Animal behaviour and welfare: Pigs Part 2

PIG BEHAVIOUR BASICS: PART 2

Reproduction: Birth behaviour: Fostering

By Dr Clive Dalton


The female

• Puberty can be affected by breed, season of the year, and social environment (e.g. crowding) but especially by live weight.
• Mixing during transport sometimes triggers puberty where the transport stress is thought to trigger reproductive hormones.
• Contact with males will also stimulate first oestrus. However if exposure is too early or for too long, the gilts may become accustomed to the boar's presence and not react.
• To exploit this male effect, expose the gilt to the boar at about 160-175 days of age, and 60-90% of then should show oestrus within 10 days after exposure.
• Most breeds of gilts today come into oestrus between 170-220 days of age, when they have been moved from their finishing pens at around 90kg live weight.
• Weaning a litter will trigger the sow to come in oestrus. She usually cycles 4-5 days after removal of her litter.
• For best results, make sure the gilts are kept totally from within sight, smell or sound of the boar.
• Rearing gilts with contemporary male pen mates does not seem to advance their age of puberty.
• In general practice, gilts are mated and their third heat, when weighing about 118kg. However mating them at their second heat has economic advantages.
  

Signs of oestrus
Sows and gilts in oestrus show any combination of the following signs:

• Swollen and reddened vulva about 2-6 days beforehand.
• Mucous discharge from the vagina.
• Restlessness and a poor appetite.
• Females coming into heat may sniff the genital area of their pen mates.
• They may ride others and stand to be ridden.
• They will show a feature unique to pigs - the "stance reflex" where they arch their backs , stand rigidly when pushed from behind, and allow a person to sit astride them.
• Prick-eared breeds carry their ears erect and held back.
• Oestrus pigs make a characteristic grunt and seek other pigs while go around searching for a boar.
  

Mating

• The female pig assumes a major role in mating by searching for the male and converting social contact into sexual behaviour.
• "Standing heat" when the female will stand for copulation lasts around 48 hours (range of 38-60 hours). Some sows can stay on heat for up to 120 hours.
• The first heat is usually shorter and sows have longer receptive periods than gilts.
• Length of oestrus is also affected by breed, season and management system such as if sows are group our individual housed.
• Ovulation occurs during the second half of the oestrus period, so it's best for the boar to serve the sow twice - at the start and end of the standing heat period.
• Females not mated will cycle every 21 days (range of 19-24 days).
• Gestation in the modern hybrid pig kept intensively averages 115 days (range 108-122 days).
• The "standing reflex" of the sow where she will not move when weight is applied to her back increases as the oestrus period advances.
• The sow is stimulated by the boar and his pheromones from his body, especially his frothing mouth and the gelatinous exudates from his prepuce.
• The order of priority of these stimuli seems to be smell, sound, sight with physical contact last.
• Some sows show a preference for a particular boar and this can cause inconvenience in breeding programmes.
• When the boar is too large and heavy and risk damaging the sow (as mating can take a very long time), the female is best held in a crate where the boar's front legs rest on the sides of the crate to take some of his weight.
• Gilts may often only stand for a boar in the presence of another female in the mating pen, or with a familiar pig in an adjoining area. However, if these support pigs are nearing oestrus, they'll only distract the boar from the job in hand.
• It's a good idea to mate gilts to an old experienced boar and mate old sows with a young boar.
  

Female behaviour before birth

• Sows show great variation in their behaviour approaching birth. This depends mainly on age, previous experience, breed, strain and the husbandry system.
• Sows carrying a litter of more than 11 pigs will have a 5-day shorter gestation than those carrying average litters of 9-10 piglets.
• To avoid stressing the sow, she should be transferred to her farrowing quarters about a week before birth. This will allow them to settle in and reduce stress levels.
• Stressed sows (especially inexperienced ones) will have higher piglet mortality through overlaying and even attacking piglets.
• Heavily pregnant sows spend most of their time resting, sleeping and feeding.
• As gestation length varies widely, recognising the signs of approaching birth is very important, to ensure the welfare needs of the sow are met.
• Sows are nest builders - and they need to express this desire in intensive farming. A sow starts to nest build 3-7 hours before farrowing, and after giving birth she stays in the nest for 24 hours, nursing every 45 minutes.
  

Signs of birth

• The vulva swells and becomes redder, especially obvious in white skinned pigs about 4 days before birth (range 1-7 days). In black pigs you will only see the vulva starting to look like a swollen prune.
• The udder swells, becomes firm and colostrum can be obtained by gentle massage up to 24 hours before farrowing. Rubbing the front teats usually stimulates the sow to lie down.
• Increased restlessness. The sow gets up and lies down or changes side more frequently, twitches the tail, and chews the pen railings.
• She also urinates, defaecates and drinks more.
• The sow chews up the bedding (when provided) and makes the nest. She paws the ground, especially where no bedding is provided. This is a key sign.
• There will be a discharge of blood, birth fluid from the sow and green-brown faecal meconium pellets originating from the piglets.
• Respiration will increase from about 54 breaths/minute 24 - 12 hours before birth, to 90/min 12 - 4 hours before birth, reducing to 25/min at about 24 hours after farrowing. This together with intermittent low grunting and jaw chomping is common.
• Sow rectal temperatures rises from about 39 - 39.5 C four hours prior to farrowing. They then stay elevated (around 40 C) for up to 24 hours after farrowing.
  

Behaviour during birth

• During birth, the sow lies on one side, and in the intervals between piglets she may change sides, stand or sit in a dog-sitting posture. These movements risk crushing or overlaying the piglets.
• Studies showed that the average time to produce a whole litter averaging 11 piglets was 2 hours 53 minutes, or 15.3min/piglet.
• But these times vary greatly with a range from 3.6 min/piglet to 44.6 min/piglet.
• Normally 55-75% of piglets are born head first and 25-45% back legs first.
• Abdominal straining is more often seen before the birth of the first pig, and less common with the remainder.
• As the sow strains, her tail is often pulled back away from the vulva, and delivery of a piglet is often accompanied by vigorous tail swishing and expulsion of gas from the rectum.
• Paddling with the legs while lying down is common.
• The sow usually just lies still as each piglet is born, and she attracts them to her head end by special grunts. She doesn't stand up and lick them and chew their birth sack like other species. She also cannot turn to lick them as they are born like a bitch as she is not as flexible.
• After the piglets are born, the sow stands up and often urinates.
• Usually the foetal membranes start to be expelled during the birth phase and they may appear in two of three lumps. Most of it is shed after the last piglet is born.
• Four hours is normally needed to expel the complete afterbirth but this varies widely from 21 minutes to 12-13 hours.

Early sow and piglet behaviour after birth

Most milk is at the front teats

• About 70% of piglets are born with their umbilical cords still attached and attached to the foetal membranes still inside the sow's genital tract.
• The cord can be stretched considerably before breaking and this helps to prevent haemorrhage.
• It takes from 1 to 30 minutes for piglets to free themselves form their cords which became shrivelled within 4-5 hours after birth. The sow rarely chews the end of a piglet's cord.
• After a brief period of 5-10 seconds of not breathing, the piglet gives 5-6 gasps and a cough. This is followed by about 20 seconds of rapid shallow panting followed by regular rhythmic breathing.
• Most piglets attempt to stand within one minute of birth, and within two minutes they can stand freely and start searching for the teats, or anything that sticks out that feels like a teat - e.g. the point of the sow's vulva.
• There's a wide interval of 3 - 153 minutes/piglet (average of 10-15) between birth and the first milk intake. Piglets clearly vary enormously in their ability to find a teat although some are greatly restricted by the trailing cord.
• Nuzzling is a very important behaviour used in teat-seeking.
• Piglets show a very clear preference for the front teats of the sow, which generally have more milk than the rear ones.
  
• So the first-born piglets get the best (front) teats, which they claim and fight for until a suckling order is established.
• The front teats are longer with more space between them and they have a greater clearance above ground level than the rear teats, so the piglet can grip them more easily.
• Clearance generally declines up to teat number 6, and as the sow ages the udder becomes more pendulous and her ability to expose the bottom teats is reduced.
• The risks of piglets being kicked by the hind feet are also greater when suckling the rear teats. There is also a danger of being kicked by the front feet.
• So the front-suckling piglets grow faster and consequently maintain their social rank in the litter.
• Piglets sort out a hierarchy in the first few days, and a clear social order is established after a week.
• As milk letdown is very rapid (about 20 seconds) and occurs about once an hour, there's little opportunity for piglets to share teats. But if space allows, they may suckle more than one teat.
• Normally breeders select females with a minimum of 12 functional teats, and preferably 14-16. In older sows, wear and tear and mastitis may reduce the number of functional teats.
• Piglet suckling behaviour moves through the following stages:
• Jostling for position along the sow's belly to find the teat.
• Squealing while jostling.
• Nosing the udder.
• Slow sucking.
• Rapid sucking.
• Final slow sucking and udder nuzzling.
• The sow's grunting increases greatly up to the slow sucking stage which is a clear signal to the piglets that letdown is imminent. Letdown starts 25-35 seconds after this signal.
• The squeal of isolated, lost, or handled piglets will alert and stress the sow and she may interrupt her suckling behaviour to investigate. So don't pick up stray piglets during suckling time.
• Piglets sleep for about 15-16 minutes every hour.
• In the wild, the sow and her piglets join the herd after a week.
  

Fostering piglets

• When sows are farrowed separately but in batches, litter sizes can be adjusted by taking piglets from large litters and giving them to sows with plenty of milk and small litters.
• Care is needed as sows vary in their acceptance of foster piglets.
• Best results are obtained if piglets from both sows are the same age and under one week old before teat preferences have been established.
• For success- remove all the piglets from the sow that is going to be given the extras.
• Wait till they are really hungry and she is anxious to have them back.
• Rub the rear ends of the removed piglets over the anogenital area of the strangers to be added. The sow usually smells this area.
• Use the afterbirth for this job if it's still available.
• Then put them all with the sow and watch to make sure she lets them all suckle and accepts them.
• Fostering will probably disrupt the whole nursing process, because of renewed competition for teats. You'll see this in the uneven growth of the litter up to weaning.
• When sows farrow together in the open, piglets seem to mix freely from birth without any problems. The main concern for the farmer is to make sure that each sow has a similar number of piglets.
• Behaviour of dry sows It's important that dry sows have their diets carefully controlled to ensure their nutritional needs are carefully monitored and met.
• The need to have strict control over a sow's diet has led to the development of systems that restrict their movement, and these have large behavioural and welfare implications.
  

The systems used are:

• Sow stalls - the sow is held in a narrow stall, allowing her to move to and fro but not turn round. There is total environmental control.
• Sows tethered in stalls by a neck strap or a strap around her chest. She cannot turn round. There is total environmental control.
• Sows at pasture in groups with communal shelters.
• Sows at pasture in individual runs or tethered to individual kennels.
• Sows in groups of 6-10 in a yard with kennel-type shelter and individual feeders.
• There is an active national campaign in many countries (including New Zealand) to make sow stalls and tethering illegal because of the stress it causes the animals. This practice has been banned in some European countries.
• Sows in stalls and tethered sows tend to develop "bar biting" when they bite the front bars of the stall, and also show a "paddling" behaviour often seen by bored tethered animals.
• Research has shown that even in stalls, providing some straw gave some enrichment to their existence.
• The ultimate in luxury, (judged with an anthropomorphic view) is to keep dry sows in large yards in deep straw. But sows can have savage fights to establish a social order when housed loosely, and it adds greatly to costs of production. This is a classical example of what the domestic contract should provide.
  

The male

• In the wild or in extensive pig keeping systems, the male pig, (unlike males in other species) does not initiate sexual behaviour. He waits for initial signals from the female.
• Boars reach puberty about 6 months of age, but are generally not used for service till 7-8 months old. These ages can vary a lot depending on the feeding level.
• They start learning their courting behaviour and show elements of sexual behaviour while still suckling and as part of play with pen mates. They develop these behaviours even more if mixed with strangers.
• Boars reared in isolation are much slower to develop successful courting behaviour. Group reared boars are better than those reared in individual pens, and intensive stocking will encourage aggression as well as sexual behaviour.
• Boars reared intensively in homosexual groups maintain this relationships for many months after parting, and they can often show abnormal sexual behaviour.
• The boar's courting ritual includes:
• Chasing the sow.
• Nuzzling her head, flanks, shoulder and anogenital area.
• Occasional pushing or leaning on the sow to test her state.
• Drinking her urine.
• He urinates frequently.
• He grinds and chomps his teeth salivating and frothing at the mouth.
• This courting ritual has an important effect on improving the conception rate of the sows being mated. In outdoor pigs boars often have rings inserted in their noses to stop them rooting up the pasture. This affects their courting ritual when it comes to nuzzling the sow and causing a negative response.
• When the boar mounts, he rests his belly along the sow's back and grasps her with his forelegs. Inexperienced boars will head mount, side mount and dismount frequently before intromission (penis entering the vagina).
• Ejaculation occurs when the cork-screw penis of the boar locks in the sow's cervix. This can take considerable time - averaging about 7 minutes but it can last up to 25 minutes.
• The boar thrusts and rests many times and eventually ejaculates up to 500 ml of sperm. Other farm species produce a 5-15 ml ejaculate.
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Boar behaviour and handling

• Treat all boars with respect and treat them as individuals.
• Handle them carefully and de-tusk them every 6 months (with veterinary advice).
• Remove the front accessory claws to protect the sow from injury during mating (with veterinary advice).
• Don't overwork the boar - one boar to 20 sows is most common.
• Four services a week are plenty till the boar is 12 months old. Don't let him serve more than 6 times a week as this will lower his fertility and subsequent litter size from the sows mated.
• Too frequent use of a boar as a teaser to locate sows coming into heat, may frustrate him too much and he may not serve when needed.
• Mate young boars to old sows in peak oestrus, and old boars to gilts.
• Don't let young boars get injured during their early matings.
• After layoffs of longer than a month, libido may drop and a boar may need the stimulus of an old sow in peak oestrus that has already been served by another boar.
• Spreading some ejaculate from another boar along the sow's back will help to stimulate a boar.
• Take the sow on heat to the boar so he doesn't waste time investigating a new environment. Otherwise he'll waste time in an elaborate ritual of urinating, rubbing scent from his body on the walls, marking the territory with salivary foam and fight the sow to establish dominance.
• Boar pens should provide a good foothold for the boar but not so rough as it will cause foot problems.
• Boars should be kept within sight, sound and smell of sows. However this assumes the boar is the dominant animal in the herd. He may be considerably stressed with other boars near by, as in the wild each boar would be solitary.
• Boars get very large and need regular exercise to keep fit. It's a good idea to have a system where the boar walks daily to the sow's accommodation to help stimulate oestrus and identify sows on heat.
• Regular quiet handling by the stockperson is ideal, walking behind with a pig board for protection, and talking in quiet reassuring tones.
  

Boars and Artificial Insemination (AI)

• AI in pigs is now well established in commercial pig improvement and is a specialist operation.
• At AI centres boars are trained to mount dummy sows and serve into an artificial vagina as this is less complicated than using a live sow.
• Boars may be harder to train if they have mated sows first. But again this varies with the personality of the boar.
• Gentle, reassurance by the stockperson is the secret of success to get a good semen sample from the boar.
• Boars will show courting behaviour to the dummy by nuzzling its flank and rear end.
• Libido varies greatly between boars, and is related to frequency of use.
• Boars can be stimulated more by giving them false mounts, or by observing a collection from another boar.
• It's a good idea to allow the sow or gilt 10-20 minutes contact (through a pen) with a boar after insemination.
  

Behaviour of housed boars

• In less intensive systems where sows are kept in straw yards (and not in stalls), boars often run with them and few problems arise.
• If a boar is put in among a group of unfamiliar loose-housed sows, he will waste time investigating the environment and not checking for sows on heat.
• In intensive pig farming, the boar does not spend time in social contact with sows and opportunities to consort with females are decided by the human in charge.
• Here, sometimes the boar pens are arranged between pens of six loose-housed sows to achieve maximum physical presence of the male.
• In other systems, including where sows are tethered or in stalls, the boar is walked daily in front of them to test for oestrus.
  
• When boars walk behind stalled sows a boar may be confused by the fact that they are immobile and hence displaying an invitation to be mounted. This can be very time-wasting.
• It's well established that depriving boars and sows full opportunity to indulge in their full courting behaviour affects pregnancy and litter size.
  

Boar behaviour problems

• Serving into the rectum instead of the vagina can be a problem. Avoid this by supervising young boars in their early work to make sure they are aligned correctly.
• Extremes of heat may affect the boar's enthusiasm. Delay his work till evening.
• Masturbation by coiling the penis inside the diverticulum of the prepuce. Make sure the boar's penis has actually entered the sow and he is not masturbating.
• Boars that masturbate persistently should be culled although the prepuce can be surgically removed.
• Some boars behave normally up to the point of mounting and then squat down on the floor and ejaculate. Great care is needed to help these boars achieve success as they may persist in this habit.
• Aggression. Boars are always potentially dangerous and need to be handled with care. Nervous and aggressive boars should be culled. Some boars will show aggression with strangers but not with their regular handlers.
• When strange boars meet, they strut shoulder to shoulder, head raised and hair bristling along their backs. Deep grunts, jaw chomping and mouth frothing continues.
• In a fight, boars face each other with their shoulders in opposition and apply sideways pressure. They circle around, biting and slashing at each other with their tusks. They may charge each other with mouths wide open and bite. The loser turns and runs away squealing.
• Subsequently after a win, the winning dominant boar need only grunt to get submission. Newly-mixed boars fight less if they are both put in a strange environment.