Abstract content
Zinc (Zn) and copper (Cu) supply recommendations for broilers were estimated decades ago to be 50 and 7 mg/kg feed, respectively [1]. Although these values are well established and already above the actual requirement, the amounts of Zn and Cu in practical diets are usually higher. The reason for this is the desired goal of fully exploiting the genetic growth potential or supporting the immune system with these trace elements used [2]. On the other hand, heavy metals such as Zn and Cu are known to pose a risk to the environment. For example, it is shown that bacteria could develop resistance to these trace minerals or even co-resistance to antibiotics [3]. Therefore, the aim of this study was first to identify the different ranges of Zn and Cu concentrations in broiler diets and excretions. Second, feasible indicators to evaluate the environmental burden between farms independent on the different Zn and Cu sources should be suggested.
Methods: A literature review was conducted. For this purpose, studies and data on the determination of requirements, the use of different trace element sources (e.g., organic versus inorganic) and excretion were collected, summarized and evaluated. Relevant studies were found through targeted search in different scientific databases using defined combinations of keywords. Used terms were variating versions of “zinc“ and “copper“ combined with the variations “feeding” / “ration” or “manure” / “excretion” and “poultry” / “broiler”. Publications were included if they were published in a peer-reviewed journal in English without any limitation on the year or geographical origin of the publication.
Results and discussion: To obtain an overview of the Zn and Cu levels used, Zn and Cu feeding studies and other investigations with published composition of the experimental diet were reviewed (n = 15). Most of them estimated or evaluated the requirement of these trace elements for broilers (n = 4), investigated the effects of different amounts and sources of Zn (n = 6) or Cu (n = 5) on broiler performance and excretion, or studied the practical feeding and excretion situation of Zn and Cu in livestock (study n = 1; samples n = 12). Six of the publications dealt with hypothesis independent of Zn or Cu level or source. The amount of trace elements in the diets varied from 32 to 200 mg Zn/kg and 4,9 and 125 mg Cu/kg feed, corresponding to concentrations of 64 to 400% for Zn and 70 to 1786% for Cu of the GfE supply recommendation. Besides that, all studies read, which estimated the requirement of Zn and Cu for broiler, agreed that the recommended amount is sufficient for optimal broiler growth. This means that excessive Zn- and Cu-supplementation will not improve performance of the birds but will increase excretion via feces and bile. Excretions of Zn and Cu were estimated in widely varying units. An interesting consideration was the determination of relative amount of bedding to the intake, but bedding needed to be considered as a source of Zn and Cu in order to mirror the balance for comparisons between farms. Using this evaluation parameter, several studies (n = 5) could be compared and showed a wide range of relative extraction of Cu and Zn from about 10 up to > 100%, whereby highest proportions originate from ignoring bedding, naming of the sample (excretion, litter, manure) and differences of the sampling itself.
Conclusion: It can be assumed that Zn and Cu can be reduced in practical diets of broiler to limit environmental impacts. To make an inter-farm evaluation of the environmental burden from broiler production, estimation of the relative excretion to intake seems to be promising, if corrected by bedding as an additional source. For such balance, feed, bedding and manure samples from practical poultry farms should be analyzed. Moreover, these parameters seem to allow an inter-farm evaluation of the environmental burden of Zn and Cu and perspectively, a risk analysis of bacterial resistance, for which little data are currently available.
Bibliographical references
[1] GfE. 1999. Empfehlung zur Energie- und Nährstoffversorgung der Legehennen und Masthühner (Broiler). 144. DLG-Verlags-GmbH. Frankfurt am Main.
[2] Tang Z G, Wen C, Wang L C, Wang T, Zhou Y M. 2014. Anim. Feed Sci. Technol. 189:98-106.
[3] Yazdankhah S., Rudi K., Bernhoft A. 2014: Microb. Ecol. Health Dis. 25:25862.
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Abstract content
Zinc (Zn) and copper (Cu) supply recommendations for broilers were estimated decades ago to be 50 and 7 mg/kg feed, respectively [1]. Although these values are well established and already above the actual requirement, the amounts of Zn and Cu in practical diets are usually higher. The reason for this is the desired goal of fully exploiting the genetic growth potential or supporting the immune system with these trace elements used [2]. On the other hand, heavy metals such as Zn...
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