Effect of ensiling duration on nutritional composition and oxalate content in dwarf Napier grass silage

Abstract

Napier grass (Pennisetum purpureum) is a common forage plant that is usually given to ruminant animals. Besides moderate nutritive values, this grass also contains anti-nutrients such as oxalate. Dietary soluble oxalate can combine with blood calcium (Ca) or magnesium (Mg) and form insoluble crystals, which can give negative effects on animal health. This study was conducted to assess the effects of ensiling durations on fermentation characteristics, nutritional composition and oxalate content of dwarf Napier grass silage. Plants were cultivated under standard level of fertiliser application, harvested at 45 days of plant maturity, and then chopped into 2-3 cm manually. Chopped grasses were mixed with 5% molasses (w/w), and filled in plastic bags, compressed and kept it in air-tight conditions in room temperature at five different ensiling durations (0, 15, 30, 60 and 90 days). Three replicates were made for each of the treatment durations. The fermentation characteristics, chemical composition and oxalate content, were evaluated. Silage at 30 day fermentation showed the highest lactic acid (10.02%) and NH3-N (1.79%) contents, while silage at 90 d fermentation showed the lowest lactic acid (3.47%) and NH3-N (1.50%) contents. The initial pH value (pH 5.01) and dry matter content (22.8%) declined to pH 4.36 and 20.2% at the end of 90 d ensiling period. Ensiling significantly improved the crude protein, ether extract and ash contents of Napier grass silage. The soluble, insoluble and total oxalate contents in silage decreased as ensiling durations increased. Ensiling also significantly improved the sodium contents of Napier grass silage, while no consistent trend was observed on Ca, Mg and potassium contents. The results suggest that at least 30 days of ensiling duration can be recommended for Napier grass silage to get the optimum nutrients and oxalate content.