Comparison of two gonadorelin formulations and two luteolytic agents on pregnancy rates in beef cattle synchronized with a 5-d CO-Synch + CIDR program
The objective of the present study was to compare the effect of two gonadorelin formulations and two luteolytic agents (PGF) injected as part of a 5 d CO-Synch + CIDR program on fixed timed AI (FTAI) pregnancy rates (PR) in beef cattle. Postpartum beef cows (n = 473) and heifers (n = 78) from 2 herds received GnRH and a CIDR insert on d 0; 5 d later, at CIDR removal, animals received two doses of PGF. On d 8, cows and heifers received a second dose of GnRH and were FTAI. At the initiation of the breeding program, cows were blocked by age and days post-partum (DPP) and randomly assigned into 1 of 2 treatment groups. For animals in the control group (CON = 280), the hormones used for the synchronization program were gonadorelin diacetate tetrahydrate (100 μg; Cystorelin®) and dinoprost tromethamine [50 mg (two 25 mg doses); Lutalyse®]; while animals in the Parnell group (PAR = 271) received gonadorelin acetate (100 μg; GONAbreed®) and Cloprostenol sodium [1000 μg (two 500 µg doses); estroPLAN®]. Determination of pregnancy status was performed by transrectal ultrasonography at 35-45 d after FTAI and after the conclusion of the breeding season. Age (CON = 4.8 ± 0.2; PAR = 4.6 ± 0.2), DPP (CON = 73.8 ± 1.6; PAR = 75.9 ± 1.5), and body condition score (CON = 6.6 ± 0.9; PAR = 6.6 ± 0.1) were not different (P > 0.05) between treatments. No difference (P > 0.05) in PR at FTAI was observed for the CON (54.9 %) and PAR (55.9 %) treatment groups. Similarly, no difference (P > 0.05) in PR was observed between treatments for cows [CON (n= 236) = 55.1 %; PAR (n= 243) = 56.9 %] and heifers [CON (n= 37) = 54 %; PAR (n= 35) = 51.4 %]. Breeding season PR (89.8 %) did not differ (P > 0.05) between treatments. In conclusion, the use of gonadorelin diacetate tetrahydrate plus dinoprost tromethamine (CON) resulted in similar FTAI PR when compared to gonadorelin acetate plus cloprostenol sodium (PAR).
Keywords: Beef, GnRH, Prostaglandin