Dinâmica ovariana de fêmeas zebuínas submetidas a diferentes protocolos de ressincronização superprecoce de estro e ovulação

Abstract

The objective of this study was to characterize the effect of 1mg of estradiol benzoate (EB) on the 12-day corpus luteum structure, as well as to evaluate the follicular growth of females submitted to four different types of hormonal protocol that provide estrus and ovulation synchronization. Thus, 33 Bos taurus indicus females, from an extensive farming, were used. Such females were submitted to a first protocol of estrus and ovulation synchronization, starting with the insertion of a progesterone device associated with the application of 2.0mg of EB. Eight days later, the progesterone devices were removed, and 12.5mg of dinoprost tromethamine, 0.5mg of estradiol cypionate and 300 IU of equine chorionic gonadotropin (eCG) were administered, all intramuscularly. After 22 days from the beginning of the protocol mentioned above, the super-early resynchronization protocols were started. Thus, 13 females received intravaginal progesterone device, comprising the females of group one and two (G1, containing seven animals and G2 with six animals, respectively), in addition, the females of G1 received 1.0mg of EB. Twenty-three days after the start of the first synchronization protocol, eight females received the intravaginal progesterone device, comprising females from groups three and four (G3 with four animals and G4 with four animals, respectively). In addition, females from G3 received 1.0mg of EB. Seven days after the beginning of resynchronization of females from G3 and G4, 12.5mg of dinoprost tromethamine (i.m.) was applied. Eight days after the intravaginal device insertion of the G1 and G2, they were removed and 12.5mg of dinoprost tromethamine, 0.5mg of estradiol cypionate and 300 IU of eCG were administered. Nine days after insertion of the G3 and G4 devices, they were removed, 0.5mg of estradiol cypionate and 300 IU of eCG were applied. From the moment of intravaginal devices insertion, for three days, all cows were evaluated every 24 hours in order to identify changes in xii the corpus luteum present in the ovaries. Evaluations to monitor follicular dynamics started from the moment of application of dinoprost tromethamine, being performed every 12 hours, until ovulation has been identified, or 96 hours after intravaginal devices removal. All evaluations of the ovaries relied on the use of B-mode ultrasound and power doppler. Diameter, area, area of vascularization of the corpora lutea were measured, as well as follicular diameter, follicular area and area of vascularization of the follicular wall. For serum progesterone analysis, blood was collected from the females on day zero of the resynchronization protocol, on the day of application of dinoprost tromethamine and on the day of fixed-time artificial insemination. The structural and functional post-ovulatory characteristics of the CL were similar in all protocols with or without application of estradiol benzoate. A Friedman ANOVA was performed to assess the extent to which ACL levels were equivalent at different times (D0, D1 and D2), obtaining statistically significant results (P=0.008). Wilcoxon Signed Rank tests, a posteriori, showed that on D0 the ACL was significantly higher than on D1 and D2. The same statistical tests were performed for the assessment of LCV over time. The results were statistically significant (P=0.01). Wilcoxon Signed Rank tests, a posteriori, showed that on D0 the VCL was not significantly higher than on D1, but it was higher than on D2. The difference in VAS level between D1 and D2 was not significant. In this way, it is suggested that there was no influence of the application of estradiol benzoate on the morphofunction of the CL, which could be a useful tool for resynchronization of females for FTAI.