GROWTH AND FORAGE INTAKE OF HEREFORD STEERS FED GIANT PARRAMATTA GRASS HAY (SPOROBOLUS-INDICUS) AND THE EFFECTS OF DIETARY NITROGEN SUPPLEMENTS

Giant Parramatta grass (GPG) (Sporobolus indicus var. Major), a seriou s weed of pastures of subtropical Australia, is poorly grazed by cattl e leading to reports of low production on badly infested pastures. To provide information for cattle producers we recorded feed intake and l iveweight change of steers in a 56-day study, and nitrogen (N) excreti on over 5 days when GPG was fed as hay. Data were compared with those for GPG hay supplemented with urea (7 g urea/kg hay), or with urea and cottonseed meal (CSM; 750 g/steer.day), and with those for steers fed a native pasture (NP) hay, which included a legume (Aeschynomene falc ata). Each steer was also fed daily a mixed mineral supplement of 35 g sprinkled on the hay. Urea increased (P<0.01) daily GPG hay intake fr om 4.2 to 5.0 kg/steer, but there was no significant increase in intak e (4.5 kg/steer) when CSM was included. Steers on NP hay had a mean da ily intake of 5.1 kg/steer which was similar to that of steers offered GPG hay + urea. Urea increased daily liveweight gain from 323 to 555 g/steer (P<0.05); the addition of CSM further increased (P<0.05) the g ain to 676 g/steer. Steers on NP hay had a mean daily liveweight gain of 480 g/steer. The gain for steers offered CSM with GPG hay + urea wa s higher than that predicted by GrazFeed (1993) for a low digestible, low NP hay, supplemented with urea and CSM. Improved production of ste ers through using nitrogen supplements, may provide an opportunity for cattle to use this weed as a hay or silage in pastures as part of a p rogram to control weed ingress in subtropical pastures.