The study compared three underused agro-industrial by-products which were pomegranate seed pulp (PSP), pistachio hulls (PH) and tomato pomace (TP) available in dry areas with respect to their potentiality influence on ruminal fermentation, performance and milk fatty acid (FA) profile of dairy goats. Eight multiparous lactating Saanen goats were randomly assigned to a 4 × 4 Latin square design with 4 dietary treatments over 21-day periods. The dietary treatments were: control diet (CON), and diets containing either PSP (120 g/kg DM), PH (240 g/kg DM), or TP (240 g/kg DM), substituting for wheat bran of the control diet. All diets were kept isoenergetic and isonitrogenous with a forage to concentrate ratio of 45:55 (DM basis). The most abundant FA in the lipids of PSP and TP werec9,t11,c13-18:3 and c9,c12-18:2, respectively, while PH was rich in c9-C18:1 and phenolic compounds. No consistent treatment effects were observed on DM intake, milk yield, milk fat, protein, and lactose yields. Pomegranate seed pulp increased (P < 0.01) milk fat concentration compared with CON and PH diets and protein concentration of the milk samples obtained from animals fed by PH diet was highest among the treatments. There was no diet effect on ruminal pH, while rumen ammonia-N concentrations, volatile fatty acid concentrations and, to a lesser extent, molar proportion of acetate were decreased following PH diet feeding. Blood cholesterol concentration increased (P < 0.01) with PSP and TP diets. The blood urea N concentration decreased (P < 0.05) when PH diet was fed. Feeding TP diet decreased (P < 0.01) 16:0 and tended (P < 0.10) to increase c9-18:1 proportion in milk fat in comparison to the other diets. Inclusion of all by-products increased (P < 0.01) t11-18:1(2-fold) and total conjugated linoleic acids (CLA, 5 to 6-fold) in milk fat compared to CON diet. In addition, concentrations of c9,c12,c15-18:3 and total polyunsaturated FA (PUFA) in milk fat component were highest (P < 0.01) in the milk samples of animals fed by PSP diet.

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