Herd health and health management in organic versus conventional dairy herds in Norway

Earlier studies from Norway indicate that organic dairy farms enjoy better animal health than conventional dairy farms. However, these studies use veterinary treatment records and may not reflect the true health status since animal health may be handled differently, i.e. there might be different treatment schemes on organic versus in conventional farms. A study of animal health and health handling on both organic (n=149) and conventional (n=159) farms was performed based on information gathered from a mailed questionnaire merged with information from the Norwegian Cattle Health Services and the Norwegian Dairy Herd Recording System. Based on the original health records, there appeared to be many and large differences in herd health (veterinary) treatment parameters between the two production systems. However, after looking closer into the major diseases problems of mastitis, ketosis, and milk fever and converting from treatment to estimated case load based on questionnaire information about the observed differences in health handling, all that remained was a lower level of acute mastitis in organic dairy herds relative to conventional. When controlling for production level - milk yield being lower in organic herds - no difference between the two groups remained. We conclude that, based on official health records, there is an apparent difference in animal health performance which is mainly related to an observed difference in health management. The remaining difference in acute mastitis which is not explained by disease handling appears, at least in part, to be associated with a lower intensity of milk production. The impact of these findings in relation to animal welfare as a central issue in organic farming needs further investigations. Finally, the study demonstrates the need for a critical assessment of routinely collected health-related data used in research, in order to make valid inferences regarding animal health performance. (C) 2007 Elsevier B.V. All rights reserved.