Altering duration of the presynchronization period in a long-term progestin-based estrus synchronization protocol for timed artificial insemination of beef heifers

• Published in: Theriogenology Vol. 136; pp. 66 - 71
• Main Authors: Knickmeyer, E.R., Thomas, J.M., Locke, J.W.C., Bonacker, R.C., Ciernia, L.A., Ketchum, J.N., Ellersieck, M.R., Poock, S.E., Smith, M.F., Patterson, D.J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.09.2019
• Subjects: Animals; Beef heifer; Cattle; Controlled internal drug release; Dinoprost - administration & dosage; Dinoprost - pharmacology; Drug Administration Schedule; Estrus synchronization; Estrus Synchronization - methods; Female; Insemination, Artificial - veterinary; Oxytocics - administration & dosage; Oxytocics - pharmacology; Progesterone - administration & dosage; Progesterone - pharmacology; Progestins - administration & dosage; Progestins - pharmacology; Time Factors; Beef heifer; Controlled internal drug release; Estrus synchronization
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/j.theriogenology.2019.06.027

An experiment was designed to evaluate the effect of extending duration of the presynchronization treatment in a long-term progestin-based estrus synchronization protocol. Heifers were assigned to either an 18 d (Day 0–18) or 14 d (Day 4 to Day 18) CIDR® treatment (1.38 g progesterone controlled internal drug release insert; Zoetis, Madison, NJ), with prostaglandin F2α (PG; 250 μg im cloprostenol sodium) administered 16 d after CIDR® removal (Day 34). Heifers at two locations (location one, n = 193; location two, n = 649) were assigned to treatment based on reproductive tract score (RTS; Scale 1–5) and body weight. Heifers that were assigned RTS 1 were not retained for the trial (n = 6). Estrus detection aids (Estrotect®) were applied at PG. Split-time artificial insemination (STAI) was utilized and AI performed based on expression of estrus at 66 h. Expression of estrus was defined as removal of ≥50% of the grey coating from the Estrotect® patch. Heifers that expressed estrus at 66 h were inseminated then and heifers that had not expressed estrus were inseminated at 90 h. Only heifers that failed to express estrus by 90 h received gonadotropin-releasing hormone (GnRH; 100 μg im gonadorelin acetate) at the time of AI. At location one, blood samples were collected at PG and AI (66 h or 90 h) from all heifers to determine E2 concentration by radioimmunoassay, and transrectal ovarian ultrasound was performed to detail ovarian structures on a subset of heifers (n = 73) at both time points. The proportion of heifers expressing estrus did not differ between treatments, either by 66 h (60%) or in total by 90 h (84%) after PG. Pregnancy rate to STAI did not differ between treatments (P = 0.3; 52%, 14-d CIDR®-PG; 50%, 18-d CIDR®-PG), or at the end of the 60 d breeding season (P = 0.2; 86%, 14-d CIDR®-PG; 82%, 18-d CIDR®-PG). No differences were detected in mean diameter of the dominant follicle at PG (P = 0.6; 10.9 ± 0.4 mm, 14-d CIDR®-PG; 11.0 ± 0.4 mm, 18-d CIDR®-PG) or at STAI (P = 0.3; 12.6 ± 0.4 mm, 14-d CIDR®-PG; 13.2 ± 0.4 mm, 18-d CIDR®-PG), nor were any differences observed between treatments in concentrations of E2 at PG (P = 0.8; 1.1 ± 0.19 pg/ml, 14-d CIDR®-PG; 1.1 ± 0.19 pg/ml, 18-d CIDR®-PG) or STAI (P = 0.6; 3.8 ± 0.19 pg/ml, 14-d CIDR®-PG; 3.6 ± 0.19 pg/ml, 18-d CIDR®-PG). These data indicate that duration of CIDR® treatment can be extended from 14 to 18 d, thus providing flexibility in scheduling without compromising reproductive outcomes. •Extending length of the presynchronization period was evaluated in replacement beef heifers using a long-term progestin based protocol and split-time artificial insemination (STAI).•Estrous response rates following prostaglandin were similar among heifers assigned to a 14 day or 18 day CIDR treatment, with prostaglandin administered 16 days after CIDR removal.•Pregnancy rates resulting from (STAI) were similar among heifers assigned to a 14 day or 18 day CIDR treatment, with prostaglandin administered 16 days after CIDR removal.•Length of CIDR treatment can be extended from 14 to 18 days, thus providing flexibility in scheduling without compromising reproductive outcomes.