226 EVALUATION OF IN VITRO EMBRYO DEVELOPMENT OF BOVINE OOCYTES EXPERIMENTALLY EXPOSED TO MYCOPLASMA BOVIS

Abstract

Reproductive biotechnologies are known to improve the quality and productivity of herds. Research on cattle health and on the conditions of oocytes and embryos produced in vitro and in vivo are carried out worldwide to prevent the transmission of infectious agents, particularly those associated with ovarian tissues, the uterine tubes, and the uterus. Thus, there is concern regarding the possibility of transmitting Mycoplasma bovis through animal reproduction procedures. The aim of this study was to evaluate morphological changes by means of optical microscopy, cleavage rate, and blastocyst formation during the in vitro development of bovine embryos experimentally exposed to M. bovis. Oocytes were aspirated from ovaries of slaughtered cows, and oocytes with an intact zona pellucida were selected and matured. After 20 h, the oocytes were divided in 2 groups: a control group (n = 260), and oocytes exposed to 2.5 × 10⁴ cfu mL^–1 of M. bovis (n = 261). The semen was treated by a discontinuous Percoll gradient technique, and the sperm concentration was adjusted to approximately 100 000 sperm for each oocyte. Statistical analysis of the experiments was conducted using Student’s t-test (P < 0.05). Embryos exposed to M. bovis showed a cleavage rate of 21.07% (55/261), whereas the control group showed a cleavage rate of 64.6% (168/260). In relation to blastocyst formation, control embryos had a rate of 39.60% (103/260) v. 12.20% (32/261) for the exposed group. Statistical analysis of the experiments revealed a significant difference in the final results. Regarding morphological aspects, we observed failures in the division and asymmetry of blastomeres, cytoplasmic shrinkage, and degeneration and disruption of the zona pellucida in embryos exposed to the pathogen. These results are important to support the development of parameters for evaluating oocytes and in vitro-produced bovine embryos and to establish more efficient methods to control the spread of disease by animal reproduction biotechnologies. Further studies will be done with oocytes exposed to the pathogen and subsequently evaluated according to the Manual of the International Embryo Transfer Society.