The objective of this study was to determine in situ dry matter (DM) and crude protein (CP) degradability of sunflower meal containing 25 and 165 g fat kg-1 DM and untreated and treated with sodium hydroxide (NaOH, 40 g kg-1 DM) and formaldehyde ( 30 and 60 g kg-1 DM). DM and CP degradation of the samples were determined using in situ technique in two fistulated Holstein steers (400±12 kg, body weight) and data were analysed to estimate soluble fraction (a), potentially degradable fraction (b), degradation rate (c) and effective degradability (ED). Formaldehyde decreased (a) fraction of DM (p<0.05). NaOH treated high fat sunflower meal had the highest (a) fraction and the lowest of (b) fraction of DM, (0.43 and 0.31, respectively). Formaldehyde and NaOH significantly decreased degradation rate (c) of DM. Formaldehyde (30 g kg-1 DM) treated low fat sunflower meal had the lowest ED of DM (0.44, k = 0.03 h 1) (p<0.05). Fraction of (a) and ED of DM of low fat sunflower meal was less than high fat sunflower meal. Formaldehyde and NaOH significantly were affected fractions of a, b, c and ED of CP (p<0.05). Fraction of (a) of CP decreased by formaldehyde and NaOH. Treatment of sunflower meal (low and high fat) with formaldehyde at 60 g kg-1 DM resulted in the highest (b) fraction and the lowest of (c) fraction and ED of CP. Crude protein (b) fraction of low fat sunflower meal was more than high fat sunflower meal but there was not any significant difference for (a) fraction and ED. DM and CP disappearance after 24 h was decreased by formaldehyde and NaOH. Therefore, it is appears that formaldehyde, NaOH and fat content of sunflower meal can affect DM and CP degradability parameters.

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