Passive immunity and association with morbidity and mortality of dairy calves reared in large-scale Estonian dairy herds ; Suurtes piimaveisekarjades peetavate vasikate passiivne immuunsus ja seos haigestumise ning suremusega

Final Thesis Curriculum in Veterinary Medicine ; Calves are born immunologically naive, thus they achieve passive immunity via colostrum intake and absorption. If the transfer of colostral antibodies is insufficient, the calf has failure of passive transfer of immunity (FPTI), which predisposes the calf on diseases and increases the risk of mortality. The aim of this study was to analyze the prevalence of FPTI and association with morbidity and mortality risk of dairy calves reared in large Estonian dairy herds. In total, the number of calves were 372 (number of herds = 30) for the mortality analysis and 209 (n = 20 herds) for the morbidity analysis (bovine respiratory disease (BRD) and diarrhea). Blood samples from jugular vein were collected from 2-7-day-old calves. Serum total protein (TP) concentration was measured by using a refractometer, a TP cut-off point of 5.2 g/dl was used to discriminate poor and good passive immunity groups. The calflevel follow-up period was 6 months. Survival analysis was used for data analysis. Prevalence of FPTI was 47.0% (175 calves out of total 372 calves). According to the mixed-effect Cox regression model, mortality hazard for calves that acquired poor immunity was on average 3.3 times higher compared to mortality risk of those calves that had good passive immunity (p = 0.007). In poor passive immunity group there was on average 33% higher chance for a calf to develop diarrhea and on average 3% higher change for a calf to develop BRD compared to good passive immunity group. These differences were statistically insignificant (p = 0.263, p = 0.929, respectively). In conclusion, roughly half of the studied calves were identified having FPTI indicating that colostrum feeding practices should be improved in large-scale Estonian dairy herds. Although morbidity was not significantly affected by low serum TP levels, calves with FPTI had considerably increased risk for mortality during the first six months of age. Further studies are motivated to analyze the reasons for FPTI in ...