Relationships between sheep liveweight production and dry matter yield for lucerne-based pastures in spring

Abstract

A five-year dryland grazing experiment explored the relationship between sheep liveweight (LWt) production and dry matter (DM) yield of lucerne-based pastures in spring. In 2011, a randomised complete block experiment with a lucerne monoculture, a lucerne/brome mix and a lucerne/cocksfoot mix were established at Ashley Dene, Canterbury and replicated six times. Pastures were managed under dryland conditions. Ewes with twin lambs at foot grazed in spring and LWt production, DM yield and botanical composition were quantified.
Regression analysis showed total DM feed on offer accounted for only 11% of the observed variation in spring LWt production. Subsequent analysis of the botanical composition of the three pastures showed total feed on offer in spring was unaffected by pasture treatment in four out of five years. However, yield of the lucerne component on offer was 77–230% greater in the monoculture than the mixes in Years 3–5. Brome yields declined from Year 3 and did not recover. By Year 5, weeds accounted for 41% of the feed on offer in spring in the lucerne/brome mix.
Net spring ewe + lamb liveweight production increased at a rate equivalent to 246 kg LWt +71 kg LWt per tonne of lucerne DM on offer (R² = 0.83). There was no effect of pasture type. Where possible lucerne should be established as a monoculture to maximise liveweight gain. A runout stand was overdrilled with a companion grass to extend the productive stand life. The loss of lucerne over time indicated renewal should be initiated within 2–3 years of oversowing to ensure LWt production is not compromised.