The relationship between failure of passive transfer and mortality, farmer-recorded animal health events and body weights of calves from birth until 12 months of age on pasture-based, seasonal calving dairy farms in New Zealand

The effects of failure of transfer of passive immunity (failure of passive transfer, FPT), defined by serum total protein (STP) ≤ 52 g/L at 1-7 days of age, on mortality, morbidity and body weight were investigated from birth until weaning in 3829 calves on 106 pasture-based, seasonal calving dairy farms in nine regions of New Zealand. A subset of 2053 calves from 35 farms in two regions from the main cohort of calves and farms were enrolled to monitor the longer term effects of FPT until 12 months of age. Calves with FPT had a greater odds of farmer-recorded animal health events (odds ratio, OR, 1.68; 95% confidence interval, CI, 1.29-2.19) prior to weaning, and a greater odds of mortality by 6 (OR 2.19; 95% CI 1.04-4.62) and 12 months of age (OR 2.21; 95% CI 1.22-4.00). FPT was associated with a lower (P < 0.05) body weight at weaning, and at 6, 9 and 12 months of age, but these differences were small, ranging from 0.93 kg at weaning to 3.30 kg at 12 months of age. For every 10 g/L increase in STP concentration, the odds of mortality was 13% lower at weaning (OR 0.87; 95% CI 0.59-1.28) and 37% lower at each of 6 months of age (OR 0.63; 95% CI 0.44-0.90), 9 months of age (OR 0.63; 95% CI 0.4-0.88) and 12 months of age (OR 0.63; 95% CI 0.60-0.66). In conclusion, FPT and decreased STP concentration were associated with increased morbidity and mortality, and slightly reduced growth rates, in calves managed under a pasture-based, seasonal calving system in New Zealand.