The techniques for artificially inseminating sows using fresh or chilled semen is presented here. The procedure for the using frozen semen requires special training and is not included.
Artificial insemination (AI) of pigs has been used in Australia since the early 1970s but only became popular after 1981 when boars and frozen semen were imported. Several AI centres supply chilled boar semen in Australia. The genetic influence of imported boars, and since then, boars with higher estimated breeding values, has been more widely spread by the use of AI.
Advantages of AI
- Semen from a range of top-performing tested boars of several breeds is available from AI centres.
- The genetic influence of good boars can be spread more widely.
- AI is a safe, cheap method of introducing new genes into pig herds, especially from those herds classified as specific pathogen-free, minimal disease or high health status, compared with bringing in live pigs.
- There is less risk of introducing exotic diseases into Australia with AI than in the importation of live pigs.
- AI overcomes size differences between boars and sows.
- It may be used during temporary shortages of boars from death, lameness or failure to work.
Disadvantages of AI
- Reduced farrowing rate (50%) with frozen semen.
- Lower than average results with chilled semen stored longer than 72 hours.
- Disappointing results where AI is poorly timed or done incorrectly.
Despite the occasional disappointing result with AI, worthwhile genetic gains can be made providing semen from top-performing tested boars is used.
Succeeding with AI
Whether using semen collected on-farm or buying it from an AI centre, successful insemination hinges on:
- detecting oestrus in the sow
- correctly timing the insemination
- using the right technique
- correct storage and handling of semen.
During her 50 to 60 hour oestrus or 'heat' period the sow will mate but she is only highly fertile for 24 to 32 hours (Figure 1).
To experienced stockhandlers, the signs of impending oestrus are obvious. In a group, the sow mounts others while swelling and reddening of the vulva (in gilts especially) gives early warning. There is little mucus secreted from the vagina at this stage.
Some sows may honk, lose their appetite and appear nervous, thus signalling approaching oestrus. This period before oestrus proper lasts 2 to 4 days.
The sow shows onset of oestrus by accepting the boar's sexual advances. The vulva is still red and swollen and watery mucous is often seen after sexual stimulation. At this time only the boar gets the sow to 'stand' and insemination results in poor fertility.
Peak fertility (for AI and natural mating) is in the middle 24 hours when both boar and inseminator can get a strong 'standing' reaction (starts about 12 hours after onset of oestrus). The swollen red vulva has noticeably subsided by this. Mucous is plentiful and has better lubricating qualities than that seen at the beginning of oestrus. The colour of the mucous changes from clear to greyish-looking at this stage.
In the last 12 to 24 hours, the sow 'stands' for the boar but increasingly less for the handler. Insemination at this time also gives poor results.
During ovulation, the ovaries shed eggs for 40 hours (range 36 to 50 hours) after the onset of oestrus. Spermatozoa in freshly collected or chilled semen have to mature or capacitate for 2 to 3 hours in the female's oviduct before being capable of fertilisation, but frozen semen requires no time for capacitation.
Spermatozoa can be found in the oviducts of naturally mated sows for 24 hours or more after copulation while the viable life of frozen and then thawed spermatozoa is only about 8 to 10 hours in the oviducts. The eggs or ova have a much shorter life, being viable for less than 6 hours in the oviduct. Ideally, the eggs should be fertilised within hours of being shed; embryos from aged eggs tend to die more readily.
Inseminations with fresh or chilled semen achieve optimum conception about 12 hours before ovulation. Since ovulation follows onset of heat after about 40 hours, the best insemination time is 28 hours (about a day) after onset. As the exact time of oestrus onset is difficult to pinpoint on-farm, inexperienced handlers particularly, should perform two inseminations 12 to 16 hours apart to achieve best results.
When to inseminate
- Test the sow for 'standing' reaction twice daily (she 'stands' more readily to back pressure when she can see, hear and smell a mature boar and be touched by him, see Figure 2).
- Inseminate twice (8-12 hours after the handler first gets the 'standing' reaction and again 8 to 16 hours later; see Figure 1).
- If only inseminating once, it should be done 24 to 32 hours after the onset of 'standing' heat. In practice, where checking for 'standing' heat twice daily, inseminate about 24 hours after the sow 'stands' to back pressure.
The third important element with AI is using the right technique. The technique should imitate natural mating as closely as possible.
Before inserting the catheter, clean the sow's vulva and the area around it with a fresh, damp cloth or paper towel. This reduces the chances of introducing infectious material into the uterus and also provides sexual stimulation.
Manually stimulate the sow in the presence of a mature boar to induce the mating stance. This is done by applying pressure between her shoulder and midback, knee pressure to her flanks and massaging her vulva and udder.
The uterine horns of a mature sow are up to 1.5 m in length and sperm cells cannot travel this distance on their own. Oxytocin secreted from the sow's brain in response to stimulation causes smooth muscles in the tract to contract and push the spermatozoa towards the oviduct. This process is critical for a successful insemination.
Inserting the catheter
Lubricate the tip of the catheter (Melrose type only) with a small amount of semen. Part the lips of the vulva and gently insert the catheter upwards into the vagina ensuring that the tip does not penetrate the urethra (the bladder opening on the vaginal floor, see Figure 3). Accidental penetration allows urine to flow from a distended bladder through the catheter. As urine harms sperm cells, a fresh catheter should then be used.
The catheter is gently pushed through the vagina until resistance is felt at the opening of the cervix. Spiral tipped catheters are rotated anti-clockwise and steadily pushed to lock into the cervix. As the funnel-shaped cervix of a sow in oestrus is firm and well lubricated the inseminator can apply positive pressure while 'locking-in' the catheter. Its shape helps to direct the catheter so that insertion is seldom difficult. In some gilts the hymen membrane may cause resistance in the first 10 cm.
The catheter is inserted as far as it will go. The flange on the non-spiral-type can be felt passing over the cervical folds while the spiral type is 'locked-in' when a gentle pull fails to free it.
Attaching the semen bottle
With semen kept within the desired temperature (15 to 20oC), spermatozoa lose their motility and settle to the bottom of the bottle. Twice a day and before use, the bottles or tubes must be gently agitated to re-suspend the cells. Thirty minutes before use, remove the chilled semen bottle from its pack and allow the semen to warm up. This can be done by placing the bottle in a warm place, for example, a shirt pocket. Immediately before use, gently rock the insemination bottle to redistribute the spermatozoa through the diluent. Cut the tip of the inseminating bottle with a clean, sharp knife. Grip the bottle by its cap and firmly fit the tip into toe inserted catheter. The bottle is raised over the sow's back and squeezed a little to remove the airlock in the catheter. With the aid of gravity, semen is drawn into the sow by wavelike muscular contractions in her uterine horns. Sexual stimulation should be continued to promote the contractions.
If semen does not flow freely from a soft-walled inseminating bottle or when gentle pressure is applied to a less pliable one:
- The opening at the catheter's tip may be blocked by a fold in the cervix; withdraw the catheter a little or slightly rotate the spiral tipped catheter.
- The sow may not be contented or sufficiently stimulated. The hormone oxytocin is responsible for uterine contractions during insemination. Aggressive handling, especially for nervous sows, triggers the release of adrenaline, a hormone that inhibits oxytocin. Boar presence, firm hand rubbing between the sow's shoulder and midback area, knee pressure in the flank and massaging the vulva and udder stimulate the sow. Periodic movement of the catheter also helps.
- A blockage is evident by resistance when the bottle is firmly squeezed. Remove the bottle and if necessary, the catheter to check for blockage (e.g. from gel particles or faulty equipment or too small an opening in the semen bottle's spout).
When the sow is well stimulated, insemination should only take 5 to 10 minutes. It is possible to let the semen gravity-feed into the catheter when using soft-walled bottles; gentle pressure may be used with any type of bottle, particularly the firmer types.
If the catheter is not far enough in or the inseminator is too hasty, back-flow may occur. When this happens, disconnect the bottle, reposition the catheter and delay insemination for a minute or two. Semen is often squeezed out by abdominal pressure when the sow moves suddenly, for example, when coughing or struggling. A small back-flow is not unusual and not detrimental provided enough semen with an adequate sperm count is used.
After semen enters the sow's reproductive tract, sexual stimulation should continue for several minutes. This ensures that the uterus actively forces the spermatozoa towards the oviducts, where fertilisation of the eggs takes place (see Figure 3). The catheter is left in place to assist with stimulation.
Stimulation is important in the sow because spermatozoa have to travel the 1 to 1.5 m in the uterine horns. When removing the catheter, ensure that the free end is higher than the vulva or semen may siphon out. Allow the sow to remain undisturbed following insemination.
The catheters commonly used for AI are the reusable rubber 'Melrose' with spiral tip or disposable plastic catheters having several types of tip. All are easy to use and achieve good results. Many inseminators prefer catheters with spiral tips that 'lock in' like the boar's penis, reducing back-flow during insemination. A drawback with reusable catheters is the high standard of cleaning and hygienic storage needed between uses.
Semen bottles or tubes
Chilled semen bought from AI centres comes in ready-to-use inseminating bottles or tubes. But if semen is collected and used fresh or diluted on-farm, a supply of clean plastic inseminating bottles will be needed.
Care of equipment
Since boar semen is an excellent medium for growing bacteria, all AI equipment must be kept clean. Immediately after use, soak reusable equipment in cold water so that semen or other material is easily removed later.
Do not use soaps or detergents because they affect sperm viability. Particles of gel can be removed with a brush.
Rinse, then boil rubber 'Melrose' catheters in distilled water for 10 to 20 minutes before reuse. Tap water must not be used for rinsing because it leaves mineral deposits on the equipment.
Store equipment in a dust-free cabinet or when completely dry, in a sealed plastic bag.
- When handling the sow, be firm but not aggressive.
- If a sow or gilt first 'stands' to back pressure in the morning, when near a boar, inseminate late in the afternoon of the same day and again the following morning.
- If she stands in the afternoon, inseminate her the following morning and again late that afternoon.
- If only doing a single insemination, time it to coincide with the second period as above.
- If mucous is present, it should be creamy in colour rather than clear. If clear, then insemination is too early.
- Use clean equipment for every insemination. Ensure the sow is adequately stimulated before insemination.
- Carefully lock the catheter into the cervix.
- Be patient, allow the semen to flow slowly.
- Continue stimulating the sow during insemination. Handle the sow firmly but not aggressively.
- Watch for catheter blockages and semen back-flow.