Agriculture Reference
In-Depth Information
the former and preventing loss of weight in the latter.
The feeding of up to 1.3 kg of sugar for 3 or more days
before slaughter of cattle or pigs has increased daily
weights. Some workers have found that loss in live weight
can be prevented by feeding sugar.
Under present-day abattoir conditions, it is doubtful
whether pre-slaughter feeding is always a practical or
economic proposition.
exhausted bulls, the carcases of which set rapidly after
slaughter owing to low levels of glycogen, and therefore
of ATP, in the muscle at the time of death. These animals
will, in addition, have a high muscle pH since little lactic
acid will have been produced. It is important to recog-
nise that rigor mortis depends only on the availability of
ATP, not on the pH of the meat.
Pre-slaughter stress, therefore, affects both the rate of
onset of rigor mortis and the rate and the extent of the
fall in muscle pH. Alterations in these parameters affect
the appearance and eating quality of the meat, the most
common manifestations being pale, soft, exudative (PSE)
pork and DFD beef. These economically significant con-
ditions are described in detail in Chapter 2.
Traumatic injury
Bruising
is defined as traumatic injury without penetra-
tion of the skin where blood vessels are damaged to such
an extent that there is extravasation into the surrounding
tissues. Several studies of cattle bruising have shown that
approximately 31% of bruises occur in the loin and hip
area, 36% on the shoulder, 13% on the ribs and 20% on
other parts of the body. In sheep, many of the bruises are
due to rough handling, resulting either from animals
being lifted by the wool or grabbed by the legs during
sorting, weighing and loading on the farm, during
unloading or while being handled prior to being stunned.
Fasting has been shown to increase bruising and there
is some evidence that chronic stress makes animals more
susceptible to it.
Pre-slaughter feeding of sugars
In order to ensure adequate pre-slaughter levels of glyco-
gen in the muscle, which will result in sufficient lactic
acid being produced to cause the required fall in pH, it is
necessary either to minimise stress, fear, excitement,
fatigue or excessive exertion on the animal or to allow for
an adequate period of rest prior to slaughter in order for
muscle glycogen levels to replenish. Another approach is
to feed easily digestible carbohydrates, such as sugar,
while the animals are in the lairage. As far back as 1937,
experiments in pre-slaughter feeding of molasses to pigs
showed a restoration of muscle glycogen and subsequent
low tissue pH. Later work emphasised this; the psoas
muscle, fillet, had a post-mortem pH of 6.0 when pigs
were starved overnight, compared with 5.43 when 1.4 kg
sucrose was fed 22 and 6 hours before slaughter. The cuts
from carcases of sucrose-fed pigs also gained more
weight during curing, the bacon and ham underwent
less shrink while maturing, and a further advantage was
a significant increase in liver weight. Better keeping
qualities of bacon and ham were also reported.
Sugar solutions have been used to overcome some of
the storage, handling and feeding problems of solid
sugar. A study at the bacon factory of Cavaghan and
Gray in Carlisle showed that carcase yields were increased
by 2.8% and liver weights by 27%, and muscle pH was
reduced by 0.2-0.3 units, when pigs fed a glucose syrup
solution and water and held overnight were compared
with those receiving water only. When compared with
pigs slaughtered on arrival, the differences were 1.3%,
13% and 0.2-0.3 units, respectively.
In cattle detained for 2 days in the lairage, a 25% loss
in liver weight may occur. In one plant in Chicago, the
effects of stress in cattle are reduced by incorporating
molasses in the drinking water. It has also been shown
that the feeding of sugar rapidly restores the energy-
yielding carbohydrate reserve (glycogen) of the muscles
and liver, allowing the development of normal acidity in
Time of bruising
Although the presence of bruises at slaughter is apparent
to the eye, knowledge of the exact time of infliction is
necessary if steps are to be taken to prevent bruising. At
slaughter, a bruise may be dated approximately by the
physical criteria listed in Table 6.4.
Although its use is largely historic, a more specific
method of dating is based on a test which utilises the for-
mation of
bilirubin
from haemoglobin in the area of the
bruise. A sample of bruised meat is soaked in Fouchet's
reagent (trichloracetic acid and ferric chloride); bruises
up to 50 hours old give no reaction; those 60-72 hours
old turn the solution light blue; those 4-5 days old give a
dark-green reaction. The bilirubin test has been used to
show, for example, that 90% of poultry bruises are
inflicted 0-13 hours before slaughter.
It has also been suggested that the age of a bruise can
also be estimated by measuring the
electrical conductivity
Table 6.4
Approximate ageing of bruises by physical
appearance
0-10 hours old
Red and haemorrhagic
Approximately 24 hours old
Dark coloured
24-38 hours old
Watery consistency
Over 3 days
Rusty orange colour (bilirubin)
and soapy to the touch
