Originally Posted by loosie
That's not correct Verona. Some nutrients, such as water soluble ones, that could be said about, but copper & zinc for eg are both mins that are cumulative & per day means per day, not per feed/amount.
It's more... simplified... than incorrect. The National Research Council publishes guidelines on horse nutrition (their most recent report was published in 2007) and is the standard that most feed companies follow when formulating their feeds. Their 2007 study changed the way they recommended minerals like copper and zinc from a concentration in feed (mg per kg, or ppm) to based on the horse's body weight (0.25 milligrams of copper per kilogram of body weight, for example)
Articles are still easy to find that give numbers like the one the OP probably read (I found 250 mg/kg and 500 mg/kg here
, for example). 250 mg and 500 mg are above the RDI for these minerals, but are nowhere near the cumulative toxic levels for these minerals; this is the result of the "/kg" tag getting lost somewhere along the way by the authors of these websites, who are using the older "by feed concentration" recommendations rather than the newer "by body weight" ones.
.com/Nutrient-Requirements-Horses-Revised-Nutrition/dp/030910212X is, unfortunately, not free, but they do have a handy tool online that is a good starting point for analyzing nutritional needs http://nrc88.nas.edu/nrh/