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.

Our results show that PregSure vaccination of a cow was strongly associated with her having a BNP calf, and that older PregSure-vaccinated cows were more likely to have a BNP calf than younger vaccinated cows. This was partly explained by the increased odds of BNP with increasing doses of PregSure and correlation between PregSure doses and lactation number. Feeding colostrum from other cows, in addition to or instead of dam colostrum, was strongly associated with BNP if the dam had not been PregSure-vaccinated, but its effect was less if the dam had been vaccinated. When calves received colostrum from other cows, most farmers were unable to identify which cows the colostrum came from, so their PregSure vaccination status was unknown. These findings suggest that if a dam had been PregSurevaccinated and the calf received colostrum from its dam then there was an increased odds of BNP. But if the calf received some colostrum from other cows (which may or may not have been vaccinated) then the dilution effect of receiving some ''non-BNP colostrum'' reduced the odds. However, for calves of unvaccinated cows, feeding colostrum from other cows was strongly associated with BNP, presumably because feeding colostrum from multiple cows increased the chance of the calf ingesting some colostrum from a PregSure-vaccinated cow. The strong association between BNP and PregSure vaccination, and consumption of colostrum from PregSure-vaccinated dams, was consistent with singlecountry case-control studies with small sample sizes conducted in the UK and Germany [13, 14] . We also found that exclusively feeding dam's raw milk was associated with an increased odds of BNP, compared to feeding milk from one or more other sources. Early lactation milk contains some antibodies that can still be absorbed up to 48 hours after birth [15] . Feeding milk powder or bulk tank milk instead of, or to supplement, dam's milk will reduce the amount of antibody ingested. Alternatively the observed effect could be due to an association between feeding dam's milk and other management factors that affect the risk of BNP. In our study, calves that suckled their dam within 12 hours of birth were more likely to be fed only dam's raw milk. We hypothesize that calves that suckle could receive a larger volume of colostrum earlier in life leading to higher levels of antibody absorption, which could increase the risk of BNP. The estimated population attributable fractions indicate that the most effective intervention would have been to avoid breeding from PregSure-vaccinated cows (86% case avoided). Not exclusively feeding dam's milk would have avoided 15% cases and not feeding colostrum from other cows would have avoided 12%.