The effects of different forms of zinc on characteristics digestibility of diatery dairy cows with high ‎production using gas production and nylon bags techniques

Zinc is an essential trace mineral for all forms of life because it plays an important role in ‎DNA and RNA synthesis by increasing replication and cell proliferation. Zn deficiency in grazing and ‎forage feed is widespread in Iran and other countries, so Zn supplements are generally required for ‎ruminants. Several kinds of Zn sources have been used in diet ruminants. Supplemental Zn is usually ‎added to animal diets in the form of inorganic Zn (Zno and Znso4), However,. Many studies reported ‎that organic Zn is absorbed more readily by ruminants than inorganic Zn. Recently, a novel elemental ‎Zn source used in animal diets. The development of nano technology holds unique properties for nano ‎Zn, because nanometer particulates exhibit novel characteristics, such as great specific surface area, high ‎surface activity, high catalytic efficiency and strong absorbing ability. The objectives of this study were to evaluate the effects different forms of zn on feed digestibility, rumen fermentation of diatery dairy ‎cows with high production using gas production and nylon bags techniques.‎

The Zno naoparticles were prepared by chemical co-precipitation method. The ‎basal diet for sheep and dairy cows were provided according to NRC (2007) and NRC (2001) ‎respectivelely, to meet requirements, except of Zn. The four various tretments in the current experiment ‎were as: (1) the basal without Zn supplementation. (2) the basal diet plus 40 mg Zn/kg DM as zinc ‎oxide (Zno), (3) the basal diet plus 40 mg Zn/kg DM as zinc glycine (ZnGly, ZnGly, B-TRA MIX R ‎‎2C, 18.5% Zn) and (4) the basal diet plus 40 mg Zn/kg DM as Zn nano (zn>99%, 15-20 nm). Four ‎ruminal fistuled male sheep were used in a replicated 4×4 Latin square, experiment with four 28-day ‎periods (21 day adaptation and 7 day sampling collection each period). Nylon bags methods 5g of ‎samples were incubated in the rumen of fistulated sheep for 0, 2, 4, 8, 12, 16, 24, 36, 48, 72 and 96 h ‎for determination degradability of dry matter (DM) and crude protein (CP). The gas production was ‎recorded after 2, 4, 6, 8, 12, 16, 24, 36, 48,72 and 96 h of incubation. Ruminal fluid were used for pH, ‎ammomia-N, voliate fatty acids (VFA). ‎

In present study, the highest amount of gas production was obtained in ‎organic, nano and in organic zin supplemented treatments respectively. Zinc supplementation ‎significantly increased the OMD, SCFA and ME concentrations (p < 0.05). The results of this study ‎showed that Zinc supplementation significantly (p < 0.05) decreased the N-NH3 concentration in ‎different experimental groups. There was no effect on molar proportion of acetate and butyrate ‎‎(p < 0.05), whereas that of propionate was linearly (p < 0.05) increased with increasing nano-zn and ‎glycine-zn supplementation. As a result, ratio of acetate to propionate was decreased. Total ruminal ‎VFA concentration was increased (p < 0.05) as Zinc Supplementation. Increasing the concentration of ‎total volatile fatty acids in the rumen can be due to improved microbial fermentation in the rumen. In ‎situ trial, adding zn in forms nano and organic increased the DM disappearance (p < 0.05). Also zn ‎supplementation significantly increased ;b; fraction of DM of diatery cows with high production in ‎different experimental groups. The present results suggested zn functions to maintain the production of ‎proteolytic digestive enzymes and activity of protein decomposing bacteria could be improved by zn. In ‎‎24 to 96 hours incubations crude protein degradability zn-glycine and nano-zn was significantly ‎‎(p < 0.05) lower than zn oxide and control treatments. Also zinc Supplementation in forms nano and ‎organic decreased (p < 0.05) ;b; fraction and ;ED; of crude protein of diatery cows with high production ‎compared to control and zinc oxide treatments. The reason for this can be because of the low solubility ‎of proteins dietary due to bonding with the zinc element in the rumen or the change in the activity of ‎the proteolytic microbes.‎

The results suggested that the addition of zinc in the forms of organic and nano increased ‎the fermentation and degradability of the dietary high production dairy cows compared with inorganic ‎form. Also, there was no difference in digestibility and fermentation between organic and nano forms; ‎hence, in order to select the nanoparticulate or organic form of zinc element in the diet of animals, it ‎was necessary to pay attention to their price and price in the market.‎