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 The relatively large, narrow head, heavily forequarters, tapering light hindquarters and compact body have been replaced by a smaller head, lighter forequarters, and a longer and wider body with bigger capacity and well-developed, meaty hindquarters.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 of pig
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 of pigs (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.
African breeds of pig
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, and some typical reproductive performance figures are shown in Table 10.1.
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. However, during the growth phase, growth rates and feed conversion efficiencies of indigenous pigs are below their exotic counterparts (Table 10.2).
Exotic pig breeds 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 characterised 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 cross�breeding 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
Characterised 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 realise 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.
0 Comments
Comment