Zinc oxide buffers organic acids in piglet feeds

Buffering capacity is an important aspect often overlooked when it comes to using "conventional" ingredients, like zinc oxide.

In 2014, the European Union updated regulations concerning feed manufacturing, making the use of normal zinc oxide in piglet feeds a futile exercise. From a personal perspective, I was using normal zinc oxide at 2-3 kg per metric tonne in my piglet feeds, only because one distributor felt it was needed in their market. But, we decided it was time to move on to something different that fits with modern times. We picked a new source of potentiated zinc oxide (basically, highly porous zinc oxide) that could be used at low levels, so as to be within EU regulations, and still elicit a beneficial effect on balancing gut microflora -- but, that’s another story.

During the replacement process, I happened to be editing the article by Giannis Karvelis on dietary buffering capacity; an article that also appears in this issue of Pig International. My eye was caught at the last two lines of the table in that article: zinc oxide and organic acids. My interest piqued because not only I was using zinc oxide at high levels, but I am also a great believer in using organic acids in non-medicated feeds, using up to 10 kg per metric tone, or more in certain cases. But, again, I digress.

I was aghast when I realized that by using normal levels of zinc oxide (2-3 kg/MT), I was virtually wiping out any pH lowering effect from the organic acids I was adding. I would have been happy enough, had I been using organic acids in medicated feeds, so as not to change the final pH of the feed, but these were non-medicated feeds relying on organic acids to control pathogenic bacteria.

Acid binding capacity

About the same time, I received an email about a new online tool offering to calculate the acid binding capacity of any feed using a rather larger database compared to mine. Here’s the website address: http://animine.eu/ABC4-calculator.

So, for my own education, and to test this new tool, I worked out a very simple diet based on normal zinc oxide and the same one with the alternative zinc oxide. I used citric acid as my reference acid (Figure 1). This acid alone, when used at 10 kg/MT) reduces the acid buffering capacity at reference pH 4 (ABC4) by 56-meq/kg feed. By switching sources of zinc oxide, buffering capacity was reduced by 48-meq/kg feed. In other words, normal zinc oxide buffered out a relatively high inclusion level of citric acid. Of course, I knew their individual effects, but this was the first time I combined such information under practical conditions. As my piglet feed products were already below the recommended maximum ABC4, I had never paid attention to the effects of individual ingredients.

Interestingly, the example diet I used for this test (Figure 1) happened to be above the recommended maximum for ABC4 (350-meq/kg), whereas by substituting to a low-inclusion zinc oxide, ABC4 dropped to an acceptable level. This can be a huge help under commercial conditions when ABC4 is difficult to control, especially in diets containing high levels of milk products and fish meal.

Now, it remains to derive some useful observations from this experience for future reference:

• If you use normal zinc oxide and your ABC4 is already marginally high (such as above 650 meq/kg), you must add organic acids to control the strong acid binding capacity of normal zinc oxide -- or switch to an alternative source.

• Low levels of organic acids (1-3 kg/MT) are practically pointless in diets containing normal zinc oxide as their acidity is neutralized, unless they are used for this purpose alone, but this greatly increases the cost of using normal zinc oxide.

• When replacing normal zinc oxide with alternative forms that reduce feed total ABC4, then organic acid inclusion levels can be reduced, offering the potential of considerable feed cost savings.

• In diets with low ABC4 based on alternative forms of zinc oxide, high levels of organic acids will provide a very strong bacteriostatic and bactericidal effect, as predicted by their own characteristics.

Based on these notes, it merits discussing two further observations that raise more questions than they answer:

• First, in the U.S. and other countries where normal zinc oxide is included at 3+ kg/MT, there is now increasing evidence that some piglet diets benefit from organic acid inclusion. Indeed, several nutrition companies and nutritionists advocate the use of organic acids, even in diets with antibiotics. Is this because they also use normal zinc oxide in these diets?

• Second, in the EU and other countries where in-feed antibiotics are banned, previous experience has shown that the use of low levels of organic acids is pointless. Was this because up to now most EU diets contained, under previous legislation, some level of normal zinc oxide? If this holds true, should we expect now to derive a greater benefit from low inclusion rates of organic acids in diets with alternative forms of zinc oxide?

In conclusion, it appears zinc oxide continues to provide new challenges to nutritionists and whether is used in one form or the other, it merits paying attention to its ABC4 effects in diets with or without antibiotics. As for my own feeds, I decided to keep the high levels of organic acids I was using -- you never know when you are going to need them.

FIGURE 1. ONLINE CALCULATOR OF ABC4

http://animine.eu/ABC4-calculator | Replacing normal zinc oxide with an alternative zinc oxide liberated the ABC4 of 10 kg citric acid in a piglet feed.

Ioannis Mavromichalis, Ph.D., is Nutrition Editor for WATTAgNet and Editor-in-Chief of Pig International