How Do I Replace Zinc Oxide on My Farm?

Weaning time is a stressful time for piglets. It is a perfect storm of a naïve immune system, a still-developing intestinal tract, and multiple stressors-including feed changes, maternal separation, regrouping, and transportation-that all affect the health and vitality of the piglets. A common outcome is a post-weaning diarrhea, which leads to reduced performance and often mortality—not to mention the economic impact.  

What is happening during weaning? 

In the conventional pig industry, weaning typically occurs at 3-4 weeks of age. Several aspects contribute to this stressful period for piglets. They experience dramatic physiological, environmental, and social changes during the weaning transition. These changes can lead to diarrhea, which increases morbidity and mortality in young piglets. Although diarrhea can be caused by pathogenic microorganisms, it is often multifactorial, including feed components and microbial composition. 

During weaning, nutrient intake is significantly reduced in the first few days after moving from the farrowing pen to the weaning pen and changing the diet from milk to carbohydrates. The reduction in feed intake leads to intestinal atrophy and periods of reduced growth and malnutrition. These events can lead to health problems and poor growth performance, increasing the likelihood of post-weaning diarrhea because of microbiome disruption. 

In addition, piglets are sensitive to changes in diet composition. Protein, amino acids, and fiber have been found to be directly related to the occurrence of diarrhea in piglets. Reducing the amount of protein intake can reduce the incidence of post-weaning diarrhea, although this may reduce piglet performance. Thus, switching from a milk diet to a carbohydrate diet at weaning can make piglets more susceptible to microbial upset—the second most common cause of diarrhea. 

Piglets are born without microbiota. The colonization of the intestinal tract of piglets occurs immediately after birth and changes dynamically during the suckling and weaning phases. In fact, the diversity of microbial communities increases during the weaning period, but it also depends on various internal and external factors such as environment, feed composition, and stress. In addition, interactions among microorganisms can affect microbiome functions and increase susceptibility to certain diseases, including post-weaning diarrhea. 

What is zinc oxide? 

Before we can learn about zinc oxide, we must first explore the importance of zinc in a pig’s diet. Zinc is an essential trace mineral required for protein synthesis and proper physiological functions of the body, weight gain, and reproduction. Zinc is required for healthy skin and claws and has several antioxidant effects. In addition, adequate zinc levels reduce the pig’s susceptibility to bacterial infections and maintain intestinal integrity. Despite its necessity, however, zinc can be toxic at excessive levels. Therefore, zinc absorption and distribution are highly controlled by the body.  

Dietary zinc is mostly absorbed in the small intestine, and the bioavailability of zinc depends on the composition of the feed. Indigestible plant components can bind zinc and inhibit its absorption. Other factors affecting zinc absorption include calcium and iron. Typically, the zinc content in the feed is insufficient. Therefore, inorganic zinc is commonly added to feed, often as zinc oxide. Pure zinc oxide is an insoluble, white powder and is used as an additive in many products. Compared to other inorganic zinc sources, zinc oxide has low reactivity and bioavailability. 

Piglets can develop signs of zinc deficiency (typically feed refusal) after approximately 10 days of low zinc intake. Consequently, dietary recommendations for zinc range from 80-150 mg/kg of feed. Excess inorganic zinc added to the diet still meets the requirements for the growth performance of the animals. In practice, pharmacological doses of zinc oxide have been used to meet dietary requirements and as an effective antibiotic replacement to prevent diarrhea in weaned piglets. In fact, pharmacological doses of zinc oxide (1,500-3,000 ppm) have been used for decades to maintain intestinal function and overall fitness in piglets.   

How does zinc oxide work?

Zinc oxide exerts a variety of beneficial effects on the gastrointestinal tract by affecting intestinal architecture, digestive secretions, antioxidant systems, and immune cells. Despite the numerous studies that have been conducted to explain the antimicrobial effect of zinc oxide, the precise mechanism of action against post-weaning diarrhea has not been fully elucidated. However, several mechanisms have been proposed. 

Since zinc oxide is not fully absorbed, the main mechanism of action appears to be related to an improvement in nutrient absorption and intestinal structure. In fact, studies have confirmed that supplementation with high doses of zinc oxide improves intestinal performance by promoting an increased villus to crypt ratio and an overall positive effect on intestinal cells. 

The beneficial effects of zinc oxide may also be related to its use as a cofactor for several intestinal antioxidants. Conversely, zinc oxide causes oxidative stress in microbial cells. In the aqueous environment of the intestinal tract, high doses of zinc oxide generate reactive oxygen species that damage bacterial cell walls. This mechanism of action may partially explain the antimicrobial activity of zinc oxide at pharmacological levels used in piglet diets. However, the effect of zinc oxide against E. coli, the major cause of postweaning diarrhea, appears to be moderate.  

High doses of zinc oxide appear to have an immunomodulatory effect. It has been shown to decrease pro-inflammatory cytokines and increase anti-inflammatory cytokine expression. Not only is zinc oxide capable of modulating cytokine expression, but zinc is an essential trace element with a key effect on the entire immune system—both for its development and proper function. In addition, researchers have shown that pharmacological supplementation with zinc oxide promotes the release of growth factors that increase muscle growth and feed intake. In addition, high dietary levels of zinc oxide appear to increase the activity of several digestive enzymes in weaned pigs, resulting in improved nutrient digestibility. Overall, multiple effects appear to contribute to the improved performance of zinc oxide in weaned piglets. 

What is the issue with zinc oxide?  

The main issue with pharmacological doses of zinc oxide is related to its environmental risks. Substantial amounts of zinc oxide are excreted in the feces of piglets as they excrete excess zinc above physiological requirements. However, because of the non-degradable properties of zinc, long-term continuous application of manure to crops can gradually increase the level of zinc in soil and groundwater—eventually reaching dangerous levels for plant and animal life. In addition, studies have shown that high-dose zinc oxide supplementation may also contribute to the acquisition and spread of antibiotic resistance in bacteria. 

The environmental impact of zinc oxide has raised questions about the sustainability of its widespread use. As of June 26, 2022, pharmacological doses of zinc oxide have been banned in Europe. Although there are no laws or restrictions in place in other countries, there is always interest in alternative strategies to manage post-weaning diarrhea. It should be noted, however, that physiological levels of zinc oxide (150 ppm of total zinc in complete feed) are still permitted, although this dose is unlikely to have the same effect as pharmacological levels of zinc oxide. Therefore, non-traditional approaches to post-weaning diarrhea are needed. 

What are my alternatives to zinc oxide? 

Many non-feed strategies have been investigated to control post-weaning diarrhea, including improving hygiene and breeding animals more resistant to E. coli. However, post-weaning diarrhea without E. coli detection is common, and it has been suggested that an imbalance in the gut microbiota may contribute to the development of post-weaning diarrhea.   

The swine gut microbiota has numerous roles that benefit the host, including maintaining the normal gut function, regulating immune responses, and protecting against pathogenic bacteria. Increasingly, alteration of the piglet gut microbiota is recognized as one of the key factors contributing to postweaning diarrhea among all the factors affected by the weaning transition.  

 A variety of dietary methods have also been used to fill the void left by the zinc oxide ban. Researchers have studied adjusting diet composition and adding organic acids, essential oils, and polyphenol-rich extracts with varying degrees of success. However, the concept of synbiotics—the combination of probiotic and prebiotic strains—has shown sustained and positive results.  

Synbiotics are just one part of Biochem’s comprehensive approach to supporting gut health in weaned pigs. To promote animal health and reduce the use of antimicrobials, we have focused on our gut health support feed additives such as pro- and prebiotics, organic acids, betaine, and toxin binders. These can be as either feed solutions—for long-term use—or on-farm solutions, formulated as ready-to-use products for short-term use. We have solutions for those who cannot use zinc oxide or are looking to reduce their reliance on it. Contact us to find out how we can be stronger together.