A farmlet study was carried out over 2 years to examine the role of milk production in dryland lamb production systems. Poll Dorset and Romney ewes were used to represent high and low levels of milk production and mated to produce reciprocal cross lambs. High and low fecundity treatments were included in replicated farmlets of 2.9 ha and stocked at 15 ewes/ha. Mean lambing dates were 5th and 8th August with lambs drafted for slaughter from mid October. In Year 1, Poll Dorset ewes produced 44% (singles) and 88% (twins) more milk in peak lactation than their Romney counterparts. In late lactation, Poll Dorsets produced 41% (singles) and 169% (twins) more milk. In Year 2, the advantages were 19% (singles) and 18% (twins) in peak lactation and 78% (singles) and 67% (twins) in late lactation. Increased milk production had small effects on lamb growth rates in the low fecundity treatments (Year 1: 338 vs 328 g/d; Year 2: 317 vs 300 g/d for the respective high and low milk treatments). In the high fecundity farmlets, dam breed differences were larger (Year 1 :280 vs 244g/d ; Year 2: 307 vs 283 g/d, respectively). Number of lambs drafted by the 2nd December were also similar in low fecundity groups (Year 1: 93% vs 95%; Year 2: 90% vs 93%, respectively). Greater numbers of lambs were drafted off high fecundity Poll Dorsets than Romney dams (56% vs 23%) in Year 1 but not in Year 2 (85% vs 81%). The greater effect of milk on lamb growth in high fecundity treatments in Year 1 was attributed to poor spring feed conditions and the buffering ability of high milk producing ewes.
Proceedings of the New Zealand Society of Animal Production, Volume 58, , 170-174, 1998
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