Abstract
The objective of this research was to evaluate the effect of phenotypic predominance on lipid content, mitochondrial activity and early developmental competence as indicators of oocyte quality. Cumulus-oocyte complexes (COCs) were recovered through follicular aspiration, and underwent in vitro maturation (IVM), in vitro fertilization (IVF), and in vitro culture (IVC) of presumptive zygotes. Lipid content and mitochondrial activity in immature and IVM oocytes were determined. A maturation rate of 80.6% and 69.3% was found for oocytes predominantly B. indicus and predominantly B. taurus, respectively. Total fertilization rate was 27.6%; 26.1% for predominantly B. indicus oocytes and 29% for predominantly B. taurus oocytes. A total of 55.5% and 57.5% of cleaved embryos after 48 and 72 h post-insemination (hpi) in predominantly B. indicus group were observed, respectively. As for the predominantly B. taurus group, 48.6% and 60.4% of cleaved embryos were found after 48 and 72 hpi, respectively. In both groups, immature oocytes showed a greater amount of small lipidic droplets (p <0.0001); IVM decreased the number of small lipid droplets (p < 0.0001) and increased the number of medium and large lipid droplets (p < 0.0001). Predominantly B. indicus oocytes had a greater number of small and medium-sized lipid droplets, while there were no significant differences in large lipid droplets. IVM oocytes had higher mitochondrial activity than immature oocytes group (p < 0.05) without any effect of phenotypic predominance on this parameter. Assessment of lipid content was not a predictive factor of oocyte quality in crossbred cows.
Highlights
Intracellular lipids are a substrate that can be used as a source of energy during invitro embryo production (IVP) [1,2]
A total of 736 oocytes were included in this study; 367 oocytes represented the experimental group with B. indicus phenotypic predominance, and 369 oocytes represented the experimental group with B. taurus phenotypic predominance
Research focusing on determination of lipid content in bovine oocytes is scarce, especially in B. indicus oocytes
Summary
Intracellular lipids are a substrate that can be used as a source of energy during invitro embryo production (IVP) [1,2]. Alterations in the quantity and the type of lipid species may result in a decrease of competence in oocyte development [3], being a paramount condition for the success in IVP, as are sperm quality and culture system [4,5]. Several studies resulted in the selection of morphologic and biochemical parameters that contribute as a whole to determine oocyte development competence. Attention has been focused to the study of lipid content as an indicator of oocyte quality, due to the possibility of taking advantage of an endogenous energy source during IVP and the susceptibility to cryotolerance related to an increase in lipid droplets [10]. An increment in concentration and variation of the composition of free fatty acids in the oocyte may impair its developmental competence [3,6]
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