Fertility following fixed-time AI or insemination at observed estrus in Ovsynch and Heatsynch programs in lactating dairy cows

The objective of this study was to compare the conception rate for fixed-timed artificial insemination (FTAI) and observed heat artificial insemination (HAI) prior to the scheduled FTAI in Ovsynch and Heatsynch synchronization protocols. In Experiment 1, lactating dairy cows (n=535) received two set-up injections of 25mg prostaglandin F(2alpha) (PGF(2alpha)) i.m., 14 days apart starting at 36+/-3 days in milk (DIM). Cows were blocked by parity and were randomly allocated to either Ovsynch or Heatsynch groups. All cows received 100 microg of GnRH i.m. 14 days after the second set-up injection of PGF(2alpha), followed by a third injection of 25mg PGF(2alpha) i.m., 7 days later. In the Ovsynch group, HAI cows (n=29) were bred on standing estrus after the third PGF(2alpha) before the scheduled second GnRH, whereas FTAI cows (n=218) that were not observed in estrus, received a second injection of 100 microg of GnRH i.m., 48 h after the third PGF(2alpha) and received TAI 8 h after the second GnRH. In the Heatsynch group, all cows (n=288) received 0.5 mg of estradiol cypionate (ECP) 24 h after third PGF(2alpha) and HAI cows (n=172) were bred on standing estrus and FTAI cows (n=116) that were not observed in estrus, received TAI 72 h after the third PGF(2alpha). In Experiment 2, repeat breeder cows (n=186) were randomly assigned to either Ovsynch or Heatsynch groups. The FTAI and HAI cows were inseminated similar to Experiment 1. All cows were observed for estrus three times daily. The associations with the conception rate were modeled with logistic regression separately for Experiments 1 and 2. Of all the variables included in the model in Experiment 1, type of AI (HAI versus FTAI, P=0.0003) and parity (primiparous versus multiparous, P=0.05) influenced the first service conception rate. Over-all conception rate and first service conception rate for HAI cows were higher compared to FTAI cows (33.8% versus 21.3%, and 35.3% versus 21.0%; P=0.001). In the Heatsynch group, cows that received HAI had significantly higher over-all conception rate and first service conception rate compared to FTAI (35.2% versus 17.3% and 36.0% versus 15.5%; P=0.0001). The conception rates in repeat breeder cows for HAI and FTAI (30.1% versus 22.3%) were not different (P>0.1). In conclusion, it was recommended to include AI at observed estrus and fixed-time AI for cows not observed in estrus in order to improve the conception rate in synchronization protocols.     

LH surge in Nelore cows (Bos indicus), after induced estrus or after ovarian superestimulation

Considering that there is limited information about the preovulatory LH surge in Zebu cattle (Bos indicus), the purpose of the present work was to assess the LH surge in Nelore cows during the estrous cycle and after ovarian superestimulation of ovarian follicular development with FSH. This information is particularly important to improve superovulatory protocols associated with fixed-time artificial insemination. Nelore cows (n=12) had their estrus synchronized with an intravaginal device containing progesterone (CIDR-B) associated with estradiol benzoate administration (EB, 2.5 mg, i.m., Day 0). Eight days later all animals were treated with PGF2alpha (Day 8) in the morning (8:00 h) and at night, when CIDR devices were removed (20:00 h). Starting 38h after the first PGF2alpha injection, blood sampling and ovarian ultrasonography took place every 4h, during 37 consecutive hours. Frequent handling may have resulted in a stress-induced suppression of LH secretion resulting in only 3 of 12 cows having ovulations at 46.7+/-4.9 and 72.3+/-3.8 h, respectively, after removal of CIDR-B. Thirty days later, the same animals received the described hormonal treatment associated with FSH (Folltropin), total dose=200 mg) administered twice a day, during 4 consecutive days, starting on Day 5. Thirty-six hours after the first injection of PGF2alpha, to minimize stress, only seven blood samples were collected at 4h interval each, and ultrasonography was performed every 12 h until ovulation. In 11 of 12 cows (92%) the LH surge and ovulation were observed 34.6+/-1.6 and 59.5+/-1.9 h, respectively, after removal of progesterone source. The maximum values for LH in those animals were 19.0+/-2.6 ng/ml (mean+/-S.E.M.). It is concluded that, in Nelore cows submitted to a ovarian superstimulation protocol, the LH surge occurs approximately 35 h after removal of intravaginal device containing progesterone, and approximately 12h before the LH surge observed after an induced estrus without ovarian superstimulation.     

Effects of copulation on timing of the LH surge following synchronization of estrus in the bovine

Forty-four crossbred postpubertal bovine females were used to study how mating with a bull affected estradiol-17beta (E(2)) secretion and timing of the preovulatory LH surge. Estrous cycles were synchronized with two injections of prostaglandin-F(2alpha) (PGF(2alpha)) 11 d apart. Females were either isolated from males (NE) or exposed to epididectomized bulls (BE) after the second PGF(2alpha) injection. Females exposed to bulls were allowed to mate once and then were separated from the bull. Blood samples were collected at 2-h intervals from the second PGF(2alpha) injection until 12-h post injection to monitor progesterone (P(4)) and luteinizing hormone (LH) concentrations and at hourly intervals from 12 h to 60 h post-injection to monitor LH secretion and timing of the preovulatory LH surge. Samples were also collected at 4-h intervals until 60 h post-injection to monitor estrogen (E(2)) secretion. LH surges were detected in 16 and 14 of 22 females from the BE and NE groups, respectively, during the 60-h period after PGF(2alpha) injection Mean P(4) concentrations and time of P(4) decline to <1 ng/ml were not different between the two treatment groups (P>0.30). Mean E(2) concentration during the 60-h sampling period was different (P<0.003) between BE and NE groups, and a significant treatment effect (P<0.002) occurred 48 h, 52 h and 60 h after the second PGF(2alpha) injection. However, mean LH concentration before the LH surge, duration of the LH surge and peak LH concentration during the surge were not different between the BE and NE groups (P>0.40). Mean time for the second PGF(2alpha) injection to the beginning of the LH surge was 51.6 +/- 1.5 h (X +/- S E) for the females not exposed to bulls and 48.5 +/- 1.4 h for females exposed to bulls (P>0.14). In this study, the presence of and/or mating by a bull did not affect LH secretion or timing of the preovulatory LH surge after PGF(2alpha) administration.     

Incidence of premature estrus in lactating dairy cows and conception rates to standing estrus or fixed-time inseminations after synchronization using GnRH and PGF(2alpha).

Fixed-time AI (TAI) after GnRH-PGF(2alpha)-GnRH treatment is a method to achieve pregnancies in dairy herds without estrous detection. However, cows that fail to respond to the initial GnRH may have compromised TAI conception rates due to asynchronous ovarian response. This study documented the percentage of GnRH-treated Holstein cows (n=345) in two herds that displayed estrus at an inopportune time for optimum TAI conception rate (< or =48h post-PGF(2alpha); premature estrus (PE)) and compared conception rates of two TAI protocols in cows that did not display PE. At biweekly herd health exams, cows diagnosed as not pregnant to a previous AI and cows >80 days postpartum with no AI were treated with 100 microg GnRH (day -7) and 25mg PGF(2alpha) (day 0). Cows detected in PE by twice-daily visual observation from day -7 to day 2 were bred by AI 8-12h later. Cows not detected in PE were randomly assigned by parity, body condition score, and postpartum interval to receive either: (1) 100microg GnRH at 48h after PGF(2alpha) and TAI 16 to 18h later (Ovsynch); or (2) TAI at 72h post-PGF(2alpha) and a concurrent 100 microg GnRH injection to those cows not detected in estrus between 48 and 72h post-PGF(2alpha) (modified Ovsynch (MOV)). All hormone injections were im. Twenty percent (68/345) of the cows were detected in estrus before 48 after PGF(2alpha), of which 5% (17/345) were detected in estrus before PGF(2alpha) (< or =day 0). Herd influenced the percentage of cows in the PE group (herd A versus herd B; 25% versus 14%; P<0.05). Conception rates were not affected by treatment (PE versus Ovsynch versus MOV; 32% (21/65) versus 30% (37/125) versus 32% (47/145); P>0.10). However, within MOV-treated cows, conception rates were greater (P<0.05) in cows detected in estrus (46% (23/50)) compared with cows not detected in estrus (25% (24/95)). In conclusion, 20% of GnRH-treated cows displayed PE and necessitates estrous detection during this period if maximal pregnancy rates are to be achieved. Although additional estrous detection is required compared to Ovsynch, reduced cow handling and hormone usage, efficient use of expensive semen through greater conception rates in cows detected in estrus, and comparable TAI conception rates, suggests the MOV protocol may be a cost effective alternative to Ovsynch in many dairy herd reproductive management programs.     

Ovulation rate after GnRH or PGF2alpha administration in early postpartum dairy cows

The objectives of this study evaluating induction of ovulation in early postpartum dairy cows were to: compare two methods of GnRH (100 mcg) administration (i.m. route and s.c. implant), and determine if prostaglandin F(2alpha) (PGF) causes release of LH or ovulation similar to that reported for GnRH. In trial #1, serum LH peaked at 2h after i.m. administration of GnRH and was declining at 4h. The s.c. GnRH implant also caused an elevation in serum LH at 2 and 4h after treatment, with LH declining at 6h. Serum LH was unchanged in control cows. Experimental treatment caused ovulation in 4 of 14 GnRH i.m. treated cows, 4 of 12 GnRH implanted cows and 0 of 13 control cows. Parity had no effect on LH response but did affect resulting ovulation rate as multiparous cows were more likely to ovulate than were primiparous cows in response to either GnRH treatment. All cows that ovulated had a follicle larger than 12 mm at the time of treatment. In trial #2, serum LH increased as before after i.m. administration of GnRH, however, serum LH was unchanged in cows treated with PGF or saline. Gonadotropin releasing hormone caused more cows to ovulate than did PGF or saline treatments, and GnRH shortened the interval from treatment to the onset of CL function over the PGF treatment; 13.9+/-2.6, 28.2+/-4.1 and 22.3+/-4.1 days for GnRH, PGF and saline, respectively. In summary, there was no difference in the ability of s.c. implantation and i.m. administration of GnRH to cause ovulation. Prostaglandin F(2alpha) did not cause release of LH or ovulation. In 22 early postpartum dairy cows treated with 100 mcg GnRH i.m. in these two trials, nearly all cows (95%) responded with a release of LH but only 45% (10/22) responded with an ovulation and subsequent formation of a CL.     

Stag exposure advances the LH surge and behavioral estrus in Eld's deer hinds after CIDR device synchronization of estrus

The impact of male presence or absence on the timing of the preovulatory LH surge and estrus was studied in 3 experimental groups (n = 6/group) of Eld's deer hinds pretreated with intravaginal progesterone-releasing devices (CIDR-type G) as follows: Group 1 = indirect male contact barn; Group 2 = direct male contact barn; and Group 3 = male isolation barn. For all hinds, the duration of the preovulatory LH surge averaged 2.5+/-0.5 h, whereas mean peak preovulatory and basal LH concentrations were 2.9+/-0.2 ng mL(-1) and 0.27+/-0.03 ng mL(-1), respectively. Nine of 12 male-exposed hinds exhibited a preovulatory LH surge within 24 to 32 h postCIDR device withdrawal, whereas 0 of 6 male-isolated hinds exhibited a preovulatory LH surge during the same time period. Onset of behavioral estrus (45.2+/-2.3, 52.7+/-5.7 and 66.3+/-1.8 h, respectively) was significantly advanced (P<0.05) after CIDR device withdrawal in male exposed hinds (Groups 1 and 2) compared with male isolated hinds (Group 3). These data suggest that stag exposure is important for modulating the timing of the preovulatory LH surge and behavioral estrus after synchronization of estrus with exogenous progestagens.     

Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2alpha and progesterone

The objective of this study was to evaluate the reproductive performance of lactating cows in seasonal dairy herds after estrus synchronization with PGF2alpha (PG) with or without supplementation with progesterone (P4). In Trial 1, synchronized cows (S1; n = 521) were compared with untreated control cows (C; n = 518) in 5 herds. Estrus of cows in the S1 group was synchronized with 2 treatments of PG (Lutalyse) 13 d apart. The breeding season started 2 d after the second PG. Cows were first bred by AI for 7 wk and then herd sires were used. Compared with C cows, estrus synchronization in the treated cows reduced the conception rate to first AI (61.1 vs 70.5%; P < 0.01) and the intervals from start of the breeding season to conception for cows conceiving to AI (11.0 vs 14.6 d; P < 0.05) or to both AI and natural mating (16.5 vs 18.4 d; P < 0.05). There was no effect on conception rate to second AI (68.8%), on pregnancy rate by Day 24 (72.3%) or Day 49 (86.3%) of the breeding season, or on the percentage of cows not pregnant at end of the breeding season (5.0%). In Trial 2, effects of P4 supplementation before the second PG on reproductive performance were evaluated in 4 herds. Estrus of each cyclic cow was synchronized with PG as in Trial 1. Half of the cows in each herd were treated with an intravaginal P4 device (CIDR) for 5 d before the second PG (S2+P4, n = 608), whereas the remaining half received no CIDR treatment (S2, n = 593). Compared with S2 cows, P4 treatment increased the estrous response rate to the second PG (89.6 vs 82.9%; P < 0.01), the conception rate to first AI (65.1 vs 59.7%; P = 0.07), the pregnancy rate by Day 6 of the breeding season (59.3 vs 49.0%; P < 0.001), and reduced the intervals from start of the breeding season to conception for cows conceiving to AI (8.6 vs 10.4 d; P < 0.10) or to both AI and natural mating (12.7 vs 16.4 d; P < 0.01). Treatment with a used CIDR from Days 16 to 21 after start of breeding to re-synchronize returns to service had no effect on conception rate to first or second AI but may decrease the conception rate to second AI in cows previously treated with CIDR. In conclusion, estrus synchronization with the double PG system can reduce fertility, while P4 supplementation for 5 d before the second PG can improve estrous response and overall reproductive performance. Stage of the estrous cycle at the time of the second PG can affect fertility following synchronization.     

Effects of physiological and/or disease status on the response of postpartum dairy cows to synchronization of estrus using an intravaginal progesterone device

Progesterone treatments are used to increase submission rates in postpartum dairy cows; however, in many cases the protocol is used as a blanket therapy for all cows without regard for physiological or disease state. The objective of this study was to identify the physiological or disease classes of cows that respond well (or not) to synchronization of estrus via progesterone. Dairy cows (n = 402) were monitored peri and postpartum to establish their physiological or disease status. Animals were classified as having negative energy balance, clinical lameness, uterine infection (UI), anovulatory anestrus, high somatic cell counts, and healthy (H). Blood samples were collected at five different time points and analyzed for metabolites. All animals received an 8-day controlled internal drug release protocol, which included GnRH at insertion and PGF_2α the day before removal. Response to the protocol was determined by visual observation of estrus synchronization. Conception rate was determined by ultrasonography between Days 32 and 35 after artificial insemination. Animals without UI were 1.9 times more likely to respond and two times more likely to be confirmed pregnant than those with UI. There was no relationship between negative energy balance and clinical lameness in the visual estrous response, but both conditions were associated with reduced conception rates. Dairy cows in anovulatory anestrus responded successfully to the protocol in both estrous response and conception rates. High glutathione peroxidase concentrations had a positive effect on conception rates, whereas high non-esterified fatty acids and beta-hydroxybutyrate had a negative effect on the estrous response. In conclusion, disease and physiological states of dairy cows determined the response to progesterone-based synchronization. The more disease or physiological problems the cows had, the lower the estrous response and conception rates; cows with these problems were not ideal candidates for synchronization. Both anestrus and healthy dairy cows were good responders to progesterone-based synchronization.     

Evaluation of GnRH treatment 12 days after AI in the reproductive performance of dairy cows

The objective of this study was to evaluate the effects of GnRH administered at Day 12 post-AI on the reproductive performance of dairy cows. Holstein-Friesian dairy cows (n=103) on a large Hungarian dairy farm were allocated randomly to treated (n=54) or control (n=49) groups. Twelve days after AI, treated cows received a GnRH agonist i.m., while the control group received a placebo (physiological saline). Progesterone radioimmunoassay was used to determine the correct timing of artificial insemination (Day 0) and the incidence of luteal insufficiency on Day 12. Ultrasonography and radioimmunoassay for pregnancy-associated glycoprotein were used to detect pregnancy and late embryonic/fetal mortality between Days 32 and 55 after AI. Three cows from each group were inseminated when progesterone concentrations were >1.0 ng/mL, and six cows (four from the treated and two from the control group) had luteal insufficiency (progesterone<1.0 ng/mL) on Day 12. Late embryonic/fetal mortality occurred in three treated cows and in two control cows. When these cows were removed from the model, calving rates after first service were 59.6% (28/47) and 59.1% (26/44) for treated and control cows, respectively (P>0.05). There was no significant difference between treated and control cows when they were inseminated before or after Day 100 from calving. In summary, administration of a GnRH agonist on Day 12 after AI did not improve reproductive performance in dairy cows. However, our approach may be used for the field evaluation of different treatment protocols.     

Ovarian and endocrine responses and reproductive performance following GnRH treatment in early postpartum dairy cows

At calving forty-eight Holstein and Guernsey cows were assigned according to age and breed to one of six postpartum periods (1 or 2, 3 or 4, 5 or 6, 7 or 8, 12 or 13 and 18 or 19 days postpartum). Thirty-six of the cows (6 cows per postpartum period) received a single intramuscular injection of 100 μg GnRH. The other twelve cows (2 cows per postpartum period) served as controls and received a single intramuscular injection of the carrier vehicle for GnRH.Four of 36 cows administered GnRH and three of the 12 control cows ovulated by the day following treatment. Four of the cows were 12 or 13 days postpartum (1 control and 3 GnRH treated) and three were 18 or 19 days postpartum (2 controls and 1 GnRH treated). Six of the seven cows that ovulated the day following treatment had a follicle > 1.0 cm the day prior to treatment. Follicular growth was detected in the earlier postpartum periods but ovulation the following day was not detected for either control or GnRH treated cows. Following estrus or silent estrus, plasma progesterone concentrations increased to about 4 ng/ml on day 13. However, in cows ovulating the day following GnRH treatment, plasma progesterone declined from about 3 ng/ml on day 9 to approximately 1 ng/ml on day 13 postestrus. In addition, LH in plasma was higher (P < .01) ? through 13 days following estrus or silent estrus in cows ovulating the day after GnRH treatment in comparison to cows during the first or subsequent postpartum estrous cycles.In summary, in addition to days postpartum other factors including follicular development and maturity are probably involved in GnRH induced ovulation.     

Reproductive performance of dairy cows with ovarian cysts after synchronizing ovulation using GnRH or hCG during the warm or cool period of the year

This study was designed to compare the reproductive response to timed AI of lactating dairy cows with cystic ovarian follicles treated with GnRH or hCG to synchronize ovulation. The effectiveness of treatment during the warm or cool period of the year was also compared. Cows were given 12 microg GnRH-agonist i.m. on day 0 of the protocol, 15 mg PGF(2alpha) i.m. on day 7, and either GnRH-agonist (GPG treatment) or 3000 IU hCG i.m. (GPH treatment) on day 9, followed by timed AI. The cows were randomly chronologically assigned to GPG (n=130) or GPH (n=136) group. All cows were inseminated at fixed time 16-22 h after the end of treatment. During the warm period the pregnancy rate to first AI was 12% (7/60) and 21% (14/68) for the GPG and GPH groups, respectively, there being no significant differences between groups; the cumulative pregnancy rate was 22% (13/60) and 21% (14/68) for the GPG and GPH groups, respectively, again with no significant intergroup differences. During the cool period pregnancy rate to first AI was not different between groups: 29% (20/70) for GPG and 32% (22/68) for GPH, respectively; whereas the cumulative pregnancy rate was significantly higher (P<0.05) for the GPH groups than for the GPG group: 56% (39/70) and 78% (53/68), respectively. These findings indicate that during the warm period, the pregnancy rates of the cystic cows were similar whether they received GPG or GPH treatment, during the cool period, there is a beneficial effect to use hCG at day 9 of the ovsynch protocol compared GnRH on cumulative pregnancy rate.     

The effects of ovarian function on estrus synchronization with PGF in dairy cows

Milk progesterone concentration (P4), milk yield, milk composition, ovarian structures and pregnancy status were studied in 108 cows treated with two doses of PGF 14 days apart and inseminated at fixed time (TAI) 80-82 h later. The synchronization protocol was started at 70+/-1.4 days after parturition. Milk P4 profiles revealed that anestrus, failure of luteolysis following treatment with PGF and failure to ovulate following luteolysis were the main reasons for low pregnancy rate with TAI. Anestrous cows had a higher percentage of milk fat (P<0.05) and higher fat to protein ratio (P<0.01), and cows that did not undergo luteolysis had higher milk yield (P<0.05) and lower percentage of milk protein (P<0.05) than cows that responded to PGF treatment. Cows that did not undergo luteolysis and cows that did not ovulate following luteolysis had lower milk P4 during the luteal phase preceding the second PGF injection (P<0.01 and P<0.05, respectively). Pregnancy rates 24 and 47 days after TAI in cows that responded as expected to the synchronization treatment were 62% and 54%, respectively. Pregnancy was precluded in non-responsive cows. The largest follicle at the time of TAI in cows experiencing late embryonic mortality was smaller (P=0.02) than in cows that successfully maintained pregnancy. Results suggest that a primary reason for low pregnancy rate in dairy cows after administration of PGF and TAI is inappropriate ovarian function prior to, or following treatment.     

The effect of a GnRH analogue on the dynamics of follicular development and synchronization of estrus in lactating cyclic dairy cows

A GnRH analogue was used to synchronize ovarian follicular development prior to an injection of PGF(2alpha) for the synchronization of estrus in lactating Holstein cows. On Day 12 (estrus = Day 0) of the experimental cycle, cows (n = 8) were injected with 8 mug Buserelin (BUS group), followed by 25 mg PGF(2alpha) 7 d later (Day 19). Control cows (n = 7) received PGF(2alpha) on Day 12 (PGF group). Ovaries were scanned daily via ultrasonography, and plasma progesterone and estradiol concentrations were determined. Sizes of all visible follicles were recorded. Follicles were classified as small (3 to 5 mm), medium (6 to 9 mm), or large (>/= 10 mm). Between Days 12 and 16 of the cycle, the number of large follicles in PGF cows remained unchanged (1.2), whereas in the BUS group, the number of large follicles decreased from 1.3 on Day 12 to 0.5 on Day 15. Only 4 of 7 PGF cows ovulated a second-wave dominant follicle. In the BUS group, 7 of 8 cows ovulated a GnRH analogue induced dominant follicle that was first identified on Day 15. During the follicular phase (last 5 d prior to estrus), plasma progesterone declined in association with CL regression in both groups, and estradiol concentrations increased, reaching higher (P<.0.05) preovulatory peak concentration in BUS cows than in PGF cows (14.0 +/- 1.0 vs 10.4 +/- 1.1 pg/ml). The number of medium-size follicles was smaller and the number of small-size follicles tended to be higher in BUS cows than in the PGF-treated group. On the day of estrus, the size of the ovulatory follicle (16.1 vs 13.3 mm) and the size difference between the ovulatory and second largest follicle (11.4 vs 6.2 mm) were both larger in BUS cows than in PGF-treated cows, suggesting a more potent dominance effect of the ovulatory follicle in the BUS cows. This study suggests that a GnRH analogue can alter follicular development prior to synchronization of estrus with an injection of PGF(2alpha) in lactating dairy cows.     

Comparison of two estrus synchronization and resynchronization treatments in lactating dairy cows

Reproductive performance in cows following synchronization of estrus with intravaginal progesterone releasing devices (IVD) has varied with the length of treatment, cyclic status and prolonged return to estrus intervals in some cows following first AI. The objective of this study was to compare two methods of synchronizing and resynchronizing estrus on the reproductive performance of lactating dairy cows. Cows were treated with an IVD (Day 0) for 7 days (n = 350) or 8 days (n = 350), cloprostenol (0.5 mg i.m.) at the time of device removal and estradiol benzoate (EB) at the time of device insertion (1.5mg i.m.), and again 9 days later (1.0 mg i.m.). Cows were also resynchronized starting on Days 23 and 46 by reinsertion of IVDs for either 7 or 8 days and treatment with EB (1mg i.m.) at the time of device insertion and again 9 days later. Cows were inseminated on detection of estrus for 4 days after removal of devices at each of the synchronized estrous cycles. No significant differences in reproductive performance were detected between each treatment throughout the study period. Synchrony of estrus was more precise at the first and second estrus after treatment with an IVD for 8 days compared to 7 days. Cows classified as anestrous had lower reproductive performance than cows classified as cycling and had longer intervals to estrus at the second (P < 0.001) and third estrus (P < 0.06), but not at the first estrus (P = 0.09). Mean time to onset of estrus after IVD removal was less in cows treated with an IVD for 8 days compared to 7 days at each synchronized estrus (P < 0.01). More Holstein-Friesian cows were classified as non-pregnant and not detected in estrus than crossbreed cows (15.7%, 54/343 versus 9.0%, 24/266; [P < 0.05). The results of the study suggested that the main effects of the treatments that were used to synchronize and resynchronize estrus were to alter the timing and synchrony of estrus without affecting fertility.     

Effect of an implant containing the GnRH agonist deslorelin on secretion of LH, ovarian activity and milk yield of postpartum dairy cows

Prevention of high plasma progesterone concentrations in the early postpartum period may improve fertility. Our objective was to determine whether a Deslorelin implant (DESL; 2100 microg, s.c.) would reduce secretion of LH and alter follicle dynamics, plasma concentrations of progesterone, estradiol and PGF2alpha metabolite (PGFM) in postpartum dairy cows. Cows received DESL on Day 7 postpartum (Day 7, n=8) or were untreated (Control, n=9). All cows were injected with GnRH (100 microg, i.m.) on Day 14 to assess LH response. A protocol for synchronization of ovulation with timed AI was initiated on Day 60 (GnRH [Day 60], CIDR [Day 60 to Day 67], PGF2alpha [Day 67, 25 mg and Day 68, 15 mg], GnRH [Day 69] , AI [Day 70]). The LH response to injection of GnRH on Day 14 was blocked in animals treated with DESL. Numbers of Class 1 (<6 mm) follicles were unaffected (P > 0.05) whereas numbers of Class 2 (6 to 9 mm) (P < 0.01) and Class 3 (>9 mm) follicles were less (P < 0.01) in DESL cows between Day 7 and Day 21. From Day 22 to Day 60, DESL-treated cows had more of Class 1 follicles and less Class 2 (P < 0.01) and Class 3 (P < 0.01) follicles, and lower plasma concentrations of progesterone and estradiol (P < 0.01). Concentrations of PGFM between Day 7 and Day 42 were not affected by treatment (P > 0.05). All cows ovulated in response to GnRH on Day 69. Subsequent luteal phase increases in plasma progesterone concentrations (Day 70 to Day 84) did not differ. The use of the DESL implant associated with PGF2alpha given 14 days later suppressed ovarian activity and caused plasma progesterone concentrations to remain < 1 ng/mL between Day 22 and Day 51. The DESL implant did not affect milk production.     

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

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

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.     

Efficacy of decreasing the dose of GnRH used in a protocol for synchronization of ovulation and timed AI in lactating dairy cows

To determine the efficacy of reducing the dosage of GnRH used in a protocol for synchronization of ovulation and timed AI, primiparous and multiparous lactating Holstein cows (n=237) were randomly assigned to 1 of 2 treatment groups. Ovulation was synchronized for cows in the first group using intramuscular injections of GnRH and PGF₂ as follows: Day 0, 100 μg GnRH; Day 7, 25 mg PGF₂; Day 9, 100 μg GnRH. Ovulation was synchronized in the second group of cows using the same injection schedule and dosage of PGF₂ but only 50 μg GnRH per injection. All cows underwent a timed AI at 12 to 18 h after the second GnRH injection. The proportion of cows ovulating in response to the second GnRH injection (synchronization rate) and pregnancy status at 28 and 56 d post AI were determined using transrectal ultrasonography. The synchronization rate, double-ovulation rate, conception rate at 28 and 56 d post AI, and pregnancy loss from 28 to 56 d post AI did not differ statistically between treatment groups. For all cows, synchronization rate was 84.0%, and double-ovulation rate was 14.1%. Conception rates calculated using all cows receiving synchronization of ovulation were 41.1% at 28 d and 34.4% at 56 d post AI. Conception rates calculated for only synchronized cows were 47.6% at 28 d and 40.1% at 56 d post AI. For all cows, pregnancy loss from 28 to 56 d post AI was 13.5%, with an attrition rate of 0.5% per day. Estimated savings in hormone costs using 50 rather than 100 μg GnRH per injection for synchronizing ovulation were $6.40 per cow and $20.27 per pregnancy. Thus, decreasing the dosage of GnRH used for synchronization of ovulation and timed AI in lactating dairy cows reduces synchronization costs per cow and per pregnancy without compromising the efficacy of the synchronization protocol.     

Hormone response of dairy cows with ovarian cysts after treatment with HCG or GnRH

Twenty lactating Holstein and Guernsey cows, diagnosed by rectal palpation as having ovarian cysts, were randomly divided within breed into two groups to receive either a single intramuscular injection of 100 μg of synthetic gonadotropin releasing hormone (GnRH) or an intravenous injection of 10,000 IU of human chorionic gonadotropin (HCG). The objective was to compare hormonal and clinical changes in cows with ovarian cysts following treatment with GnRH and HCG. Eight of ten and nine of ten cows given either GnRH and HCG, respectively, responded to treatment and subsequent fertility was not different between the two groups. Pre-injection plasma levels of LH, progesterone, and estradiol were highly variable. Mean plasma levels of LH, progesterone and estradiol did not differ between groups either following treatment (days 1–17 post-treatment), at the subsequent estrus, or during days 1–13 following the subsequent estrus. Mean LH levels did not differ significantly on the days either post-treatment or post-estrus except that levels were higher (P < .01) at the subsequent estrus as compared to the other days. Mean progesterone levels increased after treatment with either GnRH or HCG and were higher on days 5, 9 and 13 post-estrus and post-treatment as compared to the subsequent estrus. Mean levels of estradiol were higher (P < .05) at the subsequent estrus than any other time post-treatment or post-estrus. No other days were significantly different. In conclusion, GnRH and HCG are effective treatments for ovarian cysts in cattle. Endocrine response on days following treatment are similar for both compounds.