Management Strategies for Napier Grass (Pennisetum purpureum Schumach cv Pakchong): Impact on Dry Matter Yield, Nutritive Characteristics and Cattle Growth

Napier grass is widely used across the tropics and subtropics as a feed for dairy and beef cattle, but its quality is poor under current management with resultant poor animal productivity. Current management is focused on achieving high yields and, as such, is harvested at ground level with longer harvest interval when grass reaches 200 cm or higher, which reduces quality. The opportunity to improve the nutritive value of this grass is largely unexplored alongside the opportunity to increase livestock productivity and food security in the tropics and subtropics. Here we determined the impact of leaf number (total) or stage (LS; 6, 9 and 14) at harvest, and harvest severity height (SH; cutting or harvest height from the ground; 5, 10 and 20 cm), on the nutritive value of Napier grass (cv. Pakchong) across one year. Napier grass was sown (from cutting) at a density of 50 cm × 50 cm with three replicates per treatment. Increasing LS from 6 to 14 decreased crude protein (CP) content from 184 g/kg DM to 118 g/kg DM and metabolizable energy (ME) content from 10.4 to 7.3 MJ/kg DM. These results suggest that Napier grass should be harvested at a lower LS to increase plant nutritive value but there was a trade-off between yield and quality as yield decreased by half to improve such quality. The impact of offering Napier grass harvested at 6, 9 or 14 LS on cattle growth was then determined across 113 days in a second experiment. Red Chittagong bulls were enrolled at a weight of a 181.9 ± 2.30 (Mean ± SE) Kg with an age of between 18 and 22 months. The 6 LS treatment cattle had a greater growth rate and higher feed conversion ratio (FCR) than the 14 LS treatment (610 versus 270 g/day and 6.4 versus 16.2, respectively) indicating a trade-off of yield with quality. Our results demonstrate that Napier grass should be harvested at 6 LS with 10 cm SH for feed nutritive value, cattle growth and FCR. Further research is required to ameliorate yield loss associated with this recommended management strategy with a focus on increasing plant density.