292 Evaluation of two Beef cow Fixed-Time AI Protocols That Utilize pre-Synchronization
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AbstractPre-synchronization has been evaluated as a method to improve synchrony of ovulatory follicles before fixed-time AI (FTAI). The objective was to compare FTAI results in beef cows from two protocols that utilize pre-synchronization. Blood samples were collected on d-14 (d0=CIDR removal) to determine progesterone concentration at the start of synchronization (P4start: 1ng/mL=high, > 1ng/mL=low). In a subset (n=1,032), an additional blood sample was taken between d-21 and -29 to determine cyclicity. Cows (n=1,119), from 21 herds, were grouped by days postpartum and age and randomly assigned to one of two protocols. Cows assigned to the PG 6-day CIDR protocol (PG6d) received prostaglandin F2 (PG) on d-9, CIDR insertion and GnRH on d-6, and CIDR removal and PG on d0. Cows assigned to the 7&7 Synch protocol (7&7) were administered PG and CIDR insertion on d-14, GnRH on d-7, CIDR removal and PG on d0. For both protocols, FTAI occurred coincident with GnRH 66 h after second PG. Pregnancy was determined by transrectal ultrasonography 30-40 d following FTAI. The GLIMMIX procedure of SAS (9.4) was used to detect differences in estrus response and pregnancy success with herd included as a random variable. Estrus response (0 to 66 h) was influenced by treatment (P> 0.01; PG6d=605% and 7&7=744%), Body Condition Score (P> 0.01), cycling status (P=0.03), P4start (P> 0.01), and a P4start by treatment interaction (P> 0.001; PG6d-highP4=626%, PG6d-lowP4=586%, 7&7-highP4=843%, 7&7-lowP4=606%). Pregnancy success was influenced by estrus expression (P> 0.01; estrus=384% and no estrus=626%), and a treatment by P4start interaction (P=0.04; PG6d-highP4=585%, PG6d-lowP4=397%, 7&7-highP4=495%, 7&7-lowP4=558%) but was not influenced by treatment (P=0.45; PG6d=494% and 7&7=524%). In conclusion, effectiveness of pre-synchronization method depends on a cows physiological status at the beginning of the protocol. The 7&7 protocol increased estrus response compared to PG6d, but there was no difference in pregnancy success.
