Gonadotrofina coriônica humana em substituição ao gnrh em protocolo cosynch para vacas de corte

Abstract

The following study evaluated the efficiency of the human chorionic gonadotropin in replacing gonadorelin in Cosynch protocols for beef cows. Eleven cows were assigned to two treatments (T): T1 (n=6) received injections of 100μg of the GnRH analogue, gonadorelin, at D0, followed by the administration of 150μg of dcloprostenol, at D7 and 100μg of the GnRH analogue, gonadorelin, at D9; and T2 (n=5) received injections of 1000iu of hCG at D0, followed by the administration of 150μg of d-cloprostenol at D7 and 1000iu of hCG at D9. All hormones were administered intramuscularly (IMI). The fixed-time artificial inseminations were performed at D9, after hormone administration. The ultrasonographic imaging monitoring was initialized one day before D0 and up to D7, every 24 hours. From the D8 of the protocol, the assessments were done every 12 hours, being finished 12 hours after the detection of ovulation. The parameters of follicular dynamics evaluated were: the interval of the 2nd administration of the ovulation inducer, ovulation rate at the 1st administration of the inductor, ovulation rate at the 2nd administration of the inductor, follicular growth rate, diameter of the largest follicle at D0 and D9, diameter of dominant and subordinate follicles after the 2nd administration of GnRH and the description of the follicular population of the period -D1 up to D13. There was no difference for the parameters assessed in the follicular dynamics (P>0.05). Analyzing the population of small, medium and large follicles between the treatments, no difference (P>0.05) was observed; with differences detected only for the number of small follicles in the second and the tenth day of the protocol (P<0.05).Therefore, 100μg of gonadorelin can be replaced by 1000iu of hCG in Cosynch protocols for beef cows, based on the follicular growth and ovulation rate.