the chemical composition, in vitro gas production and digestibility of pistachio by-products

to study the chemical composition and qualitative comparison of the pistachio by-products and the effect of pistachio hull tannin on its digestibility and gas production, four experiments were carried out. in the first experiment, nutrient composition, phenolic and tannin components of the ohadi, kaleghuchi and white varieties of pistachio by-product from dehulling process were measured. pistachio epicarp (hull) was the main part of this by-product. the ohadi cultivar contained 9, 14, 8.7, 25.5 and 20.4% of ash, cp, ee, ndf and adf, and 8.6 and 4.1% phenolic components and tannin, respectively. the kaleghuchi had lower cp than ohadi and white varieties. the white variety had the lowest tannin level among them. in the second experiment the ruminal disappearance of pistachio by-product constituents including hull, peduncle, leaf, mesocarp and kernel until 24 h incubation were 0.77, 0.60, 0.66, 0.22 and 0.92 g/g, respectively; also the amount of soluble fraction of these constituents were determined 0.52, 0.37, 0.36, 0.05 and 0.77 g/g, respectively. the third trial was consisted of measuring in vitro dry matter and organic matter digestibility of different pistachio by-product varieties. the dry matter digestibility of the ohadi, kaleghuchi, and white cultivars were 58, 68, and 64%, respectively and were significantly different (p<0.01), but for the epicarps were not different. adding poly ethylene glycol (peg) could increase dry matter and organic matter digestibilities of the epicarp + soybean meal and the epicarp + alfalfa mixtures (p<0.05). in fourth experiment adding peg caused significant increase in gas production by pistachio hull (p<0.01). overall, it seems this by-product degrades slowly in the rumen, because the 50 percent of it dissolved in the water, but only 20 percent disappeared in the rumen after 24 h. also, it seems that the percentage of constituents and the presence of anti-nutritional factors such as tannin in this by-product could affect the digestibility of its nutrients