Legumes in maize straws : nutritive value, palatability indices and silage fermentation parameters

Abstract

Legume leaves from lablab and cowpea can be incorporated in ruminants' diets due to their high feeding value. They are rich in crude protein (CP), vitamins and minerals when compared to grasses that usually deteriorate during dry periods. The objective of this study was to determine the effect of supplementing legume leaves in maize straws on nutritive value, palatability indices and silage fermentation parameters. The study was conducted at the North-West University farm (Campus) and research farm (Molelwane), Mafikeng, North West province of South Africa. The study sites are located in the semi-arid region with geographical coordinates (25°49'22" S and 25°36'54" E) and (25°47'27" S and 25°37'18" E). Four legume species including Lablab purpureus and 3 Vigna unguiculata varieties (Dr Saunders, Betswit, and indigenous cowpea) were planted in monoculture in the experimental field, at 4 replications for every species. Maize (Zea mays) was planted in a monoculture. For the palatability experiment, each of five male boer goats was provided with four feeding troughs, with four different feeds (maize straws and 3 legumes (lablab and 2 cowpeas - Dr Saunders, and Betswit). Indigenous cowpea was excluded for palatability trial due to little quantity. For silage, the proportion of legume to maize was 20:80. Treatments were as follows, maize-lablab (ML) (20:80%), maize-indigenous cowpea (MI) (20:80%), maize-betswit (MB) (20:80%) and maize-Dr Saunders (MD) (20:80%), each with molasses (2%) to enhance fermentation. The controls were maize, without (negative control) or similarly treated with molasses (positive control). Molasses was diluted with distilled water at 1:2. The silages were opened after 45 days. The leaves and maize straw were analyzed for chemical composition and in vitro dry matter degradability (IVDMD) while silages were analyzed for chemical composition, fermentation characteristics, aerobic stability and IVDMD. All data were subjected to a one-way analysis of variance (SAS, 2010). The highest (P<0.05) CP (230.7 g/kg DM) content was recorded for Dr Saunders cowpea. The lowest (P<0.05) acid detergent lignin (ADL) content (116.7 g/kg DM)

was obtained from indigenous cowpea. Lablab had higher (P<0.05) total phenols (0.36 g/kg DM) than all forages. Lablab and indigenous cowpea had the highest (P<0.05) metabolizable energy (ME) content. Highest (P<0.05) relative feed value (RFV) was recorded for lablab. The highest (P<0.05) in vitro dry matter degradability (IVDMD) was recorded for Dr Saunders and lablab. Lablab had a higher palatability index (P<0.05) when compared to other diets. Intake (r2=0.955) and palatability indices (r2=0.971) were positively and significantly (P<0.05) predicted from total phenolics. For the chemical composition of the silage, maize-molasses had the highest DM and hemicellulose content than all other silages. Maize-Dr Saunders cowpea had the highest (P<0.05) ash, and ether extract (EE) content when compared to all other silages. Maize-lablab silage had the highest (P<0.05) CP content (116.0 g/kg DM). Maize had the highest (P<0.05) neutral detergent fibre (NDF) content (619.2 g/kg DM). The ML and MD had the highest (P<0.05) ADF content (394.7 and 393.6 g/kg DM respectively) than other silages. Maize had the highest content of ADL content (140.0 g/kg DM). The ML had the highest (P<0.05) cellulose (270.3 g/kg DM). The highest (P<0.05) IVDMD was recorded for ML silage from 24hr up to 72hrs. The highest (P<0.05) pH was recorded for MB. All silages had similar (P>0.05) concentration of LA. The MM had the highest (P<0.05) content of WSC and ML had the least (P<0.05) content of WSC. The ML had the highest (P<0.05) LAB counts than all other silages. The yeast and mould counts of all silages were similar (P>0.05). A higher (P<0.05) carbon dioxide (CO2) was recorded for MB than all silages. Except for total phenolics, all chemical composition parameters poorly predicted intake and palatability index. Although lablab had better values in most parameters measured, all legumes can be highly recommended to supplement low-quality roughages such as maize straws and grasses.