An experiment was conducted to determine the in vitro first-order disappearance kinetics of dry matter in grain of six semi-arid native barley cultivars (Hordeum vulgare) adapted to grow at different climates known as cold (Bahman, Makoeei), moderate (Reyhan 03, Kavir) and hot (Dasht and Sahra). Samples (n=10) were assessed for bulk density (BD) and chemical composition. In addition, in vitro first-order kinetics of dry matter disappearance, medium pH and NH3-N concentration were determined using fermentation culture. Data were fitted to an exponential equation model: D(t) = D(i).exp (-k. time) + I; where D(t) was potentially a digestible residues at time t, D(i) was a potentially digestible fraction, k is a fractional rate constant of digestion (h-1) and I was an indigestible fraction. Results showed there was significant effect of adaption of varieties to climate on bulk density and crude protein, ash, NDF (neutral detergent fiber), ADF (acid detergent fiber), soluble sugars and starch concentrations in grain of the barley cultivars evaluated (P < 0.01). Barley grain cultivars from cold climate had the highest concentration of NDF and starch, whilst hot climate cultivars showed the highest amount of BD and CP (crude fiber). The amount of ash, ADF and soluble sugar in moderate climate barley grain cultivars was higher than those of the other climates. In vitro first order disappearance of dry matter was significantly (P < 0.01) influenced by the climate. Digestible fraction, fractional rate constant of digestion and indigestible fraction of grain from cold (0.78, 0.15, 0.146), moderate (0.77, 0.16, 0.157) and hot (0.75, 0.19, 0.206) were not similar in pattern. Dasht and Bahman grains had the highest and the lowest fractional rate constant (0.23 and 0.12 h-1, respectively). Barley grain cultivars from cold and hot climates had the largest digestible fraction and fractional rate constant of digestion, respectively. The relationship between NDF content (g/kg DM) and fractional rate constant of digestion (X) was negative: NDF = -520.9X + 334.2, R2 = 0.723. It was concluded that ruminal dry matter disappearance kinetic differences do exist between barley grains cultivars obtained from different climates

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