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Contagious Abortion of Cattle, Sheep and Goats
[VOL. XVIII, PART III
of a drained cement floor surrounded by six-foot brick walls, cemented on the inside to the top. A
simple roof, carried on poles projecting four or five feet above the walls and with everhanging eves,
completes the structure. The entrance does not require a door and may be closed by bars fitting
in slots, whilst drainage should be carried onto cultivated land so as to be inaccessible to cattle. The
size and number of boxes or paddocks are matters for some deliberation; if it is uncommon for more
than one or two recently aborting animals to be on the farm at one time, then a single box or paddock
with accommodation for two will be sufficient, but, as it is not desirable to place more than two or
at the most three recently aborting animals in the same paddock or box, when abortions are more
frequent, proportional accommodation must be arranged. In fixing this, it must be borne in mind
that the longest continuous period a single animal will be in isolation is 60 days.
The periods during which Brucella infected animals should be isolated in these premises are as
follows:
(1) From the first signs of abortion or premature delivery until 60 days after the act of delivery.
(2) All cows isolated under (i) from about three weeks before the anticipated date of the sub-
sequent parturition, or from the time of second abortion or premature delivery should it occur. (N.B.—
animals should be watched for impending abortion in this pregnancy) until 30 days after delivery.
(3) All cows isolated under (1) and (2), from about three weeks before the anticipated date of
the next parturition, until cleansing and vaginal discharges have ceased after delivery.
Where facilities are available and where the adoption of extra special precautions seem necessary
to check a moderate epidemic in a valuable herd, the following additional refinement may be adopted.
The veterinary officer dealing with the farm should obtain, on loan, a ' quick-test' apparatus and,
once every second month, a day should be set aside for testing all previously healthy cows that are
pregnant between the beginning of the fourth and the end of the fifth month of gestation. Positive
reactors should be grouped into a segregated herd, living in temporary quarters and grazing separately.
As each positive animal either aborts or reaches three weeks of term, it should be isolated in the
same way as aborting cows in (1) above. As each healthy cow calves, it should be tested and if positive
segregated as before. This additional refinement should not be necessary for longer than a year
or two and can be stopped when a material drop in abortion rate is noted.
Hygienic precautions should be taken in all cases of abortion [Polding 1943].
A system, similar to the one just described, has been in force in all military farms, since early
in 1941. but the enormous expansion in cattle concentrations and movements due to war, entirely
masked any benefits the procedure may have conferred. However, general indications from farms
unaffected by the war and practising some similar form of hygiene, all tend to show that Brucellosis
can be checked by this means.
THE THEORY OF VACCINATION
The present popular form of vaccination against Brucellosis has been so discussed in current
literature that much introduction to the subject is unnecessary. In America, Cotton, Buck and
Smith [1934] showed that prolonged artificial culture of Brucella strains reduced their pathogenicity
for animals and they secured such a strain of lowered virulence, identifying it as strain No. 19. They
further showed that the injection of this strain failed to produce visible lesions in guinea-pigs or
generalized infection in cattle, although it seemed to invoke an immunity against reinfection with
field strains. Unhappily, the injection of Cotton's 19 also produced a serum response, which, if present
in adults, would confuse to a point of break-down American's interestate system of control by test
and disposal ; a system which the authorities were loathe to discard. It was found, however, that,
if 4 to 8 months-old calves were injected, the resulting serum reaction had disappeared by adolescence,
and it seems possible that Americans were prejudiced in favour of calfhood vaccination by their desire
to retain the interestate testing system while Cotton's vaccine was on trial. The principle of calfhood