Detailed Explanation of the Operation Methods of Pig Artificial Insemination Technology

Research on artificial insemination in pigs began in 1780 AD, when the Italian physiologist Spallanzani first successfully conducted artificial insemination experiments on dogs. It was not until the late 19th century and the beginning of this century that experiments on horses succeeded, and then it was applied to cattle, sheep, pigs and other livestock. By the 1930s, a relatively complete set of operating methods had taken initial shape, and it moved from the experimental stage into the practical stage, becoming an important means of breeding and improving livestock.

Advantages and Disadvantages of Pig Artificial Insemination

"A good sow benefits one litter; a good boar benefits a whole slope." This saying powerfully illustrates that although boars and sows each contribute fifty percent of the influence in the heredity of offspring, under ordinary natural mating conditions, one boar can mate with many sows, while one sow can only mate with one or two boars, producing 2.0-2.5 litters per year. It can be seen that the boar is far more important than the sow. If an excellent boar is fully utilized, its influence on offspring will bring several times or even dozens of times the benefit to the pig industry. Under natural mating conditions, one boar can at most handle the mating task of 25-30 sows per year. Obviously, the utilization efficiency of the boar has not yet been fully realized. So how can the role of excellent boars be fully brought into play? The widespread application of pig artificial insemination technology provides this possibility.

Pig artificial insemination technology is the simplest and most effective method adopted for the purpose of breeding breeding pigs and producing commercial pigs, and is an important means of scientific pig farming and achieving modernization of pig production. Its advantages are reflected in:

1. It improves the utilization rate of excellent foreign-breed boars and saves feed and costs for raising boars.

With one natural mating, a boar's ejaculate can only inseminate one sow. With artificial insemination technology, one boar's ejaculate can inseminate 10-30 sows. Under natural mating conditions, one boar handles the mating task of 25-30 sows per year, breeding 600-800 piglets; while with artificial insemination technology, one excellent foreign-breed boar can handle the mating task of 400-1,500 sows, breeding more than ten thousand piglets.

2. The advantages of pig artificial insemination for pig genetics and joint breeding.

By preserving the semen of excellent breeding boars or endangered pig breeds, the use of boars is not limited by their physiological lifespan, achieving the preservation of genetic resources; it makes cross-herd or cross-regional use of breeding boars more convenient, economical and safe, and facilitates the introduction of genes from exogenous populations; the reduced demand for boars can increase the selection intensity for boars; a large number of offspring of excellent boars can be obtained, and their excellent genes can be rapidly promoted, thereby accelerating the diffusion speed of genetic progress; by controlling the use of boars, a balanced population structure can be established, improving the efficiency of estimating genetic parameters and breeding values. Compared with natural mating, 50% and 100% artificial insemination increase the cumulative genetic progress of 10-year selection by 14% and 17% respectively [5]. Therefore, artificial insemination can technically solve the problem of China's numerous but small-scale breeding pig farms, realize joint breeding of pigs, and is also one of the most economical and effective means for China's pig industry to improve pig breeding efficiency and perfect the improved breed breeding system.

In short, through artificial insemination with the semen of excellent foreign-breed boars, the genetic progress of pig breeding can be accelerated, the coverage rate of excellent genes in the pig herd can be increased, the growth speed of the pig herd can be improved, the feed-to-meat ratio can be reduced, the uniformity and consistency of slaughtered pigs can be improved, and ultimately product quality can be raised to a higher level, enabling China's pig breeds to gain a place in the competition of the international pig industry. Vigorously carrying out research on the application and promotion of foreign-breed pig artificial insemination technology can rapidly and safely enable the exchange of genetic resources between farms in the form of semen from excellent breeding pigs, thus achieving joint breeding of pigs between farms over a relatively large area in the shortest possible time.

3. It is conducive to breed layout.

Artificial insemination can fully bring into play the role of excellent lean-type boars, accelerate the pace of commercial lean-type pig production, and unified semen supply can scientifically adjust breed layout, achieving diversity without chaos.

4. It overcomes differences in body size and fully utilizes heterosis.

Under natural mating conditions, it is very difficult for a large boar to mate with a small sow, and vice versa. Some pigs have preferences, and boars and sows that dislike each other are also difficult to mate. This will cause certain difficulties for the conservation of excellent boars (when designated mating is required) and the improvement of breeding pig quality. For commercial farms, using heterosis to produce commercial pigs with good fattening performance, high lean meat rate and excellent body type, especially export pigs, will also cause certain difficulties. Using artificial insemination technology, as long as the sow's estrus is stable, the above difficulties can be overcome, and mating can be selected as needed, which is conducive to the conservation of high-quality breeding pigs and the full play of heterosis.

5. It reduces the spread of disease.

The boars and sows used for artificial insemination are generally pigs that have undergone health examinations. As long as mating is carried out strictly according to operating procedures and contamination during semen collection and semen processing is reduced, the spread of some diseases, especially reproductive tract diseases, can be reduced, thereby improving the conception rate and litter size of sows.

6. It overcomes differences in time and region and enables timely mating.

During natural mating, the phenomena of sows being in estrus but no boar being available, or breed improvement being needed but introducing boars being difficult, constantly trouble people in the pig industry. With artificial insemination, boar semen can be processed and preserved for a certain period, and estrous sows can be inseminated at any time. Instead of introducing boars, semen (or frozen semen) can be purchased, which is convenient to carry, economical and affordable, and can ensure quality and timely mating, thereby promoting the improvement of the social and economic benefits of the pig industry.

7. It saves manpower, material resources and financial resources and improves economic benefits.

Compared with natural mating, artificial insemination relatively reduces the number of boars raised, saving part of the labor, feed, pens and funds. Even if a suitable boar station is newly established, the overall economic benefits will still increase; if semen is simply purchased, even more economic benefits will be created. At the same time, artificial insemination is also an important condition for concentrated weaning and concentrated mating in pig farms. Good technical conditions for pig artificial insemination can also improve the conception rate of sows, because the boars used for artificial insemination are all strictly selected, and microscopic examination is required after each semen collection, which is very difficult to achieve with natural mating.

Disadvantages of artificial insemination: If the production level itself is not high and the technology is not up to standard, it is very likely to cause sow endometritis, low conception rate and small litter size. It is recommended to learn the technology first, then conduct small-scale artificial insemination trials, or combine natural mating with artificial insemination, and then promote it as the production level and technology continuously improve.

Benefits of Pig Artificial Insemination Technology

Here an example is given to compare the costs of pig artificial insemination and natural mating. Suppose there is a pig farm raising 1,000 breeding sows. If natural mating is used, one boar can handle the mating task of 25 sows per year, so natural mating requires raising 40 breeding boars. If artificial insemination is used, 1 boar can handle the mating task of 150-400 sows. Here, calculating on the basis that 1 boar inseminates 250 sows artificially, the farm then only needs to raise 4 breeding boars. Cost comparison calculation: based on each boar consuming 800 kg of feed annually, with feed cost at least 1,500 yuan/year, artificial insemination can save 54,000 yuan in feed costs. Calculating on the basis of culling 1/3 of boars each year, natural mating culls 13 boars, while artificial insemination culls 2 boars. At a purchase cost of 4,000 yuan per breeding boar, artificial insemination saves 44,000 yuan in boar purchase costs. Using artificial insemination technology, each sow insemination requires about 33 yuan in costs per year (including disposable insemination bottles, insemination tubes, diluent and other costs). Inseminating 1,000 sows costs 33,000 yuan. On a comprehensive calculation, a pig farm using artificial insemination to inseminate 1,000 sows can save at least 65,000 yuan, plus savings in building boar pens, labor costs, etc. The economic benefits of using artificial insemination are obvious. Therefore, on the premise of improving the conception rate and stabilizing litter size, the large-scale application and promotion of artificial insemination technology will produce substantial economic and social benefits.

It can be seen that compared with natural mating, the superiority and benefits produced by pig artificial insemination are very significant.

Operating Technology of Pig Artificial Insemination

1. Boar training

Boars used for the first time with a dummy sow for semen collection must be trained. Training requires patience and repeated practice; do not rush, and strictly prohibit forcing, whipping, frightening, etc. Practice has proved that a new boar mating 1-2 times like a replacement pig helps training. The training methods are:

① Apply the urine or vaginal mucus of an estrous sow to the rear of the dummy sow to induce the boar to mount the dummy sow. After several semen collections, training can be successful.

② Confine an estrous sow in the semen collection room to lure the boar to mount, but do not allow mating. When the boar's sexual excitement reaches its peak, quickly drive the estrous sow away, then induce the boar to directly mount the dummy and collect semen.

③ Confine the boar to be trained beside the semen collection room, let it observe and become familiar with another already-trained boar mounting and collecting semen, then induce it to mount and collect semen. Production has shown that if, after one boar completes semen collection, another boar is driven in front of the dummy sow, most boars will show strong interest in the dummy sow and will carefully observe it, and after a few minutes will mount the dummy sow.

④ When training a boar, special attention should be paid to the first semen collection. The first semen collection should be complete and ensure that the boar does not suffer any form of injury or adverse stimulation. If training the boar for half an hour is unsuccessful, it should be driven away in a friendly manner, and a suitable time waited for, or it should be confined near the collection dummy more to become familiar with it before trying again.

2. Semen collection

① Preparation before semen collection

· Select and train "on-farm" expert-level operating personnel. Select and train one or more persons at the pig farm to undertake the technical work of artificial insemination. The success of artificial insemination requires this person to be precise, patient, confident, careful, enthusiastic and have a spirit of investigation. This person must proficiently master how to clean and disinfect artificial insemination technical equipment and instruments, how to train boars and collect, process and store semen, and be able to accurately perform estrus identification in sows and timely mating, etc.

· Semen collection room. Semen collection should generally be standardized in a semen collection room. Driving the boar into the semen collection room can arouse the boar's sexual excitement. The design should ensure that the semen collection room is spacious, quiet and clean. The installed dummy sow should be stable, preferably fixed in the middle of the semen collection room. To prevent individual boars from harming people, protective railings should be set up on both sides of the semen collection room. "Figure 1" is a suggested layout diagram of a semen collection room for reference in actual production (area about 3 x 3 m, with the actual semen collection area about 2.5 x 2.5 m).

· Preparation of the collection dummy. The dummy used for boar semen collection is what we all call a dummy sow in production. Dummy sows have many designs. According to actual conditions, they can be designed as single-ended type, height-adjustable movable type, etc. The simplest approach is to make a bench (collection stand), and it does not necessarily need to be covered with pig skin, nor is it necessary to pursue the shape of a pig. The length can be 1-1.3 m, the height 50-65 cm, and the back width 20-25 cm. To facilitate training the boar, the collection stand can also be shorter, lower and lighter. In production, a steel frame plus a wooden surface is mostly used, covered on top with thick coarse canvas or burlap. "Figure 2" is a simple collection dummy style.

· Preparation of the artificial insemination laboratory and related semen collection equipment and facilities. To facilitate the preparation of semen collection vessels, testing of semen, preparation of semen diluent and dilution of semen, storage of semen, disinfection and cleaning of artificial insemination instruments, etc., for on-farm artificial insemination, an internal "artificial insemination laboratory" should be established at the pig farm. In actual construction, the laboratory should be located as close as possible to the semen collection room, and if possible, should be directly connected to the semen collection room to facilitate rapid processing of semen. Using a window to connect the artificial insemination laboratory and the semen collection room helps strengthen disease prevention. The construction of the artificial insemination laboratory should fully consider hygiene and disease prevention requirements. The floor of the room should be easy to clean, the walls should be washable, and washable workbenches, sewage sinks and drying racks should be arranged. Water and electricity should be complete, room temperature adjustable, and a cold and hot water source is best. The layout of the laboratory depends on the specific operating procedures. Using small rooms makes it easier to maintain cleanliness and adjust room temperature. "Figure 3" is a schematic diagram of an artificial insemination laboratory. It is divided into three parts according to operation, namely the wet area (preparing diluent, cleaning equipment, diluting semen); the dry area (examining semen); and the dispensing area (dispensing semen, preserving semen, etc.).

· The equipment used for artificial insemination semen collection mainly includes: semen collection bottles (various containers are acceptable, but it is best to have a heat-insulating effect, be disinfectable and easy to clean); funnels; sterilized surgical gauze; disposable latex gloves (note: non-toxic); microscopes (magnification can be 100, 400, 1,000 times, preferably equipped with 2 eyepieces and a microscope warming box to maintain the temperature of the semen sample); glass slides; droppers; thermometers; beakers, graduated cylinders and bottles of various capacities (glass or plastic are both acceptable, used for preparing diluent, diluting semen, and dispensing semen, etc.); insemination bottles and nozzles; semen preservation facilities (polyethylene or polystyrene foam storage boxes, cold and hot water bags, etc., used for short-term storage of semen; constant-temperature control cabinets or warming boxes); disinfection facilities (disinfection trays or electric heating nets, electric heating insemination catheter disinfection instruments, autoclaves, etc.); insemination catheters; distilled water or reverse osmosis water; drying cabinets (for drying and storing all semen collection and testing equipment).

· Farms with good conditions should also be equipped with: water softeners, colorimeters or spectrophotometers, water bath incubators, heaters/magnetic stirrers, etc.

② Semen collection method: The hand-grip method for collecting boar semen is a widely used method at present, and its operation is simple, accurate and efficient. The operating process is as follows: the semen collector puts on sterilized gloves and stands at one side of the dummy. First, use 0.1% potassium permanganate solution to wash and disinfect the area near the boar's prepuce. After the boar mounts the dummy, use the hand to rub the boar's penis to induce it to extend out, and guide it into the palm of the empty fist, letting it rotate for a moment, then use the fingers to grip the spiral-shaped glans penis from light to tight with a rhythm, not letting it rotate. When the penis is fully erect, guide and stretch it forward (do not pull forcefully), while the fingers adjust the pressure elastically and rhythmically, which will cause the boar to ejaculate. During ejaculation, stop the elastic adjustment, open the fingers slightly to expose the glans, and let the semen ejaculate into the insulated semen collection bottle with filter gauze held in the other hand. After the boar's first ejaculation stops, keep the original posture without moving, and restore the elastic adjustment and squeezing to achieve the second, third or fourth ejaculation, until ejaculation is completely finished.

③ Precautions for semen collection

· Semen collection frequency: replacement boars are collected once a week, production boars are collected 2 times, and must not exceed 3 times when necessary; frequent semen collection is strictly prohibited.

· Before semen collection, first squeeze out the urine in the boar's urinary bladder, then wash and disinfect the boar's prepuce area. If the pubic hair is too long, it must also be cut short.

· During semen collection, the staff should be gentle in attitude and must not be rough. Operations should be standardized, and care should be taken not to injure the boar's penis.

· During semen collection, the thin semen before and after and the gelatinous portion in between should be discarded.

· If the collected semen is found to be of poor quality, under the condition of ensuring normal feeding, check the boar's semen once every half month, and decide whether to keep or cull it after one month.

· Keep good semen collection records, and conscientiously analyze and summarize semen quality and other conditions.

3. Semen examination and quality evaluation

The purpose of semen examination is to identify the quality of the semen, so as to facilitate further processing or use for insemination and preservation. Examination should be carried out immediately after semen collection, and it should be rapid, accurate, comprehensive, and scientifically and standardly operated. In actual production, it is not necessary to conduct sperm morphology examination on every semen sample of every boar, but morphology examination should be conducted on the first few semen samples of new boars, and thereafter each boar should be tested once every half month.

① Sensory examination

Ejaculate volume: Usually the ejaculate volume of a boar is 150-300 ml, but due to great differences in breed, age, sexual preparation, semen collection method, technical level, semen collection frequency and nutritional status, the range of variation is generally 50-500 ml. Correspondingly, the weight of the semen can also be weighed (1 gram is approximately equal to 1 ml) to determine the size of its ejaculate volume. Generally, when measuring a boar's ejaculate volume, one cannot rely only on a single semen collection record, but should take the average of the sum of multiple ejaculate volumes over a certain period as the standard.

Color and odor: Boar semen is light milky white or light grayish white. The thicker the milky white degree of the semen, the more sperm there are. If the color is abnormal, check whether there is disease in its reproductive organs. Clean semen has only a slight odor. If contaminated by the prepuce or if semen quality changes abnormally, the odor will be very strong.

② Measuring pH value

The pH value of pig semen is 7.3-7.9. The simplest method for measuring pH value is to use universal test paper for color comparison.

③ Motility examination

Motility examination is an important item in semen quality examination. Motility is used to measure sperm movement, and motility examination includes evaluating the proportion of sperm moving in a straight line. The operating method is: use a glass slide preheated to 35°C, use a dropper to draw a drop of semen, then use a cover glass to evenly cover the liquid surface, so that when examining this thin layer of sperm cells, a clear picture of the semen can be seen. Use a 100x or 400x microscope to examine and evaluate sperm motility (as shown in the table below). If motility is very poor, score it 0 or 1, and semen scored 0 or 1 should be discarded. In actual operation, to ensure the accuracy of the measurement and evaluation, it is generally necessary to repeat the examination once.

Sperm density examination can be carried out using the estimation method, the sperm counting method, or by using the light transmittance (turbidity) of sperm. In production, it is often carried out simultaneously with sperm motility examination. Under the microscope, according to the different degrees of sperm density, sperm density is roughly divided into "dense", "medium" and "thin", abbreviated as the three grades "dense", "medium" and "thin". Under microscopic examination, if sperm are dense and the distance between sperm is less than 1 sperm length, the density is "dense"; if the space between sperm can accommodate 1-2 sperm, it is "medium"; if the gap between sperm is large and can accommodate more than 2 sperm, it is "thin". This evaluation, like the evaluation of sperm motility, requires a certain amount of evaluation experience, but it is simple and easy to carry out and can roughly determine the dilution ratio. In addition, a colorimeter or spectrophotometer can also be used to accurately determine sperm density, but the equipment investment is expensive and generally difficult for ordinary production farms to bear.

④ Sperm morphology examination

Whether sperm morphology is normal is closely related to the conception rate. If the semen contains a large number of abnormal sperm, its fertilizing ability is low. Generally, for high-quality pig semen, the abnormality rate should be below 18%, and for ordinary-quality semen, the sperm abnormality rate should also not exceed 20%. If it exceeds 20%, it indicates poor semen quality and it should be discarded and not used for insemination. "Figure 4" shows normal sperm morphology, and "Figure 5" shows some common abnormal sperm morphology.

⑤ Other examinations

These include bacteriological examination, sperm stained smears, sperm survival time, etc. These can be carried out selectively according to the specific conditions and production scale requirements of each production farm.

4. Semen dilution and preservation

After quality examination of the semen, in order to increase semen volume to produce more insemination doses, and also to provide a good nutritional environment for semen preservation, the semen should be diluted immediately.

① Preparation of diluent

A variety of suitable diluents can be prepared, some of which are relatively complex and need to be prepared with laboratory techniques, and are generally only used in commercial artificial insemination stations. What is commonly used in production are those simple diluents that require only one mixing, and ready-prepared semen diluent powder can be purchased and prepared according to the instructions. For example, BTS, Guelph, Kiev, Merck, Zorpva, Reading, Modena and other diluents, some of which can be preserved for 3 days, and some for 5-7 days. The table below lists the formulas of some diluents for reference. When actually preparing the diluent, note that all compounds used must be "analytical grade", the distilled water added must be pure, and double-distilled water should be used for dilution when conditions permit; all materials should be accurately weighed, and must be completely dissolved and fully mixed; the diluent is best prepared and used immediately, and should be used up within 24 hours at the longest.

② Dilution of semen

Semen dilution should be carried out in a certain proportion according to sperm density. If sperm density has been accurately determined, the dilution ratio is easy to calculate. However, in actual production, due to considerations of input costs and many other factors, often only the "dense", "medium" and "thin" evaluation of semen density can be carried out. In this case, when diluting semen, the dilution ratio should be controlled at 1:4 to 1:10, preferably within 6-8 doses, that is, if you have 200 ml of semen, the diluted semen volume cannot exceed 1,000 ml. And it must be ensured that one dose of insemination liquid contains 1.5 x 109 to 6.0 x 109 sperm, and its volume should be at least more than 50 ml. It is best to ensure the dilution ratio within 8 doses, because the average sperm count of one ejaculation of a normal boar is 30-40 x 109, with a range of variation of 20-120 x 109. If the dilution ratio is controlled within 8 doses, it can still ensure enough sperm to guarantee fertilizing ability.

If sperm density has been accurately determined, the dilution ratio is easy to determine. For example, if the measured density of a boar's semen is 200 million/ml, the semen collection volume is 300 ml, and the planned density after dilution is 4 billion/100 ml per dose, then this boar's semen can be diluted to 300 x 2/40 = 15 doses, that is, 1,500 - 300 = 1,200 ml of diluent needs to be added.

When diluting semen, the most important thing is that when mixing, the temperature of the semen and the diluent must be the same. In operation, the diluent is generally heated and maintained at 36°C, and during dilution, the semen and diluent should be maintained at an equal temperature of 36°C as much as possible. If there is a temperature difference, it must be controlled within 1°C. When diluting, slowly pour the diluent into the semen and mix thoroughly. The action should be gentle and slow to prevent violent shaking.

③ Preservation of semen

The diluted semen should be preserved in a constant-temperature cabinet, maintained at 17-18°C, and gently shaken once every 12 hours to prevent precipitation of the diluent. In production, never preserve semen in a refrigerator (2-8°C) or in an environment higher than 20°C.

Operating Technology of Artificial Insemination

Insemination is the last technical step of artificial insemination. Only by timely and accurately injecting a certain amount of high-quality semen into the appropriate part of the reproductive tract of an estrous sow can a good conception rate be obtained.

The insemination dose cannot be too small. The normal dose for artificial insemination is generally 3-5 billion sperm per dose, with a volume of 80-100 ML. The United States generally uses 3 billion/80 ML per dose, while China generally uses about 4 billion/100 ML per dose. However, this is mainly determined according to actual conditions and is closely related to breed, the technical level of the inseminator, etc.

In actual production, to improve the conception rate of pigs, two inseminations are generally used, that is, after the first insemination, repeat the insemination once after an interval of 8-24 hours. For individual sows with a particularly long duration of estrus, in addition to carefully observing changes in their estrus symptoms and grasping the timing of insemination, a multiple insemination method is also used, that is, inseminating once a day for several consecutive days, to enhance their chance of conception.

Before inseminating a sow, the preserved diluted semen should also be examined. Only semen with a sperm motility of not less than 0.5 under microscopic examination can be used for insemination. The instruments used for insemination must be strictly cleaned and disinfected. From the processing room to the production line, semen should be carried in a warming box to prevent the sperm from being stressed and dying due to the external temperature being too high or too low. Before insemination, the sow's vulva should be cleaned and disinfected. The insemination time should be controlled at about 19-30 hours after the beginning of estrus. In actual operation, the best insemination time is controlled during the sow's full estrus period. During insemination, first apply a little diluent to the insemination tube to lubricate it, then insert it upward and forward while rotating counterclockwise, until it is locked in the cervix and cannot advance further, then pull it outward slightly, and slowly pressurize the insemination bottle to inject the semen into the uterus. The duration of insemination should be similar to natural mating, about 5-15 minutes. After insemination, slowly withdraw the insemination tube, and use the palm to press the lumbosacral junction of the sow to prevent backflow of semen.