This study was conducted to evaluate the effect of formaldehyde or sodium hydroxide on in situ ruminal disappearance and in vitro intestinal digestion of high oil (165 g/kg DM) sunflower meal (SM). Samples were: Untreated SM (USM), sodium hydroxide treated SM (SHSM, 40 g/kg DM), formaldehyde treated SM (F30SM and F60SM, 30 and 60 g/kg DM, respectively). Ruminal disappearance of sample was determined using four fistulated Holstein steers (400±12 Kg, body weight). Samples were weighed into nylon bags (19×12 cm, pore size 48 μm, n=6) and incubated in rumen for12 h. An in situ/ in vitro enzymatic 3-step procedure was conducted to determine post-ruminal disappearance of the samples. In this procedure, a part of ruminal-undegraded nitrogen (after 12 h rumen incubation) was included in pepsin and pancreatin to determine post-ruminal protein disappearance of the sample. DM content of all intact and incubated samples was determined using air-forced oven (65°C, 48 h). Nitrogen concentration of the samples was determined using Kjeldahl method. Data were analysed using GLM procedure of SAS. Results indicated that ruminal DM and CP of F60SM was significantly (P < 0.05) lower (0.42 and 0.39, respectively) than USM (0.7 and 0.65, respectively). Formaldehyde and sodium hydroxide caused an increase in post-ruminal CP disappearance (0.44, 0.4, 0.33 and 0.27 for F60SM, F30SM, SHSM and USM, respectively). Total tract CP digestibility for F60SM, F30SM, SHSM and USM was 0.83, 0.85, 0.88 and 0.93. It was concluded that both formaldehyde and sodium hydroxide caused an increase in the ruminal and post-ruminal CP disappearance of high oil content sunflower meal.

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