Stocking rate effects on liveweight gain of ewes and their twin lambs when grazing subterranean clover-perennial grass pastures

Abstract

Two grazing experiments were conducted on non-irrigated tall fescue–subterranean clover and cocksfoot–subterranean pastures subject to summer-dry conditions in Canterbury, New Zealand, to measure the effect of low (8·3–10 ewes and their twin lambs ha−1) vs. high (13·9–20 ewes and their twin lambs ha−1) stocking rates (SR) on lamb and ewe liveweight gain in spring. In tall fescue–subterranean clover pasture, lambs grew faster at low (374 g per head d−1) than high (307 g per head d−1) SR, but total liveweight gain per ha was greater at high (12·3 kg ha−1 d−1) than low (7·5 kg ha−1 d−1) SR. In successive years in spring in cocksfoot–subterranean clover pastures, lambs grew faster at low (327, 385 g per head d−1) than high (253, 285 g per head d−1) SR but total liveweight gain per ha was greater at high (7·26, 7·91 kg ha−1) than low (5·43, 6·38 kg ha−1) SR. These studies indicate that in summer-dry areas, subterranean clover-based pastures will support high twin lamb growth rates in spring, with lower SR leading to higher lamb growth rates and more lambs reaching slaughter weights before the onset of dry conditions.