are obvious changes to the placenta;
and cases where there is a localised
area of thick discharge on the
surface of the placenta. In all cases
there should be isolation of gut and
environmental bacteria from the
foetus and/or placenta for a definite
diagnosis of EAFL. The different
outcomes may reflect the amount
of caterpillar material that a mare
ingests during grazing as well as the
response to caterpillar exposure by
individual mares.
When is my mare at risk?
Figure 3. Processionary caterpillars, Ochrogaster lunifer on a host Eucalypt tree.
Image: Julianne Farrell
Figure 4. Golden coloured egg mass of the canopy-nesting form on an Acacia branch.
Figure 5. Canopy nest in Eucalypt. They range from cricket ball to soccer ball size,
depending on the number of caterpillars present.
Image: Julianne Farrell
It is believed that most cases of
abortion due to EAFL occur from 1-4
months after exposure to caterpillar
exoskeleton containing thousands
of setae (Fig. 2). Processionary
caterpillars only breed once a year,
with the moths emerging in early
November and depositing eggs
(Fig. 4, Fig 6) on host trees over
a 4-6 week period. Once the eggs
hatch, the caterpillars develop
through 8 growth stages (instars).
The caterpillars moult their skin
(exoskeleton) between each instar
and these shed skins accumulate
in the caterpillar nests (Fig. 5,
7-9). Studies by entomologists at
The University of Queensland have
shown that setae that have been
identified in uterine and placental
tissue are present in increasing
numbers associated with the
exoskeleton from the 4th through to
the 8th instar and that the setae are
shed with the exoskeleton with each
moult.
The caterpillars congregate in nests
associated with the trees where
the egg mass has been laid. Three
different nesting patterns have
been identified as ground-, trunk-,
and canopy-nesting forms, and it is
now thought that these are separate
species or a species complex of O.
lunifer. However, it is believed that
all 3 nesting forms can cause EAFL.
The caterpillars are commonly
seen in the environment when they
abandon their nests and form long
processions, hence the common
name, to either move to a new
feeding tree, or to leave the nests to
pupate in the soil. The risk period
for mares is from February/March
through to September with the time
of highest risk period being from
April to June when caterpillars are
on the move. Exposure may result
from ingestion of shed exoskeleton
material that is released into the
environment as the nests degrade
following the departure of the
caterpillars. Shed exoskeleton
might also drop from canopy and
high trunk nests and be dispersed
by wind, rain/flood. It may also be
inadvertently baled into hay.
July • August • 2017 • The Australian Quarter Horse Magazine • Page 19