PSII-10 - Effect of equine chorionic gonadotrophin-like glycoprotein treatment on fertility in Angus cows subjected to a 7-day CO-Synch protocol

Abstract: This study evaluated the effect of administering a glycoprotein with equine chorionic gonadotropin like activity produced by recombinant DNA technology (eCG-like) associated with a 7-d Co-Synch protocol on estrus rate (ER) and pregnancy per timed AI (P/TAI). A total of 1344 suckled Angus cows (primiparous, n = 381; multiparous, n = 963) from 11 herds were scanned at initiation of synchronization protocol by transrectal ultrasonography and the presence of corpus luteum (CL) and uterine tone was used to classify them by cycling. On Day -10, cows received 100 μg GnRH analogue and a progesterone intravaginal device (IVD; 1.0g progesterone) for 7 days. At IVD removal, cows were administered 500 μg of cloprostenol and randomly assigned to receive 400 IU of eCG-like glycoprotein (Syntex S.A., Argentina, PCT/EP2019/073277; eCG-like, n = 665) or to remain as untreated (Control, n = 679). Also on Day -3, paint was applied on the sacrum to the tail head of each cow. Finally, 100 μg GnRH analog were injected concurrently with TAI on Day 0 (66h after IVD removal) and the ER was evaluated by the degree of paint loss. Pregnancy to TAI was determined on Day 30 by transrectal ultrasonography when an embryo and fluid were detected in the uterus. Body condition score (BCS; scale = 1-9) was evaluated on Days -10 and 30. Optimal BCS was considered ≥ 5 and BCS balance between Days -10 and 30 was classified as negative (lost BCS) or positive (maintained or gained BCS). The associations among treatment, parity, cyclicity at initiation of protocol, optimal BCS on Day -10, and their interactions and ER and P/TAI were analyzed by GLIMMIX (SAS 9.3). Estrus expression and BCS balance were also included as effects in the model of pregnancy per TAI. The effect of herd was included as a random effect. The model specifications included an option to retrieve the mean, SEM, and an adjustment for multiple comparisons (Tukey-Kramer). The percentage of acyclic cows was 31.3%. The ER in cyclic cows was 64.9% and the eCG-like treatment increased ER only in anestrus cows (55.8 vs. 44.3%; Treatment x cyclicity interaction; P = 0.03). The percentage of cows with negative BCS balance was 27.2%. The P/TAI in cows with positive BCS balance was 48.4% and the eCG-like treatment increased P/TAI only in cows with negative BCS balance (44.7% vs. 30.5%; Treatment x BCS balance interaction; P = 0.01). In conclusion, the addition of a recombinant eCG-like glycoprotein to a 7-day Co-Synch protocol increased estrus expression in anestrus Angus cows and P/TAI in those with negative body condition score balance. However, this addition did not influence the estrus expression in cycling cows or on P/TAI in those with positive BCS balance.