Abstract:
Proc. Aust. Soc. Anim. Prod. (1978) 12: 283 THE EFFECTS OF RUST (PUCCINIA OAHUENSIS) ON LAMB PRODUCTION FROM PANGOLA GRASS (DIGITARIA DECUMBENS STENT.) F.E. DAVIS* and B.W. NORTON* Two limitations have been recognised as contributing to poor ewe and lamb growth on pangola grass pastures in S.E. Queensland. Norton and Hales (1976) discovered a severe cobalt deficiency, and pastures are heavily infested with rust during the growing season. The following experiments investigated the effects of the latter limitation. Lambs (28,4 + 0.4 kg) supplemented with cobalt (Cobaltic oxide 6021% an ICI product) were grazed at a fixed stocking rate (60 lambs ha-l) on either sprayed (Dithane containing 80 w/w 1lancozeb) or unsprayed Nfertilized pangola grass pastures. Liveweight of lambs, oesophageal fistula samples, pasture yield and rust levels (%) were measured every 3 weeks for 15 weeks. Initial growth rates were satisfactory for both treatment.s, but declined steadily with time (Table 1). Lamb growth was significantly lower (PcO.05) when the incidence of rust was high, and growth rates were positively correlated (PxO.01) with the percentage leaf in the sward. In a pen feeding trial, sheep consuming sprayed pangola grass hay (S) had a lower faecal nitrogen exc,retion (m) and higher nitrogen balance (NE) than sheep on unsprayed pangola grass hay (U) (F?J S 5.0 g d-l vs U 5.9 g d-l, P<O.O5; NB S 4.0 g d--l vs U 3.0 g d-l, PxO.05). Whilst the organic matter digestibility of the sprayed hay was higher than the unsprayed hay (S 64.6% vs U 61.2%, P<O.OS), there was no difference in voluntary intake (g/kg Wo-73 d-l) of organic matter (S 45.2 'vs U 48.3, LSD 5% j.6). Addition of dithane to the sprayed hay also depressed organic matter digestibility. It is concluded that rust infestation'depresses lamb growth by firstly decreasing the availability of leaf in the sward, and secondly by depressing the digestibility of both.organic matter`and nitrogen in the leaf consumed. Dithane also depressed digestibility of pasture suggesting that the effects of rust may be greater than shown. However despite the provision of cobalt and effective control of rust, lamb growth was still poor. Studies are continuing to determine additional factors limiting lamb growth from pangola grass. NORTON, ~.~.,and HALES, J.W. (1976). * Department of AgricultG, Proc. Aust. Soc. Anim. Prod. XI:393 --_L__--. -- Diversity of Queensland, St. Lucia Q 4067, 283.
