Agriculture Reference
In-Depth Information
muscular action before dressing of the carcase. Like
pithing, it is an unnecessary procedure.
The most satisfactory type of knife for the lateral stab
method, where the bleeding knife is inserted posterior to
the trachea and oesophagus, is one with a blade about
23 cm long and 4 cm wide with a straight back unsharp-
ened except at the tip, and a tapered point on the cutting
edge of about 8 cm. The knife is fitted with a circular
safety guard between blade and handle. The unsharp-
ened edge is placed in contact with the oesophagus, but
it may puncture this organ if the knife is withdrawn at
the wrong angle. Even when great care is taken with this
technique, both carotid arteries may not be severed.
Approximately 75% of the available blood is lost from
ewes within 60 seconds and in lambs within 50 seconds.
Electrically stunned lambs bleed more rapidly than those
stunned with the captive bolt. There was no significant dif-
ference in the rates of bleeding between sheep that are not
stunned and those stunned with the captive bolt pistol.
Bilateral severance
is the easiest technique to perform
and produces satisfactory bleeding. This is the best
method for bleeding sheep in lateral recumbency. When
both carotid arteries are severed, the sheep loses brain
response in less than 14 seconds; if only one carotid
artery is severed, insensibility can take more than 70 sec-
onds to occur.
In contrast with cattle, which bleed more fully in the
head-down position, trials with sheep at the UK Meat
Research Institute have shown that sheep bled in the
horizontal position lose approximately 10% more blood
than those suspended vertically.
Bleeding of the sheep carcase should last for 5 min-
utes, the amount of blood obtained from a slaughtered
sheep being 1-2.5 kg, lambs having the lower weights.
Figure 7.10
Pigs bleeding over a blood collection channel
(Reproduced with permission from David Armstrong).
may be overcome by using the hollow knife. Pigs should
be allowed to bleed for 6 minutes, as during this period
the muscles relax and the hair is more readily removed
during scalding.
Pork pigs yield 2.2 kg of blood, bacon pigs 3 kg, while
boars and sows yield 3.6 kg.
In many abattoirs,
prone sticking
of pigs has been
adopted. After being rendered unconscious, the animal
is discharged on to a conveyor belt and is stuck while
lying prone in the tonic phase, the blood draining into a
trough running parallel to the conveyor.
Immediately after sticking, the animals may come
under a holding-down belt which continues the full
length of the conveyor and restrains the involuntary
struggling that occurs during the clonic phase. The
advantages of prone sticking of electrically stunned
pigs are the more efficient recovery of blood and the
elimination of ruptured joints and joint capsules,
which are a troublesome condition in pigs bled while
suspended and are the cause of the so-called
internal
ham bruising
. In addition, a study in Austria found
that the incidence of PSE meat was reduced from
62-63% in vertically bled pigs, to 22-27% in those bled
in the horizontal position.
Pigs
In pigs, the knife is inserted in the midline of the neck at
the depression in front of the sternum, and is then pushed
towards the heart to sever the
anterior vena cava
brachio-
cephalic trunk at the entrance of the chest; sometimes the
carotid artery is also pierced. Care should be taken not to
insert the knife too far as it may penetrate into the shoul-
der, allowing blood and water from the scalding tank to
run back into the shoulder 'pocket' beneath the scapula
giving its wall a cooked appearance. The carcase should
not be placed immediately in the scalding tank; too large
a sticking wound and contaminated scalding water facili-
tate the entry of microorganisms into the carcase tissues
by way of the jugular vein and may lead to spoilage. In
some abattoirs, pigs are stunned, then hoisted and bled
while suspended (Fig. 7.10).
Urination occurring, after electric stunning, while the
pig is bleeding renders the blood unmarketable, but this
