Aurora Villarroel, Taylor B Miller, Justin K Ward, Elisha D Johnson and Kimberly R Noyes
The objectives of this study were to determine differences in total protein (TP) concentration between samples before and after freezing, and to determine the correlation between total protein in serum and plasma to evaluate passive transfer in calves. Blood was collected via jugular vein puncture from a total of 127 calves (34 Holstein and 93 Jersey) once between 1 and 3 days of age. Serum and plasma protein concentrations were measured via digital refractometer in fresh specimens; samples were then frozen for storage. After a variable period of time in storage (≤1 to 8 months), frozen samples were thawed and re-analyzed. Passing-Bablok regression showed that total protein concentration in plasma was consistently higher than in serum. Additionally, multivariate regression showed that Jersey calves had higher total protein concentration in serum than Holstein calves (0.429 ± 0.049 g/dL), and that each additional month of storage resulted in lower protein concentration in serum (-0.116 ± 0.017 g/dL). Electrophoresis showed that all protein fraction levels varied after long-term storage of serum, although albumin accounted for most of the variation. It is concluded that plasma samples can be used as a new and improved option to evaluate effectiveness of colostrum management protocols under field conditions because plasma samples are easier to handle in the field and they correlate well with fresh serum total protein concentration and are not significantly affected by frozen storage.