Average analysis figures for 2014-harvested forages are still coming back from the laboratory with much better nutritional values than that made in 2013, so much so that we hope the problems of horses “running out of steam” ,and not being able to maintain condition from February to May, as happened to quite a few hunters and other horses last year.
There is one notable exception though to these results, Selenium levels are continuing to drop and not just in the regions of the country where Se levels are known to be insufficient such as the North East of England but in all parts of mainland UK. Now this maybe because we are inclined to take more samples of forage from where we are trying to help with a problem that could well be due to insufficiency of Se or the fact that the forage made on horse establishments as opposed to livestock farms are less likely to receive any recycling of minerals back to the land or even dung spreading, both factors, could distort any average figures going back to the back to the 60/70’s. On the other hand Se levels are known to leach out of the soil due to continual forage growth and by rain and gone are the days when impure fertiliser products are spread such as basic slag to gently recharge Selenium status in the soil.
The discovery in 1957 that Selenium was an essential nutrient was not altogether readily accepted because at the same time there was conflicting evidence that feeding sodium selenite was carcinogenic and because this was accepted by the World Health Authority and others this restricted widespread study and use of Se for many years until further extensive studies failed to produce a single tumour in rats fed Sodium selenite or Sodium selenite. Indeed it was not until 1973 that the metabolic role of selenium was fully discovered and only recently has it been understood to have an independent role in immune responses and in the integrity of the pancreas to thus allow normal fat saponification and digestion and normal lipid bile salt micelle formation.
There is a close working relationship between Vitamin E and Selenium in their functions within tissues. Selenium has the important task of removing active peroxides from the cells before they oxidise the unsaturated lipids which are protected by tocopherols. To a small extent Vitamin E and Selenium are mutually replaceable but there are limits below which substitution is ineffective. Once oxidisation/cell breakdown occurs then it is Vitamin E at increasingly high levels are is needed.
Perhaps one of the conundrums presented to the early nutrition researcher was that although it had been found to be essential for life selenium is after all a ‘heavy metal’ on the one hand able to help the metabolism in minute quantities but at marginally higher levels in the diet it is a poison just as its close relative Arsenic. This fact is an ever present danger, soil levels of selenium at 1.5mg/Kg air dry soil is very high, very low is 0.3mk/Kg. Reaction with ferric oxide further complicates things by binding selenium so that it is unavailable to plants thus in the presence of high levels of Iron an acceptable level of say 0.45mg/Kg may not be necessarily adequate. Sulphur too can have binding effects as can arsenic itself if Selenium is marginal. The other big variable is stress
The fact that, a little can help and not much more can hinder, can make us think it was better when we did not know about Selenium as in the old days but that of course was when it was more uniformly contributed by natural ingredients and not leached out of overused land by rain and flood.
Always let us know if we can help with any queries about dietary Selenium, analysis of forage, standard or bespoke complementary feed formulae to help or any other information.