Horse_amp_amp_Hound__06_February_2018

VET CLINIC
An army inside
Your horse’s intestines are teeming with millions of friendly bacteria that could
provide the key to his overall health. Richard Hepburn MRCVS explains
IN both human and veterinary
medicine there is a growing
understanding of the importance
of gut microorganisms to overall
health, and their role in various
disease states.
This is an emerging science
that is complex and rapidly
evolving. In man, there is an
increasing appreciation of the link
between the gut microbiome (see
glossary, opposite) and immunity
and metabolic function. This is
in addition to the alterations to
this microbiome that are linked
to intestinal disease such as
irritable bowel syndrome, as well
as obesity and metabolic disorders
including type 2 diabetes. In
the horse, similar changes
are being identified, although
equine intestinal physiology is
fundamentally more complex.
The horse’s stomach and small
intestine lead to the hindgut,
which comprises the caecum,
ventral colon, dorsal colon, small
colon and rectum. Within the
hindgut there are differences in
the microbiota — the community
of microorganisms — between
these regions, with the main
change occurring at the junction
of the ventral and dorsal colon,
known as the pelvic flexure.
The microbiota from the dorsal
colon through to the rectum
are very similar to those found
in fresh droppings. Given the
importance of the dorsal colon
to fermentation of dietary fibre,
this allows researchers to study
the impact of changes in faecal
microbiota. If this relationship
did not exist, more invasive
techniques would be required to
sample intestinal contents.
The gut of the horse has two
sets of genetic material. The
genes inside the cells that make
up the gut wall are inherited from
the horse’s sire and dam, and
remain almost stable throughout
his life. In addition, there’s the
microbiome, acquired from the
horse’s environment and dynamic
in its population.
The bacterial component of
this microbiome is predominantly
made up of “super families”
of bacteria. These minuscule
organisms are able to exist within
the inhospitable gut environment
due to the activity of their “core
community” — a “housekeeping”
microbial population that creates
the environment and functions
necessary for microbial life and
the stability of the microbiome.
The equine core community
is smaller than that of humans,
and is smallest if the horse is on
a starch-rich diet. This less stable
gut environment can increase the
potential for adverse microbiotal
change and disease.
WHY MICROBES MATTER
LIKE a human, a horse is not
born with a functioning gut
microbiome. The uterus in which
he has developed is largely sterile,
so he must acquire this genetic
material from his environment.
The gut microbiota are already
complex within the foal on its first
day of life — although individual
microorganisms are relatively
low in number. Marked change
then occurs between two and 30
days of age as the foal encounters
‘An increased understanding of the equine
microbiota could revolutionise veterinary care’
RICHARD HEPBURN MRCVS
Pictures by Alamy Stock Photo and Steve Bardens
20 Horse & Hound 8 February 2018