UREA SUPPLEMENTATION EFFECTS ON THE UTILIZATION OF LOW-QUALITY FORAGEAND LAMB PRODUCTION IN PATAGONIAN RANGELANDS

The effect of feeding a urea-based supplement for the last 8 weeks of pregnancy was examined on ewes grazing the grass-shrub steppes of NW P atagonia, Argentina. The productivity of ewes and lambs and the utiliz ation rate of the major, less preferred, grass species (Stipa speciosa , 27% cover) was analysed. In a paddock scale experiment, ewes grazed two areas of 450-500 ha from 15 August to 15 February at a stocking ra te of 0.5 ewes ha(-1). From 15 August to 10 October, one group of ewes was given access to a urea-based supplement containing 300 g kg(-1) u rea, 320 g kg(-1) salt, 30 g kg(-1) molasses and 300 g kg(-1) bone mea l. Average supplement consumption was 35 g ewe(-1) d(-1). The perfor m ance of 100 ewes in each of the two areas was evaluated. Supplemented ewes gained 4.2 kg more live weight than the control ewes between 15 A ugust and 10 October (prepartum) (liveweight gain was 10.3 vs, 6.1 kg ewe(-1), P < 0.05). The number of live lambs at 8 weeks of age, as a p roportion of ewes mated, was 15% higher in the supplemented than in th e control group (0.634 vs. 0.553, P < 0.05). A similar increase in the live weight of lambs at 8 weeks of age in the supplemented group comp ared with the controls was also observed (12.1 vs. 10.6 kg, P < 0.05). In the paddock with the supplemented ewes, there was a significant in crease in the proportion of Stipa speciosa plants defoliated (0.62 vs. 0.38, P < 0.05) and in the intensity of defoliation of these plants. It was concluded that urea-based supplements increased productivity of ewes and that this was likely to be associated with an increase in th e intake, and possibly digestibility, of the less preferred species su ch as Stipa speciosa..