Knowledge of the ability or fertility potential of semen is of fundamental importance for the advancement of breeding biotechniques (Garcia-Alvarez, Maroto-Morales, Martinez-Pastor, Fernandez-Santos, Esteso, Perez-Guzman and Soler 2009). The evaluations performed in this study found significant variation in fertility between bulls (semen) regardless of the breed (Nelore or Brangus) or the method used (IVPE or FTAI). This variability in semen fecundity is inherent in cattle and other species, and has already been described in the literature (Ferreira et al. 2017, Takeda et al. 2019, Tsakmakidis et al. 2010, Ugur et al. 2019). Bulls and their semen undergo various evaluation processes (for motility, viability, membrane integrity, morphology, capacitation, and acrosome reaction for example) before being marketed in specialized Artificial Insemination Centers (Dias, Maciel, de Paula, Junior and Ozanan 2009, Freitas et al. 2009, Maziero et al. 2009). Therefore, the variability in semen fecundity between bulls selected by the Artificial Insemination Centers should be able to be estimated prior to the application of the semen in the field. However, the results of such evaluations do not always correlate with semen fecundity results using IVPE or artificial insemination programs (Kumaresan et al. 2017, Morrell et al. 2018, Sudano et al. 2011). It is of fundamental importance that the fertility of bull semen that is intended for artificial insemination or IVPE programs can be better predicted using more reliable tests such as those performed in this study. These tests should be implemented in addition to the main evaluation methods that are already employed at the Artificial Insemination Centers (Kumaresan, Johannisson, Al-Essawe and Morrell 2017, Morrell, Valeanu, Lundeheim and Johannisson 2018, Sudano, Crespilho, Fernandes, Junior, Papa, Rodrigues, Machado and Landim-Alvarenga Fda 2011).
The tests that are currently used in Artificial Insemination Centers present certain difficulties with regards to certifying semen fertility. This is because sperm are complex cells that need various attributes to perform their natural function in fertilization (Arruda et al. 2015, Maziero, Crespilho, Freitas-DellAqua, Junior, Antônio and Papa 2009). These inaccuracies in traditional semen evaluation procedures can generate significant variation in the fertility rates achieved in artificial insemination and in IVPE programs in cattle. This leads to losses that could be attenuated (Arruda, Celeghini, Garcia, Santos, Leite, Oliveira, Lançoni and Rodrigues 2015, Maziero, Crespilho, Freitas-DellAqua, Junior, Antônio and Papa 2009, Thundathil et al. 2016).
In recent decades, several laboratory methods have been developed in order to provide more accurate analyses of semen composition and structural integrity, with the aim of improving field performance (Arruda, Celeghini, Garcia, Santos, Leite, Oliveira, Lançoni and Rodrigues 2015, Khalil, El-Harairy, Zeidan and Hassan 2019, Kipper et al. 2017, Maziero, Crespilho, Freitas-DellAqua, Junior, Antônio and Papa 2009). These methods are indispensable but do not yet effectively predict semen fecundity. However, the association of these methods with in vitro embryo production may be essential for providing an estimate of the pregnancy rate for each semen batch or for each bull. This is supported by the results of this study. The rate of blastocyst production (IVPE) and pregnancy (FTAI) varied among the bulls in this study. However, most bulls had a good fertility performance, with values in line with those found in the literature and foreseen for these biotechnologies (Crites et al. 2018, Cunha et al. 2019, Franco et al. 2018, Sovernigo, Adona, Monzani, Guemra, Barros, Lopes and Leal 2017). The results of this study corroborate with the tests performed to evaluate semen in the Artificial Insemination Centers. This indicates that the evaluations performed in the Insemination Centers are indispensable, but more tests are essential for predicting semen fertility. These additional tests could include the IVPE performed in this study. The use of these additional tests could increase the reproductive efficiency of cattle and reduce the costs involved with management and resynchronization.
Comparing the rate of blastocyst production (IVPE) with pregnancy (FTAI) for both breeds of bull (Nelore or Brangus) evaluated in this study, there was a significant association between the variables. This indicates that increases in the rate of blastocyst production via IVPE for a given bull, correlates with increases in the rate of pregnancy via FTAI. The results of this study showed that IVPE can be used as an efficient tool to evaluate bull semen fecundity after tests carried out by the specialized Artificial Insemination Centers. The IVPE technique could be used to provide an estimate of the pregnancy rates for each bull. This could be used to validate semen fertility in preparation for artificial insemination and other assisted reproduction biotechnologies.
Despite the small number of bulls evaluated, the results of the present study indicate that IVPE may be used in addition to conventional semen analyses, to evaluate and validate the semen fertility of bulls from Artificial Insemination Centers. Such a method could benefit biotechnological productivity by promoting predictability and increasing pregnancy rates through artificial insemination.