Meat inspection protocols - Gracey's Meat Hygiene - page 205

especially evident on the surface of the bovine palate,
tongue and cheeks and in the hair, horns and eyes of
dark-skinned cattle, black and grey horses and black and
red pigs. The deposits are black or brown in colour and
usually of irregular shape and size, most being about a
centimetre in diameter.
Abnormal deposits of melanin ( melanosis ) are
encountered chiefly in the bovine and less commonly
in sheep and pigs. In the ox , melanosis is commonly
found in the lungs, liver and meninges, where it usually
involves the pia mater and more rarely the dura mater
and is termed black pith . The pigmentation may also be
found on the pleura and peritoneum, in cartilages and
bone and between muscles. The black colouration of
the kidneys of adult cattle, especially the Red Danish
breed, may be due to melanin or lipofuscin , an endoge-
nous pigment closely allied to melanin. In calves, the
liver and the cortex of the kidney are frequently
affected, but this must be distinguished from the black-
ish colouration of the kidneys of very young calves due
to bile pigments.
In sheep , melanosis is most common in the liver, but
some black hepatic pigmentation is due to lipofuscin,
especially in Australia (Fig. 9.19).
In the pig , the condition is most often seen in the belly
fat or in the udder of females, often being revealed as
radiating lines or patches distributed along the ducts of
the mammary glands.
Melanomas are malignant tumours which arise from
melanin-forming cells (melanocytes).
Melanin in itself is not harmful, but affected organs
should be condemned. Where the condition is general-
ised, total condemnation is warranted. The presence of a
melanoma justifies a very detailed examination; in meta-
static cases, total rejection may be warranted.

may also be present in the acute stage. If infection
extends along the uriniferous tubules, it may give rise
to abscesses in the cortex and irregular grey areas on
the kidney surface. Occasionally, the infection causes
complete obliteration of the kidney parenchyma,
making the organ a purulent sac.
As the disease progresses in more typical situations,
chronic tubulointerstitial nephritis supervenes with pro-
gressive fibrosis. Scarring with contraction of the fibrous
tissue and loss of kidney tissue produce marked contrac-
tion and distortion of the organ even to virtual obliteration
of some lobes. In very severe cases, the kidney assumes a
greyish, nodular appearance, becoming very small in size.

Bruising
It is now broadly accepted that:
Muscle tissue is generally sterile until it is exposed to
extraneous contamination.
Extraneous contaminants grow no faster on bruised than
unbruised tissue.
There is no difference in the microbiological condition
of meat from bled and unbled lamb carcases.
The trimming of bruised tissue is therefore purely
aesthetic.

Pigmentation
Pigments may emanate from outside the body ( exoge-
nous pigments) or from within the body ( endogenous
pigments).
Exogenous pigments are normally associated with the
grazing of livestock in proximity to certain industries
and with urban pollution. The most common is carbon
or coal dust which causes pneumoconiosis in coal miners
and various dusts. Carbon appears as black particles in
the lung tissue and associated lymph nodes.
Carotenoid pigments derived from carotene A and B
(precursors of vitamin A) and xanthophyll are of plant
origin. These lipochrome pigments are normal constitu-
ents of many different body tissues - adrenal gland,
Kupffer cells of the liver, corpus luteum, testes and the
adipose tissue of Jersey and Guernsey cattle as well as the
yolk of eggs and butter fat. They are also found in the so-
called subcutaneous xanthomas of poultry. These are not
true tumours but collections of connective tissue cells
and cholesterol-containing phagocytes.
Endogenous pigments in animals include melanin,
haematin, haemosiderin, bile pigments, porphyrin, lipo-
fuscin and cloisonné kidney pigment in sheep and goats.

Melanin
All healthy pigmented skin contains a brownish-black
protein colouring substance, melanin , produced in mel-
anocytes by the oxidation of the amino acid tyrosine. It is

Figure 9.19 Melanosis in a bovine lung.