Effect of canopy height on the nutritive value of elephant grass silage

The ideal canopy height (CH) to harvest elephant grass for making silage has not been determined. Therefore, the objective of this study was to evaluate the yield of elephant grass (Pennisetum purpureum cv. Cameroon) and the silages produced from plants harvested at five CH: 100, 140, 180, 220, and 260 cm (described as CH100, CH140, CH180, CH220 and CH260, respectively). The experiment consisted of 25 plots with four rows each. The plants used to assess forage yield and to produce the silages were cut at ground level from the two central rows of each plot every time the canopy reached the target height. To make silages, the plants were chopped with a theoretical cut length of 20 mm and packed to a wet density of 688 kg/m3 in 15-L laboratory silos. To measure effluent production, 10 kg of sand were placed on the bottom of the silos. The silos were sealed with plastic lids, weighed, and maintained at room temperature for 60 d. At silo opening, silage was removed and subsamples were taken to determine fermentation end products, microbial counts (bacteria, yeasts, and molds), and nutritive value. The experimental design was randomized blocks with five repetitions. The data were analyzed by the mixed-model method using the MIXED procedure (SAS Institute, 2004). The means were compared by a Tukey test at 5%. Canopy height was considered a fixed effect and block was considered a random effect. CH100 and CH140 had the lowest yield (on average, 12.8 ton DM/ha) and CH260 had the highest (22.4 ton DM/ha). CH180 and CH220 showed an intermediate production (on average, 17.3 ton DM/ha). The DM concentration of the plants before ensiling ranged from 11.6 to 21.5% (P < 0.001). Canopy height did not affect fermentative and microbial characteristics of the silages. Effluent losses were greater (P < 0.0001) in silages with plants harvested at CH100 (58.4 kg/ton of fresh forage), whereas the silages from CH260 had the lowest effluent production (24.1 kg/ton of fresh forage). The in vitro digestibility of the silages produced with plants harvested at CH100, CH140, and CH180 was greater (on average, 69.9%; P = 0.0007) than that of the other treatments (57.1%). As no differences among treatments were observed in terms of fermentation quality, it is possible to conclude that the right CH to produce elephant grass silage range from 180 to 220 cm due to the greater balance between forage yield and silage digestibility.