The aim of this study was to determine possible differences between first cut and second cut forage of Bir-jand ecotype of Kochia scoparia for chemical composition and fermentability, and to evaluate the changes may be induced by N fertilization in chemical composition, fermentability, and utilizable crude protein (uCP) supply at the duodenum of dairy cows of Sabzevar ecotype of Kochia. Birjand ecotype was sampled in mid bloom and Sabzevar ecotype was sampled in first bloom stage of maturity. Different in vitro gas production methods were used to determine gas production kinetics and uCP andeffective uCP (EuCP) supply of the forage samples.Results of the first experiment showed that there is no significant difference between first cut and second cut forage of Kochia scoparia for gas production kinetics (P>0.05), but sig-nificantly lower content (g/kg DM basis) of neutral detergent fiber (NDF) (451.1) and hemicellulose (233.7) and higher content of CP (100.1) and ash (133.4) were observed in the first cut than those of the second cut plants (P<0.01). The results of second experiment indicated that the application of moderate levels of the N fertilizer (115 kg N/hectare) on Sabzevar stands of Kochia scoparia induced considerable changes in chemical composition, fermentability, and protein degradability of forge, so that, dry matter (DM), NDF, and hemicellulose declined and CP and ash content of forage increased (P<0.05). Moreover, the gas pro-duction kinetics decreased and supplied amounts of uCP and EuCP increased in association with increase in CP and true protein content (P<0.05).

Keywords