182
Contagious Abortion of Cattle, Sheep and Goats
[VOL. XVIII, PART III
attempt to get results, but records, other than a very rough statement derived from the village spokes-
man, will probably never be available. Turning to farms, one private recorded herd was vaccinated
as early as November of 1941 and here alone is it possible to review the results of two completed
breeding seasons. The vaccinated animals were mainly empty adult Punjabi buffaloes and the
injection consisted of 50 thousand million organisms of Cotton's strain 19, suspended in 5.0 c.c. of
saline. A single dose was given subcutaneously. The abortion rate for the six prevaccination years
1936-41 can be seen on page 131 in (Table XXI) ; the rate since 1941 is given in (Table XLIII).
TABLE XLIII
Post-vaccination abortion rates
Animal
group
Non-reacting vaccinees . . . . . . . . . . .
Random vaccinees . . . . . . . . . . .
Positive reactors (not vaccinated) . . . . . . . . .
Pregnant not vaccinated . . . . . . . . . . .
Non-reacting controls . . . . . . . . . . .
Abortions/
pregnancies
per cent
per annum
1.56
4.69
4.17
4.72
4.65
Pregnancies
completed
32
32
12
159
24
Overall mean annual abortion rate for two post-vaccination year = 3.96 per cent
It appears then, that an overall mean annual rate of 21 per cent in the prevaccination years
dropped to an overall mean of 3.96 per cent in the two post-vaccination breeding seasons, while the
lowest abortion rate was 1.56 per cent in the non-reacting principal vaccinees. Nevertheless, it is
debateable how much this drop is due to the vaccination and how far it may be attributed to a natural
cessation of the endemic. Unfortunately, a study of the abortion rates in the various groups reveals
little, for, while it is true that the principal vaccinees show one third less abortions than the controls,
the rates in all other groups are uniformatively alike, worse still, the rates in the very large batches
of unvaccinated animals were very much lower than the lowest rate for the preceding six years. It
is hard to believe that the protection of 77 animals so reduced the concentration of disseminable
contagion that most of the remaining 150 or so animals escaped infection, and the result is as bewil-
dering scientifically, as it is gratifying in practice. At the most, but a poor case can be made out
for the vaccine, while, there is much to suggest that the endemic might well have ended spontaneously ;
for instance, no new buffaloes had been purchased for some three or four years, while the home-bred
new-entry were few. It is easy to suppose, therefore, that after a 20 per cent abortion rate for six
years much of the herd had become naturally immune.
However, as a result of renewed confidence inspired by the fewer abortions, the owners are buying
100 new adults in 1944 ; these animals are to be vaccinated and the real test will come when they
commence to breed.
Another fairly large scale trial of vaccination has been made in the young cow-stock of five
military farms Animals were inoculated in two age groups viz., at 4 to 8 months and 18 to 24 months
respectively. A single subcutaneous injection was given of 5.0 c.c. of Cotton's strain 19 suspended
at a density of 7 to 8 on the Brown's scale. As yet, insufficient results have accumulated to permit
the formation of an opinion on this work, but such records as are available are analyzed in Table
XLIV, p. 183. They are at present unworthy of discussion.