WHAT DO SCIENTISTS KNOW ABOUT ZINC?
Last September, I attended the first Animine Academy where several well-know scientists reviewed fundamental knowledge on trace minerals in Animal Nutrition. It was highly scientific materials but I believe few points raised by J.Y Dourmad from INRA, FRANCE and Daniel Brugger from Technische Universität München, GERMANY are interesting to take into account for nutritionists.
When we are formulating, it is important to take into account the bioavailability of each trace mineral in order to guarantee sufficient content for cell functioning. During the courses, the scientists explained that plasma Zinc level was regulated by a very sophisticated homeostasis process. After absorption, Zinc is stored in different organs as illustrated below. The highest accumulation is observed in tibia, liver and small intestine cells.
At the same time, a part of the Zinc is excreted through urinary, pancreatic and biliary tract. There is a balance between absorption, storage and excretion to maintain a constant level of Zinc in the blood.
In the presence of phytate, Zinc ions will be captured by the complex. This will have several major consequences in term of nutrition. Firstly the complex will reduce the absorption both the phosphorus and the associated trace minerals and secondly, the trace minerals prevent an effective action of the phytase enzymes that are supposed to release the phosphorus from the complex.
Excess of Zinc for example will bring a deficiency of phosphorus by preventing the action of the phytase enzymes. A trial made in Spain by Dr Lizardo (IRTA) shows that the growth performance of piglets is reduced when pharmacological dosage of zinc oxide (3000ppm) is associated to phytase. To compensate, we either need to reduce the level of Zinc or increase the level of phytase.
Another interesting topic at the conference was related to the digestibility of trace minerals. Because of the homeostasis mechanism, the absorption of Zinc arrived to a plateau when a certain level of plasma concentration is reached. Based on the graphic below, the scientists conclude that the optimal nutritional requirement for Zinc is at 100ppm. Above this level, the digestibility of Zinc will be drastically reduced.
The table below is summarising the total recommended level of Zinc according to the different countries. This amount includes both the Zinc supplied through the raw materials and the additional Zinc added through premix for nutritional purposes or for prevention of diarrheas.
Finally, I noticed as well that the Zinc homeostasis mechanism has its own limit. Above a certain level of supplementation, it cannot cope anymore. The amount rejected through urinary, biliary and pancreatic routes are not sufficient to balance the input. In such cases, the plasma content of Zinc is increasing dangerously and can create toxicity leading to reduced of feed intake, Cu deficiency and even anemia. This can happen when pharmacological dosage of zinc oxide is fed on a too long supplementation period.
If you have any questions regarding the bioavailability of trace minerals and more particularly the Zinc, please do not hesitate to contact me.