Nutritive value of subtropical grasses invading North Island pastures.
The possible nutritional impact of subtropical grass invasion into pastures was assessed by chemically analysing the leaves of 5 common subtropical grasses including Pennisetum clandestinum, Paspalum dilatatum, Panicum dichotomiflorum, Eleusine indica, and Digitaria sanguinalis. In comparison to Lolium perenne, subtropical species clearly showed increased levels of neutral detergent fibre (38.4% vs 57.5%) but reduced levels of total protein (23.0% vs 13.2%), soluble sugars (11.7% vs 5.9%) and in vitro OM digestibility (84.0% vs 66.6%). Similar results were obtained for grasses grown in each of the three areas. Of the subtropical grasses, D. sanguinalis was of the highest nutritive value and E. indica was of the lowest. The results of an in vitro rumen protein degradation experiment showed that net ammonia production from in vitro rumen fermentation was significantly lower for the subtropical species than for L. perenne. The present study indicates that the subtropical grasses are of considerably lower nutritive value than L. perenne. Their continued invasion of grazing pastures will probably substantially decrease the nutritive value of the pastures and animal production.