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In
association with
Mark Andrews, BVM&S
CertEP MRCVS, of
Equine Science Update
Equine Management and Training
are pleased to provide the latest Equine Veterinary Information
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Are We Poisoning Our Horses
- with Garlic, Bute?
Garlic
Are you poisoning your horse with garlic? Research has shown that
horses will voluntarily consume enough garlic to cause toxic effects.
Garlic is commonly used as a food supplement for horses. It is
credited with antibacterial, antiviral, antiparasitic, antifungal and cancer-fighting
properties; it also has the ability to lower blood cholesterol.
Because it is a natural product, it is often considered safe.
However, that is not necessarily the case as too much garlic damages the reb
blood cell (RBC) membranes. It is known that horses have been poisoned by wild onions, which are closely
related to garlic and there are confirmed reports of garlic poisoning in dogs
and sheep.
Owners routinely add garlic to their
horses' diets as a "preventive measure" against
opportunistic infections and also as is it believed
to be a good insect repellant.
Studies have been carried out in the US by Wendy Pearson, under
the direction of Dr. Michael Lindinger, at
the University of Guelph looking at whether horses would eat enough food containing
[freeze-dried] garlic to cause poisoning, to find out the maximum amount of garlic the horses would voluntarily
consume and to establish whether that maximum amount
would produce any abnormalities over a period of time
such as Heinz body anaemia.
The four horses in the study were fed a balanced diet, designed to
meet their nutritional requirements. In addition, two were given freeze-dried
garlic and molasses mixed with their concentrate food for ten weeks. The other
two horses were given molasses but no garlic. Blood samples were collected
before, during and after the garlic administration to monitor changes in
blood and bodyweight monitored.
When the garlic was originally added to the food at a rate of
0.1g/kg the horses refused to eat it. So the researchers reintroduced the garlic
at a lower rate and gradually increased.the amount fed. Once the horses had
become accustomed to the garlic the researchers found that horses would tolerate
higher levels. The dose was increased to a maximum of 0.25g/kg.
The researchers
concluded that eating too much garlic does produce a specific type of anaemia
associated with the presence of "Heinz bodies" in the red blood cells (RBCs).
Heinz bodies are caused by oxidative damage to the haemoglobin. The denatured
haemoglobin precipitates to form Heinz bodies, which appear as spherical
refractile masses attached to the cell membrane. Damaged cells either break down
in the circulation or are removed in the spleen, leading to anaemia. Heinz
bodies are rare in healthy horses.
The team first noticed toxic effects within four days of
increasing the dose of freeze-dried garlic to 0.2g/kg twice daily. The toxic
effects were reversible. After the garlic administration finished, the anaemia
resolved over a five-week follow-up period. The haemoglobin concentration in the
blood returned to pre-supplementation levels within three weeks, and the red
blood cell count recovered within a month. Heinz bodies were still present five
weeks after the horses had finished receiving garlic.
Dr Lindinger and his colleagues conclude that garlic poisoning may
occur in horses fed even a lose dosage of garlic over a long term period but
point out that more work is
necessary to decide the safe dietary dose of garlic.
Bute
Phenybutazone ( PBZ) is commonly
used for the treatment of
various ills of the horse such as infections, musculoskeletal problems - e.g.
arthritis, navicular, laminitis - as well as injuries. "Bute"
is non-steriodal and anti-inflammatory (NSAID; it reduces
swelling and inflammation as well as relieving pain
and discomfort.
Unfortunately this very
versatile and handy addition to the first aid box can
have adverse effects, which include loss of appetite,
depression/lethargy, weight loss, kidney damage, ulcers in the mouth and gut, colic, diarrhoea
and pitting oedema (fluid swellings), when given to
some horses - just as some people react to a particular
drug whilst others do not. These are more likely to occur if high doses are given, or if
treatment is prolonged. Other factors such as restricted access to water may
combine to increase the risk of toxicity. Chronic colic is the most common
long-term side effect due to colonic ulceration and
scarring. The severity of ulcers to the gastrointestinal
[GI] tract seems to be directly related to the dosage
rate and of course some horses are more prone or sensitive
to this sort of side-effect anyway.
It
is not yet known why some horses are susceptible and
what the trigger(s) might be. However it
is thought that horses most at risk would be foals and
those that are functioning under varying degrees of
stress, such as the performance horse (competition,
travel), older horses, those suffering from low protein
blood levels(hypoprotein anaemia) and those suffering
from kidney/liver problems or are prone to tying up
(rhabdomyolysis).
If a low dose of PBZ has not relieved the lameness it is
often
tempting to give a higher dose in the hope that it might be more effective. But,
as the risk of adverse effects increases with the dosage, it is important to
know that better pain relief justifies the additional risk.
NSAIDS work
by blocking prostaglandins (chemicals which are released
by damaged tissue causing swelling). However there
are also good prostaglandins which do a wonderful job
in health tissues such as regulating blood flow to the
kidneys and the GI tract as well as regulating mucus
production in the stomach. The toxic effect of NSAIDs
- and Bute in particular - occurs when the work
of the good prostaglandins is checked by the NSAID administation.
Reduced blood flow to the kidneys can result in
kidney damage and ulceration can occur in the GI tract
for the same reason. Of course the situation is
made much worse if the horse is dehydrated for any reason
because the concentation of Bute in the blood will be
all the higher.
The incidence of Bute toxicity
is not known but could well be more common than realised.
and of course there is also the risk of subclinical
symptoms which as yet have not been officially identified.
Bute mainly remains in the blood stream - making
it more toxic than of other NSAIDs - as it does not
cross membranes well. However any side effects
can show up very early in the course of treatment -
as soon as a couple of days in some cases - or may not
show up until several weeks later when of course they
are then not usually connected to Bute.
Studies
have found that Bute concentations are highest in the
kidneys, liver, heart and lungs whilst remaining low
in joint fluids and plasma. Bute is converted
by the liver to oxypehnbutazone which has the same action
as Bute but is removed from the body at a much lower
rate therefore it remains in a horse'ssystem for more
that 24 hours. It is known that an extremely low
proportion of the original Bute dose is excreted (via
urine) so it is up to the liver to eliminate the
remainder, in whatever form. However the liver can soon
struggle when dealing with higher Bute doses so that
is why owners should not "up the dose" at
their own free will.
A recent report looked at whether a higher dose of PBZ was more
effective than the standard dose. Researchers at the Oklahoma State University
used nine horses with long-term lameness for the study. All had been diagnosed
with navicular syndrome. Some had other problems as well. The severity of
lameness had not changed over a ten-day period before the study commenced.
The horses were treated with PBZ, by intravenous injection, at
either the standard (4.4mg/kg) or high (8.8mg/kg) dose rate for four days.
Saline was used as a control. Dr. Charles G MacAllister, one of the research team, assessed the
lameness 6, 12 and 24 hours after the last treatment. He was unaware which
treatment each horse had received to avoid bias in his assessment. All horses
eventually received all three treatments.
The degree of lameness was assessed in two ways. Firstly a
clinical assessment was made using a five-point lameness scale. Secondly, the
force with which the lame (or lamer) leg struck a force plate embedded in the
ground was measured. The mean peak vertical force (mPVF) was recorded. An
increase in the mPVF indicated an improvement in the lameness. The researchers found that PBZ (at either dose rate) improved the
lameness as assessed by both clinical lameness score and mPVF and the effect could
be measured for at least 24 hours but the higher dose of PBZ did not produce a
significantly better response than the standard dose.
The results indicate
that that there is no benefit giving more than
4.4mg/kg to horses (which is a common dosage rate) with chronic lameness such as navicular syndrome. Further
work is now needed to establish the lowest effective dose of
phenylbutazone (as more and more vets - in the US - reckon on a 2.2mg/kg to
be perfectly adequate, and possibly even less, and to find out how long its effects last after single or
multiple daily doses.
So what to do if your horse shows
any adverse signs whilst on Bute?
Obviously
stop the treatment immediately and consult your vet.
In the first instance a blood test should be carried
out to establish possible toxicity. Depending on the
results, then fluids will be administered to flush the
system and treatment for GI ulceratione effected, which
is usually omeprazole (Gastroguard). In fact -
yes, in the US again - Gastroguard is routinely given
in a low dose alongside Bute treatments as a preventative
measure. In more drastic situations, surgery is
sometimes required to remove damage stomach.colon tissue.
Obviously the diet has to be closely monitored
to avoid further complications.
Precautions
for horses on Bute
As with the administration
of any drug, horses should be closely monitored, their
attitude, behaviour, appetite, appearance, etc. all
being carefully noted so that any changes can be acted
on sooner rather than later. Dose rates should
be at the lowest to be effective with the longest possible
dosing interval, ensure (as should be the case anyway)
that your horse has access to plenty of fresh water
and diets should be easily digestible.
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