This study was conducted to evaluate the effect of partial and total substitution of lucerne hay with pistachio by-product on nutrient intake, apparent digestibility, rumen fermentation, digesta kinetics, blood metabolites, nitrogen retention and microbial protein synthesis in Baloochi sheep. Six sheep with a bodyweight of 40.1 ± 1.77 kg fitted with ruminal and abomasal cannulae were assigned at random to three diets in a double 3 × 3 Latin-square design. The dietary treatments included a control (basal diet), low pistachio by-product diet (50% of the lucerne hay in the basal diet was replaced by pistachio by-product), and high pistachio by-product diet (all of the lucerne hay in the basal diet was replaced by pistachio by-product). The daily basal diet was 500 g/kg DM lucerne hay, 250 g/kg DM wheat straw, 210 g/kg DM barley grain, 30 g/kg DM cotton seed meal, 8 g/kg DM vitamin–mineral supplement and 2 g/kg DM salt. Faeces and urine were collected for 8 days and used to estimate digestibility, nitrogen retention and microbial protein synthesis. Sheep were dosed ruminally with Cr-EDTA (2.27 g/L) and rumen samples were evaluated for pH, volatile fatty acids, ammonia nitrogen concentrations and digesta kinetics. The intake of neutral detergent fibre, purine derivatives excretion, volatile fatty acid concentrations in the rumen and ammonia nitrogen in the abomasum decreased (P < 0.05). Ether extract intake and ruminal pH was increased at 5 h after feeding (P < 0.05) as the level of pistachio by-product in the diet increased. Total pistachio by-product replacement for lucerne hay increased (P < 0.05) apparent digestibility of nitrogen, ether extract, organic matter and nitrogen retention and decreased (P < 0.05) microbial protein synthesis, efficiency of microbial protein synthesis and ammonia nitrogen in the rumen. The inclusion of pistachio by-product had no effect on blood metabolites and digesta kinetics. Based on these results it was concluded that pistachio by-product can be considered as a useful replacement for lucerne hay in the diet of Baloochi sheep without any negative impacts on their responses. Moreover, pistachio by-product inclusion in diet improved nitrogen metabolism in Baloochi sheep.

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