Efectividad del cipionato de estradiol inyectado al final de un tratamiento con progesterona sobre la eficiencia reproductiva

Abstract

Estradiol cypionate (CPE) has been used at the time of progesterone intravaginal device removal to replace the administration of estradiol benzoate (BE) 24 h later, without affecting pregnancy rates. The objective of this work was to evaluate the effect of the administration of two different doses of CPE, at the time of device removal, upon pregnancy rate after fixed-time artificial insemination (FTAI). Reproductive efficiency of both treatments was investigated as well. Seventy-nine Aberdeen Angus heifers, 15 month-old, were used. On day 0, intravaginal device was fitted and estradiol benzoate injected; on day 7, device was removed, D(+) cloprostenol was injected and heifers were randomly assigned to receive 0.5 mg of CPE, 1 mg of CPE or EB 24 h later. FTAI was performed 52-56 h after device removal, using semen from a bull of proven fertility. On day 22, a second-hand intravaginal device was fitted for 7 days. Treatment continued with estrus detection and AI. Pregnancy diagnosis was performed twice to evaluate the pregnancy rate of FTAI, estrus return and embryo death rate. The effect of different treatments upon pregnancy rates of FTAI, estrus return and final pregnancy rate were evaluated. There was no effect of different treatments on pregnancy rates (p>0.05): FTAI (51.9%), estrus return (61.1%) and final pregnancy (65.8%). A 7.3% embryo death rate was observed without differences among treatments (p>0.05). In conclusion, the use of 0.5 or 1 mg of estradiol cypionate at the time of removal of progesterone intravaginal device instead of estradiol benzoate, 24 h later, can be implemented without affecting the pregnancy rates after FTAI. Furthermore, reproductive efficiency is not affected.