Potential use of soy lecithin or butylated hydroxytoluene as an alternative to powdered egg yolk for ram semen cryopreservation

The aim of this study was to assess the effect of replacing powdered egg yolk (PEY) with soybean lecithin (SL) or butylated hydroxytoluene (BHT) on ram sperm cryopreservation. Two ejaculates/male were collected via artificial vagina from 8 rams during breeding season. Ejaculates were pooled and washed twice by centrifugation. The pellet was divided into three aliquots, diluted in a Tris-based media with 5% glycerol containing PEY (15%), SL (1%) or BHT (0.6 mM) and cooled for 4 h at 5 °C before freezing. Sperm motility, plasma and acrosome membrane integrity and mitochondria activity as lipid peroxidation were assessed immediately after thawing and after 4 h of resilience incubation in a modified PBS at 38 ºC. After thawing, sperm extended in BHT showed the poorest quality compared to sperm extended in PEY and SL. Similar total and progressive motility were observed in sperm preserved in PEY and SL media. Plasma membrane integrity, however, was significantly higher in sperm extended in SL, although most of them with non-functional mitochondria. Acrosome damage was significant lower in SL sperm samples compared to PEY samples. Highest level of lipid peroxidation was found in sperm preserved in PEY. Resilience test had a negative effect (P < 0.05) on plasma and acrosome membrane integrity in all samples, and on progressive motility only in sperm preserved in PEY. In conclusion, soy lecithin could be a potential alternative to PEY for ram cryopreservation, although its adverse effect on sperm mitochondria function has to be strongly considered.