Saliva Immunoglobulin Concentrations Are Associated with Colostrum Intake and with Serum Concentrations in Newborn Calves.

The transfer of passive immunity (TPI) is vital for newborn calf health and is typically assessed through blood sampling to measure serum or plasma IgG or total protein levels. Saliva offers a less invasive alternative. This study evaluated the potential of saliva for assessing TPI. Saliva and serum samples were collected from 20 calves at birth and on days 1, 2, and 7 of life to measure IgG, IgA, IgM, and total protein concentrations. Colostrum fed to the calves was also analyzed for gross composition and immunoglobulin content. Colostrum intake and composition were associated with saliva IgG (R2 = 0.48; p = 0.019), saliva IgM (R2 = 0.73; p = 0.02), and saliva total protein (R2 = 0.41; p = 0.043). Serum IgG and IgA levels were predicted by saliva IgG (p < 0.001; R2 = 0.33) and IgA (p < 0.001; R2 = 0.13), respectively, though predictive accuracy varied by calf age (IgG: p < 0.001; R2 = 0.40; IgA: p < 0.001; R2 = 0.91). In conclusion, the results suggest that both saliva IgG and IgA concentrations could be used to predict IgG and IgA serum concentrations. Nevertheless, further studies are still needed to clarify the best time for sample collection.