Effect of Polyethylene Glycol and Urea Treated Pistachio by-products Silage on Phenolic Compounds, in vitro Gas Production and Holstein Dairy Cow's Performance

Two experiments were conducted to evaluate the effect of ensiling and addition of polyethylene glycol (PEG) and urea on chemical composition, phenolic compounds and cumulative in vitro gas production of fresh pistachio by-products (PB) and effect of this treating on Holstein dairy cows performance. In the first experiment, PB was supplemented with 1 and 0.5% of DM, PEG and urea, respectively and ensiled in 12 plastic bags with the capacity of 3 kg each for 60 days. Ensiling PB treated with PEG and urea decreased total phenolics, total tannins and condensed tannins (P<0.05). Addition of PEG and urea to PB silages increased the gas production after 96h incubation, ME and OM digestibility (P<0.05). In the second experiment, eight multiparous Holstein dairy cows were used in a 4×4 replicated Latin square design. Treatments were as follows: 1) corn silage (15% of diet DM), substitution of corn silage with: 2) PB silage, 3) PB silage supplemented with 0.5% of DM, urea, 4) Pistachio-by products silage supplemented with 1% of DM, PEG. Milk yield and composition were not affected by treatments. The pH was unchanged among treatments, but N-ammonia concentration was higher for urea treated PB silage (P<0.05). It was concluded that negative effects of tannins on OMD decreased, ME increased and consequently nutritional value of PB improved by PEG and urea treatment.