his study was aimed to evaluate the pattern of fermentation of different citrus pulp sources including; orange (Citrus sinensis), tangerine (Citrus reticulate), lemon (Citrus auranifolia) and grapefruit (Citrus paradisi) by gas production method. Dried citrus pulp (DCP) is an agro-industrial by-product with high level of energy and low in CP and NDF. The DCP samples were collected from different citrus-processing industry in north part of Iran. The procedure of in vitro gas production method developed by Menke (1988) was used. Rumen fluid was collected from two ruminally fistulated, steers and mixed. The amounts of gas production were monitored at 0, 2, 4, 12, 24, 36, 72 and 96 h and cumulative gas production were calculated. Data were subjected to analysis of variance using SAS program. C.reticulata cul.younesi and Citrus aurantifolia had higher and lower Cumulative gas production compared to other DCP (487.9, 518.9, 522.9, 50.9, 492.2, 474, 530.5, 425.2, 458.1 and 466.3 ml/g DM for C. Sinensis cul. Tamson, C. Sinensis cul.siahvaras, C. Sinensis cul. Brohen, Citrus unchiu, C.reticulata cul. Page, C.reticulata cul. Celemantin, C.reticulata cul.younesi, Citrus aurantifolia, Citrus aurantium and Citrus paradisi respectively). Gas production rate of C. Sinensis cul.siahvaras was numerically higher than others (0.05, 0.08, 0.08, 0.05, 0.05, 0.07, 0.08, 0.04, 0.08 and 0.06 ml/g DM /h for C. Sinensis cul. Tamson, C. Sinensis cul.siahvaras, C. Sinensis cul. Brohen, Citrus unchiu, C.reticulata cul. Page, C.reticulata cul. Celemantin, C.reticulata cul.younesi, Citrus aurantifolia, Citrus aurantium and Citrus paradisi respectively). Total gas production was higher for C.reticulata cul and lower for Citrus aurantifolia (500.2 vs. 449.7 ml/g DM). Maximum gas production of different citrus pulp sources achieved with in 24 h and increased up to 48 h but at a much lower rate.Result indicated that various sources of dried citrus pulp have potential as feedstuff for ruminants.

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