4
Problem of Equine Strangles in India
broad consideration of the incidence or attack rate
by years, the labour involved in making the ad-
justment would scarcely have been warranted.
The data for horses at Mona and Sargodha are
recorded in Table I, and for mules at these two
depots in Table II.
From the frequency distribution shown in
Table I, it is seen that at both depots the annual
attack rate has only once fallen below 50 per cent.
and that in some years practically all have shown
clinical symptoms. Among horses at Mona there
are indications that 1920, 1925, 1929, 1933 and
1939 were peak years, while at Sargodha the yearly
distribution is more uniform. Data are not
available to show whether there is any variation
in the susceptibility of young stock, since the
number of animals at risk at different age groups
is unknown. At Mona the mean annual attack
rate over 23 years (1917-40) has been 76.2 per
cent, while at Sargodha over 13 years (1927-40)
it was 72.6 per cent. By applying the x 2 test,
it can be shown that since 1927 the attack rate in
horses at Mona has usually been higher than at
Sargodha, and the same is true since 1929 in the
case of mules.
In young stock mules (Table II) the incidence
of strangles is definitely lower at both Mona and
Sargosha than among horses, the mean annual
attack rates being 53.2 and 46.8 per cent
respectively. The yearly distribution is fairly
uniform.
Stud Farms. The information is shown in
Table III. The first point is that the incidence is
very variable from year to year. In some years
strangles is absent, or nearly so, while in others
the rate reaches 50 per cent or even higher. Thus
at Probynabad, 1914, 1918, 1924, 1928 and 1933
are peak years, and at Coleyana the same is true
of 1930, 1935 and 1937*. There are indications
then both from the depots and stud farms that a
high strangles morbidity rate has occurred with
some regularity every four or five years, and that
on the farms in intermediate years the rate may
fall very low indeed. The latter feature is in
contrast with the more uniformly high rate at the
Remount Depots. No attempt has been made to
calculate x 2 values for the stud farms, since the
figures are small and there are few overlapping
years in which a comparison can be made.
CASE INCIDENCE OF STRANGLES BY MONTHS
Full details of the position under this heading
are reserved for a paper in which the seasonal
incidence of strangles is considered. At some risk
of anticipation, however, Fig. 2, based on the
data, is introduced to show that at the depots, as
the strangles year progresses the attack rate rises
to the month of April and then rapidly declines.
As between Mona and Sargodha during the
period 1933-40, there is little difference in the date
of onset of the disease, but from 1934 on
cases continued to appear rather later at Mona
than at Sargodha. The influx of new purchases
continues during the period September to March,
after which the population remains stationary
(Fig. 1). From Figs. 1 and 2, it would appear
that the gradually increasing incidence from
September onwards is connected in some way with
the increasing number of susceptible stock within
the area.
FIG. 1. Young stock in segregation (horses), total
monthly population in seg egation as per cent of total
population during period.
Total young stock segregation at Mona, 1929-40-6525
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Sargodha, 1933-40-4075
As to the stud farms, Fig. 2, prepared from
data for Coleyana and Renala, shows high points
from December to February, a secondary rise in
June and a decline through July and August.
This curve, it will be observed, is different from
that for two depots.
MORTALITY RATES
Horses. At Mona the death rate has varied
over the period of years from 0.0 to 8.5 per cent
of animals affected, mean 5.0 (Table I). At
Sargodha, the figures for the shorter period are
rather higher, viz. 3.5 to 10.1, mean 6.1 per cent
and the x 2 test shows that in certain years the
differences from Mona are significant. At the
stud farms (Table III) the death rate, calculated
on 2123 cases of strangles, was 6.1 per cent, a
figure similar to that of the remount depots.
The mortality rates over the series of years at
Mona and Sargodha have been analysed to see if
any significant variation exists in different years.
* 1943 at Coleyana was also a peak year.