This study was conducted to evaluate the effect of feeding pistachio by-products silage with or without supplementation of polyethylene glycol (PEG) and urea on intake, apparent total digestibility, ruminal fermentation and performance of dairy cows. Eight multiparous Holstein dairy cows averaging 61 23 DIM and 38 3.6 kg of milk production were used in a 4*4 replicated Latin square design. Fresh pistachio by-products (PB) averaging 32% dry matter (DM) were supplemented with PEG and urea at 1.0% and 0.5% of DM, respectively, and then ensiled for 60 day. Experimental treatments were as follows: (1) corn silage(15% of diet DM) as a control, substitution of corn silage with: (2) pistachio-byproducts silage (PBS), (3) PBS supplemented with urea, and (4) PBS supplemented with PEG. Intake of DM and apparent digestibility were not affected by treatments (P 0.05). There was no difference in milk yield and composition (P 0.05). However, a trend (P 0.07) for more milk protein production (kg/d) and more (P 0.09) milk fat concentration (%) was observed in cows fed PBS compared to those fed corn silage.The ruminal pH was similar among treatments (P 0.05).There was significant difference in ruminal NH3–N and serum urea N among treatments (P 0.05). Results of this study show that under our experimental conditions, PBS can be substituted with corn silage upto 15% of diet DM in dairy cows ration without negative effects on animal performance.

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