VET CLINIC
In association with
Mark Andrews, BVM&S CertEP MRCVS, of
Equine Science Update
we 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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