Tratamentos hormonais e seus efeitos em vacas doadoras e receptoras de embriões de raças taurinas e sintéticas

Abstract

Superovulation (SOV) and embryo transfer (ET) allow the multiplication of the offspring from selected females. However, the variability in individual response still represents a limitation. Data from more than six thousand uterine flushings were analyzed in different taurine and synthetic breeds, during the four seasons of the year. We found that the average number of transferable embryos is similar to that reported for decades, but in autumn the proportion of degenerated structures increases, whereas an increased rate of unfertilized structures was observed in the summer. Thus, adjustments in management and hormonal treatments would make possible to improve the number of produced embryos. In this regard, the endocrine profile of donor cows was evaluated, associating the progesterone (P4) concentration with the response to SOV and embryo production, in an estrus based (EB) protocol. The effect of P4 supplementation in embryo donors was also evaluated. Cows with lower P4 concentration (≤7.7 ng/mL) in the beginning of FSH treatment had higher rate of unfertilized structures (NF; P<0.05), while cows with P4 >7.7 ng/mL had higher number of embryos and embryo/structure ratio (P<0.05). In a second study, it was observed that vaginal devices (IVD) containing 1, 1.9 or 3.8 g of P4 increased serum P4 concentrations (P<0.001) in previously synchronized cyclic cows. Subsequently, we observed that the withdrawal, washing and reinsertion the IVD on day 4 (D4) of the treatment, did not increase serum P4 levels. Finally, P4 supplementation with IVD containing 1 g did not affect the embryo production of donors from taurine or synthetic breeds, although a significant increase in the proportion of non-fertilized structures was observed in P4-treated cows. We concluded that there is a positive relationship between endogenous P4 concentrations during FSH treatment, fertilization rate and embryo production in donors submitted to SOV/EB. Finally, considering the importance of preparing recipient cows using a protocol that synchronizes estrus/ovulation and allows an adequate uterine environment for embryonic development, we evaluated the association of estradiol cypionate (EC) and GnRH for ovulation induction for timed embryo transfer (TET). It is well established that EC increases the proportion of cows expressing estrus, while GnRH promotes more synchronized ovulations. In this experiment, we did not observe a significant difference between the GnRH and EC+GnRH treatments regarding P4 concentrations nor in the pregnancy rate after TET. Collectively, the results obtained indicate that there is a possibility of increasing the in vivo production of embryos, especially through the reduction of degenerated and non-fertilized structures. Also, the concentrations of progesterone during SOV/EB are associated with embryonic production, however, P4 supplementation does not improve, the outcome of SOV. Finally, the association of EC+GnRH does not bring benefits in the synchronization of recipient cows.