Ensiling characteristics, digestibility and palatability of tropical grasses as affected by growth stage, chopping length and additives

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Virginia Polytechnic Institute and State University


Research was conducted in Sri Lanka to study the effects of growth stage, chopping length and additives on ensiling characteristics of Guinea-'A' (Panicum maximum - Ecotype-'A') and NB-21 (Pennisetum purpureum Schumac x Pennisetum americanum). The forages were harvested 1, 2 and 3 wk after growth, chopped and ensiled in small laboratory silos (3 liter cardboard cylinders double lined with polyethylene bags) alone or with additions of cassava tuber meal, coconut oil meal and formic acid. Cutting grass at 1 wk increased (P<.05) acetic and lactic acid of silage, compared to 3 wk. Addition of cassava tuber meal and coconut oil meal increased (P<.05) lactic acid and decreased (P<.05) pH and acetic acid of silage, compared with the control. The effects were greater for cassava tuber meal.

In a second study 3-wk growth of Guinea-'A' grass was hand chopped to 1.5, 7.5 and 15 cm, and ensiled in small laboratory silos. Lactic and acetic acid of silage increased (P<.01), whereas dry matter loss and pH decreased (P<.05) with fineness of chop. In a third study, 2 and 3 wk growths of Guinea-'A' were harvested and ensiled in 210 liter metal drums, double lined with polyethylene bags, chopped or unchopped. Cutting grass at 2 wk decreased (P<.05) pH and increased (P<.01) lactic acid, compared to 3 wk. Chopping decreased (P<.05) the pH and increased (P<.05) lactic acid and acetic acid of silage.

Experiments were also conducted to study the digestibility and palatability by sheep of Guinea-'A' silage prepared in the third study. Apparent digestibility of dry matter (DM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were higher (P<.01) for 2 wk compared to 3-wk growth. Chopping the grass before ensiling increased (P<.01) the apparent digestibility of DM, CP, NDF, ADF and hemicellulose. No significant differences were observed for DM intake by sheep due to the growth stage, but chopping increased (P<.01) DM intake by 17%.

Lengthening the cutting interval of Guinea-'A' and NB-21 resulted in linear increases (P<.01) in DM yield.