A. L.
ROSE
195
EVIDENCE THAT CATTLE MAY BECOME TOLERANT
TO TOXIC SUDAN GRASS
Inserted in the table is a series of analytical
figures referring to several paddocks of sudan grass
in which no losses occurred (No. 9). All paddocks
were on the same small farm, some were severely
damaged by grasshoppers, while others were affect-
ed to a less extent. In all, there was sufficient of
the crop left to allow the cattle a daily feed right
through the grasshopper invasion. Specimens of
the plant were taken for analysis from time to time
while the cattle were feeding off it. The resulting
figures were all extremely high; much higher than
those for many of the fatal crops, yet no sickness or
losses occurred. At the same time, cattle were
being lost under standard conditions on farms al-
most adjoining (Nos. 5, 6 and 7). Other examples
are less striking and are cases in which a few cows
of little value or a few head of young stock have
been left in a crop right through the period of inva-
sion and re-growth, and have suffered no ill-effects.
The case of No. 10 is not comparable, for the crops
on that property suffered little or no damage from
grasshoppers.
THE EFFECT OF HUNGER
There is both theoretical and practical evidence-
that hungry cattle, which have eaten a paddock of
toxic sudan grass, will succumb more rapidly.
Hungry cattle will obviously eat more plant in a
given time and therefore will more quickly absorb
their toxic quota.
Experience has shown, however, that it is not
necessarily safe to attempt grazing off toxic crop
with cattle which are not hungry. Such crops
must be regarded as valueless for cattle, though
they may be used for sheep with a high degree of
safety.
SHEEP ON SUDAN GRASS
Sudan grass has been quite a popular summer
feed for sheep, especially fattening lambs, and quite
often farmers have been advised to turn sheep on
to a crop which has proved toxic for cattle and
with one small exception no ill-effects have follow-
ed. The crop referred to in No. 16 of the table was
used to fatten 200 lambs after the accident to the
cattle and three of the lambs died, presumably
from HCN poisoning. At times when cattle mor-
talities were occurring, sheep were being grazed on
sudan grass under exactly similar conditions and
with no harmful effects. The only sheep mortality
referred to in the table (No. 30) was in somewhat
unusual conditions and on Johnston grass, which is
considered to be far more toxic than sudan grass.
SYMPTOMS
The symptoms shown by cattle in HCN poison-
ing from sudan grass are not very distinctive. An
increased rate of respiration is constant and this
may be shown before any other abnormality is
noted. A cow first ceases feeding and stands in an
agitated, restless manner; the respirations increase
and marked distress soon follows. There may be
some salivation and odd animals rush about and
bellow. Many cases go down quite early and lie
prostrate, moaning and breathing rapidly. Death
may take place in a few minutes, but some cows
will remain down for some hours and then die.
Cases that are on the ground for any considerable
time usually become affected with hoven.
LATENT PERIOD
The period between the time of access to the crop
and the onset of symptoms varies, the variation
being due to the amount of crop eaten in the time,
and to the concentration of hydrocyanic acid in the
crop. Reference to this latent period is made in
the table. The shortest observed time is five
minutes and it is probable that symptoms were
obvious in most cases in ten minutes and the death
of the first case would occur shortly afterwards.
Reference will be made elsewhere* to the amount
of plant that might be expected to be lethal under
varying conditions of toxic concentration, but
clinically it has been obvious that in some cases a
pound of the plant was sufficient to cause death.
TREATMENT
A consideration of the data in the table will show
that mortality may be heavy or absent, in the latter
case the animals recovering completely. Very
many cows recover without any treatment. Many
cases die much too quickly for treatment to be
applied, but the treatment of animals which
survive for half an hour or more may be the
means of saving their lives. Generally the farmer
himself has neither the knowledge nor the means
to do anything of benefit. The sudden collapse of
a number of his cattle and the early death of some
of them leads him in desperate haste either to the
telephone or to his neighbour, and on at least three
occasions the farmer has been known to cut off the
animals' tails to make them bleed.
For a long time it has been regarded by some
that the liberal sub-cutaneous injections of ether
has a very beneficial effect, the drug being used to
give a quick stimulant effect. Ether was tried on
one occasion only (No. 13). The twelve treated
animals were given 20 mils of ether about fifteen
minutes after they went down, followed by another
20 mils. The farmer credited the injection with
saving the cattle, but there was no evidence that it
was of benefit. Artificial respiration has been
* Hind Marsh, W. L. Poisoning of Cattle by sudan
grass and other Gyanogentic Plants, Austr. Vet. J.,
16, 219