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on December 15, 2014

Rethinking NRC mineral levels in swine diets

Recent research highlights the importance of trace mineral inclusions

Although dietary trace minerals are required in only minute quantities, they play essential roles in metabolic functions that safeguard animal health and regulate growth.

For example, copper (Cu) is required at 5 to 6 ppm for neonatal pigs to support the synthesis of hemoglobin and enzymes for normal metabolism. Similarly, zinc (Zn) is required at 100 ppm in weanling pigs to maximize growth and for proper function of the immune system.

How, then, does the feed industry determine appropriate trace-mineral concentrations when formulating pig diets? A reference commonly relied upon is the report from the National Research Council (NRC), “Nutrient Requirements of Swine,” which was most recently updated in 2012.

Dr. Donald Mahan, professor emeritus, The Ohio State University, recently asserted that NRC recommended mineral requirements do not accurately reflect pig nutritional needs. In his presentation at the Midwest Swine Nutrition Conference, Mahan pointed out that very little new information has been published on the mineral requirements of modern pigs and that the most recent NRC document (2012) relies on data more than 15 years old.

Since that time, significant changes have occurred in the feed industry.

Processing of feeds leads to improved digestibility of innate minerals

The contribution of innate minerals in natural feedstuffs towards meeting animal nutritional requirements is generally ignored in diet formulation, despite the fact that their concentrations often exceed current NRC recommendations. In 1998, the NRC did consider the contributions of innate trace minerals as available in meeting the requirements of pigs, but in 2012, they took a different stance, considering them to be only “safety factors” in total feed formulation, because of the limited amount of data on their bioavailability.

In 2013, a study showed that the digestibility of innate minerals should not be ignored in feed formulation because they influence overall mineral nutrition.

Utilizing organic trace mineral sources

Trace minerals are classified as either organic or inorganic. These classifications refer to the form of the mineral source and are not to be confused with strict chemical definitions. Organic sources of trace minerals mimic the forms that are naturally present in feedstuffs and, as such, may provide a metabolic advantage that can improve performance.

A 2013 study confirmed that organic minerals are more bioavailable than inorganic minerals in young pigs. In contrast, inorganic mineral salts, such as sulphates, carbonates, chlorides and oxides, are broken down in the digestive tract to release free ions, which can react to form indigestible mineral complexes. These complexes are then excreted to the environment without conferring nutritional benefits to the animal.

Trace mineral requirement studies

In two recent experiments, levels of trace mineral (Cu, manganese (Mn), Fe and Zn) supplements were evaluated. In both studies, diets were composed of conventional feed ingredients for the Midwestern United States and supplemented similarly with iodine and organic selenium. Phytase was added to diets in line with modern industry practice.

Micromineral premixes were prepared and added as percentages of the NRC (1998) recommendations, such that the inclusions of all the trace minerals were adjusted simultaneously, which, unlike past studies, did not allow independent mineral evaluations.

Nursery pig trace mineral requirements

Newly weaned pigs were fed diets that contained 0, 25, 50 or 100 percent of NRC (1998) trace mineral levels as inorganic mineral salts or as organic minerals. Additions of Cu, Fe, Mn and Zn in the first 21 days post-weaning in either organic or inorganic form did not affect daily gain. However, from 21 to 35 days post-weaning, daily gains numerically increased in response to feeding the 25 percent level.

These results are in agreement with research observations demonstrating maximal growth rates in rapidly growing weanling pigs in response to 75 ppm of additional dietary Zn. However, overall, concentrations of trace minerals greater than 25 percent did not further improve animal performance in this study. This lack of performance response may be attributed to carry-over from the sow or to the bioavailability of innate minerals. Regardless, newly weaned pigs did not appear to need dietary trace-mineral supplements at the magnitudes recommended by the NRC.

Finisher pig trace mineral requirements

Finisher pigs were fed corn and soybean meal diets that were supplemented with organic trace minerals at 0, 50 or 100 percent of NRC (1998) recommendations. Regardless of trace mineral inclusion, pigs achieved market weights of 115 kg within slightly less than five months of age. There were no effects of trace mineral addition on feed intake or feed efficiency in the trial period. Furthermore, pigs were fed ractopamine during the latter growth period, which had no effect on response to dietary trace mineral levels.

The previous dietary intake of trace minerals was not considered in this study and may have contributed a certain amount of carry-over from the nursery period.

Carcass measurements (hot carcass weight, backfat, loin muscle area, dressing percentage or percent of fat-free lean) and pork quality (color, marbling, firmness or wetness) did not differ between trace mineral treatments. Thus, finisher pigs, likewise, did not appear to need dietary trace-mineral supplementation at the magnitudes recommended by the NRC.

What does new research mean for trace mineral inclusions

Clearly, a better understanding of micromineral nutrition for growing swine is needed. The NRC recommendations for the addition of dietary trace minerals would appear to result in levels above those needed to support health and wellbeing and to maximize growth and development of swine. Advancements in feed processing techniques, exogenous enzyme technology and the use of organic minerals appear to have exhibited effects on the recommendations for dietary trace mineral additions which were previously accepted without questioning within the feed industry. 

References available upon request.
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