Egg Yolk based extenders are still commonly used and better extender.

It is determined by the animal species.

Sorry, I had forgotten to mention the species. I was going to ask about cattle, buffalo, and goat.

For cattle and buffalo egg yolk based semen extenders are better.

Egg-yolk based extenders are used widely for freeze semen of the species you asked and have very good results.

In general， the soya-based extender is better than egg-yolk based extender because the components of egg yolk is affected by many factors and cannot be determined. Especially for goat semen, the cryoprotective effects of soya-based extenders may be better, due to the damging interaction between seminal plasma and egg yolk.

However, a potentially toxic effect between Soya and buck seminal plasma may still exist based on our previous communication with a American researcher.

Egg yolk based extender is commonly preferred in large and small ruminants but the trend is shifting towards the plant based extender (lecithin). As many studies concluded that egg yolk based extender increase the risk of microbial contamination and thus allow the production of endotoxin.

The selection of the best extender should be based on animal species you studied. SOYA may be suitable for cow, sheep, or goat. However, when freezing goat semen, seminal plasma should be removed in the presence of egg yolk.

Dear Sagar,

Regarding your question on the extender type (egg-yolk vs soya-based semen diluents) in ruminants (i.e. bull, ram, buck), I would simply advise egg-yolk instead of soya. It is worth mentioning that both contain lecithin (as part of complex lipids) acting as an emulsifier and has the affinity to bind with phosphorus that is one of the main components of the membranes.

The main rationale for the inclusion of egg-yolk (of animal origin) within an extender is the low-density lipoprotein (LDL) fraction. This is a high molecular weight component that protects the sperm against cold shock. The cold-shock effect would be irreversible especially cooling below 17 degrees C to 4 degrees C. This is especially so for the routine pre-freeze handling (mainly, further dilution, glycerolisation, packaging, and equilibration) before freeze-thawing (cryopreservation). Further, egg yolk protects the sperm against the toxic effects of seminal plasma that has the potential to affect the membranes severely. Egg yolk extender has been used at various percentages (10 or 20 %) because of its superiority for sperm survival especially after freeze-thawing. Indeed, for long-term storage (at minus 195 degrees C), it would be more convenient to use the higher concentration (20%) while for cooled/chilled semen, lower doses (10%) would be better for sperm survival at 4 degrees C.

The inclusion of emulsifiers e.g. detergents (such as sodium dodecyl sulphate, SDS) may enhance the relationship between the egg-yolk lipids and the spermatozoal membranes that would modify the membrane phase transition. Hence, in the literature, it is considered that egg yolk lipids provide the main protection of membranes for which the interaction between the egg-yolk lipids contained within and sperm membranes is vital for cellular integrity.

Soybean (as with egg yolk) contains "lecithin" which also protects the sperm membrane structures against the debilitating effects of semen handling (mainly the freeze-thawing).

In a study in dogs, egg yolk-based Tris extender compared to the soya-based extender was superior for the conventional sperm parameters including motility and morphology.

However, there is a concern over the use of egg-yolk because of its animal-based origin as it may contain microorganisms likely to be harmful to the health of the female animal to be inseminated. Nevertheless, luckily enough, this potentially harmful effect would be minimized by using fresh (daily-laid) eggs from specific pathogen-free (SPF) individual hens of any flock concerned. Further, the surface of the eggs should be cleaned with alcohol (70%) before its use for semen dilution.

Regards, Good luck.

Omer