Assessment of in vitro ensilability of jack bean (Canavalia ensiformis) and cowpea (Vigna unguiculata) grains, sole or mixed with sorghum (Sorghum bicolor) grains


Abstract


Jack bean (Canavalia ensiformis), cowpea (Vigna unguiculata) and sorghum (Sorghum bicolor) grains are alternative feedstuffs for pigs in the tropics. However, ensilage as a method for conservation has to be investigated. Ripe grains of cowpea (CWP) and jack bean (JBN) were chemically analyzed and ensilability was tested by the Rostock Fermentation Test (RFT). The buffering capacity (BC) was 8.9, 6.3 and 3.1 g lactic acid (LA)/100 g DM for JBN, CWP and sorghum (SOR), respectively. For RFT, 50 g milled grains were incubated with 200 mL of deionized water (30 C). Variants were performed in triplicate: control without additive, molasses (MOL, 4 %), Lactobacillus plantarum (LAB, 3x105 cfu/g), MOL+LAB. As well, SOR was mixed with legume grains. At 0, 14, 18, 22, 26 and 38 h pH was measured and filtrates were analyzed for LA, volatile fatty acids, alcohol and NH3 after 38 h. The lowest pH (P < 0.05) at 38 h was determined for JBN+LAB+MOL, JBN+LAB+SOR, CWP+LAB, CWP+LAB+MOL and CWP+LAB+SOR. For the variants CWP+LAB and CWP+LAB+MOL the highest LA production (P < 0.05) and the lowest levels of acetic and butyric acid as well as NH3 were determined (P < 0.05). RFT revealed the necessity of LAB inoculation and addition of molasses for a sufficient acidification. Mixed silages are an option to be used when SOR
grains have to be harvested at high moistures.
Key words: Jack bean, cowpea, sorghum, in vitro ensilability, Rostock Fermentation Test

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