Introduction
The mineral nutrition of poultry has been traditionally based on the use of inorganic ores, and many currently published requirements are from research conducted more than 40 years ago (Leeson, Reference LEESON2005). Although research for broilers is well represented in the literature, ‘minor’ avian species, including layers, breeders, turkeys and ducks, often rely on extrapolation from broiler data to ascertain their mineral needs, as specific data does not exist. Regarding the age of the data available, it has been proposed that such research may not be relevant to modern breeds and ration formulations.
The availability of minerals that are in a chemically organic form (achieved by chelation with small peptides) has resulted in an increase in research to compare their bioavailability and efficacy in vivo against traditional sulphates and oxides. It has already been established by other researchers that chelated minerals are more readily absorbed and stored within body tissues (Du et al., Reference DU, HEMKEN, JACKSON and TRAMMEL1996), due to their being bound to small peptides (Webb, Reference WEBB1986; Reference WEBB1990). The goal of this extensive research project, which is being conducted on a global basis and aims to encompass all main commercial species, is to produce new requirements based on organic minerals. Such recommendations are expected to have a major impact on pollution from intensive poultry farms, whilst maintaining (or increasing) poultry performance, and improving physiological oxidation status. The purpose of the following paper is to review the current findings, including previously unpublished trials, relating to mineral supplementation in poultry and to compare inorganic and organic sources in terms of performance, retention and excretion.
Research with organic minerals for poultry
Seven trials have been conducted to date with single organic (Bioplex®, Alltech Inc, USA) minerals (including Cu, Mn and Zn) have been carried out in various sites in the USA, Russia and Australia since 2003. These replicated trials have used either caged and penned broilers fed different levels of inorganic versus organic forms of single minerals. Trials have used either 1-21 day or 1-35 day broiler chickens. Eight trials, run at sites across Europe, compared the benefits of combinations of inorganic versus organic minerals. These trials have been conducted using replicated floor pens, with broilers aged 1-49, 1-42, 1-35, 1-39 day for performance evaluation and 1-21 day for excreta mineral content assessments. In laying hens, four trials have been conducted in Poland, the USA and Brazil using caged hens, in replicated trials. Birds were fed a combination of minerals (Fe, Zn, Mn, Cu) in replacement of inorganic forms normally used in the diet and at different levels, relative to current recommendations.
copper
Several trials have been conducted comparing the effects of feeding inorganic or organic forms of copper to poultry. Dose response data from trials conducted in the USA, relating to copper requirements, have shown that inorganic copper can depress intake and performance and increase Cu liver levels. In addition, it was observed that Cu excretion increased linearly with intake. The lowest excretion rates were observed with organic Cu, and performance was maintained at the same level (P>0.05) as the inorganic mineral treatments (Pescatore et al., Reference PESCATORE, FORD, CANTOR and PIERCE2004, personal communication). Further North American studies examined the differences in Cu metabolism in 1-21 day broilers (Pierce et al., Reference PIERCE, PESCATORE, FORD and CANTOR2005, personal communication). Additional dietary Cu was supplied in both forms at levels of 0, 5, 10 or 20 ppm, and it was shown that Cu retention was 35% higher (P=0.03) for the birds fed organic Cu compared to those receiving CuSO4, although in both cases, retention increased linearly with intake. It is well known that many minerals affect the uptake and utilization of others via interaction at the gut level. Inorganic Cu also reduced retention of Zn, whereas the organic form did not. These findings confirmed those previously reported for competition between inorganic minerals for storage as well as uptake (Du et al., Reference DU, HEMKEN, JACKSON and TRAMMEL1996).
manganese
Manganese replacement trials were run during 2007 in Russia in 1-35 day broilers, fed 120, 90, 60 or 30 ppm Mn in inorganic or organic form. Birds fed organic Mn (Table 1) performed better than the inorganic groups, although levels of 30 ppm did not support (P<0.05) bodyweight for either forms (Egorov et al., Reference EGOROV, MANUKYAN, PEWTROSYAN, PAPAZYAN and SURAI2007, personal communication). Birds fed 90 ppm organic Mn had the highest body weights (P<0.05) relative to 30 ppm organic Mn and 30 or 60 ppm inorganic Mn and numerically the lowest and most sustained FCR.
Effect of manganese form and level on broiler performance (Egorov et al., Reference EGOROV, MANUKYAN, PEWTROSYAN, PAPAZYAN and SURAI2007, personal communication)1.
1Means not sharing a letter differ significantly (P<0.05)
zinc
Four trials regarding the replacement of inorganic for organic Zn have been reported. For the first trial, the same Russian research group that performed the Mn trials compared different levels of Zn, and reported better weight gain and FCR with organic forms (P<0.05). Performance for 50 ppm or more was the same as for 70 and 100 ppm (Egorov et al., Reference EGOROV, MANUKYAN, PEWTROSYAN, PAPAZYAN and SURAI2007, personal communication), and FCR was numerically lower for all levels of the organic Zn compared to the inorganic control diets (Table 2), even though the trial was conducted in low numbers of animals and did not attain significance.
Effect of zinc form and level on broiler performance (Egorov et al., Reference EGOROV, MANUKYAN, PEWTROSYAN, PAPAZYAN and SURAI2007, personal communication)1.
1Means not sharing a letter differ significantly (P<0.05)
Other organic Zn trials (Bao et al., Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON, FORD and SHAFER2007) determined the optimum requirement for 35 day broilers to be 70 ppm, via analysis of the response curve where Zn was included in the feed from 26-131 mg/kg. Performance parameters increased linearly with organic Zn (P<0.001; R2 = 0.86 bodyweight, 0.83 feed intake and 0.50 FCR).
Two further trials conducted in USA facilities examined differences in bioavailability for Zn sources in 1-21 day caged broilers. Zn was added at 0, 20, 40 and 80 ppm in both experiments (Ao et al., Reference AO, PIERCE, POWER, DAWSON, PESCATORE, CANTOR and FORD2006). The relative bioavailability of organic Zn versus ZnSO4 was 183% based on performance, and 157% for bone (by tibial ash assessment). Broken stick analysis indicated an optimum inclusion level of 9.8 ppm (P<0.05; R2 = 0.95) for organic Zn vs. 20.1 ppm for the inorganic Zn form. Further work (Ao et al., Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON, FORD and SHAFER2007, Reference AO, PIERCE, PESCATORE, FORD, CANTOR, DAWSON and PAUL2008a) showed that optimum organic Zn inclusion was 12 ppm for broilers, which reduced to 7.4 ppm in the presence of phytase enzymes in corn-soy diets.
Optimising combined minerals levels in broiler diets
It is well documented that the combination of minerals, as well as actual levels fed, is important regarding uptake and utilization, especially when inorganic forms are used in diet formulations. Trials have confirmed that 1-21 day broilers fed different proportions of organic minerals to replace inorganic forms require 66% of the level of organic minerals in combination, to replace 100% of inorganic forms without loss in performance (Tucker, Reference TUCKER2004). When the straight replacement of inorganic for organic forms of combined minerals (12.5 ppm Cu; 40 ppm Mn, Zn, Fe) was evaluated in a 1-49 day broiler trial (Nollet et al., Reference NOLLET, TUCKER, WAKEMAN and BELYAVIN2005; Reference NOLLET, GEERS and SPRING2007, personal communication), birds fed inorganic forms had the highest mineral excretion rate.
Further to these findings, research in Belgium examined the effect of reducing both mineral types for 1-42 day old broilers within three phased diets. Performance was maintained irrespective of the lower levels of organic minerals applied within the dietary phases, with economic benefits potentially resulting from using lower levels. Other Belgian trials showed that organic mineral diets (15 ppm Cu and 60 ppm Zn and Mn) gave higher bodyweights in 42 day broilers (P<0.05; Lippens and Huyghebaert, Reference LIPPENS and HUYGHEBAERT2006, personal communication). In the Netherlands, Lensing and Van der Klis (2006, personal communication) found no differences in the performance of 39 day broilers fed lower levels of organic minerals compared to feed containing higher inclusion of inorganic forms, but did report significant reductions (up to 50%) in mineral excretion (P<0.001). Work in Serbia showed that organic minerals at 30% of NRC maintained performance in 1-42 day broiler trials (Peric et al., Reference PERIC, MILOSEVIC and ZIKIC2006, personal communication).
Trials run in the USA, where inorganic minerals were replaced with organic forms at 25% of NRC recommendations, found a 34% reduction in mineral excretion, without compromising weight gain. Similar findings were reported by Bao et al. (Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON, FORD and SHAFER2007), who reported that levels of 4 ppm Cu and 40 ppm Fe, Mn and Zn were sufficient to maintain performance whilst reducing excreta mineral losses.
Organic minerals replacement for laying hens
Four trials have been carried out with layers to examine the effects of replacing inorganic minerals. Boruta et al. (2007, personal communication) monitored performance of hens fed inorganic minerals at 100% NRC levels against those fed 8, 17 or 33% of those levels in the organic form. Bone strength increased in all of the organic mineral groups, (P<0.05) alongside a reduction in excretion (P<0.01 for Mn and Zn; P<0.05 for Cu and Fe).
Two trials have been conducted by the authors of this review paper with laying hens in the USA. The first US trial compared standard EU levels against twice the inclusion for both inorganic and organic minerals. The birds fed organic minerals showed a reduction in FCR (P<0.05). The second US trial (Ao et al., Reference AO, PIERCE, POWER, DAWSON, PESCATORE, CANTOR and FORD2006) used diets to supply 25, 50 and 100% of NRC in both mineral forms. They showed an increase in shell percentage at 24 weeks of age and a 2% increase in lay. This supported the view that requirements may be reduced to up to 25% of NRC by using organic minerals for hens.
Two further trials (Ao et al., Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON and FORD2008b; Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON and FORD2009) were conducted to evaluate the effects of feeding reduced levels of trace minerals in proteinate form on the development and bone mineral status of both white and brown pullets. Treatments consisted of feeding corn-soybean meal-based starter and grower diets alone (control), or the same basal diet supplemented with Cu, Mn, Fe and Zn at 25, 50 or 100 per cent of the NRC (Reference NRC1994) requirements in the form of proteinates, or 100 per cent of the NRC requirements in the form of inorganic salts. The results indicated that 25% NRC level of supplementation as the proteinates in pullet diets had no negative influence on performance and tissue mineral concentration in comparison with 100% NRC level of supplementation with inorganic salts (Ao et al., Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON and FORD2008b, Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON and FORD2009).
In a South American study, conducted in Brazil (Nunes et al., Reference NUNES, ROSSI, ROCHA, ANCIUTI, MAJER and RUTZ2007, personal communication), researchers monitored hens from 30-42 weeks fed organic mineral diets containing 33 and 66% of NRC levels compared with 100% NRC inorganic diets. The organic diets, at 33% relative inclusion level, maintained egg production to the same level as the inorganic control.
Conclusions
From the trials conducted so far within the Redefining Mineral Nutrition project, it is evident that organic minerals can be used at lower rates to replace inorganic minerals without losses in broiler or layer performance. It has also been observed that organic minerals can increase body tissue retention of minerals, increasing reserves that may be mobilized during times of extra requirement, such as onset of lay or stress.
