Innovative pre-synchronization, synchronization and resynchronization programs for FTAI in dairy cows

Abstract

The aim of the project is to optimize the reproductive efficiency of dairy cows in Brazilian herds. The commonly FTAI protocol in Brazil is based on estradiol (E2) and progesterone (P4), however, 60% of the cows do not synchronize perfectly, in addition, the use of presynchronization did not improve the efficiency of the E2/P4 based protocols in synchronizing the cows. Conversely, gonadotrophin-releasing hormone (GnRH) based protocols, when initiated at a specific moment of the estrous cycle, which is attained by the of a presynchronization, achieve an efficient synchronization, optimum concentrations of P4 during follicular growth and noteworthy fertility. Therefore, in Experiment 1 (EXP 1), we will use a presynchronization prior to the GnRH-based synchronization protocol for the first postpartum FTAI of dairy cows. We chose to use this reproductive program because there's no study that used presynchronization associated with GnRH-based protocols in Brazil, and we believe that with this strategy, the conception rate will increase from 30-40 to 45-50%. What will actually be tested in EXP1, are different strategies of induction of ovulation in the FTAI protocols. When estradiol cypionate (EC) is used as an ovulation inducer, there is the convenience of its treatment occurring concomitant with the P4 device withdrawal, which decreases the number of handling the cows; another feature is that a higher number of cows display estrus, which in some studies improved the fertility of dairy cows. However, ovulations in response to EC occur in a very dispersed way which brings up a problem of that a proportion of cows being inseminated at non-optimal moments regarding ovulation, which can be impairing fertility. On the other hand, when GnRH is used as an ovulation inducer, fewer cows became in estrus, but ovulations are more concentrated and fertility is high. Therefore, in the EXP1, 1200 cows will be submitted to a presynchronization and assigned in 3 groups (FTAI protocols) with GnRH + P4 on D0. All animals will receive two prostaglandins (PGF), one on D6 and a second on D7. In the EC group, ovulation will be induced with EC administrated at the time of P4 device withdrawal; nonetheless, in the EC/G group, cows will receive EC on D7, but only as an E2 supplementation, since ovulation will be induced with GnRH 32 hours after P4 device withdrawal. Finally, in group G, the cows will be treated only with GnRH 32 hours after the P4 device withdrawal. FTAI will be performed 48 hours after removal of the P4 device in the 3 groups. Still, in the EXP1, an innovative proposal, since no work developed this type of study in Brazil, will be the evaluation of uterine disease using the Metricheck device on days 35 and 43 postpartum. The proposal is to evaluate the prevalence of endometritis in Brazilian herds, as well as the impact of the disease on the reproductive performance of dairy cows. Finally, in experiment 2 (EXP2), the objective is to increase the fertility of resynchronized cows. About 15 to 40% of the cows do not have an active corpus luteum (CL) at the beginning of the resynchronization, and this fact is associated with low fertility. Considering that protocols initiated with EB do not efficiently synchronize the follicular wave emergence and promote luteolysis in about 40% of the animals, the use of EB in resynchronization, physiologically, may not be the most ideal to achieve reasonable fertility results. When GnRH is used at the beginning, there is no risk of luteolysis, and in addition, CL is generated from the ovulation. Therefore, in EXP2, at 32 days after the previous IATF, 800 non-pregnant diagnosed dairy cows, will be assigned to two groups (FTAI resynchronization protocols): EB/G group, in which the protocol will initiate with EB plus GnRH and group G, in which cows will be treated only with GnRH. The rest of the protocol is the same for the two groups: PGF on D7 and D8, EC on D8 and FTAI on D10. (AU)