High-dose zinc oxide can promote piglet growth and reduce diarrhea rate, which is commonly used in weaned piglets. Because of the many drawbacks of zinc oxide itself, the use of high doses of zinc oxide to prevent piglet diarrhea often has negative effects. On the one hand, affecting the absorption of other trace elements, resulting in unbalanced absorption of copper and iron, lowering the potency of other nutrients, and poor growth performance; on the other hand, weaning pigs often have pale skin, rough hair curls, anemia, etc. Phenomenon, affecting the appearance of fur.
First, the latest research report on the role of high zinc
A recent study of 26 studies evaluated the effects of pharmacological levels of zinc oxide (ZnO) on growth performance in piglets. The results indicate that the addition of zinc has a significant positive effect on growth, feed intake and feed efficiency, as shown in Figure 1.
The results showed that the addition of zinc oxide had a significant (P<0.05) positive effect on growth, feed intake and feed efficiency, with an optimum level of 3000 ppm zinc. However, this dose of zinc oxide may have some negative effects on piglet health.
Second, the five negative effects of zinc oxide on piglets
Heavy metal pollution
The problem of zinc oxide is serious because it is derived from chemical by-products and many harmful substances remain. The quality of the product is difficult to control, especially heavy metal cadmium. A study from the French Institute of International Information Processing Consortium (IFIP) showed that when pigs fed 42-160 days of contaminated feed (0.5 mg cadmium/kg feed), the cadmium concentration in human kidneys exceeded the legal baseline ( 1 mg / kg). In this study, the level of zinc added was the normal standard (nutrition).
When a pharmacological dose of zinc oxide is added, the level of cadmium in the diet will become higher. Some analyses have shown that the cadmium content per kg of feed is as high as 2.5 mg. Although this contaminated zinc is fed in a short period of time, it is well known that cadmium is an organ toxin with a long half-life. Therefore, if the tissue is contaminated after weaning, the cadmium in the animal product is slaughtered. The level will still be higher.
In Thailand and China, the addition of pharmacological doses of zinc is permitted, while the EU prohibits them. A recent study of 214 pork kidneys in Thailand showed that more than 25% of pork kidney cadmium concentrations were higher than regulatory values. Analysis shows that contaminated zinc oxide is the main source of cadmium in the diet, although there is no relevant report in China, but this risk may exist.
2. Affect other nutritional effects
High zinc will promote the production of more metallothionein. In this way, intestinal transport preferentially binds to copper and may cause sub-deficiencies in this trace substance. Due to the high margin of safety margin, the bioavailability of iron does not appear to be significantly affected by high levels of zinc.
Pharmacological doses of zinc have a negative impact on phytase activity.
Studies on the interaction between zinc and phytase have shown that the pharmacological dose of zinc has a negative effect on phytase activity, which in turn affects the release of phytate phosphate. This means that phytase function is reduced and may cause phosphorus deficiency in animals.
The acid binding capacity of zinc oxide is the largest in the feed. At pH 4, the acid binding capacity is about 16,000 milliequivalents, the limestone powder is 13,000 milliequivalents, and the sodium bicarbonate is 12,000 milliequivalents, see Figure 2. Therefore, high doses of zinc oxide can antagonize feed acidifiers such as organic acids.
3. Zinc toxicity
The pharmacological use of zinc oxide will benefit weaned piglets, but according to the National Research Council (NRC), it may affect the health of piglets if used for long periods of time. It is known in the industry that long-term addition of high-dose zinc oxide has a negative effect on the appearance of the fur, but the precise mechanism is still unclear.
4. Environmental impact
When the zinc concentration in the feed does not exceed 150 ppm, the zinc enrichment of the soil from the feces does not exceed 3000 μg/kg DM/year. In Europe, 3 kg of zinc oxide is added to the feed for the first 2 weeks after weaning, and the zinc excreted during the pig growth cycle will reach nearly 30%.
The process of pig manure also highlights this problem because zinc is concentrated in the solid part and the zinc content in the by-products will exceed the highest level of zinc in the organic fertilizers specified by the EU.
5. Zinc and microbial resistance
Excessive use of zinc in animal diets may be beneficial for the development of bacterial resistance. The mechanism is thought to be that the bacteria use an efflux pump system to regulate the concentration of zinc in the cells. These pumps are not only specific to zinc, they may also excrete other molecules such as antibiotics. With a pharmacological dose of zinc oxide, the high concentration of zinc produced tends to increase the synthesis of the efflux pump and may reduce the sensitivity of the bacteria to antibiotics.
Dr. Jürgen Zentek of the Free University of Berlin in Germany believes that high zinc not only pollutes the environment, but also has a negative impact on piglets. He added that “zinc has a significant effect on bacteria, and high doses of zinc have a significant positive effect on multi-drug resistant E. coli. In addition, higher doses of zinc can significantly increase the genetic diversity of E. coli. Effects, other bacteria such as lactobacilli appear to be sensitive, and the number of flora decreases.
Zentek pointed out the “Janus” face of zinc (two-sided): “Zinc excess produces toxicity, undesired antibacterial effects, too little but does not exert trace elements to promote growth.”