General Principles of Pig Production


General Principles of Pig Production

Estimates of the world pig and human populations equate one pig to six people in the world. Highest world meat output is derived from pigs according to FAO (1989) statistics.

Similarly, in Nigeria the Central Bank annual reports for a decade indicated pig production as the fastest livestock enterprise in generating output. This brief statistics attests to the significant contributions of swine to human and national needs.

Perhaps pig production would have contributed much more except for constraints imposed climate and religious belief in addition to usually constraints known depress livestock productivity.

Notwithstanding these negative factors, pigs are outstanding in the number of offspring it can produce in a litter and its efficient growth rate that are in comparable to ruminant animals. The unselected indigenous types are extremely poor in performance than the proven exotic breeds such as land race, large white and duroc.

The study article is devoted to basic principles underlying the management of pigs for the overall good and productivity. The principles cover feed and feeding, growth and development, reproduction, housing and disease management.

At the end of this article, you should be able to outline global distribution, consumption and constraints to pig production and its potentials, distinguish between various systems of pig production, review basic biology and essential principle of pig production as it relates to feeding, growth and development, interpret the behaviours of pigs from the stress imposed by climatic environment and limitation of the body structure and physiology, choose out of several remedies housing facilities and designs to mitigate negative effects of the environment and apply preventive and control measures against swine diseases and pests.


Distribution Consumption and Constraints to Pig Production

The estimated world pig population of 286 million (FAO, 1988) means that there is approximately one pig to every six people in the world. Although pigs are numerically fewer than some other domestic species, more pig meat is produced than other meat. This reflects the greater productivity of the pig when compared with other domestic species.


Distribution and consumption

The distribution of pigs throughout the world is not uniform. Nearly half the world’s pig population is in Asia, with a further 30 percent in Europe and the USSR. 

In contrast, the population in large parts of the tropical and sub-tropical developing regions (e.g. Africa and Latin America) is relatively small. Nevertheless, the increase in the world pig population over the last decade is largely attributable to increase within the developing world, which now constitutes some 60 percent of the world population of pigs. It is noteworthy that the majority of the pigs in the developing world are located in one Asian country, namely China.

Similarly, marked differences exist in the consumption patterns of pig meat throughout the world. In some parts of Europe, annual per capita consumption of pig meat is over 50 kg, and represents some 60 per cent of the total meat consumed.

At the other end of the scale in areas of the developing world and particularly in Africa, estimated annual per capital consumption ranges from 1 to 3kg, and form less than 10 per cent of the total meat diet. The reasons for the uneven distribution of pigs throughout the tropical and sub-tropical world are manifold. In tropical Asia and parts of China, pork is the predominant component of the diet.

On the other hand, in areas where the Islamic religion prevails, e.g. the Middle East, Pakistan and part of Africa, Muslims are forbidden to eat any pig meat. Similarly, believers in the Jewish faith are instructed not to eat pork meat, and Zionist sects occur throughout the developing world. 

Social factors also play a part and these may have a positive or a negative effect on the pig population. 

In some Pacific islands, such as Tonga and Papua New Guinea, pigs are highly regarded as a source of wealth and associated with marriage customs.

On the other hand, in Africa people have traditionally obtained their meat supplies mainly from ruminants, particularly cattle and this preference persists.

The pig has historically been considered an unclean animal, wallowing in filth, an object of distaste and a hazard to human health.

Clearly, there is some truth in this assumption if the pig is used as a scavenger but the exact opposite pertains if the pig is well managed under confined conditions. 

Climate has an influence on distribution. Pigs can be reared almost anywhere given suitable housing and management.

But in situations of extreme temperatures, humidity or lack of rainfall they cost more to produce, because of the need for more expensive housing and because suitable feeds may not be available.


The Potentials and Constraints to Pig Production in Developing Countries

General Principles of Pig Production

The world trend is towards the consumption of more white than red meat.

Thus the potential for increased meat production from pigs in the developing world is enormous.

When compared with cattle and other ruminants, pigs have some major potential advantages, namely:

They produce meat without contributing to the deterioration of the natural grazing lands. This is of paramount importance in relation to the current steady desertification, soil erosion and loss of productive land in tropical and sub-tropical parts of the world.

Overstocking and consequent overgrazing by ruminant is a primary cause of this degradation.

They covert concentrate feed on meat twice as efficiently as ruminants.

They possess the potential to be highly productive. Because they are capable of producing large litters after a relatively short gestation period, and have a short generation interval and grow rapidly, their output in terms of yield of meat per tonne of live weight of breeding females per year is in the region of six times that of cattle.

If confined maximum use can be made of their manure and effluent.

Their relatively small size, when compared with cattle, provides for more flexibility in marketing and consumption.

The meat pigs produce is particularly suitable for processing: some of the processed products have a longer shelf life than fresh meat, and can thus be distributed to a wider section of the population.

Quicker turn-over rate to investment compared with cattle.

Apart from the social and religious constraints mentioned, other constraints to pig production are:

As simple-stomached animals, they compete directly with humans for feed, especially the staple grains and oilseeds. This can be partly overcome by making maximum use of crop by-product, waste feeds and grain unsuitable for human consumption.

They cannot provide a source of draught power for farming operations.

Since they tend to be raised close to human habitation, their effluent may cause a pollution problem

Because pigs and man are co-hosts to a number of parasites, if pigs are not confined they can pose a problem to human health.


Origin and Breeds of Pigs

Although the actual origins of the domestic pig are obscure, it is probable that it is mainly derived from the European wild boar (Sus scrofa).

Originally pigs colonised the forest and swamps (as does Sus scrofa) to this day, and were thus designed to live in a moist, shady environment. Their short legs and powerful streamlined body were built for moving through dense undergrowth and the strong head and tusks, with a cartilaginous disc in the snout, for digging and rooting.

Biblical writings indicate that pigs were first domesticated as early as 200 BC.

As man has developed the pig as a meat animal, major changes in conformation have occurred from the typical, unimproved type. The relatively large, narrow head, heavily forequarters, tapering light hindquarters and compact body have been replaced by a smaller head, lighter forequarters, and a longer and wider body with bigger capacity and well-developed, meaty hindquarters.

Breed types

Although some are numerically small in number, there are over 90 recognized breeds and estimated 230 varieties of pig in the world.

They can be broadly classified into indigenous or unimproved type or the more modern exotic type, which have been selected and developed for specific purposes.

Indigenous breeds (Domesticated)

These predominate in the tropical and developing world, and have evolved a variety of shapes and sizes in order to survive in a range of different environments.

In general, they are smaller and have shorter legs than exotic types, with the typical unimproved conformation of a large head, well–developed forequarters and relatively light hindquarters.

This renders them more mobile and better able to forage and root for themselves. They are early sexually maturing and females may show first oestrus as early as three months of age.

There are many variations of coat colour, but black and brown are most common and white is frequent. The degree of hairiness also varies, and hairless and relatively long- haired types are found.

Within the major regions of the tropics, the main breeds and types are as follows.


In many countries in Africa, pigs have not been characterised into specific breeds, and are variously referred to as ‘indigenous” “local’ or “unimproved” pigs.

The situation is further confused in some areas by inter-breeding with imported exotic strains. Clearly the productivity of these unimproved breeds in Africa is influenced by their environment.

In trials in Zimbabwe, although litter sizes tended to smaller, total live weight of the litter as a proportion of the weight of the sow at farrowing was of the same order as exotic sows (11per cent).

The efficiency of conversion of feed to body weight in indigenous sows is also equivalent to that of exotic types. Indigenous sows showed excellent mothering ability, which resulted in very low piglet mortality without sophisticated housing.

Exotic breed in the tropics

The Large White (Yorkshire)

The large white breed was first developed in Yorkshire, England in the middle of the nineteenth century, and has since become a very popular breed throughout the world. 

It is a fast growing; strong- framed pig with good length and is renowned for its strength of leg.

Females are prolific good mothers and adapt well to confinement conditions. The breed is widely distributed throughout the tropics, and is used extensively for cross-breeding.

In Africa, for instance, the Large White X Landrace female is the most popular cross for commercial production. It is also used as grandparent stock in some of the main hybrids produced in Europe.

In common with the Landrace, unless provided with adequate shade or wallows, the white skin renders it particularly susceptible to sun burn under tropical conditions. 

On the order hand, the white hair and white skin render the skin on the carcass more acceptable to the consumer than from the coloured breeds.

The Landrace

This breed originates from Scandinavia and is characterized by its forward-pointing lop ears. It was specifically developed for the bacon trade and typically possesses a long, smooth body with light shoulders and well–developed hams. It is a prolific breeder with excellent mothering qualities and produces lean, fast-growing progeny.

The landrace has a higher level of susceptibility to stress than some other breeds. Although not as numerous as the large white, it is also common throughout the tropics, and is highly favoured for cross- breeding purposes.

The Duroc

This breed has been developed in the USA, although there have been suggestions that the British Tamworth breed was involved in the original stock.

It is characterized by its deep red or rusty colour. The Duroc is a fast-growing large breed, which has been selected specifically for overall muscle and meat production.

One important characteristic is its ability to grow to heavier weights without depositing too much fat.

In the female litter–size and mothering ability are only average. It is claimed that the Duroc possesses a higher proportion of marbling fat in the meat. An outstanding trait in the Duroc is its hardiness and resistance to stress, which results in lower levels of mortality.

In tropical zones this is an important consideration, and the breed is consequently increasing in popularity. In commercial production in parts of Africa, it is frequently used as a terminal sire on white cross- bred females.

The Hampshire

The Hampshire is a medium-sized, black pig with a distinct white saddle which encircles the forequarter. Originally a native of England, it has been developed as a modern breed in the USA.

Hampshire sows are prolific, good mothers and possess above – average milking ability. They are also better able to cope with more extensive condition than white breeds. It is meaty, well–muscled breed which shows good efficiency of feed conversion.

The Hampshire is very popular in crossbreeding programmes, both in order to produce a cross–bred female and as a terminal sire.

The Berkshire

Although the Berkshire breed is on the decline on a worldwide basis, it remains popular in cross – breeding programmes in parts of the tropics. It is smaller, early –maturing pig which was first developed in England for the pork trade. It has a black coat with characteristic white feet and nose.

In the tropics it has proved very hardy, and crosses well with indigenous stock. In certain areas, for instance in Burma, it is prized for its fat content, as pig fat used extensively for cooking purposes.

Other breeds of interest

The Chester White

This breed was developed in America and has spread particularly into central and South America. Females are highly prolific, but growth rate tends to be slow, and carcasses are shorter and fatter than average.

The Large Black

A hardy British breed, sows are very good under extensive conditions. However, growth rates tend to slow and carcasses are relatively fat. Although now rare as a pure bred, there is evidence of the influence of large black throughout the tropics.

The Pietrian

Of Belgian origin, this is a very lean and meaty pig, and is widely used in the production of modern hybrids. Introductions to the tropics have largely been unsuccessful due to high level of susceptibility to stress. As an example, all the pietrain pigs imported into Zimbabwe (then Rhodesia) in the 1960s died from heart failure as a result of one stress or another.

The Poland China

This breed of pig was one of the earliest to be developed in USA. It tends to be large and fat but has been widely used in Central and South America. Improved strains of the breed are being developed. The Tamworth Characterized by its red colour, this is one of the oldest breeds of pig in England.

The breed is exceptionally hardy, but is relatively slow maturing. In the past it has been very popular for cross- breeding purpose in tropical regions.

The British saddleback

This is another hardy British breed, formed from the combination of the Essex and Wessex Saddleback breeds, with good milk production and mothering ability. It is named after its distinctive markings of black coloration with a white saddle.

In the UK it has gained a new lease of life for the introduction of hardiness and mothering ability into hybrids used in outdoor production systems.

From the point of view of genetic improvement of pigs in the tropics it is important to realize that pigs selected for their superior performance in one environment will not necessarily be superior in a completely different environment.

This is known as genotype – environment interaction. An example of this type of interaction is that restricted feeding regimes will have a greater effect in reducing back fat thickness in genetically fat pigs than in genetically thin pigs.

When selecting genotypes to help improve pig performance in tropical environments, it is crucial to understand the fact that such interactions will occur. If genotypes are selected under intensive conditions in a temperate environment and then transferred to the tropics, the environment must be modified, by means of housing, feeding and management, to suit that genotype.

In extreme cases, genotypes are selected under intensive, temperate conditions. In such situations the animals have difficulty surviving, let alone growing and reproducing, and local or cross- bred genotypes will be far superior under these conditions.


Systems of Pig Production

General Principles of Pig Production

Scavenging or Extensive Small-scale System

This is the traditional system of rearing pigs in most parts of the tropics. It is also the simplest and cheapest. Each family, kraal or village keeps a few stocks which are allowed to wander freely and pick up food when and where they can.

If extra food is available, they may receive supplementary food. 

This supplementary food will generally consist of foods of low nutritional quality such as banana, crop residues, water hyacinth, and rice bran, local herbaceous plants, by products of beer making or kitchen wastes.

Where pigs are particularly valued for festival or ritual slaughter, as in parts of Asia and Africa, a few may be confined and fed for a three-to-six month fattening period prior to important ceremonies. 

Indigenous breeds of pigs predominate on the scavenging system; because they are adapted to the local environment and their relatively small size and mobility render them best able to cope with the conditions.

Productivity is normally low with the erratic and often seasonal food supplies resulting in irregular breeding of female animals, high rates of offspring mortality and low growth rates.

Stocks raised on this system are particularly susceptible to infestation with parasites, and invariably carry a heavy burden of intestinal worms and ectoparasites. 

A particularly hazard of the scavenging system is that animals have access to sources of parasites, e.g. human waste, which can then be transmitted back to man when he eats meat.

The majorities of scavenging domestic pigs are owned by subsistent farmers, and are not produced with any particular market in mind.

Rather the animals play an important socio-economic role as a form of bank, and stock are sold at times of cash shortages or unexpected needs in the family. The numbers are usually kept small, in the region of 1-10 breeding females per herd.

Semi-intensive production

In these systems, often also known as ‘backyard’ systems, animals are confined and therefore present a commitment on the part of the farmer to feed his stock. Pens or sites are mainly of very simple construction and in some countries of south East Asia and West Africa, may be made of bamboo and elevated.

Of the other hand, animals are sometimes constrained by tethering in larger yards or paddocks. Feeding is based on kitchen waste, vegetables and by-product foods, and management is generally minimal.

As a consequence, productivity tends to be relatively low and mortality can be high. Although local and indigenous breeds of animal predominate, crosses between indigenous and exotic breeds can be found in this system of production throughout the developing world.

Marketing is largely indiscriminate and is dictated by the immediate financial needs of the owner. Generally, herd sizes and productivity tend to be higher in these systems than in the scavenging systems.

Intensive production

These systems are characterized by the fact that the small-scale producer has moved away from subsistence production to the commercial pig production. Units may comprise up to 50 head, and the producer will grow and/or purchase food specifically for his pig enterprise.

The system of housing becomes more sophisticated shade and open space, and appropriate feed and watering facilities.

In order to justify the increased capital cost, the farmer will attempt to manage his stock to optimize output, including some veterinary protection against parasites and diseases.

The breed of animal raised will tend to be mainly the higher-performance exotic, or a cross between exotic and indigenous breeds.

Marketing may be informal, through local butchers, or into the large-scale commercial sector, but in any event it will be planned to bring in a regular income for the enterprise.

Large-scale systems


This is the most common system of large-scale production. Units are generally capital intensive and may involve a large herd from 40 up to 1000 heads.

Modern high-performance breeds of pigs, or hybrids, are used, and provided as far as possible with optimum conditions of housing, feeding and management in order to ensure maximum output. Housing will often be designed specifically for the different classes of stock and environmental conditions.

These units, especially the larger ones, are particularly amenable to integration with grain production and stock feed manufacturing operations on the one hand, and processing and marketing on the other. The farm animals will invariably be marketed through a processor in order to maximize returns on the carcass.

Extensive systems

These are a trend throughout Europe and America towards less intensive systems of production. These systems, often known as ‘outdoor’ systems, entail keeping animals in paddocks or ranches and providing individual pens for parturition and shelter.

Younger stocks are generally raised under more intensive conditions. In Europe, hybrid crossbreds, with a greater ability to withstand climatic vagaries, are produced specifically for use on this type of system. Production systems of this type exist in the tropics, and there is clearly potential for further expansion. 

The major advantages when compared with intensive systems are that less capital is required for establishment, and animals can gain access to bulky foods such as pastures, crop residues, cassava roots and sweet potatoes. 

In tropical regions it is essential that adequate shade and housing be provided. Moreover, there must be tight control of parasites and adequate fencing to prevent contact with endemic disease, e.g. in Africa, contact with wild animals and avoid transfer of diseases.

Integrated systems

The integration of pig production with other ancillary enterprises has long been widely practiced in tropical Asia, involving various combinations, fish farming production of algae, methane gas generation, duck water hyacinth and vegetable production.

Such bi-or tri-commodity operations enhance the efficiency of resource use and increase output for the overall operation. For instance fertilizing fish ponds with pig manure and effluent, algae are generated which can then be utilised by fish.

As long as sufficient water is available for suitable fish ponds, pig sties can either be constructed above the ponds so that the manure can drop straight into the water, or close by so that the effluent can be channeled into the ponds.

The various species of Tilapia spp are the most commonly used fish, often mixed with small populations of carp (cyprinus spp) and catfish (clarias spp) or other predators.

Fifty to sixty pigs produce sufficient effluent for one hectare, fishpond, which, if stocked at between 20 000 and 50 000 fish per hectare, can produce annual edible fish yields or 3.5 to 5 tonnes per hectare.

In some countries, water hyacinths used to harvest nutrients from the fishponds, and this is then fed back to the pigs. Alternatively, the nutrient-rich water can be used for irrigating vegetables, or in other systems. Ponds can be dried in rotation and vegetables grown in the dry pond beds. 

In another alternative system, where other food is available, the pig effluent is used to produce algae, which is then harvested and dried and fed back to pigs or other livestock. If the pig effluent is insufficient for any particular system, ducks can be used to augment the fertilization of the ponds with their manure.

The solid fraction of animal, especially poultry, manure can be used as an effective fertilizer for crops, particularly if it is properly composted, and this may prove to be the most cost-effective use of the by-product.

A further important development has been the anaerobic fermentation of farm animal effluent for the production of methane gas. Relatively simple digesters can produce a steady source of methane which can be used as a means of energy for domestic or agricultural use.

These digesters are now in use in rural areas throughout the developing countries of Asia, and it is estimated that seven heads of pig for example will provide enough dung to ensure the supply of sufficient methane for house fuel for a family of five.


Principles of Pig Production

General Principles of Pig Production

Feeding and digestion

The first 72 hours after birth are very critical for the baby pig. During this period the colostrums of the sow has a high content of antibodies and the piglet intestine is able to absorb intact proteins.

As the piglet has very little of its own resistance to disease, it is essential that it gets a good suck of colostrums and acquires passive immunity from the sow.

Failure to take in sufficient colostrums will invariably result in the pig succumbing to infection before it can develop active immunity of its own.

Once the piglet has established a teat position, which normally occurs in the first 24 hours after farrowing, it will retain this position for the remainder of the suckling period. As long as milk production continues the dam suckles her litter every 60 to 90 minutes.

Alimentary canal

Although pigs in tropical regions may eat a lot of fibre they are simple stomached animals and not ruminants which possess a complex stomach with a large microbial population which enables them to digest large quantities of fibrous material.

Thus, their ability to digest and utilize fibre is restricted to that digested by the microbial population in the caecum which is of relatively small volume when compared with the rumen.

It has been claimed that unimproved breeds found in Africa have an enhanced ability to utilize fibrous feeds compared with exotic breeds. While this may be so to a small extent, there are no anatomical differences of the digestive tract between the two types.

Accordingly, with all pigs, high-fibre diets will have the effect of diluting the amount of nutrients available to the animal.

In contrast to ruminants, pigs are unable to utilize non-protein sources of nitrogen for the production of microbial protein in the rumen. This makes them dependent on both the amount and quantity of protein in their diet. The alimentary tract of the pig is designed to digest and absorb concentrate feeds. Feed taken in at the mouth is ground into a pulp by mastication.

At the same time it is moistened and mixed with saliva. Saliva contains the enzyme ptyalin which initiates the breakdown of starch to simpler carbohydrates. The feed then passes on into the stomach, which provides an acid environment due to the presence of hydrochloric acid. The gastric juice contains the enzyme pepsin which begins the breakdown of protein.

The small intestine is the major site where feed absorption occurs and digestive juices from the pancreas, liver and the small intestine complete the process of digestion as follows. Starch is hydrolyzed to maltose by amylase from the pancreatic juice.

Specific enzymes break down maltose and other disaccharide sugars in the intestinal juice, e.g. maltase, lactase and sucrose into monosaccharides such as glucose and fructose. These are then absorbed through the gut wall.

Trypsin in the pancreatic juice acts on protein to produce polypeptides, which are then broken down to amino acids by various peptidases in the intestinal juice and subsequently absorbed. Bile, which is secreted by the liver, serves to emulsify fats into smaller globules, which are then broken down by the enzymes lipase into fatty acids and glycerol ready for absorption.

Lipase is present in both the pancreatic and intestinal juices. Pigs are omnivores and will consume a wide range of feeds from both plant and animal sources. The natural inclination of the pig is to eat on a ‘little and often’ basis, and this is likely to maximize both total feed intake and the efficiency of feed utilisation.

Growth and Development

In practical terms, growth is measured as the increase in body weight with time, and is largely dependent on the amount of feed or total nutrient intake.

However, there are major differences between the feed intake of different breeds of pig and this affects their growth response per unit of feed ingested. Because man has selected pigs for high growth rates in order to improve biological efficiency, he has selected for a large mature size. In consequence, unimproved types of pig common in developing parts of the world which have not been selected for increased growth rates will tend to grow more slowly to a smaller mature size when compared with improved breeds.

It follows that if unimproved pigs are slaughtered at the same weight as their exotic counterparts, they will be relatively more mature and therefore at a different stage of development. Equally important as rate of growth is how the pig develops.

Selection has resulted in a greater propensity to lay down protein tissue in improved breeds. Thus the plateau for maximum growth potential in an improved breed can be 600g compared with 400 g for an unimproved pig.

As the level of feed intake increase, the unimproved pigs will deposit more fat in comparison with improved types. Because too much fat is neither a consumer desirable, nor is it cheap to produce (approximately five times the nutrient cost of lean tissue deposition), it is critical that pigs are fed according to their ability to grow and lay down lean tissue. Entire male pigs grow faster; have leaner bodies and convert feed more efficiently than females. If males are castrated the case is exactly opposite.

Traditionally, pigs have been castrated in order to improve carcass quality and to prevent boar ‘taint’ or odour in the meat, which tends to occur as boars approach puberty.

Nowadays, modern pigs grow faster and are slaughtered at younger ages and the problem of taint is considerably reduced. Unless pigs are grown slowly or are required for a highly sophisticated market, there would appear to be no justification for castration in pigs destined for meat production.

Baby pigs are born with less than two per cent of fat in their bodies, which makes them particularly susceptible to cold stress.

Thereafter they deposit fat rapidly, and will usually have a body fat level of over 15 per cent by the time they are three weeks old. This serves as a reserve of energy as they adapt to a reduction in milk intake and to overcome the stress associated with weaning.


Read: Effects of the Tropical Environment on Animal Production

Reproduction in Pig

General Principles of Pig Production


The male reproductive system is characterised by a pair of relatively large testes, which can weigh over 300 g each in some exotic breeds.

Together with the secretions from the accessory sex glands, the testes can produce up to a liter of semen in a single ejaculate. To facilitate the transfer of these large quantities of semen at coitus, the end of the penis of the boar is spiral in shape which enables it to lock, into the cervix of the sow.

The duration of coitus varies but may last for 20 minutes. Puberty, or the ability of the boar to serve a sow, generally occurs around four months of age, but may be earlier in unimproved breeds.

However, boars should not normally be used until seven months old. Young boars are susceptible to bullying by mature sows. And this may adversely affect their subsequently mating performance.


The female reproductive tract is distinguished from other farm species by the long, convoluted uterine horns (700 to 800 mm in length), which are designed to accommodate large numbers of foetus.

The sow will ovulate simultaneously from both ovaries, normally shedding between 11 and 24 eggs. Puberty, marked by the onset of oestrous cycles, occurs between five and seven months, but may be as early as three months in unimproved breeds.

The number of eggs shed at ovulation, and therefore potential litter-size, increases gradually over the first few oestrous cycles. The sow will cycle and show heat every 21 days (range 18 –24). She will not cycle when she is either pregnant or lactating, although sows will sometimes show heat during lactation when run in groups.

A heat last from one to three days, and ovulation occurs by the second day of estrous or any time thereafter. After coitus and fertilization have occurred, the embryos space themselves evenly throughout the entire uterus before implantation. 

Competition for space, nutrients and other unknown factors results in uneven growth rates in utero, which gives rise to variation in piglet birth weight.

The lighter pigs then suffer a disadvantage in the competition of early post-natal life. This problem tends to be accentuated in older sows, due to the effects of wear and tear on the uterus.

Pregnancy lasts for 114 days but will tend to be extended slightly with smaller litters. Farrowing may vary in duration from 2 to 24 hours and will tend to be longer the more piglets that are produced. 

However, due to the relative difference in size between piglets and the dam, and the type of placentation in sows, farrowing is normally a straightforward process. 

The incidence of stillborn piglets, which may be due either to death in utero or during the birth process, is greater in large than in smaller litters.

Overall, reproduction in the sow results from a complex hormonal interplay between the brain, the pituitary gland, the ovaries and the uterus.

These complex relationships must be borne in mind by the pig keepers when management strategies are designed, otherwise optimum reproductive performance by the sow will not be achieved.


Pig Behaviour and Effect of Climate

General Principles of Pig Production

Pigs are not solitary animals and will generally benefit from social contact with each other, even if only by sight or smell.

At the same time, groups of pigs will always establish a social hierarchy and this starts at birth when the piglet struggles to commandeer a teat position. If strange pigs are penned together later in life, fighting invariably ensues, and this can lead to considerable stress and physical damage to individual pigs.

Once settled, however, pigs will huddle together in order to retain body heat in cold weather.

In common with the female of those species, sows are notably more docile during pregnancy than they have just produced young. Just prior to farrowing, the sow will prepare a nest from her bedding. She is often irritable during this period, and if she is confined without access to bedding material, this can lead to stress during the farrowing process.

Contrary to popular belief the pig is not a dirty animal and will normally defecate and urinate away from its resting or lying areas. However, this pattern tends to break down if pigs are overcrowded or stressed in other ways.

Also, when temperatures are high they will often roll in their own faeces and urine in an attempt to increase evaporation and keep cool. Recent studies have highlighted the importance of the interaction between pigs and humans in relation to productivity. If pigs live in fear of their stockman, both growth and reproductively performance are likely to be depressed.

In order to cope with forest conditions, the pig has better mechanisms for retaining heat, especially a well-developed subcutaneous fat cover, than for losing heat from the body. Because the pig possesses sweat glands only on the snout, it is unable to dissipate large amounts of heat by sweating. 

Furthermore, the skin of certain breeds of pigs, e.g. Large White and Landrace, has no protection against the sun, and unless they have access to shade, or mud in which they can wallow, they can become badly sun burnt.

Like man, the pig is a homeotherm, and needs to maintain its deep body temperature constant. Nature has designed the metabolism of the pig to operate most effectively at 39oC. For a certain range of environmental temperature, known as the zone of thermal neutrality the pig finds this easy and can maintain the correct body temperature by varying blood flow to and from the skin.

The extent of this zone changes quite markedly according to the weight of the pig. At the bottom end of this zone a lower critical temperature is reached when the pig required diverting feed energy to increase heat production in order to maintain body temperature.

The lower critical temperature will vary between pigs according to a number of factors, for instance how fat (well-insulated) the pig is, how much feed it is eating and therefore how fast it is growing. Whether it has bedding to help prevent heat loss, whether it is in huddle with pen mates, and whether it can make postural changes to minimize heat losses.

Eventually, with decreasing ambient temperature the pig can no longer maintain its body temperature in spite of high heat production, and hypothermia and death ensues. Of greater interest in the tropics is the effect on the pig as ambient temperature rises.

When the environmental temperature approaches body temperature, the pig will attempt to increase evaporative heat loss by sweating (through its limited sweat glands), panting, postural and positional changes, and wallowing in water, mud or excrement. In addition, it will reduce its energy output by decreasing its feed intake.

However, as the means of dissipating heat in the pig are not very efficient, particularly in the absence of the opportunity to wallow, it will soon reach an upper critical temperature. This is associated with hyperthermia and heat stress and the pig will die if the situation cannot be reversed.

At the other end of the scale, the piglet at birth is particularly sensitive to low ambient temperatures. Pigs are born with virtually no subcutaneous fat cover and limited carbohydrate reserves and therefore at birth they will suffer an immediate drop in body temperature.

In the case of weaker piglets they may battle to obtain an adequate milk supply; if they require energy to keep warm they very quickly develop the condition of low blood sugar (hypoglycaemia), and die of cold.


From the foregoing it is clear that stress factors can take many forms, and in fact can involve fear, pain, temperature, direct sunlight, restraint, fatigue and interference with natural behaviour patterns. Stress will quickly lead to reduced performance and productivity, and specifically to gastric ulcers (just as in humans), greater susceptibility to infectious diseases and higher mortality rates.

It is therefore paramount that we understand what constitutes the major stress factors in pigs in different circumstances so that production systems can be designed to minimize these effects.


The most productive pigs are likely to be those contained in a thermally neutral environment; that is, when the environmental temperature around the pig is insistently between the pig’s lower critical temperature (LCT) and upper critical temperature (UCT).

The pig’s metabolic heat production is then at a minimum, and it is neither using feed energy to keep warm, nor reducing feed intake to keep cool.

Other considerations for pig comfort and well–being in addition to temperature are:

Protection from other climatic extremes such as direct sun, wind and rain

Provision of dry conditions which are hygienic and do not predispose the pig to disease

Allowing, as far as possible, for inherent behavior patterns of the pig, and minimizing the effect of social dominance

Provision of accessible feed and clean water

Providing conditions so that good stockman can practice

Effective disposal of effluent.


General considerations of design

General Principles of Pig Production

Any buildings, whether simple or complex, cost money, both to build and to maintain. This makes it imperative that careful thought is given to the right design, so that the investment is justified by improved productivity.

Moreover, considerations that affect design of houses in the tropics can be very different from those in more temperate parts of the world. Under tropical conditions, the paramount consideration is generally to ameliorate the effects of excess heat.

At the same time, it is important to minimise temperature variations, keeping as close as possible to the pig’s zone of thermal neutrality. This often involves keeping pig cool by even under tropical conditions; a separate creep area for the piglets which is warmer than the ambient temperature is generally an advantage, especially at night.

This is because the optimum environmental temperature for the sow is between 16 and 18oC, whereas that of the newborn pig is 33-350C. 

A simple, enclosed creep box is perfectly adequate for the piglets to creep into and generate their own warmth by huddling together. If electricity or a paraffin source is available a light or simple heater can be provided in the creep box. 

This not only provides extra warmth, but attracts the piglets into the box and away from the danger of being crushed by the sow. If separate arrangements are not made for the piglets and the whole furrowing room is warm, this reduces sow productivity.

American work has shown that for every oC rise in temperature from 25o -30oC, daily feed-intake by the sow declines by 400grams.

Multi-purpose pig pens

These are liable to be more appropriate to the tropics and the developing world, as they are cheaper and more flexible. Removable structures, such as creep barriers and furrowing rails, provide protection for the piglets and make the pen suitable for furrowing. At weaning, these are removed, leaving a fattening pen in which the winners can be fattened through to slaughter.

Follow-on pens

If specialized farrowing houses are used, sows can normally be removed into cheaper housing after 10-14 days when all danger of sow-related piglet deaths is past. Piglets then require a separate creep area, similar to that provided by a multi-purpose pen.

This has the advantage of allowing the sow to exercise and move around freely.

Weaner cages

The combined trauma of weaning from the sow and change in diet makes the young pig very susceptible to disease, particularly digestive diseases. This can result in fairly heavy mortality of weaners.

The weaner cage was originally designed in Europe with the idea of providing conditions for the weaner which would help overcome these problems.

Weaner cages have since been adapted for hotter climates and basically consist of a covered solid-floor sleeping and eating area and a dunging area floored by either wooden slats or metal mesh during cold periods, pigs can huddle and generate enough heat for their comfort inside the covered kennel section. Ventilation is provided by the centrally-hinged roof of the kennel.

In hot weather, pigs can keep cool by lying out on the meshed floors, and are protected from the sun by an umbrella roof over all the cages. As dung and urine falls through the wire mesh or slats, this can be cleaned from below and there is therefore no need for stockmen to enter the cage with contaminated boots, brooms or shovels.

Pigs normally remain in the cages for three to four weeks before being transferred to fattening accommodation. The feed hoppers can be moved to allow additional space as the weaners grow.

Weaner pools

The traditional system of housing weaners is to take litters of similar age and move them into large pens holding up to 50 weaners. After threefour weeks, pigs are batched into groups of equal sizes for transfer into growing / fatttening pens Ample watering and feed through space must be provided, and some form of bedding is preferable. Kennel area, which can be insulated by a ceiling of hay bales or wood, can provide for added warmth.

Growing / fattening accommodation

The basic needs for good fattening pens are relatively simple, namely, a dry lying area and a demarcated dunging area the building should provide shade, some protection and adequate ventilation. Solid walls are not required between pens, as they will decrease ventilation and flow within the building.

Pens designed to hold 8-10 pigs through to slaughters are the ideal size.

Extensive systems

Extensive systems are particularly appropriate for sows. Sows are run in paddocks and have access to ark or huts in which to farrow.

In trials in Zimbabwe, sows were allowed a choice of different designs of arks at farrowing time, and it was found that they preferred a design similar to those found in the UK.

The major difference is that under tropical conditions, the roof should be insulated with a 5 cm layer of grass or similar material. Arks can be constructed from cheaper materials, but it is difficult to make them sufficiently robust to avoid destruction by the sow. 

Ample deep shade and wallows should also be provided for sows run under this system. As mentioned previously, tethers can be used as a means of restricting sows within a paddock. They can then be rotated around a given area of pasture or other forage.


Disease Prevention

Once disease affects a pig herd the impact on the economics of pig production in terms of the cost of control and decreased productivity can be enormous.

The first priority must therefore always be to try to prevent the occurrence of disease.

Thus, many of the management procedures considered here are aimed at disease prevention or at mitigating the effects of those diseases that cannot be prevented.

With skilled management, combined with well-designed housing and sound nutrition, an overall strategy to minimise the possibility of disease attack can be formulated.

At the same time a basic knowledge of the main diseases which may affect a pig herd is necessary so that a producer can diagnose the condition and implement control measures as quickly as possible. 

This is of particular significance under tropical conditions where the regular services of a veterinarian are often not available.

The major disease problems are parasites, infectious disease and a few non-specific diseases. Nutritional deficiency conditions are also common causes of health problems.


Parasites are defined as organisms which live on and obtain feed from the body of another, known as the host. They may live on the exterior of the pig when they are known as external parasites or within the internal tissues and organs when they are known as internal parasites.

Parasite will seldom result in the death of the host except in the case of massive infestations or if the host is also stressed in other ways.

External parasites

These mainly cause irritation to the skin surface, often leading to wounds and an increased susceptibility to other infections.

The most common external parasites are mange-mites, ticks, lice, fleas and flies.


Mites, which are scarcely visible to the naked eyes, spend their entire lifecycle under the skin of the pig, but they can survive off the host for as long as eight days.

The most common species is sarcoptes scabiei which cause sarcoptic mange. First signs of infection are a crusty, dry-looking skin around the eyes, ears and snout.

The mites then spread and multiply over the body, and their burrowing causes the skin to become inflamed and swollen. The pig will be seen to be constantly rubbing itself and performance is depressed. Control is best affected by regular treatment, either dipping or spraying with an anti-mange medication, including spraying of pens.

Chronically infected animals should be culled. There are also some recent systemic drugs on the market which are very effective against the mite.


Ticks are only a problem in scavenging or more extensive systems of pig production. There are a number of different species which suck blood and can transmit serious disease (e.g. Babesiosis or redwater). They generally require more than one host to complete their life cycle.

Ticks are easily controlled by spraying or dipping with suitable acaricides.

Lice and fleas

Both lice and fleas can become a problem in dirty and unhygienic conditions, as they live on the skin surface, suck blood and cause irritation. Spraying of the pigs and pig quarters with suitable insecticides are effective ways of controlling the pests.

In the case of lice, particular attention should be paid to the ears.


Flies have a major nuisance-value around pigs as they causes annoyance, can bite, and carry infectious diseases. They are always attracted to any fresh abrasion or wound on the animal.

Control measures should involve spraying of insecticides on suitable fly-breeding areas, e.g. manure heaps, and refuse areas and ponds, pig buildings and the pigs. Baits which attract the flies and are poisonous to them but not the pigs can also be effective.

Internal parasites

Round worms

These are a particular hazard when pigs are free-ranging or not kept on concrete floors. The large roundworm (Ascaris lumbricoides) is very common and can cause a lot of damage in pig herds.

Adults live in the small intestine and can grow up to 300 mm long a 6mm thick.

The female is capable of laying thousands of eggs per day, which pass out in the dung and become infective, if ingested by other pigs, after 21 days. These eggs are extremely resistant and can remain infective for many years.

As part of the life-cycle, eggs hatch out in the pig after ingestion and the larva migrate through the liver and lung. Irritation in the lungs causes coughing and ill thrift, particularly in younger pigs. Damage is also done to the liver which renders it liable for condemnation at slaughter (‘milk-spot liver’).

Moreover, if infection is heavy the adult worms can partly obstruct the small intestine, causing weakness and loss of weight by the pigs. Contaminated feed and water are the usual source of infection with internal parasites.

Control can be affected by breaking the life-cycle, which means regularly moving ranges pigs on the fresh ground and frequent cleaning and removal of faces in housed pigs.

At the same time, unless there is good evidence that there is no worm infection in the herb; breeding pigs should be routinely dosed with broad spectrum anthelminthics and young stock dosed soon after weaning.


The common tapeworm is Taenia solium. The pig is its intermediate host and the adult worm lives in man. Pigs become infected by picking up eggs from human faeces and the larvae then encysted in the pig’s muscle, particularly in the region of the heart and tongue. If the pig meat is then eaten by man, the larvae hatch out and the cycle is completed.

As a consequence, bodies which are affected (measly pork) are condemned at slaughter. By preventing pigs having access to human faeces, the parasites can be eliminated. In some countries live pigs are checked at the market place by trusted experts for the presence of tapeworm’s cysts in the tongue.

The result of the examination influence the price paid to the producer.

Infectious diseases

The following diseases are notable in most countries.

African swine fever

This is a highly contagious virus disease which in the acute form can cause 100 per cent mortality. Typical symptoms are loss of appetite, pigs huddling together, small purplish blotches on the skin, incoordination and laboured breathing.

In Africa, both bush pigs and warthogs are carriers of the virus but are immune to the disease, and it is therefore very important to prevent direct contact between domestic pigs and wild species. This contact can be prevented by double penning and the control of animal movements.

Moreover a soft tick (ornithodoros moubata) which infests the warthog is a biological carrier. Otherwise infection occurs by contact with other sick pigs, or through contaminated feed or water.

There is no effective vaccine or treatment an infected pig should be isolated from healthy ones. Although the disease originated in East Africa, it is gradually spreading west through Africa.

Foot-and-mouth disease

Regarded as the most contagious of all known viral diseases, infection causes blisters on the feet, snout, and udder and in the mouth and throat. It is very painful to the pig, which cannot eat and often has to be destroyed. The disease is endemic in parts of Africa and the virus is carried by the buffalo. Infection can occur by feeding infected bones or cooked meat. There is no cure. If an outbreak occurs in adjacent area, pigs can be vaccinated, but as there are many different strains of the virus it is important to ensure that vaccination is against the right virus.

Other infectious diseases


This disease, which is caused by a bacterium, is also known as contagious abortion. Brucellosis can result in temporary or permanent sterility in females.

Abortion is the most common symptom and can occur at any stage of gestation, depending upon the time of exposure to infection with the bacterium. In boars, testicles may become inflamed and permanent sterility may result.

 The disease is transmitted at mating or by contaminated feed or water. There is no treatment and infected animals should be culled, particularly as brucellosis is transmissible to humans, and the risks of transmission are relatively high under some traditional systems of pig management. Brucellosis appears to be widespread in pig herds in south East Asia and the pacific Islands.


This is caused by organisms known as coccidia, of which are 13 known infective species in swine throughout the world. They cause damage to the intestinal wall, and are believed to be an increasing cause of diarrhea in piglets, particularly in confined housing. Piglets show a grey-green diarrhea, lose weight and rapidly become dehydrated.

Coccidiosis is spread by contaminated faeces and thus good management and regular cleaning of buildings will prevent the disease. Drugs, known as coccidiostats, are available for prophylaxis and treatment.


Salmonellosis is another enteric disease, caused by the salmonella spp. of bacteria. Pigs generally are affected around two months of age, and become gaunt, with a high temperature and a foul-smelling diarrhea. There are usually some deaths in a group of infected pigs.

An outbreak is often triggered- off by a stress condition, particularly heavy worm-infestation.

The disease can therefore be prevented by good management and sanitation. Antibiotics and sulpha drugs will aid in the control of the disease.


SMEDI is an acronym for reproductive failure conditions involving stillbirth (S), mummification (M), embryo death (ED) and infertility (I). It is caused by viruses, mainly porcine parvovirus and the enteroviruses. The symptoms will vary according to when the sow or gilt becomes infected.

If infection occurs during the oestrous cycle and at service, the sow will show a regular or irregular return to oestrus, or if only some embryo die she will produce a very small litter. If infection occurs after 35 days of pregnancy, the foetus die and dry up and are presented at farrowing as “mummified” foetus. The condition can cause a serious decrease in sow productivity within a herd.

There is no treatment but effective preventative vaccination programmes are now available. If vaccines cannot be obtained, all gilts and new animals entering the herd should be given access to farrowing house waste 30 days before breeding. This exposes them to the viruses and stimulates immunity.

Swine dysentery

This disease is caused by a large spirochaete, and is manifested by a severe diarrhea producing reddish – black faeces. Infected pigs rapidly lose weight. The disease is spread by infected dung and can largely be controlled by good hygiene.

There are effective antibiotic medications on the market. Swine influenza Swine influenza is a highly contagious respiratory disease caused by an influenza virus. It is normally triggered off by a stress, particularly rapid changes in temperature.

Although mortality is low, the disease has important economic consequences due to stunting and reduced live weight gains. The first sign of the disease is normally a cough, with a high temperature and loss of appetite.

The disease spreads rapidly, breathing becomes jerky and the hair coat develops a rough appearance. Secondary infection with bacteria may complicate the condition. There is no treatment or preventive vaccine available. Infection can be prevented by good management and the avoidance of stress.

Swine pox

Swine pox is a virus disease, and is transmitted either by direct contact or by ecto –parasites such as lice. Small red areas (about 1.25cm in diameter) appear on the skin around the head, ears and ventral surface which eventually form scabs. There is no treatment for swine pox, but although unsightly it rarely causes serious loss and clears up after a short time.

Transmissible gastroenteritis (TGE)

TGE is a virus disease which causes acute diarrhea; vomiting and early death in young piglets. It also affects older pigs causing diarrhea and vomiting, but rarely death. There is no treatment.

Infected pigs can be isolated, or killed and buried. After infection, the whole herd is likely to be immune.

Non – specific diseases Abscesses

Abscesses can occur as the result of any irritation, inflammation or wound which allows access to bacteria, normally strains of Staphylococcus or Streptococcus. The body of the pig reacts to the invasion of the bacteria, and a pocket of pus is walled off from the body.

Abscesses are seen as swellings or lumps, often hot to touch and they will in time develop a soft area which can be lanced and drained. They may be superficial or they may form deep within the body, where they can cause lameness, interfere with breathing or swallowing, or may not be discovered until slaughter.

As abscesses are painful and can markedly depress performance and reduce carcass value, every effort should be made to minimize the possible causes in a piggery.

Preventative measures include the removal of any sharp or rough object from pig pens, ensuring the floors are not too rough, especially for baby pigs, making sure that injection equipment is sterilized and providing overall good sanitation.

Abscesses can be treated with antibiotics, but this is not always effective.

Gastric ulcers

Ulcers tend to occur as a response to stress in pigs of all ages, and are particularly prevalent in genetic strains bred for fast growth and a thin covering of back fat. The nature of the ration is also important with a higher incidence of ulcers occurring on finely ground, highly –energy concentrate diets.

There may be no specific external symptoms, unless hemorrhaging occurs.

Otherwise pigs show lack of appetite, will huddle together and become thin. Mortality varies according to the extent of the ulceration. There is no specific treatment apart from reducing stress.

Changes in the ration, involving an increase in fibre levels is often useful in ameliorating the condition.


Conclusion on General Principles of Pig Production

Pig production is one of the most profitable livestock enterprises to engage in where environmental condition, feed resource and attitude favour it production. The physical characteristics of the meat output make the product amenable for industrial production valuable meat products.

Thus it is quickest means of raising meat consumption in a country where religious bias against pork consumption is not present.

This article covers basic biology that forms the basis for various principles enthused, and it further points students to simple application of the principles. Notably the system of production is related to climatic effects that dictate feeds and feeding, growth and reproductive activities as well as disease occurrence and management.

Many have made fortunes from mere keeping of pigs in their backyard. Profitability is also at the root of expansion and growth being witnessed in modern pig farming. It is desirable that students who have gone through this study should consider himself an entrepreneur that would seize every opportunity to be at the top of his colleagues.

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