The Impact of Using Extenders Containing Low-density Lipoprotein Versus Egg Yolk with or without Ascorbic Acid on the Fertility Parameters of Post-thawed Chilled Canine Semen

Egg yolk is included in semen extenders because it prevents cold shock during chilling. This study aimed to assess the impact of substituting egg yolk with low-density lipoprotein (LDL) in Tris-Citric-Fructose (TCF) chilled extenders, with or without ascorbic acid, on the canine semen quality at 24, 48, and 72 hours of cooling. Semen from three German shepherd dogs was evaluated and extended at a 1:1 ratio using four extenders: Group A (TCF buffer, 20% egg yolk, with ascorbic acid), Group B (TCF buffer, 20% egg yolk without ascorbic acid), Group C (TCF buffer, 20% LDL, with ascorbic acid), and Group D (TCF buffer, 20% LDL without ascorbic acid). The extended semen was stored at 4°C and assessed after 24, 48, and 72 hours of cooling. The egg yolk extender resulted in less reduction in progressive sperm motility after 24, 48, and 72 hours of cooling; however, reduction in normal morphology, acrosome integrity, and cell membrane integrity were lower in TCF-LDL chilled extender than in TCF-EY chilled extender. Furthermore, after 24 hours of cooling, all evaluation parameters in both extenders were greater than 50%. In conclusion, the quality of chilled canine sperm was significantly improved by adding ascorbic acid to TCF-EY, but the improvement was only marginal when applied to TCF-LDL chilled extender.