**4. The interference of diseases in AI efficiency**

In swine, the efficiency of the AI programs is related to higher pregnancy rates, reduced es‐ trus repetition rates and high number of the piglets born per litter. However, to obtain re‐ productive efficiency, several parameters must be optimized such as the animal nutrition, thermal comfort, skilled labor, genetics and mainly the sanitary aspect. This last factor is fundamental for the herd of the animals involved in reproduction to be totally free from dis‐ ease and properly immunized against the most common diseases that can lead to reproduc‐ tive disorders.

Therefore, the assurance of the animals' health is extremely important to ensure the absence of contamination of the animals' semen. From the scientific evidence that the presence of a virus or bacteria in the male' semen may reduce the fertility rates in the male and the female to be inseminated, the animal contamination by infectious diseases should be avoided.

The direct impact that occurs in males is mainly related to reduction in the sperm quality and numbers of doses produced. The reason for the impairment of the semen quality is not totally elucidated. Therefore, the losses to the farmer is considerable because it is often nec‐ essary to discard the boar because irreversible degenerative changes at testicular and epidi‐ dymal levels by diseases that lead to fever for prolonged periods.

Solis et al. [75] reported that the experimental infection of the animals with porcine rubula‐ virus (PoRV), which causes the blue eye disease (BED) was able to cause orchitis in animals, as also affecting the portion of the epididymis. The virus was detected in the semen, either in the sperm and jell fraction. Those researchers observed the ability of this virus to cause severe alterations in sperm concentration, motility and morphology of the infected animals'. Those changes were aggravated according to the time of the sperm storage. Taking into ac‐ count that the virus does not affect the adjacent glands, the seminal volume remained un‐ changed. The changes in other parameters occurred due to inflammatory event of the virus on the spermatic ducts, as leading to loss of the spermatic cells. Most viruses behave like aforementioned, however there are still many doubts about the extent of the virus interac‐ tion with the spermatozoids. Thus, future molecular studies are needed to elucidate the mechanism of those diseases.

In females, reports suggest that PRRSV was previously isolated from ovaries of infected ani‐ mals, particularly locating in either granulose cells layer and theca cells layer in atretic folli‐ cles of those animals. However, there are no reports of this virus in sows' oocytes [76, 77] neither the viral effect on their development ability. In infections associated with PCV 2, the oocytes collected from serum-positive animals for infection did not show to be positive for the presence of the virus. Thus, the contamination via oocytes in naturally infected animals is not a natural route [78]. Yet this author and collaborators found that the virus can adhere firmly to either oocyte-cumulus complex and pellucid zone of embryos at the initial devel‐ opment stage despite not affecting the embryonic development.

At embryonic level, it has been demonstrated that the replication of some viruses can occur in the embryonic cells. In this context, the Pellucid Zone (ZP) of the embryos acts as a barrier protecting the embryo against viral agents. Therefore, after disruption of the pellucid zone at stage of the hatched blastocysts, some viruses such as the classical swine fever virus and PCV-2 can replicate in embryonic cells as carrying a deleterious effect, especially in embryos produced in vitro [79, 80]. The greatest weakness of the embryos produced in vitro may be due either to a thinner pellucid zone of those embryos [81] and greater exposure to laborato‐ rial conditions and culture media that can act as contamination sources. It is known that ZP of pig embryos is much stickier than that of cattle, although the reason for this fact to be not known [82]. It is believed that lower-sized virus (20 -26 nm), such as *porcine circovirus 2* and porcine parvovirus could even surpass the ZP of embryos produced in vivo by promoting contamination of the embryonic cells [13, 80]. However, this issue is still controversial and further studies are still needed.

Thus, it is expected the contamination of the embryonic cells of the ZP-unprovided embryos will depend mainly on nature of the virus, of the embryonic development stage and the presence of viral receptors expressed in target cells [82]. Furthermore, the ZP- unprovided embryos that are produced in vitro are much more sensitive to viral contamination and, in‐ dependent of the nature, they represent a real source for contamination of the animals main‐ ly by diseases caused by virus. Finally, the disinfection of the swine embryos by using washing and treatment with enzymatic combination rather represents a reasonable alterna‐ tive for programs of the in vitro embryonic production [78].
