Agriculture Reference
In-Depth Information
be seen in stained sections (Sudan Black and Fontana
Silver) as clumps near cell nuclei. They are resistant to fat
solvents, acid-fast in reaction and negative to iron stains.
Fagopyrum sagittatum
(buckwheat), furocoumarin in
Ammi majus
(bishop's weed),
Cymopterus
spp. (spring
parsley, wild carrot, various clovers, alfalfa and brassicas)
and perloline in
Lolium perenne
(perennial ryegrass).
Ingestion of these plants in active growth can cause
primary photosensitisation.
Secondary
or
hepatogenous photosensitisation
occurs
when liver cells are damaged, for example, in hepatitis or
biliary duct obstruction.
Phylloerythrin
, an end product
of chlorophyll metabolism normally excreted in the bile,
is then liberated into the bloodstream and accumulates
in the tissues to cause photosensitisation.
Plants
respon-
sible for hepatotoxic damage and secondary photosensi-
tisation include bog asphodel (
Narthecium ossifragum
),
Lupin
spp. (
Lupinus
),
Lantana
spp. (
Lantana
) and panic
grass spp. (
Panicum
). Various fungi can be responsible,
for example,
Pithomyces chartarum
, which contains
sporidesmin, is found in perennial ryegrass (
L. perenne
)
and is the cause of
facial eczema
in New Zealand sheep
(
big head
or
geeldikop
in South Africa). Certain
chemicals
such as phenothiazine, carbon tetrachloride and corti-
costeroids may also induce photosensitisation.
The
lesions
of photosensitisation are confined to the
white, unpigmented, less hairy and woolly areas of the
skin which become reddened and oedematous.
Commonly affected parts are the face and ears, but teats,
vulva and perineum may also be involved. Skin necrosis
and gangrene often ensue. General signs of weakness,
fever, anaemia, posterior paralysis and nervous symp-
toms with death are not uncommon.
The condition must be distinguished from 'big head'
in sheep caused by
Cl. oedematiens
(
Cl. novyi
).
When bony structures are affected with pigmentation,
consideration should be given to boning-out with release
of the unaffected muscular tissue for food. In local affec-
tions, the affected part only need be rejected.
Xanthosis (xanthomatosis,
osteohaematochromatosis, brown atrophy)
Xanthosis affects the heart most often but also involves
the diaphragm, masseters, tongue, muscles of the fore-
limb and organs such as the adrenal gland, liver, kidney,
thyroid, parathyroids, ovary and testis. The actual cause
of pigment (lipofuscin) deposition is unknown, and
there is doubt as to its significance.
Xanthosis is encountered especially in old animals but is
not confined to them, being seen in otherwise healthy ani-
mals. It is being recorded fairly frequently in Ayrshire cattle
and their crosses indicating a possible recessive gene.
Examination of affected carcases shows that the
heart
is affected in all cases and the
adrenal cortex
to be com-
monly involved. Of the skeletal muscles, the
masseters
are
most severely pigmented but generally less than the heart,
the
diaphragm
being the next in order of importance.
Yellow fat disease
. Yellowish or brownish fat is some-
times seen in pigs fed on fish diets. The staining is due
to the deposition of
ceroid
, a waxy substance similar to
lipofuscin
. Ceroid is resistant to fat solvents, is acid-fast
and is stainable with fat stains.
Ochronosis (alkaptonuria)
is a rare hereditary disease
of cattle, pigs, horses and man in which
homogentisic acid
accumulates in tissues and is excreted in the urine due to
a deficiency of its acid oxidase.
Homogentisic acid polymerises to form a brownish-
black melanin-like pigment which is deposited mainly in
the fibrous tissue (tendon sheaths, ligaments, cartilage),
kidneys, endocrine gland and lungs. (Homogentisic acid
is an intermediate product in the breakdown of the
amino acids, phenylalanine and tyrosine.)
Lipofuscin ('wear-and-tear pigment',
pigment of brown atrophy,
lipochrome, haemofuscin)
A yellowish-brown granular pigment which accumulates
in the cytoplasm of cells, especially of the heart, liver,
adrenal gland and brain, and is associated with ageing,
apoptosis and chronic wasting diseases. It occurs in
Devon cattle, Nubian goats and Hampshire Down sheep,
being sometimes described as
ceroid lipofuscinosis
, which
is also seen in man. Affected animals show hindlimb
ataxia and blindness, post-mortem findings including
cerebral and retinal atrophy, neuronal and macrophage
granulation and storage of ceroid lipofuscin in nervous
tissue especially the brain.
Lipofuscins are derived from the oxidation of tissue
lipids and/or lipoproteins. Granules of the pigment can
Tumours
A
tumour
or
neoplasm
is an abnormal growth of new
cells which have become insensitive to normal growth
control mechanisms and which (i) usually resemble the
cells from which they have derived; (ii) proliferate in an
unrestrained and disorderly manner; (iii) possess no
organised structural arrangement; (iv) persist after ces-
sation of the causal stimuli; (v) serve no useful purpose,
especially in malignancy; and (vi) result from one or
more mutations of the cellular DNA, especially malig-
nant forms. (In some cases, tumours need not proliferate
progressively and may even regress spontaneously.)
The word
tumour
means a swelling, which is an indi-
cation of the general gross appearance, although this is
not always the case. For example, some malignant carci-
nomas are relatively small yet capable of causing early
