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GRAIN OVERLOAD AND SECONDARY EFFECTS AS POTENTIAL
MORTALITY FACTORS OF MOOSE IN NORTH DAKOTA
Erika A. Butler1, William F. Jensen1, Roger E. Johnson2, and Jason M. Scott3
1North Dakota Game and Fish Department, 100 North Bismarck Expressway, Bismarck, ND, United
States 58501; 2North Dakota Game and Fish Department, 7928 45th Street NE, Devils Lake, ND,
United States 58301; 3North Dakota Game and Fish Department, 2305 Elm Street, Fargo, ND, United
States 58102
ABSTRACT: The intent of this article is to alert biologists of a potential mortality factor of moose in
agricultural areas. It has long been recognized that ruminants switching from a natural diet of browse (a
cellulose-based diet) to one of more readily digestible carbohydrates (a starch-based diet), such as corn
and wheat, are predisposed to developing conditions such as enterotoxemia, polioencephalomalacia, acute
rumenitis, liver abscesses, laminitis, and to sudden death. These are often secondary to grain overload
(acute acidosis) and are frequently documented in cattle and sheep which are moved from pasture to
feedlot. Necropsies of 4 moose in North Dakota were not entirely conclusive, but suggested that grain
overload occurred and was a cause of mortality. Necropsy findings that supported grain overload as
a contributing factor to death included acute rumenitis, isolation of Clostridium perfringens coupled
with hemorrhagic enteritis, chronic laminitis, and polioencephalomalacia. Four likely scenarios exist
in which grain overload occurs in North Dakota moose including consumption of planted crops such as
corn and wheat, access to bait piles mainly intended for deer, access to cattle feeding sites, and access to
recreational feeding sites. These findings have important implications for the regulation of baiting and
recreational feeding practices in North Dakota and elsewhere in moose range of similar situation.
ALCES VOL. 44: 73-79 (2008)
Key words: Agriculture, Alces alces, feeding, grain overload, moose, mortality, rumenitis.
Moose (Alces alces) in North Dakota
have traditionally occupied forested areas in
the northeast and north-central portions of
the state. Moose were first recorded during
white-tailed deer (Odocoileus virginianus)
surveys in the winter of 1969-70. In 1979 the
first modern moose hunting season allowed the
harvest of 15 moose in Cavalier, Pembina, and
Walsh counties. Recently, based upon winter
aerial survey data for white-tailed deer, moose
have expanded their range south and west into
agricultural areas. Areas of the state open to
moose hunting include the eastern one-third
of the state south to the South Dakota border,
and much of the northern one-third of the state.
In 2008, 141 moose licenses were issued in
North Dakota.
The Red River valley (Glacial Lake Agas-
siz Plain) was historically tall grass prairie.
Due to the high productivity of the soil, flat
terrain, and ease of conversion to agricultural
use, <2% of the surface area remains as na-
tive prairie (Jensen 2001). Common crops
in these areas include corn, wheat, sugar
beets, potatoes, barley, beans, sunflowers, and
soybeans (Fig. 1). Reports of moose feeding
in these agricultural fields, both planted and
plowed, have become increasingly common
over time.
Long recognized as a concern with
domestic ruminants, grain overload (i.e.,
rumen overload, carbohydrate overload,
acute overeating, ruminal acidosis) results
from ingestion of toxic amounts of highly
fermentable and readily digestible carbohy-
drates such as grain. This frequently occurs
when ruminants abruptly switch from a diet
of natural browse (a cellulose-based diet) to
GRAIN OVERLOAD EFFECTS ON MOOSE – BUTLER ET AL. ALCES VOL. 44, 2008
74
one of readily digestible carbohydrates (a
starch-based diet) causing a change in the
rumen microbial population; the number of
gram positive bacteria increase markedly
while gram negative bacteria decline. The
gram positive bacteria produce excessive
lactic acid which lowers the rumen pH to
<5. This increase in acidity destroys protozoa,
cellulolytic organisms, and lactate-utilizing
organisms all of which normally inhabit the
rumen, and impairs rumen motility. Clinical
signs of acute overload include indigestion,
rumen stasis, acute ruminitis and acidosis,
dehydration, toxemia, incoordination, col-
lapse and recumbancy, and frequently death.
If the animal survives the initial episode of
grain overload, secondary effects include,
but are not limited to, enterotoxemia, po-
lioencephalomalacia, liver abscesses, and
chronic laminitis (Merck Veterinary Manual
2008). However, other potential causes for
these conditions also exist and are presented
in the discussion.
Ruminitis and rumen scarring have been
reported in a supplementary fed captive deer
herd (Woolf and Kradel 1977) and grain over-
load has been identified as a primary diagnosis
in captive elk (Cervus elaphus) of all ages
submitted to pathology labs (Woodbury et al.
2005). Rumenitis was diagnosed in 30 of 108
free-ranging white-tailed deer examined in
Saskatchewan; rumenitis and rumen overload
were determined to be the causes of death of
5 of these deer (Wobeser and Runge 1975). A
polioencephalomalacia-like disease, possibly
secondary to grain overload, has been reported
in wild pronghorn (Antilocapra americana)
from Saskatchewan (Wobeser et al. 1983)
and North Dakota (W. Jensen, North Dakota
Game and Fish Department, pers. comm.),
wild white-tailed deer in Minnesota (Kurtz
and Karns 1969) and South Dakota (Reed et
al. 1976), and a wild mule deer (Odocoileus
hemionus) from South Dakota (Reed et al.
1976). No documentation of grain overload
in moose was found, though moose might be
especially vulnerable to this condition as their
mean retention time for digestion is the lon-
gest documented for cervids, and is surpassed
by only 1 member of the order Artiodactyla,
the Asian water buffalo (Bubalus bubalis;
Stevens 1998).
METHODS
Reports of dead or sick moose throughout
the state are generally investigated by the North
Dakota Game and Fish Department (NDGF)
wardens or biologists. When possible, either
the entire carcass is submitted to the North
Fig. 1. Corn and wheat production throughout the
state of North Dakota. Compiled and published
by the USDA, National Agricultural Statistics
Service, North Dakota Field Office (Source:
http://www.nass.usda.gov/Statistics_by_State/
North_Dakota/index.asp).
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75
Dakota State University Veterinary Diagnostic
Laboratory (VDL) for necropsy, or samples of
major organs and serum are collected for sub-
mission. This study is a retrospective review of
necropsy reports during a period of time when
the NDGF did not have a veterinarian on staff.
The results of 4 necropsies performed from
1991-2006 suggested that grain overload and
its secondary effects could have contributed
to moose mortality in North Dakota.
Each of the 4 cases discussed below had
the entire carcass delivered to the VDL for
necropsy. Grain overload was not considered
a differential diagnosis by NDGF employees
until results of the necropsies were received.
Consequently, some pertinent information is
lacking, and/or difficult to interpret from the
available necropsy reports. Further, the VDL
may have believed that certain animals were
from captive facilities.
RESULTS
The locations of the 4 moose mortalities
were in areas of substantial corn and wheat
production (Fig. 1 and 2). All 4 cases died
or exhibited clinical signs during the North
Dakota deer archery season which runs from
September–January. Case C was euthanized
during the deer gun season which occurs for
17 days in November. No hunting-related
injuries were documented in any case.
In October 1991 the NDGF received
multiple calls regarding case A, an adult cow
moose east of Sheldon. Reports indicated that
case A had extremely overgrown hooves (both
the fore and hind limbs). On 21 October it
was decided to euthanize case A as her travel
had become extremely restricted. Case A was
in good body condition and was presented at
necropsy with moderate postmortem change.
It was noted that all 4 digits had severely
overgrown claws. The hind and front claws
were approximately 30 cm and 20 cm longer
than normal, respectively. Separation of the
dorsal claw from the third phalanx was evident
and proliferation of fibrous tissue was present.
Severe congestion was noted around the distal
aspects of the third phalanx in both front dig-
its. The rumen and reticulum contained large
amounts of grain that appeared to be corn.
Hyperemia of the ruminal mucosa was noted.
Serology for both bluetongue and epizootic
hemorrhagic disease virus was negative. A
diagnosis of severe, chronic laminitis in all 4
feet was made. The pathologist commented
that this lesion in domestic livestock is often
associated with an episode of acute grain
engorgement, most likely occuring several
months earlier. Other causes of chronic lamini-
tis, however, could not be ruled out.
On 6 December 2002 case B, a young
bull moose, was found dead near Kelso. The
reporting party stated that the moose had been
seen in that area for a few days. There were
no apparent gunshot wounds. Case B was
in good body condition at necropsy. There
were 1-2 liters of free serosanguinous fluid
within the abdomen. The rumen contents
included grain of unrecorded type and grass.
Several feet of the jejunum were flaccid and
contained a thick bloody fluid and there was
extensively petechiated hemorrhage in the
mesentery in this area. Histologically, sections
of intestine contained multifocal congestion
in mucosa and submucosa with occasional
mucosal hemorrhage. Mild lymphoplasma-
cytic inflammation was found in the mucosa.
Clostridium perfringens was isolated from the
intestine. The pathologist indicated that these
findings were consistent with a diagnosis of
enterotoxemia.
On 16 November 2004 case C, a bull
moose, was reported recumbent and kicking
in a field near Gardner; the district warden
was sent to investigate. The warden reported
that he had seen this bull the previous day and
it had appeared healthy, but when the moose
was approached it was unable to rise. It was
noted that a large amount of feces appearing
to contain blood surrounded the moose. The
reporting party claimed that a neighbor had
been feeding the moose all summer. Case
GRAIN OVERLOAD EFFECTS ON MOOSE – BUTLER ET AL. ALCES VOL. 44, 2008
76
C was shot and transported to the VDL. At
necropsy, case C was found to be in good
body condition with moderate postmortem
autolysis. The contents and gross appearance
of the forestomachs and abomasum were
unremarkable. A large mass of hemorrhage
was present within the tissue at the base of the
mesentery and the small intestine contained
frank blood. No mucosal lesions were present
and the colon appeared normal. Congestion
of the kidney and adrenal glands was noted.
Histological examination revealed multifo-
cal intraepithelial neutrophilic aggregates
(microabscesses) in the ruminal epithelium
and diffuse autolysis of all sections of the
intestines. Fluorescent antibody examina-
tions for bovine herpes virus 1, bovine viral
diarrhea virus, bovine respiratory syncytial
virus, and parainfluenza 3 virus were negative.
Bacteriology isolated Escherichia coli, alpha
Streptococcus, and Clostridium perfringens
from the liver, and E. coli, alpha Streptococ-
cus, Bacillus sp., and C. perfringens from the
intestine. A diagnosis of hemorrhagic enteritis
(with C. perfringens) and acute rumenitis was
made. The acute rumenitis was suspected to
be biochemical in origin, with grain overload
a strong possibility.
On 3 January 2006 case D, an adult female
moose, was seen circling and stumbling with
a pronounced head tilt in Cass County, and
was subsequently shot by a warden. Case D
was in fair body condition at necropsy. In ad-
dition to 2 live nematodes removed from the
abdominal cavity, a massive intrameningeal
blood clot was seen ventral to the brain at
the level of the thalamus and midbrain. The
intramenineal hemorrhages (not related to eu-
thanasia) was associated with focally extensive
polioencephalomalacia. On histopathology, a
Fig. 2. Locations of moose mortalities in North Dakota which were possibly due to grain overload or
its secondary effects.
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77
single area of the meninges showed a massive
blood clot, while the subjacent gray matter
was markedly rarefied.
DISCUSSION
Laminitis, such as the severe chronic case
documented in case A, is a common chronic
sequel to previous grain overload in both
domestic ruminants and horses. Less com-
monly, it can be secondary to postparturient
metritis, endotoxemia, colic, enteritis (Merck
Veterinary Manual 2008), copper deficiency
(Flynn et al. 1977), and epizootic hemorrhagic
disease (Prestwood et al. 1974). While serol-
ogy for both bluetongue and epizootic hemor-
rhagic disease was negative, this animal did
not have its copper levels tested. The large
amount of corn present in the ingesta proves
that large quantities were available to this
animal suggesting that grain overload could
have initiated laminitis several months earlier,
however, other causes of laminitis cannot be
ruled out.
The gross and histological intestinal le-
sions coupled with the isolation of Clostridium
perfringins from the intestines of case B were
highly suggestive of enterotoxemia. Entero-
toxemia is a feed-related condition that often
occurs in late winter when animals have not had
access to grain for an extended period of time or
with high intake of lush, green grasses (Merck
Veterinary Manual 2008). There are multiple
types of Clostridium perfringens, however, it
is generally Clostridium perfringens types D
and C that are responsible for enterotoxemia.
PCR on the Clostridium isolate to determine
its type was not performed. Grain overload
is considered a common cause of enterotox-
emia, though other less likely causes such as
E. coli infection in swine have been identified
(Merck Veterinary Manual 2008). The pres-
ence of grain in the rumen indicates that this
moose also had access to grain and supports
the possibility that case B suffered from fatal
enterotoxemia due to grain overload.
The history of case C being observed by
the warden as healthy in a field the day prior to
its euthanasia, its clinical signs of recumbancy
and kicking, and the postmortem findings of
acute rumenitis and hemorrhagic enteritis are
highly indicative of grain overload. Like most
cases of polioencephalomalacia, the pathology
observed in case D was most likely due to a
thiamine deficiency. Thiamine deficiencies
are often secondary to ruminal acidosis, as
one of the microorganisms which prolifer-
ate with grain intake produces thiaminase II,
an enzyme which catalyzes the cleavage of
thiamine (Merch Veterinary Manual 2008).
Other causes for thiamine deficiency include
water deprivation and hypernatremia (Padovan
1980), diets high in sulfate salts (Raisbeck
1982), acute lead poisoning (Merck Veterinary
Manual 2008), and thiaminase toxicity, caused
by the ingestion of certain plants (Evans et
al. 1975). While the exact cause of case D’s
polioencephalomalacia remains unknown, it is
possible that it was due to grain overload.
Based on these 4 cases, it appears that
grain overload may be a contributing mortality
factor of moose in North Dakota. Numerous
scenarios which could result in grain overload
exist. The 4 most likely include the consump-
tion of planted crops such as corn and wheat,
access to bait piles mainly intended for deer,
access to cattle feeding sites, and access to
recreational game feeding sites. Agricultural
crops, especially corn and soybean, are com-
mon in the counties where the moose mortali-
ties occurred, while cattle are less common
than in other areas of the state (Fig. 1).
All 4 of these cases died in mid-fall or
winter during the archery season. Case C was
also found during the deer-gun season and was
an acute case of rumenitis. Its euthanasia oc-
curred in the middle of November when most
crops had been harvested. This suggests that if
grain overload was the cause of the rumenitis,
the grain was most likely accessed at a baiting
site or possibly a recreational feeding site.
According to the NDGF district warden, re-
ports of moose feeding with or harassing cattle
GRAIN OVERLOAD EFFECTS ON MOOSE – BUTLER ET AL. ALCES VOL. 44, 2008
78
in this area are extremely uncommon. Case
A was an extremely chronic case of laminitis,
indicating that if grain overload had occurred,
it was quite some time prior to its euthanasia
in October. When the possible grain overload
occurred in cases B and D is unknown. Po-
lioencephalomalacia and enterotoxemia are
sub-acute results of grain overload. However,
few, if any crops, remained in the field at the
time of their death indicating that bait or feed
was the most likely source. The fact that deer
hunting season was also open supports the
possibility of availability and access to bait.
These findings could have important impli-
cations for baiting and recreational feeding
regulations in North Dakota.
If agricultural crops are contributing to
grain overload and its secondary effects in
moose in North Dakota, its incidence could
be expected to rise given the political and eco-
nomic push for increased biofuel and ethanol
production. The NDGF expects a fair amount
of conservation reserve program land, highly
erodible land taken out of crop production, to
be converted to corn fields and for corn produc-
tion to increase in existing fields as the value
of this commodity continues to rise.
Based on these necropsy findings, grain
overload and its secondary effects should be
monitored in North Dakota’s moose popula-
tion, as well as in other agricultural areas or
regions where baiting and recreational feeding
are common. It is extremely difficult to at-
tribute the mortality of free-ranging wildlife
to grain overload. Therefore, whenever pos-
sible, entire carcasses or appropriate samples,
including fixed and fresh specimens of liver,
rumen, abomasum, omasum, reticulum, small
intestine, large intestine, and brain, and when
possible, whole blood, serum, feces, and rumen
contents, should be submitted to a diagnostic
lab for investigation.
ACKNOWLEDGMENTS
We would like to thank the NDGF wardens
and field staff for their assistance in handling
and transporting moose and other wildlife to
the VDL in Fargo for necropsies. We thank
the VDL for conducting these necropsies. We
thank the editor and two anonymous reviewers
for their comments and suggestions. Finally,
we thank the citizens of North Dakota for
reporting sick and dead wildlife in a timely
manner so that we may learn the causes of
these illnesses and diseases.
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