September 2023 - 43

NATURAL DIETARY CHANGES
All members of the deer family, called
cervids, change diets with the seasons. In
summer, the animals eat mostly high-carbohydrate
leaves and forbs to build and store
fat for winter. As the days shorten and green
foods become scarce, they eat less overall and
transition to low-carb browse - shrubs, twigs,
and tree bark. They also start burning more
body fat for energy.
" This is what they're adapted for, " said
Rebecca Mowry, Montana Fish, Wildlife &
Parks wildlife biologist. " It's natural for them
to lose weight in winter. It's also natural for
some of the weaker animals to die, especially
calves and fawns entering winter in poor
body condition. "
In the long run, weeding out weaker individuals
may strengthen the population while
helping vegetation recover from over-browsing.
" The ones that survive often do very well
because there's suddenly much more food, "
Courtemanch said.
Still, most people find it hard to watch
animals struggle through the lean months. It
seems to make sense that providing food for a
hungry deer, elk or moose can ease its suffering
or save its life, but the opposite can be true.
Jennifer Ramsey, wildlife veterinarian with
Montana Fish, Wildlife & Parks, said feeding
can decrease an animal's chance of survival.
Dead moose found near populated areas in
Jackson often present with poor condition and
unhealthy kidneys, Courtemanch said. Though
it's not always possible to pinpoint why, she
suspects the animals' poor health is linked to
their high-stress existence living near humans
and eating foods they wouldn't normally eat.
" I think people don't know that they have
such a specialized digestive system and diet,
especially in the winter, " she said. " So feeding
something any different from that can really
cause serious problems. "
BAD CARBS
Strangely enough, some of the most devastating
effects from feeding are due to the
animals' gut microbes. Like cows, sheep and
goats, cervids are ruminants. A cervid's digestive
system allows it to extract enough nutrients
from plants to sustain a 1,000-pound moose or
a 200-pound mule deer. But the success of this
process relies on a finely-tuned mix of bacteria,
protozoa and fungi in the largest of their four
stomach chambers, the rumen, where partially
Mule deer have a specialized digestive system and diet, especially in the winter. (Photo by Phil Damm/WGFD)
chewed food is fermented before being regurgitated
and chewed again.
A cervid's gut microbes gradually adapt to
different food sources over the seasons. In late
fall they begin to accommodate the animal's
increasingly sparse winter diet of low-carbohydrate,
high-fiber browse. In early spring, the
balance of microbes slowly changes as other
natural foods become available. But sudden
changes spell trouble. A mismatch of meals to
microbes can lead to digestive diseases, including
rumen acidosis, which is known as grain
overload in cattle.
Ramsey said acidosis is something she considers
in the death of big game animals when
they are otherwise in decent condition and
have access to unnatural food sources. She
explained that a high-carb meal of corn or
other grain, birdseed, apples or rich hay can
set in motion a dangerous cycle - especially if
the animal is not accustomed to that diet. The
carbs trigger an explosion of stomach bacteria
that produce lactic acid, which eventually kills
healthy bacteria and causes inflammation and
ulcers.
" When it's angry and inflamed, the rumen
wall is unable to absorb nutrients, so the animal
can't take advantage of the food, " Ramsey
said. " The animal can actually be starving with
a full stomach. "
The buildup of lactic acid also causes fluid to
accumulate in the rumen. " In a necropsy we'll
Wyoming Wildlife | 41

September 2023

Table of Contents for the Digital Edition of September 2023