Development and evaluation of the 7 and 7 synch protcol for enhanced control of the bovine estrous cycle among postpartum beef cows
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Experiment 1 was designed to evaluate the effect of treatments in advance of gonadotropin-releasing hormone (GnRH; 100 [mu]g gonadorelin) administered at the start of estrus synchronization. We hypothesized that administration of prostaglandin F2[alpha] (PGF2[alpha]; 500[mu]g cloprostenol) followed by treatment with an intravaginal progesterone-releasing insert (CIDR; 1.38g progesterone) would result in increased follicle size at GnRH, thereby enhancing response to GnRH and overall response to estrus synchronization. Postpartum suckled beef cows (n = 194) in two locations were assigned to one of five treatments (Figure 1) based on age, days postpartum, and body condition score. Cows in treatment 1 (control) received the 7-d CO-Synch + CIDR protocol: administration of GnRH and CIDR insertion on day -10, and administration of PGF2[alpha] and CIDR removal on day -3. Treatments 2-5 were designed as a two-by-two factorial. On day -17, cows in Treatments 2-5 received a CIDR insert, either with (Treatments 2 and 3) or without (Treatments 4 and 5) administration of PGF2[alpha]. On day -10, all cows were administered GnRH, and CIDR inserts were either removed (Treatments 2 and 4) or remained in place until day -3 (Treatments 3 and 5). On day -3, estrus detection aids (Estrotect) were applied and a representative subset of cows (n = 64) in each treatment were fitted with estrus detection transmitters (Accubreed). Blood samples were collected on days -27, -17, -10, -3, and 0 for determination of serum estradiol and/or progesterone concentrations via radioimmunoassay. For a representative subset of cows (n = 104), transrectal ovarian ultrasound was performed to assess ovarian follicle size and presence of corpora lutea on days -17, -10, -3, and 0. Treatment with PGF2[alpha] and CIDR in advance of GnRH (Treatments 2 and 3) resulted in increased diameter of the largest ovarian follicle (P [less than] 0.001) and increased serum concentrations of estradiol (P [less than] 0.0005) on day -10. In addition, variation among cows in CL status tended to be decreased (P = 0.08) on day -3, with cows more likely to have a single CL rather than no CL or multiple CL. Lastly, estrous response prior to fixed-time artificial insemination tended (P = 0.08) to be improved. Results support the hypothesis that administration of PGF2[alpha] and treatment with a CIDR for 7 days prior to GnRH improves the likelihood of GnRH response and enhances response of mature beef cows to estrus synchronization. Experiment 2 was designed to evaluate the effectiveness of the recently developed 7 and 7 Synch protocol to synchronize estrus and ovulation among recipients prior to embryo transfer. Postpartum beef cows (n=1,358) across thirteen locations were assigned to either the 7-d CO-Synch + CIDR protocol or the 7 and 7 Synch protocol prior to estrus detection and subsequent embryo transfer. Cows were preassigned to balanced treatments within location based on age and days postpartum, with body condition score recorded at embryo transfer. Cows assigned to the 7-d CO-Synch + CIDR protocol were administered gonadotropin-releasing hormone (GnRH; 100[mu]g gonadorelin acetate) on Day 0, an intravaginal controlled internal drug release insert (CIDR; 1.38 g progesterone) from Day 0 to Day 7, and prostaglandin F2[alpha] (PGF2[alpha]; 25 mg dinoprost tromethamine) coincident with CIDR removal on Day 7. Cows assigned to the 7 and 7 Synch protocol were administered PGF2[alpha] (25 mg dinoprost tromethamine) coincident with CIDR insertion on Day -7, GnRH (100 [mu]g gonadorelin acetate) on Day 0, and PGF2[alpha] (25 mg dinoprost tromethamine) coincident with CIDR removal on Day 7. The 7 and 7 Synch protocol was hypothesized to enhance response to GnRH administration on Day 0 among mixed groups of estrous cycling and anestrous recipient cows, ultimately resulting in improved estrous response and synchrony of estrus prior to embryo transfer. Cows were observed for visible signs of estrus following estrus synchronization, with GnRH (100 [mu]g gonadorelin acetate) administered to cows failing to express estrus during the detection period. Embryo transfer was performed approximately seven days after estrusor GnRH administration. Presence of corpora lutea (CL) was determined via transrectal palpation by a single veterinarian blinded to treatment, and embryos were transferred only to cows with palpable CL. Embryo transfer was performed using either fresh or frozen embryos staged and graded according to IETS recommended guidelines, with embryo information recorded for each recipient. The proportion of cows expressing estrus was improved (P [less than] 0.0001) among cows assigned to the 7 and 7 Synch protocol (86% [529/615] vs 76% [488/640]). The proportion of cows expressing estrus and presenting with palpable CL at embryo transfer was greater (P [less than] 0.0001) among cows following treatment with the 7 and 7 Synch protocol compared to the 7-d CO-Synch + CIDR protocol (76% [466/615] vs 65% [418/640]). Consequently, the proportion pregnant to embryo transfer was greater (P [less than] 0.03) following the 7 and 7 Synch protocol (40% [263/653]) compared to the 7-d CO-Synch + CIDR protocol (34% [228/664]). In summary, the 7 and 7 Synch protocol involving administration of PGF2[alpha] and treatment with a CIDR for 7 days prior to GnRH improved the likelihood of estrus expression in recipient cows, increased the proportion of cows eligible to receive an embryo, which resulted in a greater pregnancy rate to embryo transfer.
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