Introduction: The aim of this study was to evaluate the effect of lipoprotein fraction isolated from ostrich egg yolk (LPFo) on the metabolic activity of boar spermatozoa following liquid semen storage in different extenders and temperatures. Material and Methods: Boar ejaculates were extended in Androhep, Beltsville thawing solution (BTS), and Martín-Rillo and Alias (MR-A) without (control) or with the addition of LPFo and stored for three days at either 5°C or 16°C. The analysed sperm parameters included total motility (TMOT), plasma membrane integrity (PMI), mitochondrial membrane potential (MMP), oxygen consumption, and adenosine triphosphate (ATP) production. Results: The sperm metabolic activity seemed to be higher in the LPFo-based extenders following storage for three days, irrespective of the storage temperature. Compared with the LPFo-free extenders, significantly higher (P < 0.05) sperm PMI and MMP were observed in BTS and MR-A extenders supplemented with LPFo during storage for three days at 5°C. Spermatozoa stored in the BTS-LPFo extender exhibited higher (P < 0.05) TMOT and oxygen consumption, whereas higher (P < 0.05) PMI was observed in spermatozoa stored in Androhep-LPFo and MR-A-LPFo for three days at 16°C. No significant differences (P > 0.05) in ATP content were observed between the LPFo-free and LPFo-based extenders during storage. Conclusions: Supplementation of LPFo to semen extenders had varying effects on the metabolic activity of boar spermatozoa stored at different temperatures. It can be suggested that the interactions of various components of the extenders and seminal plasma with LPFo exert beneficial effects on the sperm metabolic activity during liquid storage of boar semen.

Developing effective cooled semen protocols is essential to increase pregnancy rates and reproductive efficiency in donkeys. This study aimed to evaluate the effect on sperm kinetic parameters and membrane integrity in cooled donkey semen diluted with defined milk proteins extender with 1% or 2% of egg yolk and the removal of seminal plasma. Twenty-four ejaculates from six jackasses were collected. Each ejaculate was divided into four aliquots that were diluted in extender with 1% (EY1) or 2% (EY2) egg yolk. One sample from each group was centrifuged, seminal plasma was removed (CEY1, CEY2 groups, respectively), and the samples were then refrigerated at 5 °C for 24 h. Fresh and cooled semen samples were assessed for sperm motility, morphology, and plasma membrane integrity. Total motility, progressive motility, sperm kinetic parameters, or live sperm cells were not statistically different when semen was cooled with an extender supplemented with 1% or 2% of egg yolk. Seminal plasma removal does not affect total motility or sperm kinetic parameters. However, progressive motility decreased (P<0.05) when semen was extended with 2% of egg yolk and seminal plasma was removed. Membrane integrity was affected (P<0.05) in centrifuged samples. In conclusion, the obtained results suggest that there is no difference in sperm kinetics and membrane integrity when 1% or 2% of egg yolk was added to the Equiplus(R) extender. Also, the removal of seminal plasma by centrifugation did not have any beneficial effect on cooled donkey semen. Further studies are needed to relate these results with in vivo fertility tests with cooled donkey semen.