to conception showed that cows in Group 3 had significantly (P < 0.01) less days from calving to conception than cows in Group 1 and Group 4. There was a significant effect of time of year on pregnancy rate and days from calving to conception, but there was no interaction between time of year and these reproductive characteristics. There was no effect of body condition score and lactation number on the reproductive characteristics evaluated. From the results of this study, it was concluded that better reproductive performance was observed in cows inseminated at a synchronized ovulation than in those inseminated at a synchronized estrous period.     

Timed artificial insemination plus heat I: effect of estrus expression scores on pregnancy of cows subjected to progesterone–estradiol-based protocols

Expression of estrus near timed artificial insemination (TAI) is associated with greater fertility, and estrus detection could improve TAI fertility or direct TAI management, although accurate estrus detection can be difficult and time-consuming using traditional methods. The aim of this study is to evaluate influence of estrus on pregnancy (artificial insemination pregnancy rates (P/AI)) and to validate an alternative method to classify estrus/heat expression using tail chalking (HEATSC) in postpartum Bos indicus cows subjected to TAI in progesterone–estrogen-based protocols. In experiment 1 (Exp. 1), cows (5491) were subjected to visual observation of estrus after progesterone device removal, before TAI, and P/AI was evaluated according to estrus and body condition score (BCS). Cows received a progesterone device and 2 mg estradiol benzoate (EB). After 8 days, the device was removed and 150 μg of d-cloprostenol and 300 IU equine chorionic gonadotrophin was given. Later, animals in Exp. 1 received 1 mg EB and TAI 44 to 48 h. In the Exp. 2 – 3830 cows using similar protocol, received different ovulation inducers: 1 mg EB (n=1624) or 1 mg estradiol cypionate (EC; n=2206) on day 8 (D8). Cows were then marked with chalk, and HEATSC evaluated at TAI on D10 (HEATSC1 – no chalk removal=no estrus expression; HEATSC2 – partial chalk removal=low estrus expression; HEATSC3 – near complete/complete chalk removal=high estrus expression). In Exp. 1, cows showing estrus presented greater P/AI (48.4% v. 40.2%, P<0.05). In Exp. 2, P/AI (HEATSC1 – 40.0%; HEATSC2 – 49.7%; HEATSC3 – 60.9%; P<0.001), and larger follicle timed artificial insemination (LFTAI) (<0.001) varied according to HEATSC. There was no difference in P/AI (P=0.41) or LFTAI (P=0.33) according to ovulation inducer. Cows with greater BCS showed greater P/AI in both experiments (P<0.05). Estrus presence and greater HEATSC improved P/AI, and EC v. EB used promoted differential estrus manifestation (cows showing HEATSC2 and HEATSC3: 79.5% with EB v. 69.98% with EC use, P<0.001), however, with similar P/AI. The use of HEATSC in B. indicus cows subjected to TAI is useful to identify cows with greater estrus expression and consequently improved pregnancy rates in TAI, allowing the cows with low HEATSC to be targeted for additional treatments aimed at improving P/AI.     

Importance of estrus on pregnancy per insemination in suckled Bos indicus cows submitted to estradiol/progesterone-based timed insemination protocols

The objective was to evaluate the effect of estrus occurrence (based on removal of tail-head marks) on ovarian responses and pregnancy per AI (P/AI; 30 d after AI) in suckled Bos indicus beef cows submitted to timed AI (TAI) protocols. Cows received an intravaginal device containing 1.0 g progesterone, and 2.0 mg estradiol benzoate im; 8 d later, the intravaginal device was removed, and they were given PGF_2α (0.25 mg of cloprostenol sodium) and 300 IU of eCG, with TAI 48 to 52 h later. In Experiment 1, cows were assigned to receive one of three treatments: 1 mg of estradiol cypionate (ECP) im at progesterone (P4) device removal (N = 178); 10 μg of GnRH im at TAI (N = 190); or both treatments (N = 172). In cows given estradiol (ECP or ECP + GnRH), more displayed estrus (P = 0.002) and became pregnant (P < 0.0001) compared with those receiving only GnRH. In Experiment 2, the effect of the occurrence of estrus on ovarian responses was evaluated in cows (N = 53) synchronized using ECP at device removal. Cows that displayed estrus had a greater diameter of the largest follicle (LF) at device removal (P < 0.0001), a greater diameter at TAI (P < 0.0001), a greater ovulation rate (P = 0.02), a larger CL (P = 0.02), and a greater P4 concentration (P < 0.0001) than cows that did not display estrus. In Experiment 3, the effect of GnRH treatment on P/AI at TAI was evaluated in cows that received ECP at device removal, and either displayed, or did not display, estrus (N = 726). There was no estrus by GnRH interaction (P = 0.22); the P/AI was greater (P < 0.0001) in cows that displayed estrus (61.9%) than cows that did not display estrus (41.4%). However, GnRH did not improve (P = 0.81) P/AI (GnRH = 53.7% vs. no GnRH = 52.6%). In conclusion, exogenous estradiol at device removal increased both the proportion of suckled Bos indicus cows that displayed estrus and P/AI. Cows that displayed estrus had better ovarian responses (i.e., larger follicles at TAI, a greater ovulation rate, larger CL, and greater P4 concentrations) following an estradiol/P4-based synchronization protocol. Although occurrence of estrus improved pregnancy outcomes, GnRH at TAI did not improve P/AI in suckled Bos indicus cows treated with ECP, regardless of estrus occurrence.     

Evaluation of timed insemination during summer heat stress in lactating dairy cattle

We wished to compare the effect of summer heat stress on pregnancy rate in cows that were inseminated at a set interval associated with a synchronized ovulation vs those inseminated upon routine estrus detection. The study was carried out on a commercial dairy farm in Florida from May to September 1995. Lactating dairy cows were given PGF2 alpha (25 mg i.m.) at 30 + 3 d postpartum and randomly assigned to be inseminated at a set time (Timed group) or when estrus was detected (Control group). Cows in the Timed group were synchronized by sequential administration of Buserelin (8 micrograms i.m.) on Day 0 at 1600 h, PGF2 alpha (25 mg i.m.) on Day 7 at 1600 h and Buserelin (8 micrograms i.m.) on Day 9 at 1600 h. They were inseminated on Day 10 between 0800 and 0900 h (Day 9 + 16 h). Cows in the Control group were given PGF2 alpha at 57 + 3 d postpartum and inseminated when detected in estrus. Estrus detection or insemination rate for control insemination cows was 18.1 +/- 2.5% versus 100% for time inseminated cows (P < 0.01). Mean interval from PGF2 alpha to insemination was shorter for time inseminated cows (3 +/- 2.1 d < 35.5 +/- 1.9 d; P < 0.01). Pregnancy rate was greater for time inseminated cows (13.9 +/- 2.6 > 4.8 +/- 2.5%; P < 0.01) as was overall pregnancy rate by 120 d postpartum (27.0 +/- 3.6 > 16.5 +/- 3.5%; P < 0.05). Number of days open for cows conceiving by 120 d postpartum was less for time inseminated cows (77.6 +/- 3.8 < 90.0 +/- 4.2 d; P < 0.05), as was interval to first service (58.7 +/- 2.1 < 91.0 +/- 1.9 d; P < 0.01). Services per conception were greater for time inseminated cows (1.63 +/- 0.10 > 1.27 +/- 0.11; P < 0.05). The timed insemination program did improve group reproductive performance. However, the timed insemination program will not protect the embryo from temperature-induced embryonic mortality, but management limitations induced by heat stress on estrus detection are eliminated. An economical evaluation of the timed insemination program indicates an increase in net revenue per cow with implementation of timed insemination for first service during the summer months.     

Ovarian follicular and corpus luteum changes, progesterone concentrations, estrus and ovulation following estradiol benzoate/progesterone based treatment protocol in cross-bred cows

The objectives of the present study were to investigate the effects of the stage of the estrous cycle at the start of an estradiol benzoate (EB) and progesterone (P) based treatment protocol on new follicular wave emergence, subsequent estrus and ovulation. The experiment was conducted using a crossover design with each cow (five cross-bred cows) being assigned to one of three groups at 3-month intervals within a 1-year period. Estrous cycle stage in individual cows was initially synchronized with prostaglandin F(2)alpha. After detection of estrus, each cow was injected intramuscularly (i.m.) with 2 mg EB and 200 mg P (EB/P) on day 5, 12 or 17 of the estrous cycle (estrus=day 0), followed by 1 mg EB i.m. 12 days after the EB/P treatment. Ovarian ultrasonographic examinations showed that the emergence of a new follicular wave occurred after EB/P treatment in all groups and the mean interval from EB/P treatment to wave emergence did not differ among the groups (3.2-3.8 days). All cows in each group exhibited behavioral estrus and ovulated the newly formed dominant follicle. However, cows in the day-17 group exhibited estrus 1-3 days before the second EB injection. The concentrations of progesterone showed faster reduction, during the treatment period, in the day-12 and -17 groups compared to the day-5 group. These results indicate that the EB/P treatment induces an emergence of a new follicular wave, irrespective of the estrous cycle stage at the start of treatment, but the effect of EB/P protocol on estrous/ovulation synchronization is influenced by the stage of the estrous cycle.     

Synchronization of estrus in beef cows with Norgestomet-Alfaprostol or Syncro-Mate B

In the spring of 1986, 506 beef cows were used to evaluate the effectiveness of two estrus synchronization systems. Cows were synchronized with either a 6-mg Norgestomet implant placed in the ear for 14 d followed by a 6-mg Alfaprostol injection given 16 d after implant removal (Norgestomet-Alfaprostol) or with Syncro-Mate B (6-mg Norgestomet implant for 9 d with an injection containing 5 mg estradiol valerate and 3 mg Norgestomet at the time of implantation). The Alfaprostol injection in the Norgestomet-Alfaprostol group was given the same day as implant removal in the Syncro-Mate B group. These treatment groups were compared to a group of untreated controls. Cows were allotted to treatments by days postpartum, age and breed. Syncro-Mate B cows had a higher estrous response within 5 d after treatment (78.6 vs 64.0%) and a shorter interval to estrus (39.2 vs 66.7 h) than did Norgestomet-Alfaprostol cows (P < 0.05). Controls had a significantly lower estrous response compared to either of the synchronized groups (27.1%). The degree of estrus synchrony was identical in both synchronization systems (72.7%). Synchronized conception rate tended to be higher (P = 0.06) in the Norgestomet-Alfaprostol cows than in the Syncro-Mate B cows (74.5 vs 62.5%). Synchronized, 21-d, 25-d and breeding season pregnancy rates were 51.2, 70.8, 76.8 and 92.9% for Norgestomet-Alfaprostol cows; 48.5, 63.0, 73.2 and 87.8% for Syncro-Mate B cows; and 15.6, 56.3, 61.3 and 86.9% for control cows. The four pregnancy rates were not different between the two synchronization treatments (P > 0.10). Controls had lower synchronized and 25-d pregnancy rates when compared to either of the synchronized groups (P < 0.05). Days postpartum had no effect on the reproductive performance of cows synchronized with Norgestomet-Alfaprostol. Our results indicate that the Norgestomet-Alfaprostol system is as effective as Syncro-Mate B in synchronizing estrus in beef cows.     

Induction of synchronized estrus and fertility in anestrous ZebuxTaurus crossbred cows

A major cause for reproductive failures in Zebu x Taurine crossbred cows is postpartum anestrus. Crossbred cows were diagnosed to be in postpartum anestrus by palpation per rectum of nonfunctional ovaries. To induce synchronized estrus, the cows were treated by placement of a progesterone releasing intravaginal device (PRID) for various number of days, together with a single administration of prostaglandin F(2) alpha (PGF, 5 mg intravulvosubmucos), estradiol-17beta (E2, 1 mg i.m.) or pregnant mare serum gonadotrophin (PMSG, 500 IU i.m.). Administration of PRID for 7 d, and of E2 and PMSG on Day 6, significantly improved the degree of behavioral estrus manifestation compared to single PRID for 12 d or PRID for 7 d, and of PGF on Day 6. However, the treatment combination of PRID and PMSG alone was associated with higher (P < 0.01) conception rate to 2 fixed time A.I. at induced estrus. The mean interval from treatment to conception was also shortest (P < 0.01) for this group. These results suggest that administration of PRID for 7 d, and of PMSG on Day 6 is highly effective in achieving synchronized behavioural estrus, a near normal CR to fixed time A.I. and a shorter interval from treatment to conception in anestrus Zebu x Taurine crossbred cows under Indian field conditions.     

Persistent ovarian follicles in dairy cows: a therapeutic approach

Anestrus is common during the postpartum period in high-producing dairy cows. In a previous investigation, we were able to diagnose persistent follicles of 8 to 12 mm in anestrous cows. This report describes 2 consecutive studies. The objectives of the first were to 1) assess the association of persistent follicles with anestrus; and 2) evaluate 2 therapeutic treatments. In the second study, we compared the effectiveness of the best treatment established in Study 1 with the Ovsynch protocol. For Study 1, anestrous cows were considered to have a persistent follicle if it was possible to observe a single follicular structure > 8 mm in the absence of a corpus luteum or a cyst in 2 ultrasonographic examinations performed at an interval of 7 d. At diagnosis (Day 0), cows were assigned to 1 of 3 treatment groups. Cows in Group GnRH/PGF (n=17) were treated with 100 microg GnRH i.m., and 25 mg PGF2alpha i.m. on Day 14. Cows in Group PRID (n=18) were fitted with a progesterone releasing intravaginal device (PRID, containing 1.55 g of progesterone) for 9 d and were given 100 microg GnRH i.m. at the time of PRID insertion, and 25 mg PGF2alpha i.m. on Day 7. Cows in Group Control (n=18) received no treatment. The animals were inseminated at observed estrus and were monitored weekly by ultrasonography until AI or 5 weeks from diagnosis. Blood samples were also collected on a weekly basis for progesterone determination. The mean size of persistent follicles on Day 0 was 9.4 +/- 0.04 mm. Progesterone levels were < 0.2 ng/mL during the first 35 d in 16 of 18 Control cows. Cows in the PRID group showed a lower persistent follicle rate (16.7% < 70.6% < 88.9%; P < 0.0001; PRID vs GnRH/PGF vs Control, respectively); a higher estrus detection rate (83.3% > 29.4% > 11.1%; P < 0.0001) and a higher pregnancy rate (27.8% > 5.9% > 0%; P = 0.02). For the second study, 145 cows with persistent follicles were randomly assigned to 1 of 2 treatment groups: cows in Group Ovsynch (n=73) were treated with 100 microg GnRH i.m. on Day 0, 25 mg PGF2alpha i.m. on Day 7, and 100 microm GnRH i.m. 32 h later. Cows in this group were inseminated 16 to 20 h after the second GnRH dose (Ovsynch protocol). Cows in Group PRID (n=72) were treated as those in the PRID group of Study 1, and were inseminated 56 h after PRID removal. Cows in the PRID group showed a higher ovulation rate (84.8% > 8.2%: P < 0.0001); a higher pregnancy rate (34.2% > 4.1%; P < 0.0001) and lower follicular persistence rate (22.2% < 63%; P < 0.0001) than those in Ovsynch. Our results indicate that persistent follicles affect cyclic ovarian function in lactating dairy cows. Cows with persistent follicles can be successfully synchronized and time inseminated using progesterone, GnRH and PGF2alpha but show a limited response to treatment with GnRH plus PGF2alpha.     

An alteration in the hypothalamic action of estradiol due to lack of progesterone exposure can cause follicular cysts in cattle

Many mammals, including cattle, can develop ovarian follicular cysts, but the physiological mechanisms leading to this condition remain undefined. We hypothesized that follicular cysts can develop because estradiol will induce a GnRH/LH surge on one occasion but progesterone exposure is required before another GnRH/LH surge can be induced by estradiol. In experiment 1, 14 cows were synchronized with an intravaginal progesterone insert (IPI) for 7 days, and prostaglandin F(2alpha) was given on the day of IPI removal. Estradiol benzoate (EB; 5 mg i.m.) was given 3 days before IPI removal to induce atresia of follicles. Cows were given a second EB treatment 1 day after IPI removal to induce a GnRH/LH surge in the absence of an ovulatory follicle. All cows had an LH surge following the second EB treatment, and 10 of 14 cows developed a large-follicle anovulatory condition (LFAC) that resembled follicular cysts. These LFAC cows were given a third EB treatment 15 days later, and none of the cows had an LH surge or ovulation. Cows were then either not treated (control, n = 5) or treated for 7 days with an IPI (n = 5) starting 7 days after the third EB injection. Cows were treated for a fourth time with 5 mg of EB 12 h after IPI removal. All IPI-treated, but no control, cows had an LH surge and ovulated in response to the estradiol challenge. In experiment 2, cows were induced to LFAC as in experiment 1 and were then randomly assigned to one of four treatments 1) IPI + EB, 2) IPI + GnRH (100 microg), 3) control + EB, and 4) control + GnRH. Control and IPI-treated cows had a similar LH surge and ovulation when treated with GnRH. In contrast, only IPI-treated cows had an LH surge following EB treatment. Thus, an initial GnRH/LH surge can be induced with high estradiol, but estradiol induction of a subsequent GnRH/LH surge requires exposure to progesterone. This effect is mediated by the hypothalamus, as evidenced by similar LH release in response to exogenous GnRH. This may represent the physiological condition that underlies ovarian follicular cysts.     

Reproductive performance in anestrous dairy cows following treatment with two protocols and two doses of progesterone

The objectives of this study were to evaluate the effect using two doses of progesterone (P4) releasing devices in two different programs on reproductive performance of anestrous dairy cows. Cows (n = 1555) not detected in estrus by 10 d before the planned start of the seasonal breeding program and in which no CL was palpable were treated with an intravaginal P4-releasing device ('Single'; approximately 1.56 g of P4) or a modified device with triple the normal P4 dose ('Triple'; approximately 4.7 g of P4). The devices were in place for either 6 d ('Short') or 8 d ('Long'), with 1mg estradiol benzoate (EB) given 24 h after device removal. The 'Long' program also included treatment with 2 mg EB at device insertion. The Long program resulted in a higher first service conception rate (RR = 1.18 (95% CI = 1.03-1.33); P = 0.02), but had no effect on the 28-d, 56-d or final pregnancy rate compared to the Short program. There were no effects of dose of P4 on any outcome. In conclusion, the Long compared to the Short program, but not the dose of P4, improved first service conception rates in anestrous cows.     

Effect of one spontaneous estrus cycle (after synchronization with PGF2alpha) on reproductive performance in dairy cows

The objective of the study was to analyze the effect of a spontaneous estrus cycle after synchronization of estrus with prostaglandin F2alpha (PGF2alpha) in dairy cows on the degree of synchronization and reproductive performance. We assigned 557 Holstein cows to two treatment groups. In Group 1 estrus was synchronized by two treatments with 25 mg of Dinoprost-Trometamol in 14-day intervals. Cows were treated 27 to 33 days postpartum (dpp) and 41 to 47 dpp, respectively. Cows in Group 2 were treated with 25 mg of Dinoprost-Trometamol three times in 14-day intervals, starting at 34 to 40 dpp. The second and third injections were administered at 48 to 54 dpp and 62 to 68 dpp, respectively. All cows were inseminated on observed estrus after a voluntary waiting period of 65 days post partum. Thus cows in Group 1 were inseminated on spontaneous estrus and cows in Group 2 on induced estrus. Cows not inseminated at 80 days post partum were palpated per rectum and treated according to a predefined protocol. Herd reproductive performance measures did not differ significantly between groups. The proportion of cows with low serum progesterone levels was significantly higher 3 days after synchronization than 24 days after synchronization (97% vs 39%). The first-service conception rate was 34.8% in Group 1 and 30.7% in Group 2 (P > 0.05). Days open were 113.5 in Group 1 and 110.9 in Group 2 (P > 0.05). It is concluded that postponing artificial insemination for one spontaneous estrus cycle after synchronization decreased the degree of synchronization. This procedure, however, had no effect on herd reproductive performance compared to insemination on first observed estrus after synchronization.     

Comparison of synchronization of ovulation and induction of estrus as therapeutic strategies for bovine ovarian cysts in the dairy cow

The benefit of using timed-insemination in lactating dairy cows for the treatment of ovarian cysts lies in the fact that cows do not have to be detected in estrus for insemination and achieving pregnancy. We compared the effectiveness of synchronization of ovulation with timed-insemination and induction of estrus with insemination at estrus in the treatment of bovine ovarian cysts in lactating dairy cows. After Day 65 post partum, a total of 368 lactating dairy cows was divided into 3 groups. Cows in Group 1 (n = 209, normal, noncystic) were treated with 100 ug, i.m. GnRH on Day 0; 25 mg, i.m. PGF2 alpha on Day 7; and 100 ug, i.m. GnRH on Day 9 and then were time-inseminated 16 h later. Cows in Group 2 (n = 76, abnormal, cystic) were treated with 100 ug, i.m. GnRH on Day 0; 25 mg, i.m. PGF2 alpha on Day 7; and 100 ug, i.m. GnRH on Day 9 and time-inseminated 16 h later. Cows in Group 3 (n = 83, abnormal, cystic) were treated with 100 ug, i.m. GnRH on Day 0; 25 mg, i.m. PGF2 alpha on Day 7; and inseminated at induced estrus within 7 d after treatment with PGF2 alpha. Day 0 was the day of initiation of the study. Conception and pregnancy rates among groups were compared using logistic regression and adjusted for parity, time of year and days in milk. Conception and pregnancy rates of Group 1 cows (31.5%) were not significantly different from those of Group 2 cows (23.6%). However, the pregnancy rate in normal cows (Group 1) was higher (P < 0.01) than in cystic cows (Groups 2 and 3). Cows in Group 3 had a higher conception rate than cows in Group 2 (51.7% > 23.6%; P < 0.01). However, pregnancy rates for cows in Groups 2 (23.6%) and 3 (18%) were not significantly different. The finding indicated that synchronization of ovulation and timed-insemination resulted in pregnancy rates similar to those of synchronization of estrus and insemination at an induced estrus within 7 d for the treatment of ovarian cysts in lactating dairy cows.     

Estrus and ovulation in beef cows following use of progesterone-releasing devices, progesterone and estradiol valerate

Two hundred nonsuckling beef cows were treated with either 1) a progesterone-releasing intravaginal device (PRID) for 12 days; 2) PRID plus an IM injection of 200 mg progesterone (PRID-P); 3) PRID plus 5-mg IM injection of estradiol valerate (PRID-EV); or 4) PRID-EV-P. Cows were started on treatment on one of the first eight days of the estrous cycle. The number of cows which had P levels above 1 ng/ml one day after PRID removal was 12 to 50% lower in PRID-EV and PRID-EV-P groups than in PRID and PRID-P groups (P < 0.05). The proportion of cows showing estrus by 96 hours after PRID removal was 38, 36, 77, and 88% (P < 0.05) for the PRID, PRID-P, PRID-EV and PRID-EV-P groups, respectively. Thirty-one percent fewer cows treated with PRID on days 5 through 8 of the estrous cycle showed estrus by four days after PRID removal than those treated on days 1 through 4. In addition, 18 to 22% more cows had P levels above 1 ng/ml among cows treated with PRID or PRID-P on days 5 through 8 than among cows treated similarly on days 1 through 4. It was concluded that effective synchronization of estrus is achieved only when estrogen is used in conjunction with PRID in cows treated for twelve days during the first eight days of an estrous cycle.     

Effect of timing of second prostaglandin F2α administration in a 5-day, progesterone-based CO-Synch protocol on AI pregnancy rates in beef cows

The objective was to compare the timed AI pregnancy rate of Angus-cross beef cows synchronized with a 5-d CO-Synch + CIDR (a progesterone-releasing intravaginal insert) protocol and given two doses of PGF_2α (PGF), with the first dose in conjunction with CIDR withdrawal on Day 5, and the second dose given either early or late relative to the first dose. All cows (N = 1782) at 16 locations received 100 μg of GnRH + CIDR on Day 0. Cows received 25 mg of PGF concurrent with removal of the CIDR on Day 5, and were randomly allocated within locations to receive a second PGF either early (N = 881; from 0.5 to 3.9 h) or late (N = 901; from 4.5 to 8.15 h) relative to the first PGF treatment. On Day 8 (72 h after CIDR removal), all cows were inseminated and concurrently given 100 μg of GnRH. Cows were fitted with a pressure-sensitive mount detection device (Kamar) at CIDR removal. Cows were observed twice daily through Day 7 and at the time of AI on Day 8 for estrus and Kamar status (estrus - red, partial and lost Kamar versus no estrus - white Kamar) was recorded. Accounting for location, season, AI sire, cow observed in estrus or not at or before timed AI, and treatment by cows observed in estrus interaction, timed AI pregnancy rates were greater for the late (6.45 ± 0.03 h) than the early (2.25 ± 0.05 h) interval, 57.2 vs. 52.7%, respectively (P < 0.05). In conclusion, cows that received the second PGF late after the first PGF on the day of CIDR removal in a 5 d CO-Synch + CIDR synchronization protocol had significantly higher timed AI pregnancy rates than those receiving the second PGF early after the first PGF.