Lamb
stress measured through bleats
by Eric Hanson on 10/28/03
Lambs aren't sheepish when they are
stressed out, according to a study of
their vocal patterns. Mark Feinstein,
a professor of cognitive science at
Hampshire College, spent a year with
about 100 sheep in Ireland studying
their vocal patters when they were isolated
and after they were weaned -- stressful
situations that can affect the quality
of their meat and reproduction. Feinstein
found that the more stressed the sheep,
the more their vocal timbre changed,
unlike cattle, which get noisier when
undergoing stress. Feinstein used a
digital tape recorder and computer analysis
to discover how the quality of a lamb's
bleat indicates their stress levels.
"There's a small and subtle, but
reliable and predictable change in their
calls when they're stressed," he
said. "A farmer could probably
train himself to hear the differences,
but it's not easy to do by ear."
When a sheep is stressed, the energy
levels in some of their lower vocal
frequencies get stronger, altering the
timbre, Feinstein said. He is not sure
if the animals can communicate their
stress to each other the way an ewe
can vocally communicate with her lamb.
"That still remains an open question,"
he said. "But it's reasonable to
assume they can hear differences in
stress levels, because they can already
identify each other through the sounds
they make." Feinstein said his
research, supported by research and
advisory agency Teagasc, could lead
to the production of handheld devices
that farmers could use to monitor the
stress level of their flock. Still,
some farmers weren't impressed, according
to the Associated Press. "When
I separate the lambs from the ewes,
they bitch for two days," said
Bob Borawski, who has a 100-sheep farm.
"They want their mother. Of course
they're under stress. You don't need
to know that they're voice is somehow
changing to know they're under stress."
