In fact you're probably lucky if you get the same reply of any two people out of 50. Usually a selenium question is posed in relation to a performance problem where muscle fatigue may be an underlying issue and selenium or lack thereof can be a contributing factor.
Riders' responses to how much selenium may be involved in the diet can vary hugely from a detailed and accurate reckoning to a complete lack of knowledge as to the benefits of selenium in the equine athletes' diet. One of the pieces of information that most people seem to have come to grips with though is the fact that in large doses it can be quite toxic!
So what is generally known about selenium?
Most people recognize that in the liquid form (usually identified as the pink stuff in the blue bottle!) as brought from the vet it is a PAR1 which stands for prescription animal remedy.
This means that it can only be prescribed to your horse by a vet. Your vet may ask to see your horse/pony or may just choose to have a consultation with you in the clinic when you first begin to purchase so that you can be informed of the potential dangers of over-supplementation and advised as to the correct handling and usage.
Please don't get upset at the vet if you shift practices and although you have been using selenium for years your new vet expects to go through the consultation process again. Don't forget the new vet doesn't know you or your horse and she/he are required by law to make sure you know about selenium before it is dispensed!
So what is selenium?
Selenium is a mineral that is absorbed by forages and grains and in its natural form presents as the selenoamino acids selenocystine, selenocysteine and more commonly selenomethionine. Unfortunately for large chunks of New Zealand our soils tend to be extremely deficient, this is especially true in alluvial based areas such as Canterbury and therefore so are the feeds we harvest to give to our horses. The most commonly supplemented forms of selenium are the inorganic (i.e. cannot be fully metabolized or stored in the body) sodium selenite and sodium selenate.
Toxicity is the issue of most concern to people and selenium in its inorganic form can be extremely toxic if overdosed, there are two forms of toxicity that may appear.
Acute or sudden onset selenium toxicity which can be seen as blind staggers which is characterized by apparent blindness, head pressing, sweating, abdominal pain, colic, diarrhoea, increased heart and respiration rates and lethargy (Rosenfeld and Beath 1964).
Or chronic selenium toxicity-alkali disease (consistent long-term overdosing), which is characterized by alopecia especially about the mane and tail as well as cracking of the hooves around the coronary band (Rosenfeld and Beath 1964, Traub-Dargatz and Hamar 1986).
It tends to be hard to pin anybody down as to what is a safe amount to give which is why your veterinarian likes to talk to you. Everybody's feeding regime is different and can contain differing amounts of selenium. If you dress selenium on to the paddock your circumstances are changed again and you may not need additional supplementation. The recommended guideline is 1mg per day for the average 500kg horse but in deficient Canterbury that tends to be a little on the low side and most vets will recommend at least 10mls of sodium selenite per week (based on 1mg/ml of the PAR1 selenium available from them). Don't forget if you are feeding a commercial feed with a selenium additive in it you may need to adjust the amount you administer orally.
Most owners tend to give this oral dose in a one off amount on a given day of the week. It should be remembered though that sodium selenite doesn't metabolize well so the horses' body will only be able to use what it needs at the time of administration and then excrete the rest in urine and manure.
By far the easiest way to supplement selenium is in a good quality mineral, vitamin supplement that utilizes the natural forms of selenium selenomethionine and other seleno-amino acids.
Products such as Nutritech's Selamin Gold and Muscle Relief contain Sel-Plex© selenium yeast from Alltech. It is produced when yeast is grown in a selenium enriched medium and like all plants a high proportion of the selenoamino acid produced is selenomethionine and available to your horse. Sel-Plex is the only organic selenium supplement registered with the FDA in the States for use in horse supplements and is backed by large amounts of research conducted with horses. Nutritech's supplements are formulated to deliver a balanced nutrient intake based on New Zealand conditions and to take the guesswork out of safely feeding selenium.
The benefits of using selenium far out-weigh the risks especially in an organic form. The research from Alltech on Sel-Plex yeast selenium clearly indicates better absorption and retention of organic selenium by exercising horses, (Feedstuffs - Nov 2004).
Selenium is a key nutrient to combat oxidative stress which can only be all good for those of us with horses that tie up regularly. For those that have breeding mares in the paddock it showed that mares fed Sel-Plex Se such as found in Selamin Gold have foals with stronger immune systems due to higher antibody titres in the hours post foaling giving them every chance to develop into strong healthy youngsters. One of the anecdotal things noticed was that mares fed selenium yeast also expelled the placenta a lot faster than mares fed selenite selenium.
Selenium research doesn't just stop at animals either it has been shown that countries with low incidences of cancers particularly breast and prostate cancers have much higher levels of dietary selenium than are currently found in this country. Low selenium status has also been associated with significantly greater incidence of depression and negative mood states. So the next time you're thinking about selenium for your horse maybe you should think about supplementing a little selenomethionine into your own diet.