Validation of hand-held refractometers for assessing Merino ewe colostrum and neonatal lamb serum

Context The high incidence of lamb mortality in Merino sheep is a persistent issue for the industry. Poor-quality colostrum or inadequate colostrum consumption increases the risk of low energy intake and failed passive immunity transfer, resulting in lamb mortality. The rapid assessment of colostrum quality and intake would be a valuable tool for producers which house ewes for lambing. Aims This experiment determined the relationship and accuracy of analysis techniques to measure immunoglobulin G (IgG) and total protein (TP) concentrations within ewe colostrum and lamb serum and compared those results against digital hand-held refractometers. Methods Merino ewe colostrum and lamb blood were sampled at 4 and 24 h post-partum during autumn (n = 93 ewes) and spring (n = 79 ewes) in 2018. Colostrum was analysed for total milk solids (%) and lamb serum was analysed for total blood serum protein (%), and both colostrum and lamb serum were analysed for IgG and TP using in-house laboratory analysis techniques. Correlation coefficients were performed to identify the relationship between the different assessment methods. Key results There was a significant Pearson's correlation (P < 0.05) between 4 h total milk solids and TP (R = 0.19), between total milk solids and IgG (R = 0.19), and TP and IgG (R = 0.38). For 24 h colostrum samples, the significant correlations (P < 0.001) between TP and IgG (R = 0.54) and total milk solids and IgG (R = 0.56) were higher than the correlation between total milk solids and TP (R = 0.24; P = 0.006). Further, 4 h serum IgG (R = -0.14; P = 0.026) and 24 h total blood serum protein (R = 0.21; P = 0.009) were correlated with lamb survival to 72 h. Conclusions While the refractometer provided a crude measure of colostrum IgG and TP and was valuable in identifying lambs with low IgG transfer at 24 h, further research is required regarding analysis techniques to allow for reliable measures need to be refined. Implications The use of refractometers to assess colostrum quality and intake could benefit researchers or producers who practice indoor lambing.