top of page

The story of Totilas and Pronexcell

A first acquaintance.

In early 2010, Jorgen van der Holst added a white powder named Pronexcell to the freezing medium he had prepared to freeze the sperm cells of the famous stallion Totilas. The semen was collected and processed by Jorgen because Holstud and Totilas were stationed at the exact location.

Jorgen: "To my surprise, adding Pronexcell to the freezing extender resulted in more natural motility of the sperm cells. Totilas was the first stallion whereby Pronexcell was used in the semen freezing medium”.

From then on, Jorgen used Pronexcell in his equine semen-freezing medium. His use of Pronexcell resulted in the exceptionally high fertility of between 85% and 90% of Totilas’s sperm used in 15 countries within and outside Europe and with more than 250 mares.

The Pronexcell that Jorgen used was obtained from Bart van den Berg from Barex Biochemical Products, located in Enkhuizen. The two had met one another earlier in Enkhuizen, together with Jorgen’s father, the well-known veterinarian Walter van der Holst, to discuss equine semen extenders and semen processing. Bart: “I can still remember our lively discussions on equine semen preservation.”

Pronexcell was, at that time, a component of a new swine semen extender developed by Bart van den Berg in 2005. An investigation incorporating results of over half a million swine inseminations at 35 farms showed that Pronexcell increased fertility significantly. The same was offered for a new rabbit semen extender he developed in 2013. To date, nothing is known about how Pronexcell acts on a molecular level. Bart: "Polyunsaturated fatty acids are necessary for good sperm movement. One may improve sperm quality by optimal feed containing these substances. Still, the addition of these natural compounds to sperm cell preservation media enables the repair of sperm cells that are damaged by the cryopreservation process."

A renewed acquaintance.

The discovery of Jorgen van der Holst initiated the development of the equine semen preservation medium by Bart van den Berg in 2014 using the newest state-of-the-art computer-assisted sperm analysis system that Bart had acquired a year before (the CEROS II of the US company Hamilton Thorne). In 2015, Pronexcell was one of the ingredients of the new equine semen extender Hippex.


Sperm cell motility analysis of diluted sperm showed that the quality was improved significantly on the day after collection and dilution in the preservation medium Hippex. The sperm cell motility was enhanced, while the preservation capacity was often superior to other commercial equine preservation media. Bart van den Berg: "I think the improved sperm cell movement might explain the increased fertility. An extensive investigation by Prof. H. Sieme (University of Veterinary Medicine, Hannover, Germany) and co-workers showed a strong correlation between motility and fertility".

The development of Hippex was mainly based on analyses of the semen of Haflinger stallions. Bart van den Berg: "For my developmental sperm analyses, I had the fortunate help of Frank Smeltink, who owns a stud with Haflinger stallions nearby my place."

To test Hippex with the semen of various stallions, Bart van den Berg visited the Station of Paul Schockemöhle. There, he met Bart Kools, who is responsible for semen collection and processing. They teamed up, and Hippex was introduced and used at the Station of Paul Schockemöhle in Muhlen in 2016. It seemed like a renewed introduction between Totilas’s semen and Pronexcell since here in Muhlen, the semen of Totilas was collected and processed using Hippex as a preservation medium.

Bart Kools:  "With the use of Hippex, 80-90% of our stallions do not need to centrifuge the semen anymore. This saves us a lot of time and costs.  Further, the microscopic view of the sperm cells is much clearer, while the preservation time is longer when compared to other extenders. Finally, the 10-15% higher pregnancy rate we see when using Hippex instead of other extenders is economically rewarding".

The semen of Totilas was diluted in Hippex until Totilas sadly passed away on December 14, 2020, aged 20, due to complications following colic surgery.

The acquaintance lives on.

In February 2021, Jorgen announced that there is still a certain amount of semen available for Totilas for the breeding season 2021. Jorgen: “From the moment of the collection until the present day, this Totilas semen has always been under the careful supervision of Holstud. Research has shown that the sperm from 2010 is still pristine.”

Bart van den Berg adds: “It is a pleasure to see that Pronexcell continues to have its value. Further, as I continue with research, it is fortunate that HuVeSearch has taken over the production and sales of the Hippex extenders containing Pronexcell.”

Barex Biochemical Products

The art of semen preservation

bottom of page