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Is it time to reconsider trace mineral levels in pig diets?

Excesses of trace minerals may have pro-oxidant effects which may negatively influence pig growth performance.

By Ryan Samuel, South Dakota State University assistant professor and Extension swine specialist
Growing pigs require trace minerals such as copper, iron, manganese and zinc for various biochemical functions, including cellular development and energy metabolism, which lead to optimal health and immunity. These requirements are met through dietary supplementation from different trace mineral sources.

Current industry practices, however, often include feeding trace minerals above the defined requirements (Flohr et al., 2016). This practice seems to stem from the belief that productivity may be further improved by increased supplementation. In addition, although feedstuffs are known to contain innate levels of important trace minerals, the contributions of these trace minerals to the dietary requirements are most often ignored, further increasing supplementation above the required levels.

Unfortunately, high levels of certain minerals may interact and negatively influence the bioavailability of other minerals or minerals overall. Furthermore, excesses of trace minerals may have pro-oxidant effects which may negatively influence pig growth performance.

The facilities at the South Dakota State University Swine Education and Research Facility include two rooms with four separate shallow pits in each room that allow researchers to collect manure samples from groups of pigs throughout the wean-to-finish cycle. In proposed research, the effects of dietary mineral supplementation on the growth performance and feed efficiency of pigs as well as the trace mineral concentration of the manure from weaning to finishing will be measured. The goal of this research is to investigate some of the questions posed by the late-Professor Donald Mahan.

Mahan indicated that the National Research Council recommended mineral requirements are likely not appropriate for modern pig breeds. More specifically, it has been demonstrated that the inclusion of exogenous enzymes in swine diets can improve trace mineral digestibility (Adeola and Cowieson, 2011). However, the studies that were available to the committee in the development of the current NRC recommendations did not utilize exogenous enzymes. Therefore, there is a need to investigate the effects of exogenous enzymes on the dietary mineral requirements for growing and finishing pigs. For example, the inclusion of phytase affects the utilization of several minerals besides phosphorus. How should dietary trace mineral inclusion rates be adjusted based on the effects of exogenous enzymes?

The innate trace minerals — those that are naturally present in feedstuffs — have generally been ignored in feed formulation. However, modern feed processing methods as well as the use of exogenous enzymes have influenced the digestibility and availability of the innate trace minerals. Therefore, the contribution of these minerals toward meeting the dietary trace mineral requirements should be considered in diet formulation.

Jolliff and Mahan published the results of a trial in 2013 involving growing barrows that measured the digestibility of innate trace minerals as influenced by additional calcium and phosphorus levels in the diet. Standard diets contained 0.65% Ca and 0.55% total P and were compared to high level treatments that contained 1% Ca and 0.85% total P. Innate trace mineral digestibility averaged 45% from a corn-soybean meal diet that was not supplemented with trace minerals. To be representative of common industry practice, diets were prepared with trace mineral supplements added to provide 15 mg Cu, 150 mg Fe, 10 mg Mn, and 140 mg Zn per kilogram of diet. Trace mineral sources were: 1) inorganic — copper sulfate, ferrous sulfate, manganese oxide and zinc sulfate or 2) organic — metal proteinates of Cu, Fe, Mn and Zn. The study results showed that inclusion of high levels of Ca and P caused the digestibility of trace minerals to deteriorate.

Based on the relatively high digestibility of the innate trace minerals determined in the previous investigation, a separate trial was initiated with grower pigs fed diets with different supplementation levels of trace minerals (Cu, Fe, Mn or Zn) until harvest. Specifically, pigs were fed corn-soybean meal diets: 1) without trace minerals, 2) with metal proteinate minerals added at 50% of NRC recommendations, or 3) with metal proteinate minerals added at 100% of NRC recommendations. Growth performance, carcass characteristics and meat quality were not affected by the level of trace mineral supplementation. However, because of expected variability of innate trace mineral contents of dietary feedstuffs from different geographical regions, the authors concluded that providing metal proteinate minerals of at least 50% of NRC recommendations is warranted (Gowanlock et al., 2013).

The dietary requirements for trace minerals are based on the necessity of these elements for functions in the body. For example, trace minerals are important cofactors in the efficient use of protein and energy. However, the swine industry appears to be providing trace minerals in excess of the nutrient requirements. Is it time to consider the influence of the innate trace minerals and the effects of exogenous enzymes on how you provide trace minerals in your diets?

Source: Ryan Samuel of South Dakota State University, who is solely responsible for the information provided, and wholly owns the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.

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