The food animals - Gracey's Meat Hygiene - page 11

animals within the same species. In essence, a breed
relies on being recognisable because it possesses a num-
ber or combination of features, for example, coat colour,
body conformation, head shape, etc.
As the pig was domesticated, it was selected for a
variety of different characteristics such as fertility, moth-
ering ability, muscle and fat deposition, durability and
amenability to handling under a variety of husbandry
systems. This process continues today on two distinct
levels. There are those who breed pedigree pigs with the
aim of preserving the 'purity' of their breed and the com-
mercial pig-producing companies and pig farmers who
use cross-bred varieties to utilise hybrid pigs to optimise
production traits. Through selection, there are now esti-
mated to be some 300 different breeds of pigs.
Unlike some species, the pig has suffered little from
man's selection to maximise production and appearance.
The most noted exception was the introduction of the
halothane gene following the introduction of the Piétrain
breed. This breed was chosen with the aim of increasing
muscle production via the double muscle gene carried
naturally by the Piétrain breed. However, pigs which carry
the double recessive halothane gene tend to drop dead if
stressed, and those that do survive and are slaughtered
express a high frequency of pale, soft and exudative (PSE)
muscle tissue such that the meat appears pale and suffers
from high drip loss, making it less suitable for processing
and sale. For many years after this gene was introduced,
the commercial breeding companies tested breeding stock
by exposing all potential breeding pigs to the anaesthetic
gas halothane because it was found that if 10-week-old
pigs which were double recessive for this gene were
exposed to this gas, they would become rigid; pigs not car-
rying the gene retained a relaxed posture. Recently, a gene
probe has been developed which is cheaper and more wel-
fare acceptable. This new test has also made it possible for
the breeding companies to retain some of the benefits of
this gene in terms of muscle production without the risk
of pigs being stress susceptible and producing PSE meat.
More recently, breeding companies in the United
Kingdom and France have imported and experimented
with genes introduced by crossing European breeds
with the Meishan breed which originates in China. The
Meishan is a highly prolific breed with the potential of
producing up to 30 piglets per litter. The aim is to intro-
duce the genes for prolificacy while retaining the leaner
carcase characteristics of the European breeds.

Figure 1.11 Middle White.

'maintain the purity and improve the breeds of swine in
the United Kingdom of Great Britain and Ireland by the
means of livestock inspection and herdbook recording
all pedigree pure-bred pigs.
Today, the BPA recognises 14 pedigree pig breeds: Large
White, Landrace, Welsh, Berkshire, British Hampshire,
British Saddleback, Duroc, Gloucester Old Spot, Large
Black, Middle White, Tamworth, Mangalitza, Oxford
Sandy and Black and Piétrain (Fig. 1.11, Fig. 1.12, Fig. 1.13
and Fig. 1.14). The main breeds used commercially are
Large White, Landrace, Duroc, Hampshire and Piétrain.
Commercial breeding companies in the United
Kingdom supply approximately three-quarters of all the
replacement gilts bought by commercial pig farmers.
These companies use pedigree pigs at the top of their
breeding pyramids to produce cross-bred grandparent
and parent pigs.
Increasingly, the force which has been driving the
selection made by the breeding companies is coming
from the retail sector where the demand is for a leaner,
'healthier' carcase which produces a tender, succulent
meat not showing signs of PSE or excessive drip loss and
which has sufficient intramuscular fat to provide flavour.
Added to this is a new demand which places emphasis
on the production system used, with the requirement
being for what are termed 'high-welfare' production sys-
tems but which equate to loose housing systems. These
demands influenced the choice of breed used by the
breeding companies in their breeding programmes. For
example, although the traditional crosses of the White
breeds still account for 84% of all commercial indoor
production, sales of Duroc crosses to produce hardier
pigs, more suited to the more demanding outdoor envi-
ronment, are on the increase. Pig breeds in the United Kingdom

In the United Kingdom, pedigree pig breeding is care-
fully recorded by the British Pig Association (BPA),
which began keeping breeding records in 1884 when the
association was known as the National Pig Breeders
Association (NPBA). The aim of the NPBA was to

Pig production
The United Kingdom, with some 25% of its pigs out-
doors, has the highest percentage of outdoor production
in Europe. The availability of suitable outdoor sites will