|
|
|
Original
Article About Dexters
"The
Significance of an Achondroplasia-Like Condition Met With in Cattle"
Part
IV
by F.A.E. Crew
in Proceedings of the Royal Society of London,
volume 95, 1923, pages 228-255.
Page 235 (Cont'd)
IV -The Pathology of the Monstrous Calf
Foetal Anasarca in the great majority of cases is present. This condition is
not uncommon in cattle and is almost invariably associated with the death
and abortion of the foetus at the sixth to seventh months. According to
Williams, foetal anasarca has been recorded only in ruminants among the
domesticated mammals. The cause is not known; it has been ascribed by some
writers to a congenital absence of the thoracic duct. In the case of the
“bull-dog” it is invariably associated with hydrops amnii, and it is
reasonable therefore in this case to suspect that both conditions are due to
one and the same cause,
Page 236
although in ruminants generally there is no doubt that the two conditions
can occur quite independently.
Hydramnios -The normal amount of fluid present in the amnion of the cow is
about five to six litres, the amount in the allantois about six to fifteen
litres. Any material excess is considered abnormal. The amniotic fluid is
clear and the allantoic turbid in later pregnancy; the fluid evacuated in
the case of the “bull-dog” is clear; the condition present in the case of
the monstrous calf is probably hydramnios and not hydrallantois. When
examined, no definite cell elements can be recognised in either stained or
unstained preparations. The amount of fluid evacuated in one case was 160
litres approximately. Hydramnios is not uncommon in cattle and is the rule
in such species crosses as Bos americanus x Bos taurus or Bos americanus x
Bos indicus.
The exact cause of hydramnios is not known, nor can it be until the origin
of the liquor amnii itself has been demonstrated. The prognosis in cases of
severe hydramnios in cattle generally is very unfavourable both for cow and
calf, for, as a result of the pronounced uterine dilatation and uterine
paresis, the cervix is not dilated naturally and the abdominal muscles,
losing tone for the same reason, do not aid in the expulsion of the foetus.
Delivery is always by operative procedure, as is also the removal of the
placenta. In the Dexter, however, the prognosis is entirely satisfactory as
far as the cow is concerned; normal labour pains come on, the cervix is
dilated, and the foetus is expelled without any artificial interference,
unless it is an older foetus, for then the head cannot pass the pelvic brim
and operative interference is imperative. The placenta must be removed
manually in most cases. The difference in the prognosis in the case of the
Dexter and other breeds rests on a difference in the general musculature.
The Dexter is a peculiarly muscular individual and can withstand the
stretching which hydramnios involves much better.
Hydrocephalus - In one case, hydramnios and foetal anasarca were associated
with pronounced hydrocephalus. Literally, there was no brain.
The Skeleton - The shape of the skull of the monstrous calf is
characteristic. Brachycephaly is marked, the cephalic index being about 100
per cent, and the skull being diminished in length and enlarged in width.
The head is large with bulging forehead and parietal eminences; the nasal
region is much depressed; the bones of the vault are thicker than is usual,
and the most striking feature of all is the extreme shortness of the base.
The supra-, ex- and basi-occipitals, the basi-, ali- and pre-sphenoids are
fused into one mass of bone and no suture of any sort can be identified. The
orbito-sphenoid is
Page 237
distinctly delimited. In a normal Dexter foetus of seven months the basi-occipital
measured 3.1 cm, and the basi-sphenoid 2.5 cm, giving a total antero-posterior
length of 5.6 cm when measured on the exterior of the skull, and one of 5 cm
when measured on the interior aspect. These combined bones in a “bull-dog”
foetus of the same age measured 1.2 cm and 1.3 cm respectively. In the
normal the foramen measured 2.6 x 2.8 cm, in the “bull-dog” it was 1.8 cm
long and was waisted, measuring 0.9, 0.8, 0.9 cm in width. No distinct
condylar faces were discernible. Internally the ethmoid in the normal
covered the orbito-sphenoid; in the “bull-dog” it did not. The vomer is
extremely robust in the monstrous calf and has a very broad articulation
laterally with the palatines. There is no hard palate and the nasal portion
of the skull is completely exposed ventrally in consequence of the entire
absence of any inward growth of the maxillae and palatines. The posterior
palatine processes of the pre-maxillae are present, being fused with the
anterior end of the vomer. The maxillae are greatly fore-shortened as are
also the nasals. The fore-shortening of the maxillae is illustrated by the
unusual prominence of the lachrymals and by the fact that while the general
contour and proportions of the post-palatine processes of the maxillae are
normal, the pre-maxillae, normal in design, practically come back to the
level of the maxillo-palatine suture. .Viewed ventrally, the pre-maxillae
lie much deeper than the inner margin of the maxillae and palatines, the
contour of these latter, bones being such that there is no suggestion of any
effort to make a palate. In this respect the skull is distinctly reptilian.
The abnormalities of the skull are such as affect its posterior fossa, and
save for various degrees of asymmetry and for the greater thickness of the
vault, the remaining peculiarities are such as could follow from the
abnormality in the ossification of the base.
The skull of the “bull-dog” foetus resembles that of the “bull-dog” in one
respect only: both show fore-shortening of the facial region due to an
arrest of development of the nasals and maxillae.
In the case of the limbs of the “bull-dog” foetus the epiphyses of the long
bones do not differ materially from those of the normal, but there is a
profound difference in the length of the shaft. The shortening affects the
proximal bones of the limb more than the distal. The digits are separated
more widely than in the normal calf of the same age.
Sections of the epiphysial line of the long bones of the limbs show certain
characteristic features. Normally, bone formation proceeds by (1)
endochondral ossification at the junction of epiphysis and diaphysis,
determining growth
Page 238
in length, and (2) periosteal ossification determining growth in thickness.
In endochondral ossification three zones can be distinguished in the area
between the undifferentiated cartilage of the epiphysis to the diaphysis:
(1) the zone of proliferating cartilage cells in which the multiplying
cartilage cells lie in a clear matrix, (2) the zone of parallel columns of
cartilage cells, in which the hyaline matrix is the seat of calcification,
and (3) the line of ossification in which each column of zone extends as far
as the bone marrow from which vascular loops extend to erode the cartilage
columns in a regular manner. The septa separating the columns become eroded
and denuded of their cells and become encrusted with calcareous salts, and
on their surfaces osteoblasts are deposited by the vascular loops. These
osteoblasts lay down successive layers of true bone whilst the calcareous
material of zone 2 is removed by osteoclasts.
In the case of the monstrous calf zone 1 is unaltered, but on the surface of
this there is a vascular fibrous area enclosing small islets of cartilage.
There is no zone 2, the columnar arrangement of the cartilage cells being
entirely absent and the cells, few in number, are scattered irregularly. The
matrix is not hyaline but shows fibrillation, and the deposition of
calcareous salts is irregular. Zone 3 is thin and irregular. Endochondral
ossification occurs but the absorption of bone trabeculae is defective so
that reconstruction of the cancellous tissue fails. The trabeculae are
excessively thick, with com¬paratively small rounded areolae between them.
The condition is one of abnormal endochondral ossification, in that there
has been defective absorption at the stage of secondary areolar formation.
Periosteal ossification in these cases is normal and the abnormality is
restricted to the epiphysial line where the cartilage cells are entirely
passive, where there is no division, no column formation and no vacuolation
and hypertrophy.
The vertebral column is also involved, in some cases being less than half
the length of that of a normal foetus of the same age, and along with this
abnormality there are others affecting the size and shape of the thorax and
of the pelvis.
On to Part V
|
