Fetal Pig Natural History and Dissection Information Use in Biology Labs

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Fetal Pig Natural History and Dissection Information

Use in Biology Labs

Along with frogs and earthworms, fetal pigs are among the most common animals used in classroom dissection. There are several reasons for this, the biggest being that pigs, like humans, are mammals. Shared traits include common hair, mammary glands, live birth, similar organ systems, metabolic levels, and basic body form. Fetal pigs are the unborn piglets of sows that were killed by the meat packing industry. These pigs are not bred and killed for this purpose, but are extracted from the deceased sow’s uterus.

Geographic Range

Of all members of the pig family, Sus scrofa occupies the largest range. They originally occurred in Europe, Asia, North Africa, and the Malay Archipelago. Included in this native range were a number of island populations, including the British Isles, Corsica, Sardinia, Japan, Sri Lanka, the Ryukyu Islands, Taiwan, Hainan, Sumatra, Java, and smaller islands of the East Indies. Sus scrofa was later introduced throughout the world as domesticated animals by humans. Currently, Sus scrofa can be found nearly everywhere, from homes to barns to boggy marshes and mountainous terrain.

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Mammalia

Order: Artiodactyla

Family: Suidae

Subfamily: Suinae

Genus: Sus

Species: Sus scrofa

The domestic pig, known in some areas as the hog, is a domesticated livestock animal, farmed for meat (pork, bacon, ham, sausages, etc.)

Most domestic pigs have rather sparse hair covering on their skin, although woolly coated breeds are known (Mangalitsa pig), and some were popular in the past.[1]

The domestic pig is most often treated as a subspecies of its wild ancestor, the wild boar, and in this case it is given the scientific name Sus scrofa domesticus. Some taxonomists treat the domestic pig as a separate species, when it is called Sus domesticus, and wild boar is S. scrofa.[2] Wild boar were in human association as early as 13,000–12,700 BP. Escaped domestic pigs have become feral in many parts of the world (for example, New Zealand) and have caused substantial environmental damage.[3][4]

Pig farming terminology

  • Pig hog or swine, the species as a whole, or any member of it. The singular of "swine" is the same as the plural.

  • Shoat, piglet or (where the species is called "hog") pig, unweaned young pig, or any immature pig.

  • Sucker, a pig between birth and weaning.

  • Runt, an unusually small and weak piglet, often one in a litter.

  • Boar or hog, male pig of breeding age.

  • Barrow, male pig castrated before puberty.

  • Stag, male pig castrated later in life, (that is, an older boar after castration).

  • Gilt, young female not yet mated, or not yet farrowed, or after only one litter (depending on local usage).[16]

  • Sow, breeding female, or female after first or second litter.

Pigs are omnivorous animals, eating a highly varied diet. Most of the foods consumed by pigs are plant tissues, especially underground roots, rhizomes, and tubers, which are excavated using the snout. Pigs also eat the foliage of many plants, as well as nuts, seeds, and fruits that may be found on the ground. Pigs are opportunistic predators, and will eagerly eat birds eggs and nestlings if these are discovered, as well as small rodents, snakes, and other prey. Pigs will also attack larger, disabled animals, and will eat carrion.

Pigs occur in a wide range of habitats, from alpine tundra, through most types of temperate and tropical forests, savannas, swamps, and the vicinity of human settlements. Wet places are a necessary component of all pig habitats, because mud bathing is important to the physical and mental health of these animals.

Most species of pigs are social, with the animals generally living in family groups consisting of at least a mature female (or sow) and her young. Mature boars are generally solitary, except during the mating season. Grunting and squeaking noises are important in the communications among pigs. Baby pigs are precocious, and can move about only a few hours after their birth. Broods of pigs can be quite large, and can exceed a dozen piglets. Young pigs often fall victim to predators, but mature animals can be ferocious in their self-defense, and are not an easy mark as prey. Pigs can live to be as old as 25 years.

The most critical period in the life cycle of a pig is from birth to weaning. On the average, about two pigs per litter are lost during this period. Poor management is the major contributing factor, although the actual cause may be crushing, bleeding from the navel, anemia, starvation or disease.

Weaning large litters of thrifty, heavyweight pigs is a key factor for a profitable swine herd. This publication attempts to outline management practices that help keep pigs alive and profits high.

Preparation for farrowing

The average gestation period for sows is 114 days. To prepare for farrowing, producers should know when sows are due. They also need a method to identify all sows. The gestation table (Table 1) is designed to help producers determine farrowing date based on the date sows are bred.

The Domestic Pig is bred from the wild pig, specifically to improve certain qualities such as size and temperament. It is considerably larger than its wild relatives and much slower. There are several variants of Domestic Pig, due to crossbreeding with the woolly boar, but this is the most typical.

Appearance. The Domestic Pig is very much like the wild pig in appearance, with shaggy, coarse brown or black fur, which is heaviest over the back and shoulders, and scant on the belly. In general, this fur tends to be somewhat sparser than that of the wild pig, (except in the woolly boar crossbreeds). The hide is thick, dark brown, and leathery. Both genders have two large sharp yellowish tusks, but these are usually cut short or filed down to minimize their danger. If the tusks are left uncut, they can grow to be nearly two palmspans long. Since this Pig is much less active than its wild cousin, the hooves often need to be filed down as well. This pig is comparatively much bigger than the wild one, with some of the bigger boars achieving a body length of nearly 1 ½ peds and a height of 2 fores from cloven hooves to shoulders. It has a thin, short tail, hanging just to the hocks, with a wispy tuft of black hair at the end. The shoulders are heavier than the hindquarters. The snout is the most sensitive part of the Pig. It is long and turned up at the end, with large nostrils which tend to be wet and sticky most of the time. The ears are large and pointed, though some pigs may have "lop" ears, which fold over and hang down. The Pig’s deep-set, small dark brown or black eyes are somewhat nearsighted - pigs tend to rely far more on their hearing and sense of smell than on vision. The Pig’s head is large and thick, and comes straight out of the heavy shoulders with almost no discernable neck. It weighs about 3-4 hebs and is quite wide-- nearly 3 palmspans - across the forehead. The Pig’s legs are short and stubby and quite thick. The domesticated pig is usually extremely fat - with no need to forage or compete with other Pigs for food, it spends a great deal of time eating and growing. Some Domestic Pigs can achieve nearly twice the weight of a comparable wild pig. A good-sized sow usually weighs around 1 ½ -2 pygges, while the boars are normally about 2 pygges but can weigh as much as 2 pygges, 4 hebs. Scholars suggest that the term “Pygge” originally comes from the average weight of a wild pig, many, many years ago, before farmers began to breed the domestic variety.  

Special Abilities. Like most pigs, the Domestic Pig has an amazing sense of smell. A legend says that a farmer once used a Pig to find his lost child, but this is unsubstantiated. The mild tempered ones can sometimes be trained to dig up tuberroots or hunt for certain types of edible mushrooms such as the squilla since a Pig can almost always find food. Usually the runts of a litter will be selected to be trained for this purpose, since they will not be worth much for meat.

The Pig is an unusually intelligent animal and is sensitive to climatic changes. Farmers swear that they can tell when bad weather is on the way before a weather mage can. Two days before a major storm, Pigs will start behaving very agitatedly, digging up great piles of dirt or hay. Just before the storm hits, they will burrow into the piles and hide there until the worst of it is over. This instinct is so deeply rooted in them that they will do this even if kept indoors. Sows with litters will often carefully bury their babies around their bodies so they can still feed, heaping the straw about them.

Territory. Domestic Pigs may be found almost anywhere there are people (pork is not usually as popular with other races as with humans). Although they thrive best in temperate climates, occasionally northern peoples will crossbreed Domestic Pgs with the woolly boar for a hardier breed of animal, usually with good results. The Domestic Pig was originally bred in southern Sarvonia, but has since spread across most of the continent. There are domestic pigs on other continents as well, notably Nybelmar and Yamalquain. Most farmers keep their Pigs in a pig barn with access to a large outdoor yard. Sows with litters are kept inside in a special stall with extra straw or wood shavings to keep them warm.

Habitat/Behaviour. The Domestic Pig is a pack animal and they are usually kept in groups of about ten pigs, five mated pairs. Larger groups tend to fight more, as Domestic Pigs are still somewhat aggressive. Biting and rough shoving (especially for food) is fairly common. The sows are much more dangerous when they have young litters (see Mating) and need to be housed separately then. Generally, however, the Pigs are rather indolent and greedy. A common rural expression is “living the life of a pig”, often in reference to spoiled children or very rich people. In spite of their reputations, Pigs are very clean, fastidious animals. Some have been trained as house pets (again, usually the runts because they don’t get so big) and they can get very attached to their owners, just as a dog might.

Diet. The Domestic Pig will eat nearly anything; household scraps, most plants and non-poisonous fungi, roots, grains, berries and even fish. It is not a finicky eater. Some farmers like to supplement their pigs’ diet with weeprouts or fermented fruit mash, claiming that this adds a delectable flavour to the hams. Pompion is also popular, since it is cheap and easy to produce. Corn, wheat and different kinds of grains are used to bulk the Pigs up quickly. Farmers keep large blocks of sea salt in the pens for salt licks as well. 

Mating. Like its cousin the wild pig, the Domestic Pig mates for life. During the mating season (twice yearly in winter and summer) the amorous boar courts his mate in a charmingly clumsy way, bringing her choice tidbits of food, nuzzling her tenderly, using his tusks to scratch her back gently, and so on. The actual act of mating is quick, aggressive - and noisy! Sows usually have litters of 6-8 piglets, though if food is plentiful and living conditions optimal, sows have been known to produce up to 12 piglets in one litter. The sow is a savagely protective mother, and it is wise to stay out of reach when bringing food to her pen. Post-partum sows have been known to bite and trample people, though they are normally relatively placid. The piglets grow very fast and mature within four or five months. The average pig, if not sold for meat, lives approximately 9-12 years.

Usages. The Domesticated Pig is very popular with people, as it is bigger, slower and less aggressive than the wild pig. The meat tends to be tenderer and considerably higher in fat. Thus it is both easier and more profitable to sell domestic pork, hams and other cuts of meat. Back bacon is currently fashionable among the richer classes as a luncheon meat. The lower classes enjoy the cheap pickled pigs feet.

But the other parts of the Pig are useful too: Pigskin is commonly used for inexpensive shoes, belts and gloves, as it is tougher and cheaper than leather. The intestines are used to make sausage casings. Artists prize the coarse bristly hair for use in making paintbrushes. Pighair brushes are popular with Bardavos students as they make inexpensive and good quality writing/painting implements. The cut-off tusk pieces may be carved into intricate jewelry or decorative knickknacks. Altogether the Domestic Pig is a very useful animal.

Myth/Lore. Because of the pig’s strong sensitivity to weather changes, it is said that they are sacred to Grothar the Weather God, and any farmer hoping to have good weather is sure to treat his Pigs very well! Sarvonian peasants tell the legend of how Grothar created the wild pigs in answer to the prayers of many devout farmers who were struggling through a particularly difficult spring, with rain, sudden frosts, and terrible storms. However, the capricious god chose not to make things too easy for his subjects, and the wild pigs were fierce, ill-tempered beasts. Only those farmers who were particularly determined (and lucky) could catch, tame, and successfully breed them.

As you read earlier, in order for pig gestation to reach maturity and a full- grown baby pig to be born is about 112-114 days. Consider the difference in human birth. For a human fetus to grow to maturity is 39-40 weeks or 312-320 days. Gestation in domestics pigs is determine similarliy to humans. Today we have all sorts of tests that are run using ultra sounds. The same can be done on pigs. However a simple test to determine gestation age is by measuring the length of the pig, as well as the size of all organs. The table below shows an estimate length and the corresponding gestation age:

Approximate Gestation age of the pig:




54 days


68 days


75 days


86 days


100 days


114 days (fully grown)

Pigs are also considered quadruped. Quad simply means four and ped means feet. So pigs are a four legged animal instead of biped which means two feet or legged animal which is what humans are. As we look at the number of feet pigs have we also have to look at how they walk and how that compares or differs to humans. Pigs are what is considered unguligrade which means they walk on the tips of their toes using their hooves for balance and to walk. This also enables them to extend their stride longer and move faster. Humans on the other hand are called plantigrade. This means that we put the full length of our feet on the ground as we walk. We use the soles of our feet, our heals and our digits. There is a third group called digitigrade which means they walk mostly using their digits.

Determining the sex of pigs is usually pretty easy. An easy way to determine what type of pig you are working with in a classroom dissection is to check for mammary glands. The presence of mammary glands signifies a female fetal pig. The absence of mammary glands but the presence of the scrotum identifies the pig as a male fetal pig. There are other differences and similarities as well but not as noticeable as these two.

Before beginning a dissection, it is important to have an understanding of some of the basic directional terminology associated with the dissection of specimens.   Some of these terms include proximal, which means toward the body, and distal, which means to move away from the body.  Other important anatomical directions are indicated below.

Key Anatomical Directions

Some other words you may not know related to dissections especially pig dissections:

Caudial: Pertaining to the tail.

Cephalic: Pertaining to the head

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