Performance of sheep systems grazing perennial pastures: 3. Fertility, fecundity and lamb survival

Management system has the potential to alter the reproductive output of sheep flocks and so farm profit. A study was conducted between 2006 and 2010 to evaluate the reproductive performance of four management systems with differing combinations of time of lambing, stocking rate and ram breed, while grazed at a similar mid-winter dry stock equivalent/ha (8, 10.2, 13, 11.2 and 11.2 in 2006 to 2010, respectively). Three systems (Winter Lambing Merino (WLM), Split Lambing (SL) and Later Lambing (LL)) grazed replicated farmlets where 20% of the farm was comprised of lucerne pastures, 20% was comprised of tall fescue pastures, and 60% was comprised of phalaris pastures. A fourth system (High Lucerne (HL)) grazed farmlets of 40% lucerne, 15% tall fescue and 45% phalaris. All systems used Merino ewes, the WLM mated to Merino rams, lambing in July; SL with half the ewes lambing to Terminal rams in July, the other half lambing in September to Merino rams and LL and HL lambed in September, half to Terminal and half to Merino rams. The number of lambs weaned per ewe joined was 10% higher (P<0.05) in the WLM system (0.99 ± 0.034) than in the September lambing systems LL and HL, largely due to more fetuses per ewe and despite lower (P<0.05) lamb survival to marking in some years. The SL system weaned a similar (P>0.05) number of lambs per ewe (0.95 ± 0.034) as all other systems. However, the number of lambs weaned per hectare was least in WLM (4.6 ± 0.23) being 2.7 lambs/ha lower than in the HL and LL systems due to a lower stocking rate. The ranking of systems for fetal number and lamb survival was not consistent between years. Spring lambing systems produced more lambs/ha due to a higher stocking rate, and less lambs per ewe than the WLM system, but system differences in pregnancy rate, fecundity, and lamb survival were not consistent between years.