The majority of pigs today are raised in total confinement. Good, efficient housing makes management easier and helps the farmer to successfully rear 85 % or more of all the live born piglets to market weight in the shortest possible time.
Pork production systems
Some farms still keep and mate sows, farrow the liters and raise piglets to market weight. These are called farrow to finish operations.
Other farmers engage in weaner production, maintaining breeding herds but selling all their piglets at around ten weeks of age to some other farmer. Those who keep no breeding animals but purchase all of their pigs from weaner producers are called finishing or feeder operators. The pig finishers or feeders then takes care of these purchased animals until they reach market weight.
The pork production sequence can be divided into five phases: mating, gestating, farrowing, nursery and growing-finishing.
Animals have specific needs at each of these stages, requiring appropriate husbandry and facilities to ensure that they receive proper attention and care.
The comfort zones and management requirements change substantially throughout a pig’s life.
Confinement housing is capital intensive for both buildings and equipment but provides opportunity for automation and labor reduction. Proper operation of these systems demands considerable management expertise.
Special areas must be provided for animals in various stages of the production sequence.
Intensive pig farming
Intensive piggeries (or hog lots) are a type of factory farm specialized in the raising of domestic pigs up to slaughter weight. In this system of pig production, grower pigs are housed indoors in group-housing or straw-lined sheds, whilst pregnant sows are confined in sow stalls (gestation crates) and give birth in farrowing crates.
Pigs are kept in large stalls with large numbers of pigs per square meter. The temperature is raised which allows the pig to spend less energy on keeping its body heat at the right temperature so it gets fat quicker enabling the process to be much more efficient.
Intensive piggeries are generally large warehouse-like buildings.
Indoor pig systems allow the pigs’ conditions to be monitored, ensuring minimum fatalities and increased productivity.
Buildings are ventilated and their temperature regulated.
Most domestic pig varieties are susceptible to heat stress, and all pigs lack sweat glands and cannot cool themselves.
Pigs at different stages of growth need different environments (temperatures). If they are to produce and grow to their maximum potential, piglets need special protection against very low temperatures. Growing and reproducing pigs must be protected against high temperatures.
Pigs have a limited tolerance to high temperatures and heat stress can lead to death. Maintaining a more specific temperature within the pig-tolerance range also maximizes growth and growth to feed ratio.
Pig production cycle. From: UK Agricolture
Swine estrous cycle
The estrus cycle length averages 21 days. Gilts come in to first estrus around 8 months of age.
The sow is polyestrous, with a period of lactational anestrus occurring until after weaning.
Estrus (heat behavior) occurs for 2-3 days, averaging 60 hours in mature sows, but is only about 48 hours long in gilts. Ovulation occurs during the last third of estrus.
The goal is to recognize when the sow or gilt reaches “standing heat”.
The standing reflex is stimulated by contact with a mature boar. The boar’s submaxillary salivary glands produce pheromones that are secreted into the saliva. Direct physical contact is the best way to ensure that these stimulatory chemicals are transmitted to the female. The pheromones signal to the female that a mature boar is present and initiate the standing reflex if the female is in estrus. The female may or may not also exhibit other visible signs.
Sows in estrus will often assume this rigid stance when pressure is applied on the rump (“back-pressure”) by the herdsman. This is an instinctive response that braces her to support the weight of the boar.
The classic sign of standing heat is “ear popping,” in which the female holds her ears erect with the tips nearly touching when weight is applied to her loin.
Detection of standing heat is critical because it determines when the animal should be inseminated.
Gilts should be bred 12 hours after standing heat is detected, and again 12 hours after the first insemination. Sows should be bred 18-24 hours after detection of standing heat, and again 12 hours later.
Physical signs to consider for mating
Modern units are designed to allow convenient movement of animals to appropriate quarters as their needs change during the production sequence from birth to market or during the reproductive cycle.
Requires good lighting, footing, access to pens, and facilities for convenient movement of animal to facilitate handling of individuals and mating pairs.
For an adequate housing, the following are necessary:
The boar pen
Boars are kept separately in their own pen. One boar is kept for every 15 to 20 sows. Sows are brought to the boar to be served in the boar pen. This pen should be 9 to 10 m2, with the short side at least 2 m wide so that the boar can easily turn around in it. An under-roof sleep area, about a third of the size of the pen, must be covered in bedding. Straw, grass or sawdust can be used for this purpose. It is important that the temperature does not rise higher than 22 °C for long periods. On very hot days boars can be kept cool by sprinkling them with water.
Natural, hand mating
Boars and females kept in separate pens with daily checks for estrus and matings as required.
Advantages are better identification and recording (essential for purebred herds), more effective use of boar-power, ability to cull infertile animals plus the information necessary to adjust the feeding and management as gestational needs change.
AI, commercial supply
Semen can be obtained in individual doses or bulk lots. AI allows importation of semen from distant regions or from other countries. Some specialised handling and storage equipment is necessary.
AI, within herd
Operators collect semen from their own boars and inseminate their own sows. This requires some training and equipment.
Within herd AI makes the most efficient use of boar-power. It requires a little more time than using commercial semen suppliers but less time than properly supervised hand mating in larger herds.
Natural mating. From: Uk Agricolture
Semen collection for AI. From: University of Pennsylvania, School of Veterinary Medicine
One of the disadvantages of AI is that it may require a higher level of management. When a boar naturally mates a sow, the semen is not subjected to severe changes in environment and is generally deposited into the female more than once during a period that spans the optimal time for fertilization. In contrast, many environmental changes are possible when semen is collected, diluted, transported and then deposited artificially.
The inseminations must be done correctly and at the optimal times. To obtain a high conception rate and litter size, estrous detection (heat checking) must be done carefully and without fail.
The goal is to recognize when the sow or gilt reaches standing heat, which is the period when she stands still and rigid when you put weight on her loin. Detection of standing heat is critical because it determines when the animal should be inseminated.
The standing reflex is stimulated by contact with a mature boar. The boar’s submaxillary salivary glands produce pheromones that are secreted into the saliva. Direct physical contact is the best way to ensure that these stimulatory chemicals are transmitted to the female. The pheromones signal to the female that a mature boar is present and initiate the standing reflex if the female is in estrus.
Swelling of the vulva is perhaps the most easily-recognized physical sign that an animal is coming into heat. In many animals the vulva swells and reddens 2 to 5 days before she is ready to breed. Some sows (and gilts) show little or no swelling.
When a female is in standing heat, the clitoris is engorged with blood, causing it to protrude outward and have a bright red color.
Most sows and gilts discharge mucous from the vulva as they approach standing heat. At first the mucous is clear, slick and oily, but becomes cloudy and sticky during standing heat.
A female in standing heat will stand still and rigid and often “push back” by arching her back slightly when weight is applied to the loin. This is an instinctive response that braces her to support the weight of the boar.
The classic sign of standing heat is “ear popping,” in which the female holds her ears erect with the tips nearly touching when weight is applied to her loin.
In gilts, estrus may last only a day or two, while a sow may be in estrus for three days.
Although ovulation usually occurs 23-48 hours after the onset of estrus, this event is extremely variable. In fact, a sow may ovulate before estrus occurs.
It is for this reason that producers generally inseminate females more than once.
Gilts should be bred 12 hours after standing heat is detected, and again 12 hours after the first insemination.
Sows should be bred 18-24 hours after detection of standing heat, and again 12 hours later.
Artificial vagina for semen collection is not widely used owing to inability to observe penis and secretions.
The “gloved hand method” is easy and allows the observation of penis and seminal fluid.
Shipment, dilution, storage temperature, fluctuations in temperature and length of time since collection may all affect the shelf life, motility and viability of the semen.
Quality parameters for semen
Volume (without gel mass) > 100 ml
Motility at time of collection > 65%
Concentration > 100 x 103 sperm cells/ml
Abnormal sperm cells < 20%
One AI dose: ≥ 2 x 109 motile sperm cells and ≥80 ml
Artificial vagina. From: Minitube
It is necessary to lubricate the tip of the spirette or catheter using any lubricant or a few drops of extender.
The spirette/catheter, with the tip pointed up, is gently guided through the vagina to the cervix. The bottle of diluted semen is not attached to the spirette/catheter at this point. A counterclockwise rotation will insert the spirette into the cervix. Subsequently, the bottle must attach to the end of the spirette and the semen slowly discharge. A gentle squeeze to start the process may be needed, but after that the semen should be allowed to be taken up by uterine contractions.
This process will usually take at least three minutes. Because of the variation in intensity of uterine contractions, gilts will usually take longer to inseminate than sows. Depositing the semen too rapidly will cause a backflow of semen out of the vulva.
Females should always be handled calmly and gently. Having a boar present, applying some back pressure and massaging the female’s flank during insemination may increase the number or intensity of uterine contractions that draw semen from the bottle and transport it into the uterus.
When all of the semen has been deposited into the female, the spirette can be removed by rotating it clockwise while gently pulling.
Group pens involve more social interaction but the submissive animals may get insufficient feed and possibly injuries and the dominant animals may get too fat.
Individual stalls or crates restrict animal movement but allow hand feeding to actual requirements and eliminate competitive injuries.
Gilts and dry sows – Dry sows come on heat three to seven days after weaning when they have to be served by a boar again. Gilts and sows should not be kept in the same pen.
An area of ~ 5 m2 per pig is required. The construction and specifications (apart from the size) of the sow/gilt pen are the same as that of the boar pen.
Individual feeding is, however, important to ensure that each pig receives the correct quantity of feed every time. Enough trough space with partitions that allow the pigs to eat individually is therefore necessary.
Nineteen days after the pigs have been served by a boar they are again brought into contact with a boar for five to seven consecutive days to make sure that they are pregnant. If the boar does not serve them again, it can be concluded that they are pregnant and they can then be placed in the pregnant sow house.
Pregnant sows – Sows are put in the pregnant sow pen about 24 days after service and are only moved to the farrowing pen seven days before they give birth. They stay in these pens for about 85 days.
The pens can be similar to dry sow pens.
The most common area for pig parturition is the farrowing crates. These come in many designs and still allow scope for improvement.
The major challenge in designing a suitable farrowing facility is that the comfort zones for sows and newborn piglets are considerably different. Thus, supplemental heating is necessary to provide an optimum environment for the piglets.
Supplemental heating can be from electric heat lamps, radiant gas heaters, forced air or floor heating.
Inclusion of individual kennels for piglets in the farrowing crate design creates a two-environment situation where piglets can choose between different temperatures. Piglets often lie with their snouts outside and the rest of their bodies inside the curtain, taking advantage of both options.
Sows are moved in groups to farrowing sheds approximately one week prior to giving birth.
Once the sow begins to farrow, the whole litter is born within 2 to 3 hours.
Sows “farrow” litters of between 10-16 pigs, but can nurse only about 12 and excess pigs are cross fostered to sows that have less than 12 pigs.
The farrowing pen is the most important pen on the farm.
It is advisable to build a farrowing house containing five or six farrowing pens.
Each pen must have a farrowing crate where the sow is kept from one week before the piglets are born until they are weaned when they are 28 or 35 days old. The crate is placed in the pen allowing a space of about 1 m on the one side and 0.5 m on the other side.
A farrowing crate houses the sow in one section and her piglets in another. It allows the sow to lie down and turn around to feed her piglets, but keeps her piglets in a separate section. This prevents the large sow from sitting on her piglets and killing them, which is quite common where the sow is not separated from the piglets.
At birth, piglets lack adequate fat or sufficient glycogen reserves to maintain body heat for long if chilled or starved. Therefore, they require early colostrum for energy and antibodies, and a warm, dry environment.
The creep is important because it provides a draught-free area where the piglets heat one another. In this way the creep area provides the required temperature of 27 to 32 °C for piglets during the first 10 days of life.
The temperature where the sow is kept (in the farrowing crate) should preferably not be higher than about 21 °C.
It is vital that pigs nurse soon after birth since colostrum gives them some protection against infection in the first few weeks.
soon after birth:
Very shortly after birth, piglets will nurse. A heat lamp or pad and a warm farrowing room temperature ensures piglet comfort. Supplemental heat is provided via heat lamps, radiant heaters or perhaps heat in the floor.
After the first two days of life, piglets have their own teatlet that they suckle from. A good sow will have 14 functional teats. Milk yield tends to be higher at the front of the udder compared with the back.
Piglets are normally weaned at around 4 weeks of age which is an optimum time for both the welfare of the sow and the piglets.
After weaning the sow dries off.
At weaning, sows are moved from the farrowing facilities to pens or stalls near the breeding area in preparation for mating.
The recovery period usually takes around 6 days and during this time, mammary involution occurs, and endocrine function changes to initiate follicle growth on the ovaries.
Newborn piglets. From: Pig Progress
Newborn piglets have very limited ability to digest feed. The sow compensates for this by producing milk, a readily digested diet supplying almost all the nutritional requirements of her offspring, and offering this frequently.
Also, the immune system is immature at birth so piglets have no inherent resistance to disease and cannot generate any real protection for five or six weeks. Antibodies concentrated in sow colostrum compensate for this initial deficiency but protection is short and usually has disappeared by weaning time (i.e. in 3 to 5 weeks).
Weaning, particularly at younger ages, involves a sudden change of diet and environment, so is certainly one of the most potentially distressing stages in a piglets life.
Piglets are moved from the farrowing rooms at a weaning age which can be anywhere from 21 to 28 days depending on the producer’s system.
Pigs are grouped at weaning into pens sorted by size.
Weaning (Nursery) area
Smaller piglets do not generate sufficient body heat to warm a large area so supplementary heat is necessary at the beginning of the period in the nursery area. The nursery pigs at left have just been moved out of the farrowing facilities and placed in the nursery pen. Farmers continue to provide very warm temperatures for the pigs.
The weaned piglets will remain in nursery pens until they are between 5 to 10 weeks old. They will then be moved to a grower area. The main goal of the growing phase is to achieve high growth performance.
Weaned and growing pigs are usually group-housed in pens.
In well-ventilated sheds, pigs will instinctively select clean and dry areas for sleeping, resting and feeding. Pigs are very clean animals and choose to defecate in an area separate to their feeding area.
There is considerable disparity in recommendations on space requirement for growing and finishing pigs.
All housing is a compromise between maximizing performance of each pig in a pen and optimizing the financial return from investment.
Traditionally farmers produced pigs to two different weights to satisfy distinct market requirements:
Special measures should be used regarding the stunning methods to ensure a humanitarian animal death (to avoid the risk of cruelty).
Meat animals may be stunned by passing an alternating electric current through the brain. With a simple, hand-held electric stunner, the current is applied to the pig’s head with two electrodes that protrude from an insulated handle. The electrodes must be cleaned at frequent intervals to ensure good electrical contact with the pig.
Pigs may be stunned by placing them in an atmosphere which contains 65% carbon dioxide. Carbon dioxide is heavier than air and is trapped in a pit or deep tunnel into which the pigs are conveyed. After about one minute, the pigs are withdrawn in a cage or on a conveyer belt, and are then exsanguinated as rapidly as possible.
If the period between stunning and bleeding is too prolonged the meat quality level will decrease because the heart continues to pump the blood and it can increase the blood pressure and burst the vessels. This willcause blood coagulation (“blood splash”) inside the muscles as an undesirable meat characteristic.
Scalding – Scalding is the most important part of the dehairing process. If the temperature of the scald is too high, there can be physical damage from dehairing. Also, too hot a scalding temperature and/or too long a time in the scalding tank has been associated with a higher level of meat damage.
After scalding the carcass is dehaired. After scalding for approximately five minutes at 60 °C the carcass is removed to the scraping table. Once a pig is clear of the scraping table the next pig can be placed in the scalding tub.
Singeing – When the method of dehairing is done by special equipment it consumes large quantities of energy and water. One alternative to dehairing is to dehide the pig, but dehiding carcasses involves more work. Besides, dehairing is an interesting operation to make use of the skin as a food product. The easiest way to dehair the carcasses is by singeing them. Carcasses are singed in cabinets, which are fired by either oil or gas, depending on the production setup.
After cleaning and dehairing, the carcasses are opened by a straight cut in the centre of the belly to remove the viscera (the digestive system including liver, stomach, bladder, and intestines and the reproductive organs), pluck (thoracic contents including heart and lungs), kidneys, and associated fat (called leaf fat). The intestines are washed and cleaned to serve as natural casings for sausage products.
The carcasses are then split down the centre of the backbone into two sides, which are placed in a cooler before fabrication into meat cuts.