Long-term changes in the biology of a livestock farm system associated with the shift to organic supply

Abstract

A long-term replicated farm systems study (1997-2005) examined changes in the biology of mixed-livestock systems associated with the shift to organic production. Two farmlets were managed using conventional farm practices (Con) and two low chemical (LC) farmlets complied with the organic production standards of BIOGRO New Zealand. The Con farmlet had higher (P<0.01) lamb, hogget, 2TH and mixed-aged ewe (P<0.01) performance than the LC farmlet due mainly to differences in the parasite challenge between the two systems. There was no evidence that the use of the Ivermectin® bolus for 8 consecutive years in the Con system led to Ivermectin® drench resistance. Lamb liveweight at weaning was 1.77 kg lower (P<0.001), in LC than in Con. Post-weaning, high parasite burdens (FEC) reduced (P<0.001) LC lamb growth rate. LC systems had smaller 2TH's (P<0.001) and mixed aged ewes (P<0.001) than Con systems, despite similar feeding levels, leading to lower ovulation rate and numbers of lambs born. Lamb mortality rates between lambing and weaning were similar between systems. Until production losses in young stock following weaning in LC systems are reduced, the ability of the organic industry to expand will continue to be constrained. Performance differences between systems did not change over the 9-year trial, suggesting that this study provides a good insight into the relative performance of these two systems at the stocking rate at which they were compared. Pasture composition and production, and soil biophysical and biological characteristics were similar in the two farm systems. Keywords: low chemical, organic, farm systems Ivermectin