The pig industry is undergoing rapid change and is faced with many challenges, such as a deterioration in pig health status in many countries and a growing concern by the community about how we care for animals and the environment. Minerals play an important role because not only are they essential for growth and reproduction, but their presence also influences the quality of the end product and ultimately human health.
However, published recommendations on the inclusion rate of trace minerals may not be appropriate for the modern pig industry, especially as a greater proportion of these minerals are supplied in the organic form. We thus need to re-evaluate our current recommendations as well as consider how we undertake future research to better understand the requirements for organic minerals to optimize animal performance while reducing the effect on the environment.Mineral requirements
The numerous functions of trace minerals in animal physiology are well established and documented, and there is little disagreement about the levels required to overcome deficiencies. Tables of requirements have been established by groups such as the NRC; and while these are used as a starting point, many in the commercial feed industry have adjusted these levels based on their own ‘gut feel’ rather than on any scientific basis.
Mateos et al. (2005) and Mahan (2005) both found that the levels of inorganic minerals being used by commercial industry in Spain and the United States, respectively, are generally higher than levels recommended by research institutions (Table 1). This practice suggests a lack of confidence by industry in the recommendations currently available, which to a large degree are based on research conducted more than 30 years ago and are most likely no longer appropriate. For many nutrients there is an extreme paucity of data to support any recommendations (Lindemann and Kim, 2006).
Since inorganic trace minerals are relatively inexpensive, does it matter if higher than required levels are used in the diet? In a study with sows over two parities conducted by Peters and Mahan (2004), NRC (1998) standards for dietary trace minerals were compared with what was considered to be normal industry levels. The same study evaluated inorganic and organic (Bioplex®/Sel-Plex®) sources of trace minerals (Cr, Cu, Fe, Mn, Se and Fe).
Reproductive performance of sows over two parities was improved when trace minerals were fed in the organic form, but performance was reduced when the industry average levels were provided (Figure 1). Mahan (2005) suggests that when additional trace minerals are added to the diet at ‘insurance’ levels, they may in fact contribute to the accumulation of free radicals, which can result in a decline in performance when the animal is placed under stress. For modern genotypes to grow and/or produce to their potential, we clearly need to know much more about the requirements of all trace minerals.
|Table 1. NRC (1998) mineral levels (ppm) and those recommended by industry and university nutritionists for the breeding sow.|
|1 Mahan, 1995|
|Figure 1. Reproductive performance of sows over two parities provided either inorganic or organic trace minerals at levels recommended by NRC (1998) or by industry (Peters and Mahan, 2004; referenced by Mahan, 2005).|
Establishing mineral requirements of pigs
Many factors affect the mineral requirements of animals (Underwood, 1966). The most important of these are:
• species or breed
• age, sex and rate of growth
• the nature and the rate of production sought
• the level and the chemical form in which the mineral is ingested
• overall balance and adequacy of the diet in relation to the purpose for which it is given
• hormonal and other physiological activities within the animal
• the climate or the non-dietary environment
• criteria of adequacy employed
The most common criteria of nutrient adequacy are growth rate, production rate and efficiency of feed conversion. Important as these are from the viewpoint of economy of production, estimates of mineral needs based on such criteria alone may not be entirely satisfactory (Underwood, 1966). The animal has the capacity to make adjustments to sub-optimal intakes by reducing the amount of mineral in its products or stored in tissues, and hence quality might be reduced to maintain quantity. Depletion of mineral reserves is usually of little consequence in the short term, but if prolonged can seriously affect the health and productivity of the animal.
Establishing the requirement for individual minerals is, unfortunately, expensive and complicated research to conduct. This situation is exacerbated by the decline in funding for research by many governments and the increased reliance on private companies to fund such research.
A number of factors need to be considered when we undertake research to determine the mineral requirement of pigs. Interactions between inorganic minerals are well acknowledged, and this means that the optimal level of one mineral may depend on the levels of others in the test diet. A major advantage of organic minerals is the reduction in interactions with other minerals, because chelation offers a degree of protection in the digestive tract and this should to some degree simplify the establishment of requirements. Despite this, it is still difficult to prioritize which minerals should be studied first, and then at what levels other minerals should be set in the test diet.
There is currently little consideration given to the mineral content of other components in the diet and the contribution that this might make to total mineral supply. Changes in farming practices, such as through plant breeding, weed control, soil type and use of different forms of fertilizers may all contribute to a change in the mineral content of our base feed ingredients, and these at least need to be taken into consideration in the conduct of future research.
Research also needs to be conducted under conditions that remove as many of the interfering variables as possible, such as health status and environment, but then the results need to be extrapolated to commercial conditions for them to be relevant to industry.
The opportunity to use tools that examine regulation of metabolism at the level of gene expression (Dawson, 2006) needs to be part of a research program that uses both traditional and new methodologies. The approach taken by Alltech to bring together scientists with different expertise to help guide nutrition research in a more coordinated approach is to be commended, and should mean that we do not have to wait as long to determine the requirements for minerals in organic form as we did for inorganic mineral forms.
Organic vs. inorganic minerals
There is little argument within the animal feed industry that trace minerals in the organic form have an exciting role to play and will in time replace all or some of the inorganic forms for a number of reasons. Inorganic salts are traditionally added to the diet to meet the animals’ needs. However, these salts are broken down in the digestive tract to form free ions that can form complexes with other dietary molecules and may also interact with other components in the diet, making them more difficult to absorb. For example, phytate has a high binding affinity for copper and zinc (Mateos et al., 2005).
While inorganic minerals are relatively inexpensive to use, their properties need to be taken into account when formulating diets. Organic minerals are less reactive with other minerals and have a higher bioavailability, thus it should be possible to replace inorganic minerals at a lower level while maintaining or even enhancing performance. The basic research conducted by Power (2003) has greatly increased our understanding of the mechanism by which organic minerals are absorbed from the digestive tract, and this research is an important component in determining mineral requirements.
Pig research with organic minerals
A number of studies have been conducted to compare the performance of pigs of all stages of production when fed diets containing one or more organic minerals, especially with selenium (Se), copper (Cu) and zinc (Zn). These studies include research at both the basic and applied levels that has seen adoption by industry in new feeding strategies in a relatively short period of time.
For example, the research conducted by Professor Don Mahan and colleagues on the role of Sel-Plex® as a source of organic selenium instead of using sodium selenite is well recognized. Not only is organic selenium better utilized by the animal, but the improvements in performance more than compensate for the additional cost of using the product.
These results have been tested on a commercial piggery by Gourley et al. (2005), where 0.3 ppm Se from sodium selenite or selenium yeast (Sel-Plex®) was fed in sow diets from 80 days of gestation through to the end of lactation. Data were analyzed from more than 370 sows per treatment, and showed a significant improvement in the number of pigs weaned when sows were fed Sel-Plex® (Table 2).
Other studies with copper and zinc fed to weaner and grower-finisher pigs provides overwhelming evidence that pigs can be fed diets containing lower levels of these minerals in the organic form (i.e., Bioplex® Cu and Bioplex® Zn) than when fed as inorganic minerals, yet animal performance is not affected and the level of minerals in the effluent is decreased dramatically (Mullan et al., 2005).
|Table 2. Effect of the source of selenium in the diet of sows on litter performance.|
|Gourley et al., 2005|
Expectations of the feed industry
The animal feed industry is always looking for ways to reduce diet costs so as to maintain market share. At the same time many companies seek to provide a product to improve animal performance, although in many cases it is difficult to prove this on farm because of poor monitoring of performance, especially in the grower herd. Regardless of the product under consideration, some of the issues that should be considered by feed companies include:
• What evidence is there from refereed published papers that the product works? This should include both in vivo and in vitro studies.
• Who else in the industry is using the product? How are they using it and what responses are they getting?
• Will it be cost effective in my range of diets?
• What level of technical support is available to use the product commercially?
There will be increased interest from society and consumers as to what products are being fed to animals, the effect on the quality of the end product, and also any impact on the environment. Unfortunately, retailers are always looking to reduce the relative price of meat for the customer and so are not inclined to want to pay extra for an improvement in quality. This will often mean producers and support industries must either accept lower margins or improve their own efficiency.
Research into trace mineral requirements has received little attention in recent years, but this is now changing with the development of high quality organic minerals. It is important to better understand their mode of action, and to determine the requirement for organic minerals under a range of commercial conditions. The quantity and source of trace minerals fed to pigs influences their performance and impact on the environment. Pork is an excellent source of several trace minerals for human health, and opportunities exist to improve its nutritional value using organic minerals.
Author: BRUCE MULLAN
Dawson, K.A. 2006. Nutrigenomics in pig and poultry production: Feeding the genes for fertility. In: Nutritional Approaches to Arresting the Decline in Fertility of Pigs and Poultry (J.A. Taylor-Pickard and L. Nollet, eds). Wageningen Academic Publishers, The Netherlands. pp. 13-24.
Gourley, G.G., J.F. Lampe, J.C. Sparks and T.T. Stumpf. 2005. Piglet survivability and performance: Sel-Plex® versus sodium selenite in sow and nursery diets. In: Nutritional Biotechnology in the Feed and Food Industries, Proceedings of Alltech’s 21st Annual Symposium (T.P. Lyons and K.A. Jacques, eds). Nottingham University Press, UK, pp. 153-156.
Lindemann, M. and B.G. Kim. 2006. Recent advances in sow reproductive function. In: Nutritional Approaches to Arresting the Decline in Fertility of Pigs and Poultry (J.A. Taylor-Pickard and L. Nollet, eds). Wageningen Academic Publishers, The Netherlands. pp. 25-34.
Mahan, D.C. 2005. Feeding the sow and piglet to achieve maximum antioxidant and immunity protection. In: Re-defining Mineral Nutrition (J.A. Taylor-Pickard and L.A. Tucker, eds). Nottingham University Press, UK, pp. 63-73.
Mateos, G.G., R. Lázaro, J.R. Astillero and M.P. Serrano. 2005. Trace minerals: What text books don’t tell you. In: Re-defining Mineral Nutrition (J.A. Taylor-Pickard and L.A. Tucker, eds). Nottingham University Press, UK, pp. 21-61.
Mullan, B.P., A. Hernandez, D.N. D’Souza and J.R. Pluske. 2005. Modern pig nutrition for performance: minerals, metabolism and the environment. In: Nutritional Biotechnology in the Feed and Food Industries, Proceedings of Alltech’s 21st Annual Symposium (T.P. Lyons and K.A. Jacques, eds). Nottingham University Press, UK, pp. 185-200.
NRC. 1998. Nutrient Requirements of Swine (10th Ed.) National Academy Press, Washington, DC.
Peters, J.C. and D.C. Mahan. 2004. Sow and litter responses to dietary trace mineral source and level over two parities. J. Anim. Sci. 82(Suppl. 2):81.
Power, R.F. 2003. Organic trace mineral supplementation: can success in animal nutrition be extrapolated to humans? In: Nutritional Biotechnology in the Feed and Food Industries, Proceedings of Alltech’s 19st Annual Symposium (T.P. Lyons and K.A. Jacques, eds). Nottingham University Press, UK, pp. 355-364.
Underwood, E.J. 1966. The Mineral Nutrition of Livestock. Commonwealth Agricultural Bureaux. The Central Press Ltd., Aberdeen, Scotland.
Animal Research and Development, Department of Agriculture and Food, Western Australia, Australia