Effect of stage of harvest on the yield, chemical composition, in vitro and in sacco digestibility of hybrid napier (Penniserum purpureum) variety APB N1

APBN1, a variety of hybrid napier was analysed at five stages of harvest (30, 40, 45, 50 and 60 days) for yield, leaf to stem ratio, chemical composition, in vitro dry matter digestibility, in sacco dry matter and protein degradation to find out optimum stage of harvesting. The yield of green fodder, dry matter (DM) and crude protein (CP) (MT/ ha/year) of forage harvested at 30, 40, 45, 50 and 60 days of growth ranged from 274.68 to 387.95, 47.35 to 98.81, 7.44 to 11.45, respectively. Highest (P<0.05) CP yield (11.45 MT/ha) and nitrogen free extract content (46.12%) was observed at 45 d of growth. Crude protein (15.72 to 11.34%), ether extract (3.65 to 2.26%) decreased, whereas total ash (10.88 to 13.86%), crude fibre (23.81 to 29.88%) and acid insoluble ash (3.92 to 5.14%) levels increased when forage was allowed to grow from 30 to 60 d. Similarly, NDF, ADF, hemicellulose, cellulose, lignin and silica levels also increased gradually as plant matures. The in vitro dry matter digestibility was maximum (57.87%) at 30 d and minimum (51.40%) at 60 d of growth. Effective dry matter and protein degradability decreased from 55.80 to 43.78 and from 38.30 to 33.17 per cent, respectively as plant matured from 30 to 60 days. The insoluble but degradable protein fraction ‘b’ was highest (77.07%) at 45 d of growth. Based on the biomass yield, leaf to stem ratio, chemical, in vitro and in sacco evaluation, the optimum stage of harvesting for APBN1 forage was found to be at 45 d of growth.