An in vitro experiment was conducted to determine the effect of chemical or physical treatments on disappearance kinetics of dry matter, neutral detergent fiber (NDF) and acid detergent fiber (ADF) of cottonseed hulls (CH). For chemical treatment, CH were treated with NaOH as 20 g/kg DM [a 20% solution of NaOH was sprayed on CH and kept for 0.5 h (CH2S0.5) or 48 h (CH2S48)] or 40 g/kg DM [a 40% solution of NaOH was sprayed on CH and kept for 0.5 h (CH4S0.5) or 48 h (CH4S48) at room temperature]. Physical processing was done using microwave irradiation (900 W) for 4, 6 and 8 min (CHm4, CHm6, CHm8, respectively). Fifty-five ml of medium was supplied into 100 ml bottle containing 0.45 g of each sample DM (4 replicates). Then, each bottle was inoculated under carbon dioxide with 5 ml of mixed rumen microbes 24, 48, 72 and 96 h. Then, contents of each bottle were filtered through a 22 µm filter, DM and neutral detergent fiber (NDF) of the unfiltered medium was determined. Kinetic disappearance parameters were determined using first order exponential model of D(t)= D(i).e(-k. time)+ I; D(t) is potentially digestible residues, D(i) is potentially digestible fraction, k is fractional rate constant of digestion (/h), and I is indigestible fraction. Chemical or physical treatment improved DM disappearance significantly (P<0.05). There was no significant difference in disappearance of NDF between microwave irradiated CH for 4, 6 and 8 min. Microwave irradiation for 8 minutes at 48 and 72 h incubation showed the highest ADF disappearance among the treatments. Physical or chemical treatment had no significant effect on first order DM disappearance of CH.

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