Effects caused by different doses of dietary chromium nanoparticles fed to broiler chickens

Abstract

Chromium is important chemical element for humans and animals which essentiality is manifested in reducing the amount of glucose and cholesterol in blood, reducing body fat. Factors which influence the absorption of chromium are source, size and composition of diet. Reducing size of Cr particles allows one to increase absorption. Replacement of traditional sources of microelements for organic and ultrafine metal forms is prospective due to their surface area, higher reactivity and bioavailability. In this paper, we show for the first time that Cr2O3 nanoparticles (NPs) at doses of 50 to 100 µg/kg of feed have no toxic effect, improve productive performance through stimulation of digestive enzymes and have positive effect on accumulation of the element in broiler chicken carcass. Our goal was to estimate effects of various doses of dietary chromium nanoparticles on the activity of digestive enzymes, biochemical blood parameters and gut microbiota in Arbor Aikres broiler chickens (Gallus gallus) (OAO Orenburg Poultry Farm, 2018). Five groups of chickens were formed, control and test groups 1, 2, 3, and 4 (n = 30 each) with live weight from 160 to 180 g. The control birds during experiment (0-14-21-42 days) received the basic diet, the birds of groups 1, 2, 3, and 4 additionally received 50, 100, 200 and 400 μg/kg feed of dietary Cr2O3 NPs (d = 91 nm; Plat-ina LLC, Moscow, Russia). Addition of 200-400 µg/kg Cr2O3 NPs increased body weight and improved feed conversion by 3.1-3.9 and 7-11 %, respectively (p 0.05), compared to control. Cr incorporation into carcass was 28.2 and 25.6 % higher when broilers were fed with NPs at 200 and 400 μg/kg, respectively, while this index in droppings was 15 % lower. Increased Crfeed/Crdroppings (1.5-2.5) and Crfeed/Crcarcass (4.6-6.4) values in the test groups indicate better absorption of chromium in the gastrointestinal tract. Cr2O3 NPs caused higher activity of endogenous transferases, the alanine aminotransferase and aspartate aminotransferase. Catalase and superoxide dismutase activity remained unchanged as well as concentration of malonic dialdehyde. That is, chromium acts as antioxidant, with up to 18 % increase (р 0.05) in blood NO-metabolites. Cr2O3 NPs stimulate activity of blood enzymes: by 29.5 % (group IV, p 0.05) on day 21 for amylase, by 19-30 % (group III and IV, p 0.05) on days 21 and 42 for lipase, followed by a decrease in lipolytic activity by the end of the experiment in the test groups compared to day. NPs of 50 and 400 μg/kg suppressed amylase and activated lipase and protease in the duodenal chymeduction, with an increase in pH of the intestinal contents from 4.62 to 9.34 in all test groups. In droppings, digestive enzymes showed a reverse trend. Dietary Cr2O3 NPs at 50 µg/kg decreased the number of bifidobacteria, staphylococci and Salmonella in droppings, at 100 μg/kg increased the counts of enterobacteria, and at 400 μg/kg, on the contrary, reduced enterobacteria by 20 %, with simultaneous restriction Salmonella abundance in the cecum. Dietary Cr2O3 NPs decreased bifidobacteria. Thus, the dietary Cr2O3 NPs at 50-100 µg/kg has more pronounced positive effect and can be used as a chromium additive for poultry (for example, in premixes or vitamin-mineral complexes).