De-hulling of pistachio soon after harvest produces large amounts of Pistachio by-product ((. Storage of this by-product is difficult due to its high moisture content. Three experiments were conducted to determine the possibility of ensiling , nutritive value and its potential as a feed ingredient for Holstein male calves. In the first experiment, chemical composition, more specific physical and chemical characteristics, in vitro digestibility, ruminal and post ruminal disappearance of nutrients and contamination with B and G aflatoxin were compared between and Pistachio by-product silage (). There was no difference between CP, EE, ADF om , buffering capacity, hydrolysable tannins, condensed tannins and total tannins, non protein nitrogen (), acid detergent insoluble nitrogen (ADIN), ruminal and total gastrointestinal tract disappearance of dry matter and CP, in vitro digestibility of dry matter and aflatoxin poison of B and G. The was lower in NDF om , water soluble carbohydrates (WSC), pH and insoluble protein. The post ruminal disappearance of DM and CP and higher in total phenolic compounds and soluble protein than sundried . In the second experiment, was ensiled without additive (Control) or with the additives beet sugar molasses (3% of DM), bacteria ( Lactobacillus plantarum, 0.0625 g/ 25 Kg fresh ) and enzymes (multi enzyme, 12.5 g/25 kg fresh ) in either for 1 or 2 months in a random design, using a factorial procedure (4×2). The addition of molasses to decreased seeping and pH more than other additives (P 0.05). The lactic acid in the enzymatic treatment were lower than the control silage, but there was no difference in NH 3 -N, acetic acid, propionic acid and total volatile fatty acids (VFA) between treatments, however silages stored for 1 month had a lower pH and were higher in acetic acid, butyric acid and total VFA compared to silages stored for 2 months. The CP and NDF om in the molasses treatment were higher than other treatments, and the total amount of tannins in the silage containing additives was lower than the control silage (P 0.05). The aerobic stability in was very desirable and was not affected by any of the additives. had a lower water holding capacity (WHC) than the corn silage (P 0.05). Two month silages had higher buffering capacity than the silages of one month (P 0.01). The amount of gas production was significantly lower with the enzymatic additive than with the molasses and bacterial additives (P 0.05). Adding poly ethylene glycol (PEG) increased gas production of in all treatments (P 0.01). In the third experiment, the effects of experimental diets containing 0, 6, 12 and 18 % (DM basis) on health, growth performance, nutrient digestibility, ruminal fermentation parameters, microbial protein synthesis (MPS), blood metabolites, physical and chemical properties of urine and chewing activity of calves were investigated. Twenty-four Holstein male calves (4-5 months of age and 155.6 ± 13.5 kg body weight (BW)) were randomly assigned to one of four experimental diets (n=6) for six months. All the calves were healthy at the end of experiment and no clinical symptoms of disease were found during of experiment. Throughout entire experiment, the final BW, average daily gain (ADG), dry matter intake (DMI) and feed conversion ratio (FCR) was not adversely affected by the different levels of up to 12% of the diet. Increasing levels of linearly decreased (P 0.05) digestibility of CP, NDF om and ADF om of the diets and increased rumination time. Increasing the levels of to 12 and 18% in diets, significantly decreased NH 3 -N, total VFA and MPS (P 0.01). The substitution of different levels of (?18% of DM) over a long period did not affect the concentration of blood metabolites hepatica enzymes, hematology parameters urine parameters and all remained within the normal range for calves. It can be concluded that could be a silage and under our experimental conditions, can be substituted with corn silage up to 12% in fattening calves without adverse effect on their performance, kidneys function, blood metabolites and hepatica enzymes. Key words : Pistachio by-products, silage, fattening calf, performance, bloods metabolites and microbial protein.