Resynchronization Of Ovulation Research Articles

Review: Current status of corpus luteum assessment by Doppler ultrasonography to diagnose non-pregnancy and select embryo recipients in cattle.

A number of potentials uses of Doppler ultrasonography have been explored in the last decades, both as research tools in reproductive physiology investigations and for the reproductive management of farm animals. The objective of this review was to address some of the recent strategies developed in fixed-time reproductive programs and resynchronization of ovulation in cattle, based on the evaluation of corpus luteum function by color-Doppler ultrasound imaging. Recent studies in dairy and beef cattle pointed out to a high accuracy when Doppler ultrasonography is used to assess the functionality of the corpus luteum and identify non-pregnant females at 20-24days after breeding. Therefore, super-early resynchronization programs starting in the second week after timed-artificial insemination or embryo transfer have been developed and are being implemented in commercial assisted reproduction programs; thus, anticipating conception with proven semen or genetically superior embryos. In addition, assessment of corpus luteum blood perfusion can be used for identifying high fertility embryo recipients in fixed-time embryo transfer programs.

Influence of eCG and reproductive management in the resynchronization of ovulation in dairy goats.

Resynchronization protocols have been proposed as a way of shortening females’ unproductive time in the flock, with good results in cattle and sheep. In goats, initial studies have shown that a second progestogen device inserted before luteolysis and pregnancy diagnosis does not interfere with the corpus luteum lifespan or functionality. This study aimed to evaluate the follicular growth, ovulation pattern and pregnancy rate after insertion of a second and new progestogen device for resynchronizing, with or without equine Chorionic Gonadotrophin (eCG), submitted to natural mating (NM) or artificial insemination (AI) to propose a viable resynchronization protocol for dairy goats. A total of 38 multiparous Saanen goats underwent a short-term progesterone protocol [six days exposed to medroxyprogesterone acetate (MAP) intravaginal sponges + 200 IU eCG and 0.12 mg of cloprostenol sodium on the 5th day + 0.025 mg of lecirelin 34 hours after sponge withdrawal] and, on day 16th after the ovulation, received a new MAP device which was retained until day 21. At this moment females were split into four groups: GeCG+NM – 100 IU eCG with NM; GSal+NM – saline solution with NM; GeCG+AI – 100 IU eCG with AI; and GSal+AI – saline solution with AI. Ultrasound scans were performed every 12 h from sponge withdrawal (day 21) until 108 h after sponge withdrawal (day 25) for follicular dynamics evaluation, at 240 h (day 31) for assessing the presence of active corpus luteum, and on day 60 for pregnancy diagnosis. No differences were found regarding ovulation time, synchronization and follicle size. However, GeCG+NM presented a greater estrus manifestation rate (100%) and pregnancy rate (62.5%) when compared to GSal+AI. In conclusion, resynchronization protocols in dairy goats may present satisfactory results.

Increase in the reproductive efficiency of primiparous and multiparous Nellore cows following moxidectin treatment at the onset of a fixed-time artificial insemination protocol

The aim of the present study was to evaluate the effects of moxidectin (MOX – 200 µg/kg/sc) administered on Day Zero of a fixed-time artificial insemination (FTAI) protocol on fecal egg counts and the reproductive efficiency of primiparous and multiparous Nellore beef cows kept in the pasture. A simulation was performed of the possible correlation between the fecal egg count and helminth load per animal (cow versus calf). An economic analysis was performed of the magnitude of the return over investment (ROI) of moxidectin treatment at the onset of the FTAI protocol. Three experiments were performed with a total of 6,320 Nellore females (primiparous and multiparous) and calves approximately 45 days old. The animals were subdivided into two groups: control and treated with MOX subcutaneously on Day 0 concomitant with the reproduction protocol adopted in the first FTAI. Egg counts per gram of feces (EPG) were performed on Days 0 and 11. Resynchronization of ovulation (RO) was performed in cows diagnosed with negative pregnancy 30 days after the first FTAI. Nellore bulls were used for natural service at a proportion of one bull per 25 Nellore cows 10 days after the second diagnosis of gestation (D92). The results of the three experiments indicated that treatment with MOX at the beginning of the FTAI protocol (Day 0) increased the pregnancy rate at the first FTAI and had no effect on the pregnancy rate at the second FTAI (RO), leading to a larger number of pregnant cows at the end of the breeding season, with an ROI of 44.9 and 19.0 for primiparous and multiparous cows, respectively. The mean parasite load (EPG) decreased significantly after treatment with moxidectin in both primiparous and multiparous cows. However, the statement that the difference in the pregnancy rate for the treated cows occurred due to the control of helminth infection should be interpreted with caution. Further studies are needed to gain an understanding the unknown physiological mechanisms of moxidectin that could be affecting the reproductive results.

Resynchronization of ovulation with new and reused intravaginal progesterone-releasing devices without previous pregnancy diagnosis in Bos taurus indicus cows subjected to timed-artificial insemination.

The study aimed to evaluate pregnancy per artificial insemination (P/AI) of cows subjected to synchronization and resynchronization in ovulation protocols using intravaginal progesterone-releasing insert (P4) before pregnancy diagnosis (PD) and the relationship of PR with the diameter of preovulatory follicles (ØPOF) before TAI. Cows (n=378) were distributed into two groups: a resynchronization group with new devices (GRN; n=185) and resynchronization group with used devices (GRU; n=193). On Day 0, both groups received a new P4 and estradiol benzoate (EB). On D8, P4 removal+D-cloprostenol+eCG+estradiol cypionate (EC) was done. On d10, TAI was conducted. On d32, cows were resynchronized and divided into two groups, GRN (n=185) and GRU (n=193). The GRN group received a new P4+EB, and the GRU group received a used P4+EB. On d40, the P4 was removed+PD. The non-pregnant cows received D-cloprostenol+eCG+EC. US was done again on d42 to determine ØPOF before the second TAI. The P/AI of the GRN and GRU groups after synchronization were 56.2% and 57.0% (p=0.87), respectively, and those after resynchronization were 58.0% and 37.3% (p<0.008), respectively. The P/AI of the GRN and GRU groups observed after TAI (synchronization+resynchronization) were 81.6% and 73.1%, respectively (p=0.047). No difference (p=0.067) in ØPOF between the pregnant and non-pregnant cows in the GRN was found, whereas the GRU group showed a significant difference (p=0.003). Resynchronization protocols optimized the P/AI in both groups. New intravaginal devices resulted in greater P/AI and P/AI accumulation in resynchronization as compared with the GRU; the ØPOF was related with P/AI.

16 False-positive rate after anticipation of early pregnancy diagnosis for resynchronization of ovulation in Bos indicus heifers

The objective was to determine the incidence of false-positive pregnancy diagnosis following the use of colour Doppler ultrasonography 20 and 22 days after fixed-time AI (FTAI) in Bos indicus heifers submitted to resynchronization 14 days after first FTAI. In the study, 512 Nellore heifers at 24.5±0.8 months of age and body condition score of 3.4±0.1 were used beginning 14 days after FTAI. On Day 14, heifers received 50mg of short-acting progesterone (Afisterone®, CEVA, São Paulo, Brazil) and a progesterone device (Prociclar®, CEVA). Eight days later (Day 22), the progesterone device was removed. A duplex B-mode (grayscale) and pulse-wave colour Doppler ultrasound instrument (M5, Mindray, Shenzhen, China) equipped with a multifrequency linear transducer was used for the examination of luteal blood flow on Days 20 and 22. The percentage of luteal area with colour Doppler signals of blood flow at each examination was determined as previously described (Ginther 2007) and was classified as low [corpus luteum (CL) with less than 25% vascularized area], intermediate (CL with 25-75% vascularized area), or high (CL with more than 75% vascularized area). Heifers with intermediate and high luteal blood flow were diagnosed as pregnant by Doppler ultrasonography, and heifers with low luteal blood flow were diagnosed as nonpregnant. Heifers diagnosed as pregnant by Doppler ultrasonography were examined 30 days after FTAI by B-mode ultrasound examination for pregnancy diagnosis and to determine the number of false positives (heifers pregnant by Doppler ultrasonography and nonpregnant by B-mode ultrasonography). Statistical analysis was performed by the GLIMMIX procedure of SAS (SAS Institute Inc., Cary, NC, USA). Pregnancy rate by Doppler ultrasonography [Day 20=60.5% (310/512), Day 22=55.3% (283/512); P=0.10] and false-positive percentage [Day 20=29.7% (92/310), Day 22=23.0% (65/2830); P=0.06] were similar on pregnancy diagnoses by Doppler ultrasonography performed 20 and 22 days after FTAI. Furthermore, in the period from 20 to 22 days after FTAI, luteolysis was verified in 5.8% (30/512) of heifers. In conclusion, anticipation of pregnancy diagnosis in 2 days by evaluation of luteal blood flow with colour Doppler ultrasonography (20 days after FTAI) does not interfere with pregnancy rate by Doppler ultrasound and percentage of false positives in Bos indicus heifers.

Adding a second prostaglandin F2α treatment to but not reducing the duration of a PRID-Synch protocol increases fertility after resynchronization of ovulation in lactating Holstein cows

Our objective was to evaluate the effect of a second PGF2α treatment and duration of an Ovsynch protocol that included a progesterone-releasing intravaginal device (PRID) on progesterone (P4) concentrations and pregnancies per artificial insemination (P/AI) after resynchronization of ovulation and timed artificial insemination (TAI). Lactating Holstein cows (n=821) were assigned randomly at a nonpregnancy diagnosis (d 0) to 3 resynchronization protocols: (1) GnRH, d 0; PGF2α, d 7; GnRH, d 9.5 (7D1PGF); (2) GnRH, d 0; PGF2α, d 7; PGF2α, d 8; GnRH, d 9.5); (7D2PGF); or (3) GnRH, d 2; PGF2α, d 7; PGF2α, d 8; GnRH, d 9.5 (5D2PGF). All cows received a PRID at the first GnRH treatment of the resynchronization protocol, which was removed at the first PGF2α treatment, and all cows received TAI approximately 16h after the second GnRH treatment. Blood samples were collected from a subgroup of cows at each treatment of the resynchronization protocols. At 32 d after TAI, cows receiving a second PGF2α treatment (7D2PGF + 5D2PGF cows) had more P/AI (42.6 vs. 35.7%) than cows receiving a single PGF2α treatment (7D1PGF cows). For cows treated with a second PGF2α treatment, decreasing the duration of the protocol did not increase P/AI (41.4 vs. 43.8% for 7D2PGF vs. 5D2PGF cows). At 60 d after TAI, P/AI did not differ between cows treated with the 1 PGF2α (7D1PGF cows) or 2 PGF2α (7D2PGF + 5D1PGF cows) treatments (32.5 vs. 37.9%, respectively). In addition, reducing the duration of the protocol did not increase P/AI at 60 d after TAI (37.8 vs. 38.5% for 7D2PGF vs. 5D2PGF cows). Pregnancy loss from 32 to 60 d after TAI was not affected by the number of PGF2α treatments (8.5 vs. 10.6%, for 7D1PGF vs. 7D2PGF + 5D2PGF cows) or the duration of the protocol (9.1 vs. 12.1%, for 7D2PGF vs. 5D2PGF cows). The percentage of cows with incomplete luteal regression at the second GnRH treatment tended to differ among treatments and was lowest for 7D2PGF cows, intermediate for 5D2PGF cows, and greatest for 7D1PGF cows (1.9 vs. 6.9 vs. 11.0%, respectively). In conclusion, addition of a second PGF2α treatment tended to decrease the percentage of cows with incomplete luteal regression and increased P/AI 32 d after AI, whereas decreasing the duration of the Ovsynch protocol did not increase P/AI.

Effect of presynchronization with human chorionic gonadotropin or gonadotropin-releasing hormone 7 days before resynchronization of ovulation on fertility in lactating dairy cows

Our objectives were to (1) compare the effect on pregnancies per artificial insemination (P/AI) of presynchronization of the estrous cycle with human chorionic gonadotropin (hCG) 7d before resynchronization of ovulation (Resynch) initiated 25d after timed artificial insemination (TAI) and compare the presynchronization treatment with the Double-Ovsynch (DO) protocol, and (2) evaluate whether hCG for presynchronization could be replaced with GnRH. In experiment 1, lactating Holstein cows were blocked by parity and were randomly assigned to receive (1) Resynch-25 (D25), the Resynch protocol (GnRH-7 d-PGF2α-56h-GnRH-16h-TAI) initiated 25d after TAI (n=418); (2) HGPG, presynchronization with hCG (2,000IU of Chorulon) 7d before D25 (n=450); and (3) DO (Pre-Resynch, GnRH-7 d-PGF2α-72h-GnRH; Breeding-Resynch, GnRH-7 d-PGF2α-56h-GnRH-16h-TAI) initiated 22d after TAI (n=405). At 29d after TAI, cows in the HGPG (37.3%) and DO (35.8%) groups had more P/AI than did cows in the D25 group (28.0%), and cows in the HGPG and DO groups continued to have more P/AI than did cows in the D25 group at 53d after TAI. Presynchronization with hCG induced ovulation in 76% of the cows, which increased the percentage of HGPG cows with a corpus luteum at the initiation of Resynch compared with cows in the D25 group. In experiment 2, the D25 (n=368) and HGPG (n=338) treatments described in experiment 1 were compared in addition to a third treatment (GGPG; n=351), in which the hCG injection 18d after TAI was replaced with a GnRH injection (200µg of gonadorelin). At 32d after TAI, cows in the HGPG group had more P/AI than did cows in the D25 group (33.7 vs. 25.5%), whereas cows in the GGPG group had intermediate P/AI (31.6%). At 53d after TAI, P/AI tended to be greater for cows in the HGPG group than for those in the D25 group, whereas P/AI for cows in the GGPG group did not differ from that for cows in the D25 group. Treatment with hCG and GnRH 18d after TAI induced ovulation in 58.8 and 48.2% of cows, respectively, but did not increase the percentage of cows with a corpus luteum at the initiation of Resynch. More cows in the HGPG and GGPG groups had their estrous cycles synchronized after the resynchronization protocols compared with cows in the D25 group. We conclude that presynchronization with hCG increased fertility by increasing synchronization to the Resynch protocol, whereas presynchronization with GnRH improved synchronization to the Resynch protocol but did not improve fertility when compared with no presynchronization or presynchronization with hCG.

Effect of timing of Cosynch on fertility of lactating Holstein cows after first postpartum and Resynch timed-AI services

To compare two intervals from the PGF 2α injection to the second GnRH injection + timed artificial insemination (TAI) of Ovsynch, lactating Holstein cows received their first postpartum TAI after Presynch + Ovsynch ( n = 352) and second and greater postpartum TAI after resynchronization of ovulation using Ovsynch (Resynch; n = 458). Each week, cows housed in each of four breeding pens were randomized by breeding pen to receive the second GnRH injection of Presynch + Ovsynch or Resynch and TAI either 48 h (Cosynch 48; n = 382) or 72 h (Cosynch 72; n = 428) after the PGF 2α injection of Ovsynch or Resynch. Overall, pregnancies per AI (P/AI) did not differ for cows receiving Cosynch 48 (29%) versus Cosynch 72 (33%). Furthermore, treatment did not affect P/AI for cows receiving first postpartum TAI after Presynch + Ovsynch, for cows receiving second and greater TAI after Resynch, or the proportion of female calves born. In conclusion, delaying the second GnRH injection and TAI from 48 to 72 h after the PGF 2α injection of Ovsynch did not affect P/AI or calf sex ratio. The lack of a difference in fertility between these Cosynch protocols may offer more flexibility for implementing a systematic synchronization protocol when a Cosynch strategy is used.

Resynchronization of ovulation and conception in nonpregnant dairy cows and heifers (2006)

Our objectives were to determine various factors influencing upfront single and multiple ovulation in response to GnRH in a timed arti-ficial insemination (TAI) protocol and subse-quent fertility after altering timing of the sec-ond GnRH injection and AI relative to PGF2αinjection. Replacement heifers (n = 86) and 613 lactating cows previously inseminated were diagnosed not pregnant at biweekly in-tervals to form 77 breeding clusters spanning 36 months. At not-pregnant diagnosis (day 0), females received 100 μg of GnRH, and they received 25 mg of PGF2α7 days later. Females in 2 treatments received GnRH 48 hr (G48) after PGF2αinjection and TAI at the time of the second GnRH injection (G48 + TAI48) or 24 hr later (G48 + TAI72). Females in the third treatment received GnRH 72 hr after PGF2α, when inseminated (G72 + TAI72). Ovaries of females in 65 clusters were scanned at day 0 (first GnRH injection) and 7 days later (PGF2αinjection). Ovarian struc-tures were mapped, and ovulation in response to the first GnRH injection was detected on day 7. When estrus was detected before scheduled TAI, females were inseminated; otherwise TAI conception of remaining fe-males was based on timing of GnRH and AI in 3 treatments. On day 7, 1 or more luteal struc-tures (CL) were detected in 46% of females. Conception rate was 26.5% (98/701) in fe-males that showed estrus and were insemi-nated early. Pregnancy rate was greater in fe-males that ovulated after the first GnRH injec-tion (day 0) and during nonsummer months. Compared with females in late diestrus at nonpregnant diagnosis, cows in early diestrus or those with functional cysts had greater pregnancy rates, but rates were not different from those of cows in proestrus or in metestrus or anestrus. Pregnancy rates did not differ among treatments, but a tendency was detected for a treatment x lactation number interaction. In heifers and first-lactation cows, the G72 + TAI72 treatment produced fewer pregnancies, whereas G48 + TAI48 treatment was least efficacious in older cows. In a TAI protocol for previously inseminated dairy fe-males that are diagnosed not pregnant, subse-quent timed AI pregnancy rates are greater when females are in early diestrus, ovulate in response to the first GnRH injection, or both. (Key Words: Luteolysis, Ovsynch, Ovulation,; Dairy Day, 2006, Kansas State University, Manhattan, KS, 2006

Resynchronization of ovulation and timed insemination in lactating dairy cows: III. Administration of GnRH 23 days post AI and ultrasonography for nonpregnancy diagnosis on day 30

The objective was to compare pregnancy rates to resynchronization and timed AI (TAI) protocols in lactating dairy cows that received GnRH at 23 d and were diagnosed not pregnant at 30 d after the pre-enrollment AI. Nonpregnant cows (624) at ultrasonography on day 30 (study day 0) were classified as diestrus (74.8%), metestrus (5.6%) and without a CL (19.5%). Cows in diestrus were assigned either to the GnRH group (PGF 2α on day 0, GnRH on day 2 and TAI 16 h later, n = 238) or the estradiol cypionate (ECP) group (PGF 2α on day 0, ECP on day 1, and TAI 36 h later, n = 229). Cows in metestrus were assigned to the Modified Heatsynch Group (GnRH on day 0, PGF 2α on day 7, ECP on day 8 and TAI on day 9, n = 35). Cows without a CL ( n = 122) were classified either as proestrus (10.6%), ovarian cysts (7.5%) or anestrus (1.4%), and assigned to factorial treatments (i.e., use of GnRH versus CIDR) to either the GnRH group (GnRH on day 0, PGF 2α on day 7, GnRH on day 9 and TAI 16 h later, n = 28), the CIDR group (CIDR insert from days 0 to 7, PGF 2α on day 7, GnRH on day 9 and TAI 16 h later, n = 34), the GnRH + CIDR group (GnRH on day 0, CIDR insert from days 0 to 7, PGF 2α on day 7, GnRH on day 9 and TAI 16 h later, n = 32), and the control group (PGF 2α on day 7, GnRH on day 9 and TAI 16 h later, n = 28). For cows without a CL, plasma P 4 concentrations were determined on days 0, 7, 10 and 17 and ovarian structures determined on days 0, 7 and 17. Pregnancy rates were evaluated at 30, 55 and 90 d after the resynchronized AI. For cows in diestrus, there were no differences in pregnancy rates on days 30, 55 and 90 for cows in the GnRH (27.5, 26.5 and 24.2%) or ECP (29.1, 25.5 and 24.1%) groups. In addition, there were no differences in pregnancy losses between days 30 and 55 and 55 and 90 between the GnRH (7.0 and 8.6%) and ECP (9.8 and 5.4%) groups. For cows without a CL, GnRH on day 0 increased the proportion of cows with a CL on days 7 and 17 and plasma P 4 concentration on day 17 in cows with ovarian cysts but not for cows in proestrus. The CIDR insert increased pregnancy rate in cows with ovarian cysts but reduced pregnancy rate for cows in proestrus.

Resynchronization of ovulation and timed insemination in lactating dairy cows: I: use of the Ovsynch and Heatsynch protocols after non-pregnancy diagnosis by ultrasonography

The objective was to compare pregnancy rates and pregnancy losses in lactating dairy cows that were diagnosed not pregnant and re-inseminated following either the Ovsynch ® or Heatsynch protocols. Also evaluated were the effects of stages of the estrous cycle, ovarian cysts and anestrus on pregnancy rates for both treatments. Non-pregnant cows ( n = 332) as determined by ultrasonography on day 27 post-AI (study day 0) were divided into two groups. Cows in the Ovsynch group ( n = 166) received GnRH on day 0, PGF 2α on day 7, GnRH on day 9, and timed AI (TAI) 16 h later (day 10). Cows in the Heatsynch group ( n = 166) received GnRH on day 0, PGF 2α on day 7, estradiol cypionate (ECP) on day 8, and TAI 48 h later (day 10). Cows detected in estrus on days 8 and 9 were inseminated and included in the study. On day 0, cows were classified according to different stages of the estrous cycle, or presence of ovarian cysts or anestrus. Pregnancy rates were evaluated 27, 45 and 90 days after resynchronized AI. Overall, there was no difference in pregnancy rates on days 27, 45 and 90 between cows in the Ovsynch (25.2, 17.5, and 13.9%) and Heatsynch (25.8, 19.9, and 16.1%) groups. There was no difference in pregnancy losses from days 27 to 45 and days 45 to 90 for cows in the Ovsynch (25.0 and 17.9%) and Heatsynch (14.7 and 10.3%) groups. However, pregnancy rates were increased when cows in metestrus were subjected to the Heatsynch protocol and cows with ovarian cysts were subjected to the Ovsynch protocol.