Another great paradigm of the extension of the ejaculates has been the degree of dilution, a parameter that relates the volume of the ejaculate, the concentration, the number of doses and the volume of extender to be added.
- When you have large volume ejaculates, but with a low concentration, the number of doses to be produced will be low and the volume of extender to be added will be small. So it will mean low dilution degree (ratio extender volume-ejaculate volume).
- On the contrary, in the case of very concentrated ejaculates with low volume, with which a high number of doses can be made, the volume of extender will be very high and the dilution degree will be high.
Generally the limits of the extension degree have been established> 1: 4 and <1:16
The negative effect of the degree of dilution was due to the fact that the resulting doses would have a greater or lower amount of seminal plasma, and this could have an undesirable impact on the preservation of seminal doses. Besides, sperm may suffer an osmotic shock.
Nowadays, the biological effect of a greater or lesser amount of seminal plasma in the doses is still unclear, since, on the one hand, it has components that favour sperm preservation, and, on the other hand, it contains others that lead to sperm capacitation. In addition, there is great difference in its composition among boars, within different periods of the year and in the same animal (since its composition varies throughout its productive life).
Regarding the possible osmotic shock when the ejaculate comes into contact with the extender, in the past the extenders used had a different composition in comparison to the current ones. Indeed, they showed higher osmolalities (Ex: Kiev 425 mOsm / kg; Zorlesco 240 mOsm / kg) than the ones of the ejaculate (290-300 mOsm / kg, tolerating between 250-380 mOsm / kg, but being better when it is closest to the physiological one). In very concentrated ejaculates, that need higher volumes of extender, this could cause the final osmotic pressure of the seminal doses to be high, compromising, therefore, their quality and preservation.
However, current extenders have osmolalities similar to that of the ejaculate. So the degree of dilution is a parameter that has been decreasing in importance over the years.