A Complete Analysis of 30 Questions About Boar Semen
Meritxell Donadeu, DVM, MSc - Western Europe PIC Veterinary Manager - This article answers 30 key questions about boar semen.
1. What is in boar semen?
Boar semen is a suspension of sperm cells, secreted by the boar's reproductive organs including the accessory glands. The liquid portion of the suspension is called seminal plasma, which helps carry and protect the sperm cells. Boar semen also contains a large amount of gel.
2. How long does it take for boar sperm to be produced?
Producing a single sperm cell takes approximately 5 weeks, plus an additional two weeks in the epididymis 'the epididymis is a very long, coiled tubular structure attached to the upper surface of the testicle, where sperm slowly move, gradually mature and acquire potential fertilizing ability; the epididymis is also the main site of sperm storage'. It must be noted that the semen collected on any given day was produced 7 weeks earlier.
3. What does normal boar sperm look like?
A normal sperm consists of a head and a tail, and the entire sperm cell is covered by a membrane. The head contains the genetic information (chromosomes). At the tip of the head is the acrosome. The acrosome is a sac-like structure surrounded by a unit membrane, rich in enzymes. During fertilization, it helps the sperm penetrate the egg. The tail includes the neck, midpiece, principal piece and end piece. The midpiece is rich in mitochondria, which produce the energy needed for sperm motility.
4. What are abnormal sperm?
There are several types of abnormal sperm. For example: head abnormalities (enlarged head or malformed shape, etc.), tail abnormalities (double tail, bent tail, coiled tail, etc.), acrosome defects (segmented, incomplete, etc.) and retained cytoplasmic droplets. Cytoplasmic droplets form during spermatogenesis and normally detach on their own after the sperm matures. Sometimes the cytoplasmic droplet does not detach; whether it remains proximal or distal depends on how close it is to the head.
5. How are abnormal sperm produced?
Some abnormalities arise during spermatogenesis - that is, during production within the testicle - some arise as sperm pass through the epididymis, and some may arise during or after ejaculation due to improper handling and storage. Different factors at each stage can cause sperm abnormalities. For example, if a boar has a fever (elevated body temperature), this can affect spermatogenesis. Changes in temperature, pH, or osmolarity during semen dilution can all cause sperm abnormalities.
6. What do sperm abnormalities mean?
Most abnormal sperm are not capable of reproduction, although depending on the degree of maturity some abnormal sperm may still be fertile. Therefore, when counting sperm in semen, the percentage of abnormal sperm (which can be as high as 30%) must be taken into account.
7. How big is a boar sperm?
A normal sperm is about 45μm (approximately 0.0045cm). To give you an idea: if you lined up sperm cells head to tail in a chain, you could string 220 sperm cells together to make 1cm.
8. Since sperm are so small, how do they reach the egg? Do sperm swim to the egg under their own power?
No! Considering that the uterus has two uterine horns each up to 1.5 meters long (see Figure 3), it is impossible for such tiny sperm to swim the entire distance. During fertilization, it is mainly uterine contractions that drive sperm rapidly to the site of fertilization (where sperm and egg meet). This is why stimulating the sow during fertilization is important. Once sperm reach the site of fertilization, the sperm's own motility becomes important. Tail movement helps the sperm move to the egg and drives the sperm head into the egg.
9. How many sperm reach the site of fertilization?
Only a very small fraction of sperm reach the site of fertilization (less than 1%). After fertilization, passing rapidly through the uterus, only 10,000 sperm reach the sperm reservoir in the oviduct - most sperm are lost to backflow as they pass through the uterus, that is, they flow out beyond the cervix, or are phagocytosed by the sow's somatic cells, which occurs when the sow's body is stimulated by foreign substances. When ovulation occurs, sperm are slowly released from the storage area and move toward the site of fertilization, and during this process fewer than 100 sperm survive.
10. Is sperm motility related to fertility?
Billy Flowers' research in North Carolina confirmed that when boar sperm motility exceeds 60%, fertility and litter size are no longer affected by sperm motility. Therefore, PIC sets a target of over 70% for sperm motility.
11. Is there a single test that can accurately predict the fertility of semen ejaculated by an individual boar?
Unfortunately, no. Currently, because of shortcomings in the feasibility of the technology and the reliability of its execution, we can only evaluate a few components of sperm quality rather than all of them. However, if that component is not the limiting factor, then there is no necessary relationship between the aspects we can evaluate and fertility. For example, we can look at some components of the sperm such as the tail or head and check whether their shape is normal, but we cannot guarantee that the sperm will therefore function normally, or assess whether the chromosomes (genetic material) are in good condition. Imagine a car: you can look at it and know whether the tires are intact or whether the shape is quite good. You can even test the lights to see whether they work properly, but when it comes to the engine or the driving, you cannot be sure it will get you to your destination. But if you see that the car has no tires, then you can be certain that the car is no good. This is what happens with sperm today. We can look at sperm and know whether the sperm is of poor quality, but we cannot be sure that such sperm is definitely of good quality. At PIC, we carefully examine every ejaculate before and after dilution to ensure that sperm motility and morphology are normal, so that we can avoid using semen that appears to be of poor quality, but we cannot predict fertility based on semen quality.
12. How many sperm are in each ejaculate of a boar?
This is determined by several factors, such as age in days and the frequency of collection, and is generally between 20 and 60 billion.
13. What is in the insemination bottle?
Semen: sperm and seminal plasma
Water
A mixture or diluent: this provides nutritional and metabolic support for sperm, protects sperm from changes in environmental temperature and pH, inhibits bacterial growth and increases semen volume to a dose that can be used for reproduction. It usually contains glucose, electrolytes, buffers and antibodies.
14. Are the sperm in the insemination bottle ready to bind with the egg?
No. Because they have not yet undergone a process called capacitation (by which sperm acquire the ability to fertilize), and capacitation usually occurs after sperm enter the sow's body and takes 6-8 hours.
15. How long can sperm survive inside the sow?
Typically, good-quality sperm can survive for about 24 hours in the sow's reproductive tract. The egg can only survive for 12 hours, so it is best for sperm to have already reached the site of fertilization before ovulation.
16. At what age do young boars start having semen collected?
Puberty in boars begins at 5.5 months of age, and sperm can be found in their semen. Once the boar is physiologically mature enough to produce sufficient quantities of good-quality mature sperm, training the boar to mount the dummy can begin, at roughly 6-7 months of age.
17. How long is the shelf life of sperm in the insemination bottle?
Typically 3-10 days, depending on the diluent used and whether the semen is stored properly. At PIC, with a certain diluent, we guarantee a shelf life of at least 5 days.
18. How many sperm are in the insemination bottle? How does PIC know?
PIC's target is: 2.3 billion sperm cells per insemination bottle. To ensure this value is reached, every ejaculate is measured and diluted according to sperm concentration. At PIC, we place great importance on measuring the number of sperm in each ejaculate so that the result is as accurate as possible, and the mixing is thorough. Therefore, all insemination bottles contain an average of 2.3 billion sperm cells.
19. Why do the insemination bottles need to be shaken twice a day?
If the insemination bottle is not shaken, the sperm will settle to the bottom of the bottle. Shaking is therefore needed so that the sperm can obtain nutrients and metabolites and be redistributed in the diluent.
20. Why do I need to keep the diluent away from sunlight?
Ultraviolet (UV) light in sunlight can damage or kill sperm. This is why semen must be kept in a box during transport.
21. Why must semen be stored at 17℃? What does it mean if it is above or below this temperature?
The ideal storage temperature for sperm is 17℃. If sperm are stored at high temperatures, such as 20℃, sperm activity is not sufficiently suppressed (which accelerates the use of nutrients and energy). As a result, sperm viability decreases. In addition, at higher temperatures there is also a risk of bacterial growth. If sperm are stored at 15℃, the sperm's protective membrane, including the acrosome, may be damaged (you may not be able to observe this phenomenon with a simple microscopic examination, because under these conditions sperm motility may not be affected).
22. How is sperm morphology measured? How often is it measured?
At PIC, after every semen dilution, sperm morphology must be observed under the microscope, and a detailed analysis is carried out every four weeks.
23. How does PIC ensure semen quality?
We have a strict quality control system, including compliance with the British Pig Executive (BPEX) protocol. We have our own quality control program, and in addition we send samples to an independent third-party laboratory for evaluation. The independent laboratory's veterinarian inspects all populations once a week, assessing not only the health status of the boars but also whether the sperm meet high quality standards.
24. How does PIC handle the testing of reserve breeding boars before they are used as breeding boars for commercial semen sales?
All new boars must pass strict quality control tests, including morphology, motility and the osmotic resistance test (ORT, a special test used to assess the integrity of the sperm membrane). Before reserve boars are used as breeding boars, they must have multiple consecutive semen collections that all pass testing.
25. Why does PIC GP semen have color?
Is this harmful to the sperm? We are using some dyes in GP semen to make it easier to distinguish. (These dyes, as well as some of the materials that come into contact with the sperm, are non-toxic.) They come from reliable manufacturers, and in addition we carry out toxicity testing on every batch.
26. Is sperm sterile?
No! Sperm is not sterile; it may contain bacteria. Bacteria may come from the semen itself, from the sow, or from the environment. They are generally not pathogenic to sows, but if they are present in large numbers they may affect sperm quality. This is why most diluents contain antibodies and why storage at 17°C is required, and why special care must be taken during collection and handling to ensure that bacterial contamination is minimized.
27. How do I ensure that PIC sperm will not transmit disease?
At PIC, we have many ways to ensure that sperm do not transmit disease. All boars from PIC farms must be strictly monitored under the PIC health program. This ensures that the number of sources for each population is minimized and that all sources must be PRRS (blue ear disease) negative.
Every day, staff must carry out clinical observation to ensure that all boars are eating normally and appear in good condition.
Boar body temperature is measured once a day to detect any potential problems in time.
All populations must be EU-approved; they undergo extensive serological testing, including for brucellosis, classical swine fever and pseudorabies.
PRRS is monitored through regular serological testing (at least once a month) and semen PCR testing (at least twice a month). PCR testing is relatively expensive, but it has a special advantage: it can detect the virus in time (serology looks for antibodies, and the production of these antibodies takes 10-14 days).
28. Can you mix semen from different boars?
Yes, you can, but in order to minimize any possible health risk, PIC has decided not to do so. Therefore, the semen in your insemination bottle comes from a single boar.
29. Why do we use fresh semen and not frozen semen?
Frozen boar semen is technically feasible, but the results are not as good as with fresh semen; litter size and newborn piglet survival rate are usually lower; there also appears to be considerable individual variation, that is, the semen of some boars seems to be of higher quality than that of others. In addition, considering the technical level on farms, frozen semen technology has never been commercially applied.
30. When will sexed semen be available?
Sexed semen has become a reality in cattle production, but the production process is slow and relatively expensive. If we consider that, compared with cows, sows require a larger volume of semen, then there is still a long way to go before it can be converted to commercial production.