**6. Mineral absorption and metabolism**

The amount of mineral absorbed and retained is termed as bio-availability, and this can be reflected by improved performance of animals or birds. Better bioavailability is indicated by more amount of mineral deposits in the organ, serum, and also better biological responses, and is affected by factors that influence absorption such as concentration, chemical forms, transport pathway, nutrient-nutrient interactions and excretory losses. Reports suggest that the bioavailability of inorganic salts is less, which results in high excretion of minerals into the environment through urine and feces [39]. Considering the other potential replacement of inorganic salts, organic and nano-minerals have provided encouraging biological effects when fed to animals and birds [1, 8, 21, 40, 41] with certain limitations.

Of the different mechanisms of transportation through intestinal epithelium, paracellular transport involves passage of substances across the epithelium through the intercellular spaces whereas transcellular transport involves passage of substances through the cells [42, 43]. Paracellular transport does not include any transporter or energy expenditure for transport and the absorption occurs along the concentration gradient, thus is not very efficient [42]. Tight junctions act as gatekeeper of paracellular transport and they exclude entry of macromolecules [42, 43]. Transcellular absorption involves either diffusion across concentration gradient or active carrier mediated transportation utilizing energy or through endocytosis [42]. Intestinal absorption can be improved by altering paracellular and transcellular transport. Compared with CuSO4 and CuO microparticles, CuO NP are believed to be rapidly transported into cells, and subsequently interact with the Cu transport

*Advances in Poultry Nutrition Research*

*Different methods of nano-minerals synthesis.*

**Figure 1.**

manipulation of matters at the nanoscales. Use of NP is gaining importance in diversified disciplines starting from medicine, environment, food, electronics, pharmaceutical applications, biotechnology, agriculture, and animal science [2]. Nano-minerals are specially synthesized mineral particles with its particle size ranging from 1 to 100 nm [20]. Like NP, nano-minerals possess higher physical activity and chemical neutrality, which may be a reason for efficient absorption in the animal system [21] and are reported to be stable under high temperature and pressure [22] as well. Nano-minerals as feed supplement can increase the feed efficiency, diminishing feed cost by reducing the supplemental doses, and simultaneously intensifying the yield and value of animal products by virtue of their superior bioavailability [1, 23, 24]. For example, nanominerals, due to their smaller size, were reported to be easily taken up by the gastrointestinal tract and efficiently utilized in vivo, and hence were more effective than the larger sized zinc oxide (ZnO) at lower doses [20]. Moreover, nanominerals exhibit lesser adverse effects as compared to their conventional counterparts. For instance, Reddy et al. [25] reported that nano-ZnO had less adverse effect on human cells. Nanominerals can cross the small intestine and further distribute into the blood, brain, and other different organs [26]. The functional properties of nanominerals, such as chemical, catalytic or biological effects, are highly influenced by their particle size, shape, composition, crystalline structure, surface ions, and morphology [27–29]. Nano minerals can be synthesized by physical, chemical or biological methods (**Figure 1**) [1, 19]. In physical method, physical forces are used to break down the larger sized materials to nanoscale, whereas in chemical method, reducing agents are used to reduce the particle size. Nanomaterials produced from physical method have wide range of particle size, but chemical method produce tentatively uniform particle size [19]. In biological method, also called green synthesis, different plant products or cultures are used for reducing the size of the intended materials. This method is free from use of corrosive chemicals which is the main constraint in chemical synthesis of NP. However, maintaining the culture needs technical expertise and is considered as a limitation in this method. Considering all points and methods, for use in livestock and poultry feeding, chemical method seems preferred as they are cheap, easy to

produce and do not require any special instrument and expertise [19].

Nanoparticles are quite different in physical properties from bulk materials, contributing to wide range of new applications. Due to the much-reduced particle size they exhibit novel and improved physical, chemical, and biological activity that do not necessarily resemble the bulk mineral counterpart, and thus numerous modes

**5. Mechanism of action of nanominerals**

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proteins [44], with a non-antagonism of CuO NP with Zn. Na et al. [45] suggested the possibility that CuO NP are absorbed through a different pathway that other Cu sources use [1].
