Evaluation of a
report of effects of propylene glycol on keel-billed toucans
by Lynn Pottenger, PhD (DOW Chemical)
A publication, by Worell et
al. (2000)
describes several cases of keel-billed toucans in zoos becoming ill, with some
birds that did not respond to supportive treatment and died.
For several of the cases, the publication lists “before” and
“after” diets administered to the birds, and for one case report, the
publication describes administration of a medication to an already sick bird.
The publication asserts that the clinical effects, and subsequent deaths
of some birds, were due to propylene glycol, present in the “after” diet or
in the medication, respectively.
In order to investigate the likelihood
that propylene glycol was involved in the clinical effects and eventual deaths
described, we obtained samples of the diets mentioned in the publication and
subjected them to chemical analysis for propylene glycol content.
Table
1 lists the commercial names of the diets investigated and the propylene glycol
content quantified in each, using a standardized analytical methodology (GC/FID
detection). The limit of detection
was 500 ppm, or 0.05% (w/w).
Table 1. PG content in
brandname animal diets cited in Worrell et
al. (2000)
Animal
Feed Analyzed
|
Diet
status
|
PG
Content
|
Wayne’s Dog Kibble |
“Before”
|
ND
|
Scenic Low Iron Diet
|
“Before”
|
ND
|
Hill's Science Diet Maintenance Dog Kibbles
|
“Before”
|
ND
|
Reliable
Protein Products
|
“After”
|
2.5%
(w/w)
|
Zeigler Bird of Paradise Diet
|
“After”
|
ND
|
As can be seen from
Table 1, only one diet contained quantifiable levels of propylene glycol.
Thus one of the “after” diets, which were described as causing the
deaths of keel-billed toucans based on their content of propylene glycol, did
not have any quantifiable amount of propylene glycol.
The other “after” diet did contain propylene glycol, at 2.5% (w/w), a
level which has been shown to cause no effects in repeated exposures to quails
and chicks,,
in addition to many mammalian species (rats, mice, rabbits, dogs, guinea pigs,
etc.).
Based on these
analytical determinations of propylene glycol levels present in the commercially
available diets cited in Worrell et al. (2000), it is highly unlikely that propylene glycol was the
cause of any of the clinical effects, including deaths, described in the
keel-billed toucans, and attributed by Worrell et
al. (2000) to administration of the “after” diets.
It is not clear what may have been the causative factor in these
incidents.
This conclusion is
supported by the published literature demonstrating no effects from feeding
quails and chicks diet including up to 2.5% PG (w/w).
In fact, according to the USEPA and OECD, PG is an accepted oral carrier
for guideline toxicity testing in birds.
An additional
critical flaw in the Worrell et al.
(2000) publication is the lack of any controls for the hypothesis of PG
toxicity. There were no healthy
birds fed defined PG-supplemented diet, nor any clearly identifiable birds that
received defined PG-free diets, nor any birds that did not change diet.
With the limited information available, there is no way to rule out the
possibility that the clinical effects reported are unrelated to the low iron
diets.
In conclusion, the
Worrell et al. (2000) publication does
not offer any proof that PG was related to the clinical effects, including
deaths, reported by the authors. The
analytical results on PG content of the diets conducted by Dow and reported
here, do not support any causative role for PG in the clinical effects reported
in keel-billed toucans by Worrell et al.
(2000).
Worrell et
al. (2000). Suspected
propylene glycol sensitivity in keel-billed toucans. Proceedings of
the 21st Annual Conference of
the Association of Avian Veterinarians