Calf-Level Factors Associated with Bovine Neonatal Pancytopenia – A Multi-Country Case-Control Study

Jones, Bryony A.; Sauter-Louis, Carola; Henning, Joerg; Stoll, Alexander; Nielen, Mirjam; Van Schaik, Gerdien; Smolenaars, Anja; Schouten, Matthijs; den Uijl, Ingrid; Fourichon, Christine; Guatteo, Raphael; Madouasse, Aurélien; Nusinovici, Simon; Deprez, Piet; De Vliegher, Sarne; Laureyns, Jozef; Booth, Richard; Cardwell, Jackie M.; Pfeiffer, Dirk U.

It was anticipated that BNP incidence would decline during the study period due to withdrawal of PregSure from distribution in 2010, and advice given to some farmers to avoid feeding colostrum from cows that had previously had BNP calves. A multi-country study was therefore necessary to obtain sufficient BNP cases to have the statistical power to detect important risk factors. A casecontrol study is the most appropriate design to investigate a rare disease, and for the investigation of calf-level risk factors it was necessary to match by farm. This meant that most management factors were the same for both cases and controls on the same farm, and, even where there were differences, the farmer could have reported routine practices rather than what had happened to individual calves, leading to misclassification and an underestimation of effect. The multi-country design meant that there was variation between countries in case-reporting, farm visits, sample collection, post-mortem examination, laboratory testing and questionnaire interpretation. There were also differences between countries in production methods, cattle breeds, and policies on BVD control and vaccination programmes. The matched design minimised the effect of these country differences on our results.