Abstract
Trace minerals are commonly supplemented in the diets of farmed animals in levels exceeding biological requirements, resulting in extensive fecal excretion and environmental losses. Chelation of trace metal supplements with ethylenediaminetetraacetic acid (EDTA) can mitigate the effects of dietary antagonists by preserving the solubility of trace minerals. Lack of EDTA biodegradability, however, is of environmental concern. l-Glutamic acid, N,N-diacetic acid (GLDA) is a readily biodegradable chelating agent that could be used as a suitable alternative to EDTA. The latter was tested in sequential dose–response experiments in broiler chickens. Study 1 compared the effect of EDTA and GLDA in broilers on supplemental zinc availability at three levels of added zinc (5, 10, and 20 ppm) fed alone or in combination with molar amounts of GLDA or EDTA equivalent to chelate the added zinc, including negative (no supplemental zinc) and positive (80 ppm added zinc) control treatments. Study 2 quantified the effect of GLDA on the availability of native trace mineral feed content in a basal diet containing no supplemental minerals and supplemented with three levels of GLDA (54, 108, and 216 ppm). In study 1, serum and tibia Zn clearly responded to the increasing doses of dietary zinc with a significant response to the presence of EDTA and GLDA (P < 0.05). These results are also indicative of the equivalent nutritional properties between GLDA and EDTA. In study 2, zinc levels in serum and tibia were also increased with the addition of GLDA to a basal diet lacking supplemental trace minerals, where serum zinc levels were 60% higher at the 216 ppm inclusion level. Similar to the reported effects of EDTA, these studies demonstrate that dietary GLDA may have enhanced zinc solubility in the gastrointestinal tract and subsequently enhanced availability for absorption, resulting in improved nutritional zinc status in zinc-deficient diets. As such, GLDA can be an effective nutritional tool to reduce supplemental zinc levels in broiler diets, thereby maintaining health and performance while reducing the environmental footprint of food-producing animals.
Highlights
Trace minerals, in particular trace metals such as zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe), are essential to ensure health and performance in highly productive farm animals
Analyses of the feed confirmed the high levels of Ca and phytic acid intended by design and the required Zn, ethylenediaminetetraacetic acid (EDTA), and GLDA levels (Table 1)
Significant differences were observed for feed intake between the treatments at the 5 mg/kg supplementation with birds fed the EDTA having a higher intake compared with the birds fed the GLDA
Summary
In particular trace metals such as zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe), are essential to ensure health and performance in highly productive farm animals. It is common to supply trace minerals as inorganic sources (i.e., sulfates and oxides). The most common inorganic sources typically undergo hydrolysis into the metal ion form during digestion, leaving them susceptible to precipitation with dietary antagonists such as phytate, which reduces their nutritional availability. Nutritionists formulate diets where mineral inclusion is in amounts many fold higher than the quantity retained by the animals, resulting in excessive excretion (Brugger and Windisch, 2015). The fate of dietary trace minerals, Cu and Zn, can be an environmental burden, and improving the bioavailability of trace minerals is an important step toward more sustainable animal food production (Moore et al, 1995; Dozier et al, 2003; Burrell et al, 2004)
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