Sincronização da ovulação utilizando acetato de lecirelina em substituição à gonadorelina em protocolo Cosynch para vacas de corte

Abstract

The efficiency of lecirelin acetate replacing gonadorelin was evaluated in Cosynch protocols for beef cows. Twelve cows were distributed into two treatments (T), T1 (n=6): 100μg of gonadorelin, on D0; 150μg of d-cloprostenol, on D7 and 100μg of gonadorelin, on D9 and T2 (n=6): 25μg of lecirelin acetate, on D0; 150μg of d-cloprostenol, on D7 and 25μg of lecirelin acetate, on D9. All hormones were administered intramuscularly (IM). Fixed-time artificial inseminations were performed on D9 of the protocol, after hormone application. Ultrasound monitoring was performed from D0 of the protocol to D7, every 24 hours. From protocol D8, evaluations were performed every 12 hours, ending 12 hours after ovulation detection. The parameters of follicular dynamics evaluated were: interval from the 2nd application of GnRH to ovulation, ovulation rate to the 1st application of GnRH, ovulation rate to the 2nd application of GnRH, follicular growth rate, diameter of the largest follicle on D0 and D9 of the protocol , diameter of the dominant and subordinate follicle after the 2nd application of GnRH and determination of the follicular population from -D1 to D13 of the protocol. There was a difference in the ovulation rate at the 2nd application of GnRH (P<0.05), with means of 33% for T1 and 100% for T2; for the number of small follicles on D10 and D11, medium follicles on D3, D6 and D11B and for large follicles on D4, D11A and D12 of the protocol (P<0.05). There was no difference for the other evaluated parameters. Thus, the application of 100μg of gonadorelin can be replaced by 25μg of lecirelin acetate in Cosynch protocols for beef cows, based on the ovulation rate obtained after the second application of GnRH and the number of large follicles on D11 and D12 of the protocol.