Horse_amp_amp_Hound__06_February_2018

The gut’s community of organisms is
already complex within the foal on its
first day of life, after which it starts to
become similar to that of its dam
GUT GLOSSARY
The horse’s gut has its own
language:
O MICROBIOTA
The community of
microorganisms (bacteria,
viruses, single-celled organisms
and fungi, sometimes called
microbes) living in a specific
environment — in this case,
the gastrointestinal tract. An
estimated 1,000 different
bacterial species perform many
of the functions vital for the
survival of the host animal.
a wide range of maternal and
environmental organisms.
These come from ingestion of
colostrum (the mare’s first milk)
and as the foal starts to eat the
mare’s droppings and explore
his surroundings.
These transient organisms
quickly reduce in number as the
true colonisers take hold. From 60
days of age, the foal’s microbiota
remain relatively stable and are
similar to that of his dam.
An established and stable
microbiome brings many benefits.
As hindgut fermenters, horses are
reliant upon microbiotal activity
to break down the fibre in their
diet efficiently. This produces
the short-chain fatty acids that
are crucial to the horse’s daily
energy requirements, along with
essential nutrients.
The microbiome also boosts
immune function — both
locally, through production of
antimicrobial products, which
limit pathogenic (disease-causing)
activity in the gut and neutralise
toxins, and also by guiding the
development and regulation of the
horse’s immune system on a wider
scale throughout his body.
Within adult horses, the
gut microbiome shows great
individual diversity and is more
variable than our own: only
about 65% of the equine bacterial
community is retained over
a six-week period — even when
the horse is fed a consistent diet.
Given the importance of
the microorganisms to fibre
digestion, it is not surprising
that dietary change alters the gut
microbiota rapidly — within
just four days. Stability and
resistance to change are
greater in horses fed plenty of
fibre, compared to those on a
concentrate-supplemented diet.
Starch fed in small quantities
is digested and absorbed in the
small intestine. If more is fed,
the small intestine’s absorptive
capacity can become overloaded.
The starch is then delivered to the
hindgut, where it undergoes rapid
microbial fermentation, leading
to production of lactic acid and
reduction in the hindgut pH (an
increase in acidity).
This alters the microbiome,
increasing the population of
certain bacteria and reducing
those that break down fibre.
This change has been found in
horses fed a high-concentrate
diet and those with colic due to
intestinal impaction.
To limit starch overload,
the concentrate level should be
gradually increased over a threeweek
period to allow sufficient
time for increased production of
a specific starch-digesting enzyme
in the small intestine.
STRESS RESPONSE
THE equine gut microbiome
also responds to stressors such as
fasting, exercise, anaesthesia and
transport, all of which lead
to a reduced population of
a family of bacteria that break
down fibre and could have
anti-inflammatory functions.
Additionally, the use of
antimicrobials to treat bacterial
infection, both orally and by
injection, leads to reduced
diversity of the hindgut
microbiota and population
changes that are specific to
the antimicrobial given. After
finishing treatment, however,
the microbiota gradually return
to their pre-treatment population
over 30 days.
For general health, the best
advice is to maintain a diverse,
stable hindgut microbiota
by keeping your horse on a
forage-based diet with the
minimum amount of
concentrates needed for the
work performed.
There is no evidence of
a beneficial effect of probiotics
to the hindgut microbiome,
because it is unknown which
microorganisms are beneficial
and in what quantity or
formulation. Neither is there
evidence to suggest that they are
harmful, however, so keep feeding
them if you think that they help
your horse.
One day it may be possible to
manipulate the gut microbiome
in a good way. A current example
of this is faecal transplantation,
where droppings from a healthy
horse are given by stomach tube
to one with diarrhoea — in some
cases causing complete resolution.
Keep watching this
space, because an increased
understanding of equine
microbiota in general could
revolutionise vet care. H&H
NEXT
WEEK
Dealing with
diastemata — gaps
between the teeth
O MICROBIOME
Genetic material (DNA and
RNA) from the microbiota
— which is about five million
genes. Recent technological
advances have made it easier
to identify this genetic
material. It’s still a painstaking
task, but much easier than
trying physically to grow,
separate and identify all of
the microorganisms by
traditional methods.
O METAGENOMICS
Scientific techniques used
to identify and study the
complexity of the microbiome.
Many microbiota will not grow
outside the gut, but nextgeneration
sequencing enables
quick and easy identification
of microorganisms with similar
DNA, which can then be
grouped together.
O METABOLOME
Chemical products made
by the microbiota. These
include enzymes that deal
with the otherwise indigestible
components of the diet,
products required for synthesis
of vitamins, as well as proteins
essential for the horse’s
immune function and many
other physiological processes,
such as fermentation. Foragefed
horses may obtain 50%
to 70% of their daily energy
requirements from short-chain
fatty acids, which are produced
by microbial fermentation
within the hindgut.
For general health, keep your horse on a forage-based diet with the
minimum amount of concentrates needed for his workload
8 February 2018 Horse & Hound 21