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Abstract
In current farm animal practice, the uncertainty in the availability of zinc (Zn), as affected by dietary and digestive factors, is compensated by calculating gross requirements from net requirements using a worse-case availability factor in the conversion. Consequently, the higher levels of Zn inclusion lead to a reduction in relative efficiency of uptake, as levels fed are higher than Zn requirements. Ultimately, the result of this is an increase in Zn manure which can result in high Zn levels in soil when this manure is used, increasing the environmental impact of farm animals. A novel chelator, L-glutamic acid N,N-diacetic acid (GLDA), is a chelating agent, capable of binding di- and trivalent metal ions. By binding to these metal ions, it potentially provides stability of the complex in the upper gastrointestinal tract, which minimizes the formation of insoluble complexes, thereby improving nutritional bioavailability. This thesis aims to improve our understanding on trace mineral nutrition and determine the potential of using GLDA to increase the availability of minerals in livestock production.
In Chapter 2 the impact of GLDA was compared to the well-established chelating agent ethylenediaminetetraacetic acid (EDTA). Previous work in literature showed effects of EDTA on trace mineral retention, but EDTA suffers from low biodegradability and its high chelation strength can be considered to be too high compared to metal transporters in the body. In experiment 1 broilers were fed Zn sulphate with GLDA or EDTA in molar amounts equivalent to chelate the level of Zn added. In experiment 2 the effect of GLDA on a basal diet containing no additional minerals was established. Serum and tibia Zn clearly responded to the increasing doses of dietary zinc with a significant response to the presence of EDTA and GLDA. These results are also indicative of the equivalent nutritional properties between GLDA and EDTA. In experiment 2, zinc levels in serum and tibia were also increased with the addition of GLDA to a basal diet lacking supplemental trace mineral, where serum zinc levels were 60% higher at the 216 mg/kg inclusion level. The study demonstrated that dietary GLDA enhanced availability of Zn.
The aim of Chapter 3 was to quantify the reduction of dietary Zn that could be achieved in broilers to obtain the same Zn status. Broiler were fed Zn in a dose response manner with and without GLDA. The results indicated that when GLDA was included in the diet, based on tibia Zn, the same Zn status was achieved with a 19 mg/kg smaller Zn dose while based on serum Zn this was 27 mg/kg less Zn.
Chelators are known to have negative side-effects when fed at high levels, for example due to chelation of minerals within the cell walls, leading to cell wall disruption. In order to determine the effects of high GLDA inclusion a dose response with GLDA up to 10000 mg/kg was performed in Chapter 4. The results of this study indicated that there are no negative side effects of GLDA inclusion up to 3000 mg/kg of GLDA/kg feed. The GLDA residue levels in breast tissue indicated that 0.01% of total GLDA absorption is stored in breast tissue. Higher values are found in kidney and liver for the highest inclusion level, indicating that the fraction of GLDA that is absorbed is actively excreted by the animal. The limited absorption of GLDA indicates that the role of GLDA affecting Zn availability takes place within the gastrointestinal tract of the animal, by sustaining solubility during digestive processes.
As the Zn load in manure of pigs is greater than that of broilers, the effect of GLDA in piglets was determined in Chapter 5. On top, pigs are a better model for potential human implications than broilers, which is important considering the high prevalence of Zn deficiency in the developing world. GLDA appeared to protect a significant fraction of soluble luminal Zn from being captured by phytic acid and mediated it towards the Zn transport mechanisms in the gut mucosa, thereby promoting higher Zn retention in GLDA-supplemented animals compared to control animals. This led to lower necessity for mobilization of body Zn stores to compensate for endogenous losses in the presence of GLDA, lowering the chance of subclinical or clinical Zn deficiency.
In Chapter 6 we discussed the impact of GLDA on Zn availability and retention in farm animals by combining the results of previous chapters with existing literature. The importance of study design when assessing trace mineral availability is discussed. The impact of GLDA on trace mineral availability is discussed by showing the increased retention of Zn when using adding GLDA to diets of animals. The potential impact on the environment by implementing GLDA is discussed and put into context regarding sustainable farming, emphasizing the key role GLDA can play.
Original language | English |
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Qualification | Doctor of Philosophy |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 15 Oct 2021 |
Place of Publication | Wageningen |
Publisher | |
Print ISBNs | 9789463959063 |
DOIs | |
Publication status | Published - 15 Oct 2021 |
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Dive into the research topics of 'Trace mineral chelation for sustainable animal nutrition : enhancing zinc availability with L-glutamic acid N,N-diacetic acid'. Together they form a unique fingerprint.Projects
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Trace minerals with Chelator and the effect on oxidative status
Boerboom, G. (PhD candidate) & Hendriks, W. (Promotor)
1/03/18 → 15/10/21
Project: PhD