Agriculture Reference
In-Depth Information
In many cases, diagnosis of icterus can present a
problem. In both live animals and carcases (especially
of cattle and horses), yellow colouration occurs even
when serum bile acids/bilirubin levels are normal.
Conversely, hyperbilirubinaemia can occur where
jaundice is not very evident, perhaps owing to masking
by erythema of the mucous membranes. In cases of
doubt, therefore, it is necessary to resort to
tests
for
plasma bilirubin
.
There is marked yellowish colouration of the super-
ficial fatty tissues, the fat deposits within the visceral
cavities and the serous membranes. Closer inspection
may reveal an abnormal colour in connective tissue
which varies from lemon to orange yellow or greenish
yellow. These changes may also be seen in the kidney
cortex, calyces and renal pelvis. Yellow pigmentation is
often evident in large nerve trunks and in the endothe-
lium of medium-sized arteries such as the internal and
external iliacs and brachial and femoral arteries, which
are coloured even in slightly icteric carcases. Icteric col-
ouration may also be seen in the lungs, sclera of the eye,
tendons and cartilaginous extremities of long bones.
In doubtful cases, for example, the presence of slight
icterus in a well-nourished carcase, it should be detained
for 24 hours and then re-examined since the action of
normal muscle enzymes may remove the yellow colour.
If the pigmentation is only slightly evident after the
24-hour detention, the carcase may be safely released for
food. This is especially so in mild cases of obstructive
jaundice, icterus associated with fractures, torsion of the
spleen, etc.
Icterus in the pig associated with hepatic cirrhosis
may also be accompanied by an abnormal odour and
taste; overnight cooling tends to deepen the yellow
colour, and the skin then appears freckled. Icteric pig
carcases should therefore be detained for a similar period
and then subjected to a
bile acids
and/or
boiling test
, the
latter to detect abnormal odours. In the absence of these
changes, the carcase may be passed as fit.
In all animals, a marked degree of icterus present after
a 24 hour detention of the carcase warrants total con-
demnation. This is the situation in haemolytic, toxic and
the more severe cases of obstructive jaundice. Icteric
carcases should preferably be examined in daylight since
artificial light may distort colours. If, under natural light,
carcases show any degree of icterus along with paren-
chymatous degeneration of organs (the result of bacterial
infection) or show an intense yellow or greenish discol-
ouration without evidence of infection, they should be
totally condemned.
Jaundice must be distinguished from the yellow col-
our of fat commonly seen in old bovines and certain
dairy breeds like Jerseys and Guernseys in which it is
Laboratory tests for icterus
Icterus index (depth of colour of serum compared with
standard solution) and serum bile acid assay are used.
A useful test is to boil 2 g of fat from the suspect carcase
in 5 ml of a 5% solution of NaOH for 1 minute in a boiling
tube. Cool under the tap and carefully add 3-5 ml of ether.
Shake and allow to stand. Layers will separate.
A greenish-yellow colour in the upper layer indicates
presence of carotenoid pigments; if colour is in the lower
layer, bile pigments are indicated.
confined to the adipose tissues as the pigment carotene.
This yellow colouration is also occasionally met with in
pigs and sheep.
Porphyrin
Porphyrins are a group of reddish constituents of haem,
the red iron-containing pigment of Hb in animals,
of green photosynthetic chlorophylls of higher plants, of
cytochrome (a red enzyme found in most cells) and
of catalase, an enzyme responsible for the breakdown of
hydrogen peroxide in mammalian tissues.
The porphyrias are a group of disorders in which there
is excessive production of porphyrins or their precursors
in the tissues due to enzymic deficiencies in haem bio-
synthesis. Symptoms include skin fragility and blister-
ing, abdominal pain, paralysis, anaemia, reddish-brown
teeth and bones with death in acute attacks.
In man and animals (cattle, sheep, horses, goats and
pigs), the presence of photodynamic porphyrins and
other substances in the blood (ingested, injected or
present as a result of liver damage) causes them to be
hypersensitive to sunlight, resulting in dermatitis and
oedema -
photosensitisation
.
A rare
congenital
form (pink tooth, congenital por-
phyria) occurs in cattle, pigs, cats and man in which
urine, bones and teeth are discoloured pink or reddish
brown owing to excess porphyrin along with typical skin
lesions on exposure to sunlight in cattle but not in pigs
and cats. The lesions also occur in the lungs, kidneys,
liver and lymph nodes.
The cattle type (
bovine congenital erythropoietic proto-
porphyria
(BCEP)) affects herds in which inbreeding
and close linebreeding are practised - particularly
Limousins. Cattle show signs of agitation, head shaking
and ear twitching. Scaliness, oozing small scabs and flak-
ing debris affected the pinnae of the ears, which were
very sensitive to the touch.
Various plants contain photosensitising substances,
such as hypericin in
Hypericum perforatum
(St. John's
wort), fagopyrin in
Fagopyrum esculentum
and
