title: Failure of passive transfer and colostrum quality in Scottish dairy calves
Creators: name: Haggerty, Alexandra
Publisher: name: University of Glasgow
Year: 2022

description: Bovine neonates are born agammaglobulinaemic and therefore immunologically naïve. They are dependent on the ingestion and passive transfer of immunoglobulin G (IgG) from dams’ colostrum to confer sufficient immunity to disease in the first few weeks of life. Failure of passive transfer (FPT) is defined as the failure to absorb colostral antibodies sufficient to achieve a serum IgG concentration of &gt; 10mg/mL. FPT has well defined health, welfare, and economic implications for calves. IgG can be measured directly in calf serum using radial immunodiffusion (RID) or indirectly by measuring total protein (TP), total solids (Brix) or turbidity (ZST). Colostrum quality, in terms of IgG concentration and bacterial contamination, is one of the crucial factors in achieving adequate passive transfer. The aims of this study were to determine the prevalence of FPT in Scottish dairy calves, to compare the diagnostic test performance of direct and indirect methods for determining serum IgG concentration and determine the risk factors associated with FPT and colostrum quality. Between February and June 2019, 392 serum samples from calves aged between 1 – 7 days were collected from 38 farms. Two mixed veterinary practices were recruited as collaborators and farms were selected prospectively from their client base in the Stirlingshire, Lanarkshire and Dumfries and Galloway regions of Scotland. Farms were selected on a convenience basis according to willingness to participate and having routine reproduction visits which enable practitioners to attend each farm on a regular basis. The IgG concentrations of the serum samples were measured directly via RID to determine the FPT prevalence and indirectly via Brix, TP, ZST and Biuret methods. The IgG concentration (via Brix), total bacteria count (TBC) and total coliform count (TCC) of 252 colostrum samples collected at the point of feeding during this time were also measured. A questionnaire detailing calf and colostrum management at farm-level was completed at enrolment, prior to sample collection. Multivariable mixed effect logistic and linear regressions were carried out to determine significant risk factors (p&lt;0.05) for FPT and colostrum quality. FPT prevalence was estimated to be 14.2% (95% confidence interval (CI)= 10.8 – 18.2) based on RID testing. Only 39.4 % (99/252, 95% CI = 33.2 – 45.6%) of colostrum samples were of acceptable quality when assessed in terms of IgG concentration and bacterial contamination thresholds. Risk factor analysis revealed an increased time spent in a bucket prior to feeding or storing was significantly associated with a TBC ≥100,000cfu/mL (p=0.01) and a TCC ≥10,000cfu/mL (p=0.03). Increasing volume of colostrum administered to neonatal calves at first feed was found to be significantly associated with reduced odds of FPT (p=0.05). There was fair agreement between the reference (RID) and indirect tests (kappa= 0.28 for Brix, 0.34 for TP and 0.24 for ZST). Brix, TP and ZST testing underestimated IgG concentration, resulting in an overestimation of FPT prevalence (40.5%, 29.5%, 46.3% respectively). Overall analysis of indirect testing methods compared with RID, the direct reference test revealed no perfect test exists for the diagnosis of FPT. The performance of all three indirect screening tests was improved by lowering test cut points (to 5 g/dL for TP, 8.2% for Brix and 15 units for ZST) which improved test specificity and accuracy. However, TP and Brix offer cheap, reliable calf-side diagnostic capacity. Clinicians should be mindful of the clinical context in terms of expected FPT prevalence and overall calf health on farm when interpreting FPT results at a herd level.