Semen Doses: The Technological Drive from Quantity to Quality

All of us are the result of a single successful sperm completing a long and hostile journey to fertilise an egg. Every pig on the farm is also the outcome of a single successful sperm but with normal litter sizes on the farm generally being 25 piglets or less, have you ever considered why we put billions of sperm in a single dose for artificial insemination (AI) when we clearly only need 25 sperm.

One reason for what appears to be a hugely wasteful process is due to the varying quality of sperm. Whilst a single ejaculate can easily contain over 100 billion sperm not all sperm are equal. Within that quantity there will be some sperm with visible abnormalities such as bent tails or deformed heads meaning that they are incapable of navigating the long journey through the female reproductive tract. It is for these reasons abnormality scores have historically been taken by looking down a microscope and counting abnormal sperm.

Unfortunately another challenge for the laboratory is that the equipment that has historically counted sperm, counts all sperm both live and dead. This means that whilst a dose of 2.3 billion sperm may be reassuring to the technician inseminating the sow that figure alone fails to determine how many of them are capable of fulfilling their role of navigating the tract and fertilising the egg. Historically the lab have viewed a sample of the ejaculate down the microscope and assigned a motility score, typically from 1 (poor) to 5 (highly motile).

Whilst these steps have ultimately been very successful in delivering fertile semen to the industry they do have their limitations. The process of assessing semen down a microscope can be subjective, even with training someone assessing a sample may consider it a low 4 whilst someone else a higher end 3 (the latter would be discarded and not processed and sold). Obvious abnormalities are easy to identify but more subtle flaws are easily missed and motility was generally done based on general movement of the sample not on whether it was capable of moving in a specific direction.

The latest video imaging technology and associated software is now allowing semen processing labs to overcome these hurdles and potentially can offer huge benefits to pig producers. It does however require us to change the way we think about semen standards. Computer Automated Semen Analysis (CASA) systems are now available to commercial laboratories and remove the subjective nature of semen assessment. By amassing short videos of a semen sample and applying video analysis software the system can accurate measure levels of semen abnormalities, semen motility but most importantly, progressive motility. The distinction between motility and progressive motility is important because it distinguishes between sperm that simply move versus those that are capable of moving in a forward direction (as opposed to swimming in circles or moving but failing to propel themselves forward). The previous human microscope assessment would never have been able to achieve this distinction.

So how does this help pig producers? The answer is that it allows laboratories to lower the semen dosage levels without lowering the number of progressive motile sperm. Historically the level of sperm per dose were set with the possibility that the pack could contain a significant proportion of sperm that were dead or whose motility was not progressive, this lead to dosage levels being set high to cope with this eventuality. By now having the technology to distinguish between these cells laboratories can supply semen with lower numbers of sperm per dose but with a minimum level of progressively motile sperm.

This approach has been used successfully in many other countries with great success with levels of 1.5-1.8 billion per dose now being regularly used in countries like the Netherlands. So whilst the laboratories may sell more doses per boar, what is the commercial benefit for pig producers? The answer to that is due to the fewer boars required to fulfil the same set of orders. Fewer boars at stud means that the genetic standard of those boars are higher. If for example the lowest 20% of boars at stud are not need at this moment in time the improvement in genetics supplied equates to a saving of 90p per slaughter pig sold due to the improvements in growth, FCR and carcase traits in the progeny from that semen. The benefit for an average UK indoor farm (as determined by AHDB Pork figures) is therefore over £23 per sow per year using less semen from better boars.

Lowering semen dosage rates therefore has multiple benefits across the supply chain provided it is done using investment in the newest CASA technology. To benefit from this, pig producers should change their focus to the number of progressively motile sperm delivered per dose and stop the focus on the total number of sperm put in the pack. After all, you wouldn’t assess your livestock haulier based on total number of pigs delivered regardless of whether they are living or dead so don’t use this criteria to judge your semen supplier!

Dr. Grant Walling
Director of Science & Technology
JSR Genetics Ltd