Tannins reduce the protein degradation in the rumen, shift the site of N metabolism from rumen to the lower digestive tract and large intestine. Shifting excretion pattern of nitrogen from urine to faces and formation of tannin–protein complex are beneficial environmentally. High levels of tannins in the diet may have negative effects on feed intake and digestibility of nutrients and polyethylene glycol (PEG) could eliminate it. We aimed to evaluate the effects of feeding pistachio hull (PH, source of tannin) and PEG on nitrogen metabolism in Saanen dairy goats. Nine animals were used in a 3 × 3 Latin square design. Treatments were: T1) Control, without PH, T2) 30% PH (DM basis) that provided 18.1 g condense tannin per kg DM of diet, and T3) 30% PH + 1% PEG (DM basis). In T2 and T3, PH replaced alfalfa hay. Statistical analysis was performed using the MIXED procedure of SAS (P < 0.05). Addition of PH in T2 and T3 (despite of addition PEG) reduced the nitrogen intake. In addition, urinary nitrogen excretion was significantly decreased and fecal nitrogen excretion was increased by addition of PH in T2 and PEG supplementation in T3 increased or decreased them respectively but not to the similar values like control group. Milk nitrogen excretion was not affected by experimental diets. Nitrogen digested was significantly decreased by substitution of PH in diet in T2 and T3 (despite of addition PEG). Nitrogen retained was not affected by experimental diets. To sum up, using of high levels tannin in the diet could alter protein metabolism positively from an environmental aspect and supplementation with PEG could reduce possible negative effectsof tannin on performance.

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