Aust. J. Agric. Res., 1987, 38, 195-207 Responses to Nitrogen and Maize Supplements by Young Cattle Offered a Low-quality Pasture Hay G. J. ~ e e ~ ~ , D. W. ~enness~~, J. V. ~olan~, and R. A. ~eng~ AN.S.W. Department of Agriculture, Agricultural Research Station, Grafton, N.S.W. 2460. Department of Biochemistry, Microbiology and Nutrition, The University of New England, Armidale, N.S.W. 2351. Present address: Agricultural Research Centre, Trangie, N.S.W. 2823. Abstract Twenty-seven Hereford steers (227+3 kg) were offered ad libitum low-quality grass pasture hay containing 4.3 g N/kg DM. These steers were offered one of three maize supplements (nil, 570 g/day crushed maize or 680 g/day whole maize) alone or with one of two nitrogen (N) supplements (1 12 g/day urea: 250 g/day molasses, or 800 g/day pelleted protein meals). The crushed maize, whole maize and protein meal supplements were calculated to be isoenergetic on a metabolisable energy basis, and the urea and protein meal supplements were isonitrogenous. Both urea and protein meal supplements increased the intakes of hay and total digestible organic matter (DOMI), but there was a significant interaction between maize and N supplements such that maize increased hay and DOM intakes when offered alone. Unsupplemented steers ate only 1.98 kg OM of hay/day, whereas N supplemented steers ate 3.96-4.40 kg OM/day, and those supplemented with crushed and whole maize alone ate 2.45 and 2.85 kg OM/day respectively. The intakes of hay by the urea and protein meal supplemented groups were not significantly different. Both N and maize supplements had positive effects on liveweight change (P < 0.01), with N having the largest effect. Steers supplemented with protein meal gained 210 g/day more than those offered urea (P < 0.05), although DOMI was only 110 g/day more, indicating an effect of protein on the efficiency of utilisation of absorbed nutrients. N supplements increased rumen ammonia concentrations from 10+3.0 mg NH3-N/1 in unsupplemented steers to 1 6 9 i 19.3 and 105i 19.0 mg NH3-N/l in steers offered urea and protein meal b respectively; there was a significant interaction between the form of N supplement and form of maize supplement ( P < 0.05). Total volatile fatty acid concentrations in the rumen (65+ 1.9 m ~ ) did not differ significantly between supplements. Glucose entry rate was positively related to liveweight change and was increased by both the N supplements and whole maize. Glucose entry rate, adjusted for DOMI, was higher in protein meal supplemented steers than those receiving urea or no N supplement (P < 0.01), and these steers had the highest growth rate. Urea pool size, and synthesis rate in the body, were greater in steers given the urea and protein meal supplements ( P < 0.05), but there were no significant differences in these measurements between urea and protein meal supplements. Introduction Cattle grazing unimproved pastures in the subtropics during dry seasons generally lose liveweight or gain it only slowly (Cohen and O'Brien 1974) because of a low voluntary intake of feed associated with its low digestibility and low nitrogen (N) content. Supplementation with urea can be an effective way of removing the N limitation to microbial growth, and of increasing intake (see Winks et al. 1970). Increases in intake of low quality hay by urea supplementation have been attributed to