Defining colloid osmotic pressure and the relationship between blood proteins and colloid osmotic pressure in dairy cows and calves.

Objective: To establish the reference interval for colloid osmotic pressure (COP) in neonatal and adult cattle and to investigate associations between COP and total protein, albumin, or globulin in the two populations sampled.

Design: Cross-sectional observational study.

Setting: Animals were sampled on commercial dairy farms in Southern Wisconsin, and samples were processed and analyzed in a clinical pathology laboratory at a university teaching hospital.

Animals: Forty adult lactating Holstein cows between 2 and 4 years of age and 40 healthy Holstein calves of both sexes between 2 and 7 days of age.

Interventions: Adult cows were sampled by coccygeal venipuncture into standard heparinized vacutainer tubes, calves were sampled by jugular venipuncture also into heparinized vacutainer tubes.

Measurements And Main Results: For adult cows, the mean COP was 22.52 mm Hg, with a standard deviation of 1.0. For calves, the mean COP was 19.6 mm Hg, with a standard deviation of 1.9. Good correlation was demonstrated in adults between COP and albumin concentrations (r(2) = 0.72) and between COP and both total protein concentration (r(2) = 0.74) and globulin (r(2) = 0.65) in calves. For adults, regression plots established best fit relationships of COP = 0.472 (albumin) + 6.49, whereas for calves, two regression equations could be described; COP = 0.305 (globulin) + 8.62, and 0.268 (total plasma protein) + 2.73.

Conclusions: Suggested normal ranges (mean ± 2 standard deviations) for COP in adult lactating dairy cows and calves between 2 and 7 days of age were 21-25 mm Hg and 17-23 mm Hg, respectively.