Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 16 GROWTH OF WEANED LAMBS ON SOME APHID-RESISTANT LUCERNE VARIETIES A. AXELSEN*, J.B. NADIN* and R.I. FORRESTER** SUMMARY Over nearly four years spring-born Dorset cross carry-over lambs were grazed on Sirosa phalaris or Hunter River (HR) lucerne, or on four aphid-resistant lucerne varieties (Nova, WL318, Cuf101 or Siriver) at two stocking rates. During each year, as groups of lambs were fattened and sold as prime, the next heaviest lambs were brought into the system to allow the marketing of carry-over lambs as quickly as possible. As aphids were almost absent throughout the experiment HR lucerne was at its full potential. Nevertheless, lamb gains on all of the other lucerne pastures were equal to or better than HR, and were higher on lucerne pasture than on Sirosa (Keywords : Lucerne, aphid-resistance, lamb growth) phalaris. INTRODUCTION Growth rates of young cattle (Morley et al. 1978) and young sheep (Reed et al. 1972) are usually higher on lucerne than on grass-subterranean clover pastures. Lucerne is particularly useful for finishing lambs that are not in prime condition by mid-December when grass-clover pastures mature. However, when Hunter River (HR) lucerne pastures were heavily infested by the blue green aphid (Acyrthosiphon kondoi Shinji) and spotted alfalfa aphid (Therioaphis trifolii (Monell) f. maculata) in early 1977, many thousands of hectares of lucerne were threatened with destruction. Task forces were set up by State Departments of Agriculture and CSIRO, and the program of control included importation of lucerne varieties known to be resistant to the aphids, for immediate sowing, and the breeding of new aphid-resistant varieties for Australian conditions. The potential of some of the newer lucerne varieties was studied by comparing pasture production and growth rates of carry-over weaner lambs with those on HR lucerne, and phalaris, at Ginninderra Experiment Station, near Canberra. MATERIALS AND METHODS Experimental design and sowing Sirosa phalaris was sown as a control and compared with the following lucerne varieties Winter semi-dormant varieties - HR, Nova (described by Oram 1980a) and (a> WL318 (imported). Winter active varieties - CuflOl (imported) and Siriver (selected from 09 crossings of HR with CuflOl; described by Oram 1980b). Nova and WL318 are resistant to the spotted alfalfa aphid, and CuflOl and Siriver are resistant to both the spotted alfalfa aphid and the blue green aphid. Seed of the five lucerne varieties was inoculated and lime coated, and sown in early September 1980 at 5.5 kg/ha with 200 kg/ha of molybdenum-superphosphate. Phalaris seed was sown at 4.0 kg/ha. Sowing took place in three blocks so that there was one 0.13 ha plot and one 0.09 ha plot of each lucerne variety, and of phalaris, allocated at random within each block. Woogenellup subterranean clover *Division of Plant Industry, CSIRO, GPO Box 1600, Canberra, A.C.T. 2601. **Division of Mathematics and Statistics, CSIRO, GPO BOX 1965, Canberra, A.C.T. 2601. 135 Proc. Aust. Soc. Anim. Prod. Vol. I6 00 kg/ha of * 1981 and then spelled ny aphids were present were sprayed with lucerne varieties were Lambs were grazed on the plots for the periods shown in Table 1. Animals used were mainly spring-born Dorset x (Border Leicester x Merino) carry-over lambs which weighed between 20 and 30 kg at weaning. Border Leicester x (Border Leicester x Merino) hoggets were used in early spring 1981 and 1984 (periods 1 and 7), and Border Leicester x (Border Leicester x Merino) lambs in spring-summer-autumn 1983-84 (period 6). Groups of four lambs were allocated at random to each of the 12 plots in Block 1 to give two stocking rates (SR; 10.2 and 14.8/ha) on each variety, and lambs were rotationally grazed through Blocks 1, 2 and 3 so that plots were grazed for two weeks and spelled for four weeks. Because of increased pasture growth in spring 1981 (period 1) and spring 1983 (periods 5 and 6), each plot was grazed with ten lambs to give stocking rates of 25.6 and 37.0/ha. Grazing by lambs in period 6 commenced before period 5 lambs were sold off. At the end of each period most lambs weighed between 32 and 40 kg and were sold as prime. When measurements indicated enough pasture was present, another group of lambs was allocated for a succeeding period. Lambs grazed on all varieties for the same length of time. &qeasurements Lambs were were made during were converted to quadrats (Vickery weighed full every two weeks. Estimates of pasture availability grazing using an electronic capacitance meter. Meter readings pasture masses using regressions established with standard and Nicol 1982). Statistical Analysis Analyses of variance were performed on the total lamb liveweight gains/ha over each period. The 5 degrees of freedom for pasture main effects were subdivided into orthogonal contrasts, those of most interest being HR with Siriver and lucerne with phalaris. Since the mean squares for the period analyses of variance were homogeneous, total green herbage available was used as a covariate on a pooled analysis for the nine periods, and also for the period analyses. Analyses of variance were also carried out on the mean liveweight gain/d for lambs grazing each species during each period, and on total green herbage DM available within each grazing period. No transformation of the data was necessary. RESULTS AND DISCUSSION Annual rainfall was 803, 313, 983 and 902 mm from 1981 to 1984, compared with the long term average of 701 mm. No summer grazing was possible from 22 November 1982 to 16 February 1983, or from 14 December 1984 to 10 April 1985 because of drought conditions. Liveweight gains ranged between 100 and 170 g/d, except in autumn 1982 and in spring 1982, 1983 and 1984 when they were higher, and in summer-autumn 1984 (period 6), when gains of Border Leicester cross lambs were only 77 and 36 g/d at the low and high SR respectively (PcO.01). Gains/d were higher at the low than at the high SR (e.g. period 3, 231 vs 193 g/d, P < 0.10; period 4, 172 vs 127 g/d, P < 0.001) in all periods except in spring 1981 and 1984 when there was always sufficient pasture at both SR, even during spring 1981 when higher SR were used. Total green herbage was not significant as a covariate in the pooled analysis of liveweight gains/ha, but was significant as a covariate in the analyses for periods 2 and 4. Despite the advantages in gains/d at the low 136 Proc. Aust. Soc. Anim. Prod. Vol. 16 Liveweight Gains/ha (kg), with adjusted means using total green herbage Table 1 as a covariate for periods 2 and 4 in parentheses SR, liveweight gains/ha were higher at the high than at the low SR at all times except in period 4 when there was no difference, and in period 6 when gains/d had been so poor at the high SR. Total gains/ha over nearly four years were 8% higher at the high than at the low SR (1670 vs 1542 kg). Overall, the rankings of lamb gains on lucerne pastures were Siriver, WL318, Nova, CuflOl and HR. Siriver produced 9% more lamb than HR with the largest differences occurring in autumn-winter 1982 and 1983 (Periods 2 and 4). Lambs gained more on phalaris than lucerne (except Siriver) in periods 2 and 4, and more on lucerne than phalaris in periods 5, 6 and 7, and overall production on lucerne pasture was 21% greater than on phalaris (Table 1). The percentage of lambs sold off as prime overall was higher at the low than high SR (95 vs 85% on lucerne pasture only), higher on Siriver than HR lucerne (92 vs 86%) and higher on lucerne pasture than on phalaris (90 vs 74%). Total green herbage DM available during grazing is shown in Fig. 1. for HR and Siriver lucerne pastures and for Sirosa phalaris, Lucerne was the dominant species in all lucerne pastures, but annual grass and subterranean clover contributed up to 70% of the green herbage in winter (less for the winter active varieties CuflOl and Siriver than for the semi-dormant varieties), to as little as 5% in the summer and autumn. Siriver lucerne pastures contained more green herbage than HR lucerne pastures at all times except in November and December 1983, but these did not always result in higher liveweight gains. Total herbage available for other lucerne pastures was mostly between that of HR and Siriver, except that CuflOl was higher than Siriver in May 1982 and April 1983, WL318 was higher from November 1983 to March 1984, and Nova was higher in November 1983 and March 1984. These differences did not result in significant liveweight differences. The fattening of carry-over lambs depends on the area of lucerne (or legume pasture) available, and the management used in this experiment was most satisfactory. The heaviest lambs were fattened and sold off, and.when more lucerne was available the next heaviest lambs were brought into the system. For a flock of 1000 ewes with possibly 400 weaned lambs to fatten over the summer, an area of 15 ha of lucerne would be of great benefit. Lambs can be fattened on a high protein supplement if lucerne is not available, but the high cost of feed makes this of doubtful economic value (Freer et al. 1985). 137 Proc. Aust. Soc. Anim. Prod. Vol. 16 All of the new lucerne varieties were equal to or better than HR for If aphids had damaged the HR lucerne (and possibly fattening lambs and hoggets. Nova and WL318 in the case of the blue green aphid), the differences could have been much greater. ACKNOWLEDGEMENTS We thank Dr. R.W. Downes and Mr. G.T. McKinney for advice, and Messrs M.D. Crouch, L.G. Coulton and J. Boehm for their technical assistance. REFERENCES FREER, M., DOVE, H., AXELSEN, A., DONNELLY, J.R. and McKINNEY, G.T. (1985). Aust. J. Exp. Agric. 25: 289. MORLEY, F.H.W., AXELSEN, A., PULLEN, LG., NADIN, J.B., DUDZINSKI, M.L. and DONALD, A.D. (1978). ,Agric. Systems 3: 123. ORAM, R.N. (1980a). J. Aust. Inst. Agric.=Sci. ii: 133. ORAM, R.N. (1980b). J. Aust. Inst. Agric. Sci. $2: 200. REED, K.F.M., SNAYDON, R.W. and AXELSEN, A. (1972). Aust. J. Exp. Agric. Anim. Husb. 12: 240, VICKERY, P.77 and NICOL, G.R. (1982). CSIRO Aust. Anim. Res. Lab. Tech. Pap. No.9. 138