Maintaining growth without zinc oxide

Zinc is one of the most important nutrients for animal growth and health. It is the key component for numerous proteins, crucial enzymes and transcription factors. Throughout the world, pharmacological levels of zinc oxide are used in weaning pig diets to promote growth and improve feed efficiency, as well as help to cope with post-weaning challenges like post-weaning diarrhoea, bowel oedema disease and reduced feed intake.

Unfortunately, zinc oxide has an antagonistic effect in that it is easily dissociated in the stomach and can bind to other compounds of the diet resulting, for instance, in the formation of zinc-phytate complexes. The formed complex can hinder phytase efficacy, resulting in less phosphorus being released from the phytate molecule.

Beyond this waste of nutrients, in some parts of the world environmental concerns have resulted in an increase in regulations surrounding the use of minerals in animal feed. In 2016, the European Medicines Agency ruled that the environmental risks of zinc oxide outweigh the benefits to livestock. Studies found significant increases of zinc in fields fertilised with swine manure, which raised concerns about run-off risks to aquaculture as well as zinc levels of food farmed in that soil. As a result, in 2017 the European Commission confirmed a ban on pharmacological dosages of zinc from zinc oxide, giving member states until 2022 to phase out all use. In China, producers have been limited to 1600 ppm zinc for the first two weeks post-weaning since July 2018.

Producers seeking zinc replacement

According to reports, an estimated 70-90% of piglet starter diets in the EU contain pharmaceutical levels of zinc oxide. Understandably, producers throughout Europe oppose the ban. Their concerns are that without zinc oxide there will be more incidents of post-weaning diarrhoea in piglets and that the industry may resort to using more antibiotics to maintain piglet health thereby increasing the potential that animals will build up a resistance to medications. Coupled with an increasing consumer demand for low antibiotic or antibiotic-free meat, this regulation poses serious challenges to those in swine production.

For these reasons researchers at Novus International, Inc. investigated if lower levels of organic trace minerals provided as Mintrex Zn (Zn-MHAC), thanks to superior bioavailability, do not produce the same environmental impact as its inorganic counterpart zinc oxide, thus, can serve as an appropriate surrogate for zinc oxide.

A recent research trial examined this substitution in 288 weaning barrows over a 42-day period and found that piglets fed 100 mg of zinc per kg of feed (ppm of zinc) from Zn-MHAC showed nearly the same average daily gain in the entire nursery period as the pharmacological dose, 2000 mg of zinc per kg of feed (ppm of zinc), from zinc oxide. Zinc oxide did perform better than Zn-MHAC in terms of average daily gain during day 0-14, see Figure 1.

Figure 1 – Effect of zinc sources on average daily gain in pig trials.

Under these specific conditions, Zn-MHAC was effective at a level 20 times lower than zinc oxide. Pigs supplemented with Zn-MHAC also tended to have greater (P= 0.06) gain-to-feed during day 14-28, see Figure 2. What accounts for the increased feed efficiency? The study found that piglets supplemented with Zn-MHAC tended to show a shorter villus width in the ileum of the small intestines on day 42. Researchers suggest this is indicative of less gut inflammation and could signify a healthier digestive tract, which could be the reason for the improved feed efficiency during day 14-28.

Figure 2 – Effect of zinc sources on gain-to-feed (G:F) in pig trials.

Methionine improves absorption

When considering the results of this research trial, it’s not enough to say “the organic trace mineral outperformed the inorganic mineral” since that doesn’t explain why. Inorganic trace mineral sources, like zinc oxide, are at a disadvantage the moment they enter the animal as they are subject to antagonisms and interactions with other components in the digestive tract. The mineral can become bound, unable to be absorbed and ultimately excreted. A disruption in nutrient bioavailability, metabolic deficiencies or over-feeding can be the result.

The organic trace mineral Zn-MHAC doesn’t suffer the same fate of its inorganic counterpart as it is chelated to the amino acid ligand, HMTBa (Novus’s Alimet feed supplement), an 88% active source of methionine. The mineral-ligand combination forms a double coordinate covalent bond of zinc and HMTBa that essentially protects the zinc, creating a stable molecule and reducing the impact from antagonisms. With this stability in the gastrointestinal tract, less phytate-metal complexes are formed and phytase efficiency is maintained as a result. This allows for more efficient delivery and uptake in the small intestine.

Better phosphorus and calcium digestibility

Along with performing similarly as zinc oxide at lower inclusion where growth was concerned, piglets receiving Zn-MHAC also exhibited better phosphorus digestibility (12.68% increase) even in the presence of 500 FTU/kg phytase. The evidence of higher phosphorus digestibility could explain the compensatory growth performance of piglets supplemented with Zn-MHAC compared with zinc oxide. Researchers also found that 100 ppm of zinc from Zn-MHAC provided a greater uplift in calcium digestibility (6.45% increase) than zinc oxide even with the presence of 500 FTU/kg phytase. This result suggests that Zn-MHAC optimises the effect of the phytase, allowing the body to absorb more calcium.

This research demonstrated that Mintrex Zn can be used as an alternative to pharmacological levels of zinc oxide with far lower inclusion. Researchers also illustrated that Mintrex Zn could improve phytase efficacy in terms of releasing more phosphorus from the phytate molecule than zinc oxide. This means less inorganic phosphorus would be required to supplement in the diet.

Author: Dr Ping Ren, Novus International, Inc., St Charles, Missouri