Tannins ability to modify the fatty acid composition of milk and meat has received great attention recently. There is limited information pertaining the effects of tannins on ruminal biohydrogenation process and content of C18:1, trans-11 (vaccenic acid) and C18:2, cis-9, trans-11 CLA (rumenic acid) in ruminants meat and milk. We aimed to evaluate the effects of feeding pistachio hull (PH, source of tannin) and polyethylene glycol (PEG) supplementation on milk fatty acid profile particularly vaccenic and rumenic acid in Saanen dairy goats. Nine Saanen dairy goats were used in a 3 × 3 Latin square design. Three treatments were formulated: 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). Percentage of C18:1, trans-9, C18:1, cis-9 and C18:1, trans-11 (vaccenic acid), and C18:2, cis-9, trans-11 CLA (rumenic acid) significantly increased with addition of PH in T2. Blocking of PH with PEG significantly reduced the fatty acids but not to the same level as control group. Percentage of C18:0, C18:2, trans-9, 12, C18:2, cis-9, 12, and C18:3, cis-9, 12, 15 with increasing PH in T2 significantly increased and addition of PEG in T3 could not reduce them back to levels of control group. In conclusion, addition of PH could increase the level of polyunsaturated acids content of goat milk and PEG supplementation will conserve it while blocking PH tannin content.

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