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Issues with Zinc Oxide

Dr Ioannis Mavromichalis
It is hardly necessary to reiterate the benefits of using zinc oxide in piglet diets: not only diarrhoea is contained, but also, growth performance is enhanced, and this is possible at a very reasonable cost, with a high degree of repeatability. Thus, zinc oxide (at high doses reaching up to 3000 ppm Zn) is a common ingredient in many piglet diets worldwide, or at least in those countries where it is (still) allowed. But, like many other things, zinc oxide does not come free of problems.

Here, we must note that zinc (from any source) causes toxicity when fed at levels exceeding 1000 ppm Zn for long periods of time (reaching into months depending on animal age and weight); this is an established fact. The fact zinc oxide in piglet diets is not 'so toxic' is because it is used only during the first few weeks post-weaning, when feed intake is almost invariably very low. Thus, toxicity is largely avoided in most cases.
But, there are many incidents in practice where producers have actually complained of depressed appetite (and growth) when high levels of zinc oxide are fed for prolonged periods of time. This has been the case when the high dosage of 3000 ppm Zn is kept up to four weeks (or longer) post-weaning. Or, as in some other minor cases, even when lower doses of Zn were employed, an early high feed intake of diets supplemented with
zinc oxide has caused toxicity resulting in a decline of feed intake in the later nursery period. And, finally, we have the interactions between zinc and phytase. Indeed, high levels of zinc reduce phytase efficacy, but also phytase enhances zinc solubility and absorption. Thus, it is possible zinc toxicity can be a problem in diets supplemented with high levels of zinc oxide and phytase (and fed for a long period of time).
What to do? The answer is quite simple. Go back to the original research and study how zinc oxide was used in those trials to find the best way to use it under most practical conditions. Indeed, such an exercise reveals that zinc oxide needs to be fed at 3000 ppm Zn only in the first week post-weaning, followed by 2000 ppm Zn in the next couple weeks, and then only at 1000 ppm Zn for the remaining nursery period. Of course, local regulations should be followed in case these contradict with the above dosages or timing.
Another route could be the use of copper sulfate in the later nursery period (where still allowed at high dosages), and the alternatives to zinc oxide, such as organic acids and essential oils, to name only but two. But, a word of caution is required here. When it comes to alternatives, not all such ingredients are equally effective as zinc oxide. Only through experience a specific blend of acids and essential oils can be identified and employed in each farm. At least, this has been my own experience!


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    Kurt Handlos

    Ioannis is the best nutritionist I have ever met!

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    Dr Nikolaos Kotrotsios

    We should differentiate Zinc, in the form of ZnO, has been largely used as a promoter of growth among piglets. This leads to a zinc excess over the nutritional requirement and increases the zinc output through the manure. Inorganic zinc sources like ZnO has a common use in pig nutrition in order to control diarrhoea after weaning. While the nutritional requirement for piglets is 100 ppm, the widely use of the levels between 2000 and 3000 ppm, increases the excretion of zinc through the manure. The control mechanism of diarrhoea by which zinc works is not clear, but differences in zinc solubility from organic and inorganic sources and their effects on intestinal bacteria may be involved. The absorption of zinc is affected by the level of calcium in the diet. High levels of calcium include in the diets cause zinc to be bound in a complex that renders both zinc and phosphorus unavailable to the pig. Extremely high levels of zinc can lead to a copper deficiency, which is characterized by anaemia. Because of metabolic interactions, zinc sources with relatively low bioavailability (zinc oxide) might be superior to sources with high availability (zinc sulphate) when including zinc at high levels for nonnutritional purposes. ZnO promoted better performance than other treatments. The linear effect of different zinc doses suggests that higher levels of organic zinc may improve pig performance. Nutritional programmes for weanling pigs are still largely based on the inclusion of antimicrobial compounds such as antibiotics and ZnO, even in countries where these compounds are still permitted for use. However, there is a need to search for other products to enable pigs to handle the post-weaning period.

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