Fatores que influenciam a produção comercial de embriões in vitro

Abstract

Brazil accounts for almost 70% of the worldwide production of in vitro embryos. The OPU-IVP (ovum pick-up/in vitro production) technique has advantages over other breeding programs, since it provides an accelerated advance of the genetic improvement of the national herd, generating superior animals due to the selection pressure, besides allowing the use of females of different ages, at any stage of the estrous cycle, including those with acquired reproductive problems. Combined with the use of sexed semen, it has benefits, especially for dairy farmers, since they can have a higher proportion of females in the herd, making the use of IVP viable on a large scale. However, the technique presents variability in the production of blastocysts and in the pregnancy rate. Thus, to verify and demonstrate the factors that influence the results obtained by a commercial laboratory is necessary, since these companies include different variables such as: breeds, localities, management, seasonality and thus portray the reality of the field. Thus, the present study aimed to verify the factors that influence in vitro embryo production (IVP) and the pregnancy rate using data from a commercial laboratory. For analysis of IVP, data from the year 2014 to 2016, referring to the 776 ultrasound guided follicular aspiration (OPU) sessions of oocyte donor adult females for commercial purposes of the Nelore (n=83), Girolando (n=73), Brangus (n = 49), Holstein (n=10) and Senepol (n=10) from different localities were evaluated. The influence of five variables: donor breed, donor aspiration frequency, semen type (sexado vs conventional), seasonality (spring/summer vs. autumn/winter) and donor genetic group (Bos taurus taurus, Bos taurus indicus and crossover) on the rates of: viable oocytes, cleavage and blastocyst production. In vitro embryo production followed the protocols already established by the Laboratory. As for the analysis of the pregnancy rate, data from 20,297 innovations carried out between November 2009 and April 2016 were evaluated. The influence of five variables: seasonality (spring/summer vs. autumn/winter), type of semen (sexed vs conventional), embryonic stage, donor and recipient breed on pregnancy rate were analyzed. The in vitro production of the embryos was performed by only one laboratory technician and the innovations by two equally trained technicians. Statistical analysis of the data was performed using the Statistical Analysis System for Windows (SAS Inst., Inc., Cary, NC) software using the chi-square test at a 5% level of significance (p<0.05). The Girolando breed had a higher blastocyst rate when compared to the other breeds. Donors aspirated between 9 and 17 times resulted in a higher rate of cleavage and of blastocysts compared to those aspirated 2 to 8 times (p=0.0001). When evaluating the rates of cleavage and blastocyst according to the type of semen, these were higher when using semen sexed compared to conventional semen. Seasonality influenced the rate of viable oocytes, being better in spring / summer (p=0.0001), however, without affecting the rate of cleavage and blastocyst. When comparing the genetic group of the donors, a superiority of the Bos indicus, represented by the Nelore breed, was obtained for viable oocytes and blastocyst rates, while Bos taurus presented the lowest values. For the analysis of the data of innovations, we obtained: superiority in the pregnancy rate in the spring/summer period when compared to autumn/winter, regardless of the breed of the donor as well as when the conventional semen was used in the in vitro fertilizations. When transferring embryos in expanded blastocyst stage, blastocyst and blastocyst the pregnancy rate is higher (p=0.0046). Donors from the Brangus, Bonsmara and Gir breeds had the highest rates and the lowest Holstein and Senepol breeds (p <0.0001). The recipients with the highest pregnancy rate are Bonsmara, Angus and Nelore. By grouping the breed with seasonality of innovation, Nelore and Brangus donors have higher pregnancy rates in the spring/summer, while the Holstein and Gir dairy breeds express themselves better in the fall/winter. For the recipients, it followed the same pattern, the Nelore and European breeds showed higher rates in spring/summer and Holstein in autumn/winter. We conclude with the accomplishment of this retrospective study that: in the IVP, the Girolando donors followed by the Nelore breed showed the best performance in the production of blastocysts; this production associate to sexed semen demonstrates that it can be used successfully in a commercial program, especially in the Girolando breed. In the field, the highest pregnancy rates are concentrated in the spring/summer season; embryos at a more advanced stage of development result in more pregnancy; the use of conventional semen was superior to sexed; and the donor and recipient breed is a preponderant factor in the results. In this way, it is possible to obtain satisfactory results with the adequacy of the database to the analyzed variables.