*Dr. David Parker works as a technical consultant for Novus International Inc. and is based in Brussels, Belgium.
POULTRY nutritionists are increasingly focusing on and evaluating the importance of key micronutrients for maintaining metabolic balance in the bird.
Trace minerals, for example, play specific roles in avian metabolism, all of which are relevant to the laying hen (Table). Their role becomes apparent when diets deficient in these micronutrients are fed to high-performing laying hens.
Recently, studies have been carried out using both inorganic trace minerals (ITMs) and organic trace minerals (OTMs), including a defined chelate based on the interaction between a trace mineral and two molecules of the hydroxy analogue of methionine (HMTBa).
The OTM that most improves the tissue supply of the key trace minerals zinc, copper and manganese has the greatest direct effect on connective tissue and bone development, in addition to improving immune response in poultry.
A poultry diet's trace mineral supply traditionally was achieved through the use of ITMs. These are the sulfate or oxide salts of the mineral and, commercially, often are included in the diet at levels in excess of those recommended by national bodies such as the National Research Council. This reflects the uncertainty as to the availability of mineral elements from ITM sources and the desire to ensure an adequate supply to the tissues of the bird.
It has been known for many years that the absorption of mineral cations is inhibited by antagonistic interactions between elements. For example, excess copper will inhibit zinc uptake. In addition, the charged mineral element binds to dietary components such as the phytic acid found in grains and oilseed meals. This latter effect can be ameliorated by adding phytase to the feed, although the extent of this process is not well quantified.
Concern over the availability of key trace minerals has resulted in the development of sources bonded to organic ligands, i.e., OTMs. This process reduces interactions within the gut and delivers the mineral to the site of absorption in the intestines, improving uptake to the tissues. There are, however, a wide range of such ligands, and their relative stability and efficacy at chaperoning the trace mineral to the site of absorption is the subject of considerable debate.
Studies in broilers (Richards et al., 2007; Manangi et al., 2012a; Yuan et al., 2011) have shown improvements in intestinal breaking strength, foot pad quality and bone strength when HMTBa chelates are included in the diet. Recent research with layers provides further evidence that inclusion of HMTBa chelates of zinc, copper and manganese improves bird health and performance.
One study (Manangi et al., 2012b) was conducted during a laying cycle using four treatments: (1) a control, (2 and 3) zinc, copper and manganese ITMs at 100% or 50% of commercial levels and (4) HMTBa chelates at 50% of commercial inclusion. In addition to production parameters, tibia bone strength was measured at 80 weeks.
The results are shown in Figure 1. The ITMs provided little benefit over the control. The tibia breaking strength of HMTBa chelates was 9% greater than with the control and 6% greater at the 50% commercial inclusion rate.
As a consequence of its role in the activation of key enzymes, zinc status has a direct effect on immune function in the bird, and the source of the mineral influences this process.
In a challenge study (Richards et al., 2005), broilers showed an enhanced immune response following coccidial challenge when the dietary zinc source was zinc-HMTBa versus a control, zinc sulfate and zinc methionine treatments (Figure 2).
A further study in which layers were challenged with sheep red blood cells reported an enhanced immune response at week 63 in hens fed diets containing the HMTBa chelates versus ITM sources (P = 0.04).
Further evidence of the role of trace mineral supply in the health of the bird is shown by studies investigating the oxidative stress status of broilers.
Oxidative damage to the tissues is regulated by a number of systems, including the activity of the enzyme superoxide dismutase, which is sensitive to tissue trace mineral supply.
In an experiment in which broiler diets were supplemented with zinc, copper and manganese as either ITM, HMTBa chelate or other OTM, the plasma concentration of peroxide, a breakdown product of tissue lipid damage, was measured. Peroxide concentration, an indicator of oxidative stress, was significantly lower in the birds supplied with the HMTBa chelate (Figure 3).
Key processes associated with eggshell deposition and egg formation would also be expected to be sensitive to trace mineral supply. Recent trials support this thesis. In terms of eggshell production, the role(s) of the three key trace minerals are summarized in Figure 4.
Formation and calcification of the collagen matrix is dependent on enzymes that require trace minerals as essential co-factors. For example, manganese-deficient layers have a lower shell mass and more shell defects due to low activity of glycosyl transferase, which is essential for proteoglycan synthesis.
Similarly, the enzyme carbonic anhydrase is zinc dependent and essential for calcium deposition to form shell structure. Egg production decreases in zinc-deficient birds.
The use of OTMs in layer diets is designed to improve the supply of key trace minerals to the tissues of the bird in order to enhance both productivity and health.
In addition, due to their improved absorption efficiency, OTMs have the added benefit of reducing the overall mineral content of the diet and the subsequent environmental impact of the layer operation.
Studies to investigate these effects have been carried out in both field trials and experiments, with replication of dietary treatments to allow statistical analyses of the data.
In an early field study with layer breeders, eggshell strength was investigated during a 45-week period with two diets: one containing ITMs at 100 parts per million each of zinc, copper and manganese and a test diet with HMTBa chelates at 50 ppm of zinc, 10 ppm of copper and 65 ppm of manganese.
The effect of the HMTBa chelate treatment on eggshell strength during the period of lay from 35 to 80 weeks is shown in Figure 5. Eggshell strength, measured in Newtons, was consistently higher (P < 0.05), with 3.6% stronger eggs in the HMTBa chelate group during the experimental period, which resulted in more salable eggs.
In a second experiment (Manangi et al., 2012b), layer performance during 44 weeks on a control diet with no added trace minerals was compared to birds fed diets containing two levels of zinc, copper and manganese ITMs or HMTBa chelates. A total of 144 W-36 laying hens were allocated to four treatments, with 36 hens per treatment and one hen per cage. The two ITM treatments had inclusion rates at industry levels and 50% of these levels, while the HMTBa chelates were included at 50% of the industry standard rate.
Layer performance showed a significant improvement with the chelates included in the diet at 50% of the commercial level (Figure 6).
Use of the HMTBa chelate sources of zinc, copper and manganese resulted in improved bird performance when compared to both an equivalent level of ITMs (40 ppm of zinc, 10 ppm of copper and 40 ppm of manganese) and the commercial level (80 ppm of zinc, 20 ppm of copper and 80 ppm manganese), demonstrating the value of using a highly available source of these key trace minerals in layer diets.
Further analysis of eggshell structure showed a consistent increase in eggshell thickness in the birds fed the HMTBa chelated minerals, which was statistically significant (P = 0.02) at week 74 of the study. Similarly, eggshell strength measured during the study period showed a significant improvement for the birds fed diets containing the chelated trace minerals at week 68 (P = 0.05).
This effect on eggshell quality was confirmed in a field study in Brazil where, during a nine-week period (weeks 72-81 of lay), substituting 50% of the ITMs in the diet with HMTBa chelated minerals resulted in a 3.2% reduction in cracked eggs and a 2% reduction in broken eggs (Figure 7).
To identify the potential benefit of individual HMTBa chelates on layer performance, a recent study (Qiujuan et al., 2012) compared the effect of each OTM source included in a diet with inorganic salts (ITMs). The control diet was supplemented with zinc, copper and manganese at 30:10:30 ppm as sulfates. In the experimental diets, zinc or manganese was substituted at 20 ppm with the appropriate HMTBa chelate, and the copper source was included at 10 ppm.
The experiment lasted for 14 weeks (weeks 39-52 of age). At 48 weeks, eggshell thickness and hepatic enzyme activities were measured.
Eggshell thickness was significantly increased by the inclusion of either the zinc or manganese HMTBa in the diet compared to the ITM group (P < 0.05). In addition, inclusion of the zinc chelate increased the hepatic activity of the enzyme carbonic anhydrase (P < 0.05), and the presence of the manganese chelate stimulated manganese-superoxide dismutase (P < 0.05) compared to ITM sources.
These data confirm that the increased availability of the trace minerals from the HMTBa chelate results in specific effects in the tissues of the bird, improving both health and performance.
In the same study, eggs were sampled at 52 weeks of age. A total of 15 eggs per treatment were stored at room temperature for 10 days. Then, freshness was assessed by measuring albumen height and was expressed as Haugh units.
Supplementation with HMTBa chelates significantly increased (P < 0.05) Haugh units after 10 days in storage (Figure 8).
HMTBa chelates improve the tissue supply of the trace minerals zinc, copper and manganese and have a direct effect on connective tissue and bone development, in addition to improving immune response in poultry.
In laying hens, this affects bird health, eggshell strength and egg quality factors, which are critical to performance under current production conditions. Therefore, HMTBa chelates can provide additional support when the period of lay is extended.
HMTBa chelated trace minerals allow nutritionists to reduce the inclusion rates of trace minerals while meeting the requirements of the bird. In this way, use of the HMTBa chelated trace minerals provides a direct benefit to the environment by reducing the mineral content of the litter.
Manangi, M.K., J.D. Richards, B. Wuelling, C. Atwell, P. Fisher, C.D. Knight, M. Vazquez-Anon and S. Carter. 2012b. Feeding laying hens diets with supplemental chelated trace minerals improves immune response, eggshell quality and tibia breaking strength. XXIV Int. Poultry Symp. WPSA Abstract 64, Poultry Science Meeting, Atlanta, Ga.
Manangi, M.K., M. Vazquez-Anon, J.D. Richards, S. Carter, R.E. Buresh and K.D. Christensen. 2012a. Impact of feeding lower levels of chelated trace minerals versus industry levels of organic trace minerals on broiler performance, yield, footpad health and litter mineral concentrations. J. Appl. Poult. Res. 21:881-890.
Richards, J., R. Shirley, P. Winkelbauer, C. Atwell, C. Wuelling, M. Wehmeyer and P. Buttin. 2007. Bioavailability of zinc sources in chickens determined via real time polymerase chain reaction (RT-PCR) assay for metallothionein. Proceedings XVI Symposium of Poultry Nutrition, WPSA, Strasbourg, France.
Richards, J.D., T.R. Hampton, C.W. Wuelling, M.E. Wehmeyer, D. Parker and J.J. Dibner. 2005. Mintrex Zn and Mintrex Cu OTMs improve intestinal strength and immune response to coccidiosis infection and/or vaccination in broilers. WPSA, 28th Poultry Symposium Proceedings, Avian Gut Function -- Health & Disease. p. 45.
Sun, Q., Y. Guo, J. Li, T. Zhang and J. Wen. 2012. Effects of methionine hydroxy analog chelated Cu/Mn/Zn on laying performance, egg quality, enzyme activity and mineral retention in laying hens. J. Poult. Sci. 49:20-25.
Yuan, J., Z. Xu, C. Huang, S. Zhou and Y. Guo. 2011. Effect of dietary Mintrex Zn/Mn on performance, gene expression of Zn transfer proteins, activities of Zn/Mn related enzymes and fecal mineral excretion in broiler chickens. Anim. Feed Sci. Tech. 168:72-79.
Primary roles of selected trace minerals on laying hen performance
Effect of deficiency on layer performance
Enzyme function -- carbonic anhydrase; immune function
Reduced shell weight, poor feathering, dermatitis
Anemia, bone structure, cartilage formation
Leg problems, connective tissue/ligament weakness
Superoxide dismutase antioxidant activity, keratin formation
Eggshell abnormalities, bone weakness, reduced resistance to metabolic stress