Nutritional characteristics and in vitro digestibility by near-infrared spectroscopy of local and hybrid napiergrass varieties grown in rain-fed and irrigated conditions

Napiergrass can produce large amounts of biomass and its nutritive value has a significant effect on its effectiveness for animal production. However, temperature and drought stress limit its productivity. Drought-tolerant pearl millet · napiergrass hybrid (PMN) varieties were developed and produce high biomass yields. The nutritional content and digestibility of PMN is not well known, which limits its use in animal feeding. It was hypothesised that PMN hybrids are more drought tolerant and have higher nutritive value than napiergrass varieties. Four napiergrass varieties (Bana grass, Mott, MB4, and N51) and four PMN (PMN2, PMN3, 5344, 4604) were tested with or without irrigation treatment in a strip-plot design, with the objective of evaluating the nutritional value and in vitro digestibility of PMN hybrids and napiergrass. The forages were harvested on Day 110 of planting. Samples were hand chopped, oven-dried, ground to pass through a 1-mm screen and analysed for their nutrient content and in vitro digestibility using near-infrared spectroscopy. Dry matter (DM) content of PMN2 (24.3%) and PMN3 (22.9%) was significantly higher (P < 0.05) than 5344, Bana grass and N51 napiergrass varieties. No differences (P > 0.05) in acid detergent fibre, neutral detergent fibre, crude protein and metabolisable energy were found among napiergrass varieties. With no effect (P > 0.05) of irrigation, lignin content was highest (P < 0.08) in 4604 (8.2%) and lowest in 5344 (5.2%). Starch was highest (P < 0.05) in irrigated MB4 than both irrigated and non-irrigated 4604. Non-fibre carbohydrate content was highest (P < 0.05) in PMN2 (12.8%) than MB4 (8.7%). The in vitro true digestibility was significantly higher (P < 0.05) in 5344 and Bana grass (70.0% and 68.0% of DM, respectively), than PMN3 (54.5%). Rate of digestion was significantly higher (P < 0.05) in 5344 (4.9%/h) than PMN2 (2.7%/h), others were in between. Neutral detergent fibre digestibility (NDFD) of 5344 and Bana grass (56.7% and 53.2% of neutral detergent fibre, respectively) was significantly higher (P < 0.05) than PMN2 (38.0%). Although no effect of irrigation was observed, there was an interaction (P < 0.05) between variety and irrigation on neutral detergent fibre digestibility of napiergrass varieties. In conclusion, among four PMN varieties tested, PMN3 and 5344 has higher nutritional value and in vitro digestibility than PMN2 and 4604 even when grown in non-irrigated condition. Thus, PMN3 and 5344 is the preferred napiergrass variety for animal feeding, even in rain-fed farming conditions. Additional keywords: hybrid napiergrasses, in vitro digestibility, nutrient content. Received 13 March 2014, accepted 27 June 2014, published online 19 August 2014