The physiological properties of copper and zinc are well known and appreciated to the point of being called essential trace elements in animal nutrition. Insufficient supply of these elements can lead to negative effects on physiological processes and as a result to (major) animal health problems, not to mention reduced productive performance.
In addition, certain salts of zinc (zinc oxide) and copper (copper sulphate) supplied at very high dosages (beyond normal requirements for health and production purposes) are known for their positive effects on further improving animal health and performance.
For example, zinc (from zinc oxide) supplied at levels of 2000-3000 ppm is effectively reducing diarrhea in young pigs after weaning, enhancing thus their health status and increasing their weight gain; nevertheless, it should be noted here that this effect is limited to the first two weeks post-weaning. Similar results are obtained with levels of copper (from copper sulfate) reaching up to 250 ppm (where still allowed!).
One of the most important problems when dosing these trace elements at high levels is excretion. Due to the limited use of the surplus trace elements by the animal, the greater part of the ingested minerals is excreted in the environment via manure. The level of excretion depends on the source of zinc and copper, diet composition, and on several animal related parameters.
However, it is generally assumed that excretion of ingested zinc and copper is around 80-90 percent. This is considered problematic because it might lead to excessive accumulation of these trace elements in the environment, in soil and (drinking) water, where the manure is applied.
The question how to solve the problem of excretion is not easy to answer because these specific mineral salts allow pig producers to combat piglet diarrhea around weaning; a very important and persistent problem that becomes even worse where in-feed antibiotics are already banned. However there are some ideas to resolve the problem of excretion:
1. Organic sources of minerals. Zinc and copper from organic sources are generally more stable and have a higher efficiency in reaching target organs. The bioavailability of organic sources has been found to be much higher compared to inorganic forms of both zinc and copper. However the data regarding replacing pharmacological dosages of zinc oxide and copper sulfate with organic equivalent forms remains inconsistent and largely variable.
2. Enhanced surface. The effective surface of minerals, with which they can contact microbes to exert their bacteriostatic and bacteriocidic effects, can be enhanced by using several methods; for example absorption by clay minerals. A disadvantage of this method is that these products often vary in quality and stability. Another method is micronization of normal zinc oxide, for example, that results in a very fine powder with enhanced effective surface area. Still, this technology is in its infancy, although recent research reports continue to support this idea.
3. Encapsulation. Minerals can be covered with certain types of fats, reducing thus their actions in the stomach, so that they can be released in the enteric digesta to exert their effects. It is claimed that lower dosages of encapsulated products will give good results, due to more effective delivery, but again results remain unclear and product-specific at best.
All of these methods offer benefits in terms of stability and bioavailability of the product. However, when it comes to reducing piglet diarrhea post-weaning, there is still considerable work that needs to be done before a clear solution offers unequivocal results that satisfy the environmental issues and promote piglet health.