ASSOCIATIONS BETWEEN HEALTH DISORDERS AND CULLING OF DAIRY-COWS - A REVIEW

Research into the relationships between diseases of cows and culling in dairy herds is reviewed with emphasis on both results and their factors of variation. Tables provide comparisons between studies depending on their designs and their results. Differences between the study populations are outlined. The studied health disorders are extensively reported and their risks of misclassification are discussed. The other variables considered as possible risk factors for culling are reviewed. Some individual characteristics of cows (age, milk production level, reproductive performances) are usually taken into account in the analyses, whereas the herd effect on the individual risk of culling is poorly documented. The statistical methods for the analysis of health disorders as risk factors for culling are summarized. Certain health disorders (dystocia, mastitis) increase the risk of culling regardless of the production systems considered. However, for other health disorders (milk fever, metritis, cystic ovaries, retained placenta, locomotor disorders), contradictory results are reported. These discrepancies may result from either actual differences in the production systems studied or differences in methodologies used. The interest of further studies investigating especially the herd effect on the individual risk of culling is displayed.