Prevalence and calf-level risk factors for failure of passive transfer in dairy calves in New Zealand.

AIM To determine the prevalence of failure of passive transfer (FPT) in dairy calves in New Zealand and to assess a range of potential calf-level risk factors for their association with FPT. METHOD Between July and September 2015, 107 dairy farms in nine regions across New Zealand were visited on three occasions: before 20% of cows had calved, when ∼50% of cows had calved, and when the last 10-20% of cows were calving. Farms were randomly selected from the client list of participating veterinary practices. On each farm, blood samples were collected from 10-20 calves between 24 hours and 8 days old and concentrations of total protein (TP) in serum determined. Calf identification, date of birth, dam's age and breed, details of colostrum feeding and the farmer's health assessment of the calf on arrival at the calf rearing facility were recorded. Concentrations of TP in serum ≤52 g/L were used to define FPT. RESULTS Of 3,819 calves sampled, 1,263 (33 (95% CI=31.6-34.6)%) were diagnosed with FPT, and the prevalence within farms ranged from 5-83%. Calf-level risk factors that were associated with increased odds of FPT were increasing age of dam (OR=1.12; 95% CI=1.08-1.16), calves recorded as unhealthy compared to healthy upon arrival at the calf rearing facility (OR=2.59; 95% CI=1.60-4.19), calves sampled on farms in Otago (OR=2.85; 95% CI=1.42-5.74) and Southland (OR 2.31; 95% CI=1.15-4.67) compared to the Far North, and calves sampled in the middle compared to the early calving period (OR=1.24; 95% CI=1.03-1.51). CONCLUSION On the farms visited FPT was diagnosed in one third of dairy calves. Calf-level risk factors for FPT included age of dam, health status of calf, region, and time of the calving period. Further investigations are required to establish why these are associated with increased odds of FPT. CLINICAL RELEVANCE These results provide a baseline for benchmarking, which, alongside the reported calf-level risk factors, can be used by veterinarians to improve colostrum management.