GnRH-treated Cows Research Articles

Morphologic, Steroidogenic, and Transcriptomic Assessment of the Corpus Luteum in Holstein Cows after Spontaneous or Hormone-Induced Ovulation.

There is evidence that replacing the gonadotropin-releasing hormone (GnRH) with porcine luteinizing hormone (pLH) to synchronize ovulation prior to artificial insemination (AI) increased pregnancy per AI in dairy cows without affecting blood progesterone (P4) concentrations. Whether morphologic, steroidogenic, and transcriptomic differences exist among corpora lutea (CL) formed after ovulation induced by GnRH and pLH is unclear. Our main objective, therefore, was to compare CL characteristics between GnRH- and pLH-induced CL. In 24 non-lactating Holstein cows, ovulations were spontaneous (Spont-Ov) or induced with 100 µg GnRH, 25 mg pLH, or 1 mg estradiol benzoate (EB), with CL excised 12 d after ovulation. In pLH- versus GnRH-treated cows, the duration of elevated LH (above baseline) was prolonged (10 versus 6 h, respectively, p < 0.01), but CL dimensions, pixel intensity of CL images, proportions of steroidogenic and non-steroidogenic luteal cells, and mean plasma LH did not significantly differ. Post-ovulation mean plasma P4 (ng/mL) did not differ among Spont-Ov (3.0) pLH (3.1) or GnRH (3.0) cows but were lower in EB cows (2.0). In vitro P4 concentration was greater in luteal explants of pLH-treated cows than in all other groups (combined means, 16.0 vs. 12.3 µg/mL, p < 0.02). Relative abundance of mRNA for oxytocin receptor (OXTR) was 2-fold higher (p < 0.01) in CL of pLH vs. GnRH cows and highest in Spont-Ov CL. In summary, pLH-treated cows had a longer LH peak, and greatest luteal tissue concentrations and in vitro production of P4. We inferred that increased P4 concentrations at the ovarian-uterine level in pLH-treated cows could have promoted embryo development and increased pregnancy per AI.

Inducing ovulation with human chorionic gonadotrophin improves the pregnancy rate in lactating dairy cows receiving an in vitro-produced embryo.

While the global use of in vitro-produced embryos in dairy cattle is on the rise, several technical aspects of embryo transfer procedures have not yet been optimized. This study compares the effects of inducing ovulation using human chorionic gonadotropin (hCG) versus gonadotropin-releasing hormone (GnRH) at the end of a 5-day progesterone(P4)-based protocol for oestrous synchronization on the pregnancy rate of lactating dairy cow recipients of in vitro-produced embryos. Fresh embryos were transferred on Day-seven post-oestrus to ovulating cows receiving GnRH or hCG (groups GnRH and hCG, n=60 each). Pregnancy was diagnosed by ultrasound on Day 28 post-oestrus. Forty-nine cows became pregnant: 16 in GnRH (26.7%) and 33 in hCG (55%). Taking GnRH-treated cows as reference, the odds ratio for pregnancy of hCG-treated cows was 3.3 (p=.002). In conclusion, hCG treatment given at the end of a 5-day P4-based protocol for oestrous synchronization improved the pregnancy rate in lactating dairy cows receiving an in vitro-produced embryo.

Induction and Formation of Accessory Corpus Luteum after Artificial Insemination (AI) Might Increase Pregnancy Rate per AI in Heat Stressed Dairy Cows

Abstract The present study aimed to evaluate whether the induction and the formation of an accessory corpus luteum (CL) after AI might increase the pregnancy per AI (P/AI) in heat stressed dairy cows. Starting at d 50±3 post-partum, 113 lactating Holstein cows from one commercial herd during summer were scored for body condition, blood sampled and examined by ultrasound. Those bearing a CL&gt;25mm and progesterone (P4) level&gt;2ng/mL were synchronized using a double PGF2α injection given 12 h apart and AI-ed at detected estrus. In total 18 cows, there were not any signs of estrus (n=10) nor a P4 level &lt;2ng/mL at the time of enrolment (n=8) and therefore they were excluded from the study, leading to 95 cows finally enrolled.. At d5 post-AI, cows were randomly allocated into 2 groups: control group (CON, n=45) without any additional treatment, and treatment group (GnRH, n=50), treated with 0.008 mg Buserelin – a GnRH agonist. Blood sampling and ultrasound examination were done at d5, d14 and at d21 after AI, whereas the pregnancy diagnosis was done at d21 and d30 after AI. Average daily temperature and relative humidity values were used to calculate the temperature-humidity index (THI). The average THI during the experiment was 79.5±0.6. At d5, no differences were observed neither between the number of the CL nor between the P4 level in both groups. At d14 and d21, 82% of the GnRH-treated cows had more than one CL versus 0% of the CON cows. Both at d14 and 21, GnRH-treated cows had higher P4 levels compared to the CON cows (p&lt;0.05). In addition, P/AI were higher in the GnRH group than in the CON group (65% vs. 48.3%, p&lt;0.05), whereas late embryonic losses were higher in CON in comparison to GnRH cows (10.6 vs. 4%, respectively). The BCS at the moment of insemination did not affect P/AI (p&gt;0.05). In conclusion, the induction of an accessory CL at d 5 after AI might increase P/AI in heat stressed dairy cows.

Effects of GnRH or hCG on day 11 after artificial insemination in cows luteal activity

In order to optimize luteal function by human chorionic gonadotrophin (hCG) or gonadotrophin releasing hormone (GnRH) on day 11 after artificial insemination (AI). 33 cows synchronized by the Ovsynch and divided into 3 groups according to the type of treatment: 1) hCG (1500 IU, n=11); 2) GnRH (100 µg, n=11); and 3) control (2 mL of saline, n=11). Blood samples were collected from all animals every 3 days from day 5 to day 23 to determine progesterone concentration. Ultrasonography was used to monitor the luteal surface structures at the time of blood sample collection. An accessory corpus luteum (CL) formed in 63.63% of cows treated with GnRH and with hCG, resulting in an increase in the total luteal tissue area compared with the controls. Thus, the volume of the principal CL was increased by hCG but tended to be similar to GnRH compared with the controls. Additionally, compared with the control group, hCG-treated and GnRH-treated cows had increased progesterone concentrations (p&lt;0.0001). Among the hCG-treated cows, their progesterone concentration increased compared with GnRH-treated cows.

The GnRH analogue dephereline given in a fixed-time AI protocol improves ovulation and embryo survival in dairy cows

This study compares the fertility effects of inducing ovulation using the GnRH analogue, dephereline, versus natural GnRH at the end of a 5-day progesterone(P4)-based protocol for fixed-time artificial insemination (FTAI) in in heat-stressed and non-heat stressed lactating dairy cows. Cows were given GnRH (GnRH group, n = 369) or dephereline (DEPH group, n = 379) and were inseminated 14–20 h later. Dephereline treatment increased corpus luteum (CL) size on Day 7 post-AI compared with GnRH (P < .0001) while a one-mm increase in CL size was found to give rise to a 1.1-fold increase in the pregnancy rate at FTAI (P = .001). Based on odds ratios, the interaction between treatment and heat stress had a significant effect on the ovulation failure rate (P < .01). This meant that relative to non-heat-stressed GnRH-treated cows, ovulation failure was 2.9 times more likely in heat-stressed GnRH-treated cows (P = .001), 0.3 times less likely in non-heat-stressed DEPH-treated cows (P = .04) and was similar in heat-stressed DEPH-treated cows. Further, non-heat-stressed DEPH-treated cows were more likely to conceive by a factor of 1.6 than the remaining cows (P = .03). Finally, GnRH-treated multiparous cows were 9.9 times more likely to suffer pregnancy loss than the remaining cows (P = .03). Our results indicate that, compared to treatment with GnRH, dephereline reduced the risk of ovulation failure and consequently increased the pregnancy rate under heat stress conditions. In multiparous cows, dephereline treatment also reduced the negative age effect on pregnancy maintenance.

Inducing ovulation with hCG in a five-day progesterone-based fixed-time AI protocol improves the fertility of anestrous dairy cows under heat stress conditions

This study compares the fertility effects of inducing ovulation using human chorionic gonadotropin (hCG) versus gonadotropin releasing hormone (GnRH) at the end of a 5-day progesterone(P4)-based protocol for fixed-time artificial insemination (FTAI) in heat-stressed and non-heat stressed anestrous lactating dairy cows. Heat stress (HS) was defined as an environmental temperature-humidity index (THI) > 72. A P4 intravaginal device (CIDR) was fitted for five days and GnRH administered upon CIDR insertion and a double dose (24 h apart) of prostaglandin F2α upon CIDR removal. Cows then received either GnRH (GnRH group; n = 506), or hCG (hCG group; n = 493) 36 h after CIDR removal and were inseminated 50–56 h after CIDR removal. Ovulation failure was investigated in a subset of 425 cows: 223 and 202 receiving GnRH and hCG, respectively. Based on odds ratios, the interaction between treatment and HS had a significant effect on the ovulation failure rate (P = 0.01). This meant that compared to the rates recorded in non-heat-stressed, GnRH-treated cows (13%), ovulation failure in heat-stressed GnRH-treated cows (25.3%) was more likely by a factor of 2.3 (P = 0.04), in non-heat-stressed hCG-treated cows (2.3%) was less likely by a factor of 0.16 (P = 0.02) and was not significantly different in heat-stressed hCG-treated cows (7%). Interactions between treatment and HS and between treatment and parity had a significant effect on the pregnancy rate (P = 0.0001 and P = 0.001, respectively). The treatment-HS interaction determined that compared to the rates recorded in non-heat-stressed, GnRH-treated cows (30.5%), pregnancy in heat-stressed GnRH-treated cows (17.6%) was less likely by a factor of 0.48 than the remaining cows (P = 0.001), whereas because of the treatment-parity interaction, compared to the rates recorded in primiparous, GnRH-treated cows (31.4%), pregnancy in GnRH-treated multiparous cows (18.9%) was less likely to conceive by a factor of 0.51 than the remaining cows (P = 0.002). No significant effects of treatment on the rates of pregnancy loss or twin pregnancy were identified by binary logistic regression. In conclusion, hCG treatment given at the end of a 5-day P4-based protocol for FTAI improved ovulation and pregnancy rates in anestrous cows under conditions of HS and also had a beneficial impact on the pregnancy rate in anestrous multiparous cows throughout the year.

Effect of GnRH treatment at embryo transfer on pregnancy rate and early embryonic death of Holstein-Friesian cows

This study was undertaken to explore the influence of gonadotropin-releasing hormone; GnRH treatment at embryo transfer on pregnancy rate and early embryonic mortalities of Holstein-Friesian cows. This study was executed at the Department of Artificial insemination, Directorate of Animal Resource, Ministry of Agriculture using 58 Holstein-Friesian cows prepared for embryo transfer. The cows were randomly distributed into two groups following their normal estrus cycle. The first group (n=21) was left without any treatment and regarded as control (T1), while the second group (n=2) was injected with GnRH (10 µg per cow; T2) at the 7th day of their normal estrus cycle, and the estrus was monitored for 6 sequential cycles. The pregnancy was checked at days 45, 60 and 120 post-mating (PM) using rectal palpation. Pregnancy and calving rates as well as early embryonic mortality percentage were estimated for all cows. The bulls that born for the embryo transfer (n=5) was used for artificially inseminated of cows following evaluation of their semen. Greater pregnancy rates were observed for the GnRH-treated cows (T2) at days 45 (43. 24%) and 120 (37.84%) PM as compared with T1 group (33.33 and 28.57% respectively). Concomitantly, the early embryonic mortality percentage was reduced in T2 groups (56.76%) in comparison with the T1 group (66.76%) at day 45 PM. Greater (P≤ 0.05) calving rate was recorded for T2 group (37.84%) as compared with T1 group (28.57%). Using of GnRH treatment at embryo transfer has positive economic return resulting from higher pregnancy and calving rates as well as reducing early embryonic mortality percentage. Four bulls from the T2 group were born versus one bull born from T1 group. These bulls was used currently for semen collection and cryopreservation at the Department of Artificial Insemination, and produced 158,016 and 39,504 semen straws respectively with net profit of US$ 701,227 for T2 group and US$147,228 for T1 group.

Effect of estradiol cypionate and GnRH treatment on plasma estradiol-17β concentrations, synchronization of ovulation and on pregnancy rates in suckled beef cows treated with FTAI-based protocols.

Two experiments were conducted to evaluate the effect of different ovulation inducers on E-17β plasma concentrations, synchronized ovulations and pregnancy rates. In Experiment 1, cows received a progesterone intravaginal device (PID) with 1g of progesterone (P4) plus 2mg of estradiol benzoate (EB) (day 0). At PID removal (day 8), cows received 0.150mg of D-cloprostenol and were randomly assigned to four treatment groups (n=10/treatment): Group ECP: 1mg of estradiol cypionate at PID removal, Group EB: 1mg of EB 24hr after PID removal, Group GnRH: 10μg of GnRH 48hr after PID removal, Group ECP-GnRH: 1mg of ECP at PID removal plus 10μg of GnRH 48hr later. Ultrasonographic examinations were performed to detect the dominant follicle and ovulation. GnRH-treated cows ovulated later (p<.05) compared to ECP- and ECP+GnRH-treated cows. There were effects of treatment, time and their interaction on E-17β concentrations (p<.05). ECP treatment affected plasma E-17β concentration, which increased earlier and decreased later compared to treatments without ECP. In Experiment 2, cows received (i) ECP: n=126; (ii) EB: n=126; (iii) GnRH: n=136; (iv) ECP+GnRH: n=139; FTAI was performed 48-50hr after PID removal. Pregnancy rates did not differ among ovulation inducers (p>.05; ECP: 54.0%, 68/126; EB: 49.2%, 62/126; GnRH: 40.4%, 55/136; ECP+GnRH: 43.9%, 61/139). In conclusion, ECP administration (ECP and ECP+GnRH treatments) affected E-17β concentrations, determining its earlier increase and later decrease compared to treatments without ECP (EB and GnRH treatments). ECP+GnRH-treated cows achieved the best distribution of ovulations without affecting pregnancy rates.

Alterations in bone morphogenetic protein 15, growth differentiation factor 9, and gene expression in granulosa cells in preovulatory follicles of dairy cows given porcine LH

In a previous work, using porcine LH (pLH) in lieu of GnRH for synchronizing ovulation in dairy cows improved pregnancy rates without increasing plasma progesterone concentrations after ovulation. The LH profile is known to remain elevated above basal concentrations (≥1 ng/mL) for up to 20 hours in pLH-treated cows compared to less than 6 hours in GnRH-treated cows. Because LH triggers a cascade of signaling networks in the preovulatory follicle to promote final maturation and support oocyte competence, we hypothesized that dissimilar LH profiles will differentially regulate the intrafollicular factors and expression of downstream genes associated with improved oocyte competence. Specific objectives were to determine differences in the abundance of oocyte-secreted factors in the preovulatory follicular fluid and target genes in granulosa cells associated with oocyte competence, in response to exogenous porcine LH or GnRH-induced endogenous bovine LH exposure, in dairy cows. Follicular contents were aspirated by a transvaginal ultrasound-guided procedure from the preovulatory follicle of cyclic, nonlactating Holstein cows 21 ± 1 hour after administration of either pLH (25-mg) or GnRH (100-μg). Mature forms of bone morphogenetic protein 15, growth differentiation factor 9, and transforming growth factorβ1 were approximately 2-fold more abundant in pLH-treated cows which were exposed to an extended, low LH profile, than in GnRH-treated cows that had a short, high LH profile. The relative abundance of messenger RNA for cyclooxygenase-2, LH receptor, and progesterone receptor in granulosa cells, was about two-, eight-, and two-fold higher, respectively, in cows subjected to pLH than GnRH treatment. We infer that the improved pregnancy rate after pLH-induced ovulation reported previously, occurred through greater activation of intrafollicular transforming growth factor-β1 superfamily members, as these proteins promote cumulus expansion and oocyte competence.

Treatment of Ovarian Cysts in Dairy Cows with Simultaneous Administration of GnRH and PGF2α has no Clear Advantage Over the Use of GnRH Alone

Abstract The aim of the study was to determine the therapeutic efficacy o f simultaneous administration of GnRH and PGF2α in dairy cows with ovarian cysts. Ovarian cyst-affected dairy cows were divided into two experimental groups: 54 cows treated with GnRH and PGF2α, and 42 cows treated with GnRH alone, whereas 22 untreated cows served as the control group. Clinical response and reproductive performance were evaluated. The cumulative disappearance was better in treated cows than in the control group; however, there were no differences between the treatment groups (92.6; 95.2% vs. 72.3%). The mean interval from calving to conception was not significantly shorter (being so by 29 d) in the GnRH/PGF2α group than in the cows treated with GnRH alone (P &gt; 0.05). The intervals from treatment to conception were also similar in these groups. The pregnancy rate in both treated groups was similar (62%) and higher than in the control cows (53%). In the cows with luteal cysts, the total pregnancy rate was higher in all experimental groups; however, only in GnRH-treated cows was this difference statistically significant (77.8% vs. 50.0%, P &lt; 0.05). With time after parturition, the pregnancy rate decreased in all groups. In general, the cows treated with GnRH and PGF2α simultaneously displayed a good clinical response and slight improvement in reproductive performance compared to the single-therapy GnRH group; however, this was not fully convincing.

Inducing ovulation early postpartum influences uterine health and fertility in dairy cows

The objective of the current study was to evaluate the effect of GnRH early postpartum on induction of ovulation, uterine health, and fertility in dairy cows. Holstein cows without a corpus luteum (CL) at 17±3 DIM were assigned randomly to receive i.m. GnRH (n=245) at 17±3 and 20±3 DIM or remain as controls (n=245). Ovaries were scanned by ultrasonography twice weekly totaling 4 examinations. Ovulation was characterized by the appearance of a CL ≥20mm at any ultrasound or CL <20mm in 2 consecutive examinations. Clinical and cytological endometritis were diagnosed at 35 DIM. Compared with control, GnRH increased ovulation up to 3.5d after the last treatment (78.7 vs. 45.0%) and did not affect the prevalence of clinical endometritis (23.9 vs. 18.6%) or cytological endometritis (30.9 vs. 32.8%). Prevalence of clinical endometritis increased in cows that had calving problems (32.6 vs. 15.9%) and metritis (40.6 vs. 15.8%). Metritis increased prevalence of cytological endometritis (50.7 vs. 23.5%). Treatment with GnRH did not affect pregnancy per artificial insemination at 32 (37.6 vs. 38.6%) or 74d after artificial insemination (35.0 vs. 31.5%), but reduced pregnancy loss (6.8 vs. 18.1%). No overall effect of GnRH treatment on hazard of pregnancy was observed; however, an interaction between GnRH treatment and ovulation showed that GnRH-treated cows that ovulated had increased hazard of pregnancy by 300 DIM compared with GnRH-treated and control cows that did not ovulate (hazard ratio=2.0 and 1.3, respectively), but similar to control cows that ovulated (hazard ratio=1.1). Gonadotropin-releasing hormone early postpartum induced ovulation without affecting uterine health, but failed to improve pregnancy per artificial insemination or time to pregnancy, although it reduced pregnancy loss.

Progesterone Profiles in the Caudal Vena Cava and Jugular Vein in Response to Pulsatile Luteinizing Hormone Stimulation Induced by GnRH Treatment During the Mid-luteal Phase in Lactating Dairy Cows

The aim of this study was to examine whether increased frequency of luteinizing hormone (LH) pulses influences luteal progesterone (P4) secretion by measuring progesterone concentrations at the secreted (caudal vena cava) and circulating levels (jugular vein) in lactating dairy cows. Cows received six intravenous administrations of 2.5 μg of GnRH (gonadorelin acetate, n=4) or 2 ml saline (n=3) at 1-h intervals on 12.4 ± 0.4 (mean ± SE) days after ovulation. Blood samples were collected from the caudal vena cava and jugular vein every 12 min for 12 h (6 h before and after treatment). During the 6 h after treatment, frequency of LH pulses (5.3 ± 0.3 and 3.0 ± 0.0 pulses/6 h) and mean LH concentration (0.50 ± 0.06 and 0.38 ± 0.05 ng/ml) were greater (P<0.05) in GnRH-treated cows than in saline-treated cows. Mean P4 concentration and amplitude of P4 pulses in the caudal vena cava during the 6 h after treatment were greater (P<0.05) in GnRH-treated cows than in saline-treated cows, but the frequency of P4 pulses was not different between the groups. Mean P4 concentration in the jugular vein during the 6 h after treatment was also higher (P<0.05) in GnRH-treated cows than in saline-treated cows (7.0 ± 1.3 and 5.4 ± 0.9 ng/ml). These results indicate that the increased frequency of LH pulses stimulates progesterone secretion from the functional corpus luteum and brings about higher P4 concentrations in the circulating blood in lactating dairy cows.

New Trends For Estrus Synchronization Using A Combination Of Gonadotropins, Prostaglandin And Estradiol Cypionate In Dairy Cows

This study was conducted to through the light on a recent method for estrus synchronization in lactating dairy cows using PGF2α, GnRH and estradiol cypionate (ECP). Four treatments were performed on sixty dairy cows. In treatment 1 (PP), cows received two injections of PGF2α on days 0 and 11 (n=14); while in treatment 2 (PGP), cows were injected twice PGF2α on days 0 and 11 and 100 ug of GnRH on day 3 after the 1st injection (n=14). In treatment 3 (PGPE-0), cows were treated with PGP and 1 mg of ECP at the same time of 2nd PGF2α injection (n=16). In treatment 4 (PGPE-1), cows were treated with PGP and 1 mg of ECP one day after 2nd PGF2α injection (n=16). The cows were examined rectally and ultrasonographically by B-mode Ultrasound System [Pie-Medical Scanner-240] with a 6-8 MHz linear rectal transducer. Every cow was blood sampled at selected intervals for progesterone and estradiol assay and inseminated at estrus. The results showed a higher percentage of GnRH-treated cows (PGP) ovulated after 1st PGF2α injection than the non treated (PP) cows (64.3% vs 50%; P<0.05). The GnRH-treated cows tended to have a larger mature follicle present at 2nd PGF2α injection. Subsequently, the percentage of cows that ovulated after 2nd PGF2α injection was 71.4% vs 50% for GnRH-treated cows than none treated ones, respectively. Two days after 2nd PGF2α injection, cows treated with PGP had a higher peak preovulatory concentrations of estradiol compared to PP treated cows (3.2±0.48 vs 2.6±0.45 pg/ml). Additionally, cows treated with ECP (PGPE-0 and PGPE-1) had a higher peak preovulatory concentrations of estradiol (6.3±0.43 and 6.99±0.63 pg/ml; P<0.01); and a higher percentage ovulation (75.0% and 87.5%) than the other treated groups (PP or PGP). Thus, a higher percentage of ECP (especially PGPE-1 group) treated cows were observed in standing estrus and ovulated after 2nd PGF2α injection than the other treated groups. Submission rates (number of inseminated/totalX100), differed statistically across treatments, especially those treated with ECP, as well as; the conception and pregnancy rates were observed higher with the ECP treated cows than the other treatments. In conclusion, PGP protocol increased the number of cows that ovulated after 1st PGF2α injection and produced more mature follicles at the time of 2nd PGF2α injection. The combination of ECP and PGP (PGPE-1) enhanced the expression of estrus and increased ovulation percentage, thus it is potentially a new method to routinely synchronize estrus and ovulation in dairy cows.

Comparison of the effect of estradiol benzoate plus progesterone and GnRH on the follicular wave emergence and subsequent follicular development in CIDR-treated, lactating dairy cows with follicular cysts

This study examined the effect of estradiol benzoate (EB) plus progesterone (P4) as compared with GnRH on follicular wave emergence and follicular development, and synchrony of ovulation and pregnancy rates following a second injection of GnRH in a controlled internal drug release (CIDR)-based timed AI (TAI) protocol in lactating dairy cows with follicular cysts. Lactating dairy cows diagnosed with follicular cysts received a CIDR device, with an injection of 2 mg EB plus 50 mg P4 (EB + P4 group) or with an injection of 100 μg GnRH (GnRH group) at the beginning of the experiment (day 0). Thereafter, all received PGF 2α at the time of CIDR removal on day 7, GnRH on day 9, and TAI 16 h later. Follicular wave emergence occurred within 7 days in 12/15 EB plus P4-treated and 14/15 GnRH-treated cows ( P > 0.05). The interval to wave emergence was longer in the EB + P4 group (4.8 ± 0.4 days) than in the GnRH group (2.0 ± 0.2 days). The mean diameters of preovulatory follicles and the proportion of cows with preovulatory follicles greater than 12 mm on day 9 did not differ between groups ( P > 0.05). The proportion of cows with synchronized ovulations by 40 h after the GnRH injection on day 11 and pregnancy rates to TAI did not differ between the EB + P4 (13/15 and 36.7%) and the GnRH (14/15 and 53.3%) groups, respectively. Results suggest that a single treatment with EB plus P4 as compared with GnRH simultaneously with CIDR insertion in lactating dairy cows with follicular cysts will result in relatively asynchronous emergence of a new follicular wave, but subsequently similar sizes of preovulatory follicles and synchronous ovulation, resulting in similar pregnancy rates to TAI.

19 EFFECTS OF ESTRADIOL OR GnRH ON FOLLICULAR WAVE EMERGENCE AND PREGNANCY RATES FOR A CIDR-BASED TIMED AI PROTOCOL IN REPEAT BREEDER DAIRY COWS

Repeat breeding of a high yielding cow causes enormous economic loss to the dairy producers. In this study, we examined the effect of estradiol benzoate (EB) or GnRH on follicular wave emergence and follicular development, and on pregnancy rates for a CIDR-based timed AI (TAI) protocol in repeat breeder dairy cows. Repeat breeder cows received a CIDR device (InterAg, Hamilton, New Zealand), with an injection of 1 mg EB (SY Esrone�; Samyang, Seoul, Korea) plus 50 mg progesterone (P4; SY Ovaron�; Samyang) (EB + P4 group, n = 36) or with an injection of 250 �g Gonadorelin (GnRH, Fertagyl�; Intervet, Boxmeer, The Netherlands) (GnRH group, n = 35) at the beginning of the experiment (Day 0). On Day 7, CIDR devices were removed and all cows received PGF2� (Lutalyse�; Pharmacia &amp;amp; Upjohn, Puurs, Belgium). Thereafter, cows in the EB + P4 group received an injection of 1 mg EB on Day 8, and TAI 30 h later; those in the GnRH group received an injection of 250 �g GnRH on Day 9, and TAI 19 h later. In a subset of cows for both groups (15 cows from each group), the ovaries of the cows were examined by transrectal ultrasonography (Sonoace 600 with 7.5 MHz linear-array transducer; Medison Co., Seoul, Korea) every 24 h from Days 0 to 8, on Day 10, and on Day 13 for the EB + P4 group, and every 24 h from Days 0 to 9, on Day 11, and on Day 14 for the GnRH group, to observe changes in ovarian structures (follicles and corpora lutea). Pregnancy was diagnosed 35 to 60 days after TAI, using both ultrasonography and rectal palpation. Data were analyzed using Fisher&amp;apos;s exact, Student&amp;apos;s t-, and chi-square tests. Follicular wave emergence occurred within 7 days in 12/15 EB + P4-treated and 13/15 GnRH-treated cows (P &amp;gt; 0.05). The mean diameters of preovulatory follicles were smaller (P &amp;lt; 0.05) in the EB + P4 group (12.1 � 0.1 mm) than in the GnRH group (13.8 � 0.1 mm). However, the proportion of cows with synchronized ovulation and pregnancy rates to TAI did not differ (P &amp;gt; 0.05) between the EB + P4 (11/15 and 19.4%, respectively) and the GnRH (13/15 and 34.3%, respectively) groups. In conclusion, treatment with either EB or GnRH for a CIDR-based TAI protocol in repeat breeder dairy cows results in synchronous follicular wave emergence, follicular development, and ovulation, and thus similar pregnancy rates to TAI.

Use of Estradiol Cypionate as a Substitute for GnRH in Protocols for Synchronizing Ovulation in Dairy Cattle

Our purpose was to determine whether estradiol cypionate (ECP) could be substituted for the second GnRH injection of the standard Ovsynch protocol (injection of GnRH given 7 d before and 48h after PGF2α, with timed AI [TAI] 12 to 20h after the second GnRH injection). Lactating dairy cows ranging from 61 to 82 d in milk at TAI were studied in 14 replicates. Main effects were hormone (ECP vs. GnRH) to induce ovulation and exposure to progesterone (P4) or not during the week preceding PGF2α-induced luteolysis. Four treatments were: 1) 100μg of GnRH at 48h after PGF2α (Ovsynch; n = 27); 2) same as Ovsynch, plus a P4-releasing intravaginal insert (CIDR) placed for 7 d beginning at the first GnRH injection (Ovsynch + CIDR, n = 20); 3) same as Ovsynch, but substituting 1mg of ECP for GnRH, and injecting ECP at 24h after PGF2α (Heatsynch; n = 33); or 4) Heatsynch + CIDR (n = 26). The largest follicle was identified by ultrasonography 24h after PGF2α and was monitored every 6h until ovulation. Incidence of estrus was less after GnRH (54%) than after ECP (87%), but more GnRH-treated cows had LH surges detected (95 vs. 65%) and ovulated (100 vs. 86%). Duration of LH surges, but not peak concentrations, was less after GnRH than after ECP (6.1±0.7 vs. 12.2±0.9h). Pre-treatment with P4 reduced the incidence of LH surges but had no effects on incidence of estrus or ovulation. Intervals to the LH surge and ovulation were less after GnRH than after ECP, but intervals between onset of the LH surge and ovulation did not differ (26±2 vs. 30±3h). We concluded that substituting ECP for GnRH resulted in more cows in estrus and slightly fewer ovulating.

Follicular wave emergence, luteal function and synchrony of ovulation following GnRH or estradiol benzoate in a CIDR-treated, lactating Holstein cows

This study evaluated the effect of GnRH or estradiol benzoate (EB) on follicular wave emergence and progesterone concentrations, and following a second injection of GnRH, synchrony of ovulation, and pregnancy rates in a controlled internal drug release (CIDR)-based timed AI (TAI) protocol in lactating Holstein cows. Cows received a CIDR device without hormone (controls), with an injection of 100 μg GnRH or with an injection of 4 mg EB. Thereafter, all received PGF 2α at the time of CIDR removal on Day 7, GnRH on Day 9, and TAI 16 h later. Follicular wave emergence occurred within 7 days in 19/20 GnRH-treated, 14/20 EB-treated and 5/20 control cows ( P < 0.05). The interval to wave emergence was the shorter and less variable ( P < 0.01) in the GnRH group (2.9 ± 0.2 days) than in the EB (4.7 ± 0.5 days) or control (4.8 ± 1.0 days) groups. Serum progesterone concentrations from Days 4 to 7 were higher ( P < 0.01) in the GnRH-treated cows that ovulated than in those that did not ovulate, or in control and EB-treated cows. The diameters of dominant follicle on Day 7 differed among groups ( P < 0.01), and the diameters of the preovulatory follicle on Day 9 were larger ( P < 0.01) in the control and GnRH groups than in the EB group. The proportion of cows with synchronized ovulations did not differ among groups, but pregnancy rate to TAI was higher ( P < 0.05) in the GnRH group (65%; 13/20) than in the control (30%; 6/20) or EB (35%; 7/20) groups. Results suggest that GnRH treatment of CIDR-treated lactating Holstein cows will result in synchronous follicular wave emergence, large preovulatory follicles and synchronous ovulation, resulting in an acceptable pregnancy rates to TAI.

Effects of GnRH Administered to Cows at the Onset of Estrus on Timing of Ovulation, Endocrine Responses, and Conception

Two experiments examined effects of GnRH administered within 3h after onset of estrus (OE) on ovulation and conception in dairy cows. In experiment 1, 46 cows received either saline, 250μg of GnRH, or 10μg of the GnRH analogue, Buserelin. Cows were observed for estrus, blood samples were collected, and ovulations were monitored by ultrasound. In controls, 76% of cows had intervals from estrus to ovulation of≤30h and 24% had intervals>30h. Treatment with either GnRH or GnRH analogue (data combined) increased magnitude of LH surges and decreased intervals from estrus to LH surge or to ovulation. Treated cows all ovulated≤30h after OE. Among control cows, plasma estradiol concentrations before estrus correlated positively with amplitudes of LH surges. Higher plasma progesterone was observed in the subsequent estrous cycle in GnRH-treated cows compared to control cows with delayed ovulations. Experiment 2 included 152 primiparous and 211 multiparous cows in summer and winter. Injection of GnRH analogue at OE increased conception rates (CR) from 41.3 to 55.5% across seasons. In summer, GnRH treatment increased CR from 35.1 to 51.6%. Across seasons, GnRH increased CR from 36.0 to 61.5% in cows with lower body condition at insemination and GnRH increased CR (63.2 vs. 42.2%) in primiparous cows compared to controls. Use of GnRH eliminated differences in CR for cows inseminated early or late relative to OE and increased CR in cows having postpartum reproductive disorders. In conclusion, GnRH at onset of estrus increased LH surges, prevented delayed ovulation, and may increase subsequent progesterone concentrations. Treatments with GnRH increased conception in primiparous cows, during summer, and in cows with lower body condition.

Synchronisation of oestrus in dairy cows using prostaglandin F 2α, gonadotrophin-releasing hormone, and oestradiol cypionate

An oestrous synchronisation protocol was developed for use in lactating dairy cows using PGF 2α, GnRH, and oestradiol cypionate (ECP). In experiment 1, lactating dairy cows received two injections of PGF 2α (on days 0 and 11) (PP; n=10) or two injections of PGF 2α (days 0 and 11) and 100 μg of GnRH on day 3 (PGP; n=10). In experiment 2, cows were treated with PGP ( n=7), or PGP and 1 mg of ECP at the same time (PGPE 0; n=7) or 1 day after the second PGF 2α injection (PGPE 1; n=7). In experiment 3, 101 lactating dairy cows in a commercial herd were assigned to one of three treatments; PP, PGP, or PGPE 1. Follicular growth was measured by ultrasound in experiments 1 and 2. Every cow (experiments 1, 2, and 3) was blood sampled at selected intervals for progesterone and oestradiol assays and inseminated at oestrus. In experiment 1, a higher percentage of GnRH-treated cows ovulated after the first PGF 2α injection (90% versus 50%; P<0.05). The GnRH-treated cows tended to have a larger dominant follicle present at the time of the second PGF 2α injection (16.5±0.5 mm versus 15.0±0.7 mm; P<0.10). The percentage of cows that ovulated after the second PGF 2α injection was similar (60%). In experiment 2, cows treated with ECP had higher peak preovulatory concentrations of oestradiol in plasma (6.99±0.63 versus 3.63±0.63; P<0.01) following the second PGF 2α injection and a higher percentage ovulated (86% versus 43%; P<0.05). A higher percentage of PGPE 1-treated cows in experiment 3 were observed in standing oestrus and ovulated after the second PGF 2α injection (standing oestrus, 26.4, 34.3, and 62.6%, P<0.01; ovulated, 56, 63, and 78%, P<0.05; PP, PGP, and PGPE 1, respectively). In conclusion, the PGP protocol increased the number of cows that ovulated after the first PGF 2α injection and produced a more mature dominant follicle at the time of the second PGF 2α injection. Adding ECP to PGP (PGPE 1) enhanced the expression of oestrus and increased ovulation percentage. The combination of PGP and ECP is potentially a new method to routinely synchronise oestrus and ovulation in dairy cows.

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

Fixed-time AI (TAI) after GnRH-PGF 2α-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 (≤48 h post-PGF 2α; 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 μg GnRH (day −7) and 25 mg PGF 2α (day 0). Cows detected in PE by twice-daily visual observation from day −7 to day 2 were bred by AI 8–12 h later. Cows not detected in PE were randomly assigned by parity, body condition score, and postpartum interval to receive either: (1) 100 μg GnRH at 48 h after PGF 2α and TAI 16 to 18 h later (Ovsynch); or (2) TAI at 72 h post-PGF 2α and a concurrent 100 μg GnRH injection to those cows not detected in estrus between 48 and 72 h post-PGF 2α (modified Ovsynch (MOV)). All hormone injections were im. Twenty percent (68/345) of the cows were detected in estrus before 48 after PGF 2α, of which 5% (17/345) were detected in estrus before PGF 2α (≤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.