Estimation of Bovine Plasma Protein from Refractive Index

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Abstract
Refractive indices of 56 plasma samples obtained from overtly healthy cows and heifers were determined with a temperature-compensated refractometer. Plasma protein concentrations were determined by the Kjeldahl method. The correlation between these two variables was .967 and the linear regression equation was Y=435.55×-580.25, where X is the refractive index and Y is protein concentration in gm./100 ml. plasma. The standard error of estimate was 0.12. At the mean refractive index of these plasmas (1.3500) the error in estimating protein concentration would be ±3.10% (P<.05). Twelve Hereford heifers were watered for 30 days once daily or once on alternate days with tap water, 0.50 or 0.65% NaCl water. The animals were venipunctured on the last day just before drinking. Plasma protein concentration was estimated from refractive index. Watering on alternate days increased predrinking plasma protein concentration 2.9%, but this effect was not related to salinity of the water. At 3 hr. post-drinking, hemodilution was indicated by a 6.6% reduction in plasma protein concentration. The reduction was greatest in those animals drinking 0.50 or 0.65% NaCl once per 48 hours. Plasma protein concentration, as determined by refractometry, appears to be a sensitive indicator of hemoconcentration and hemodilution. Copyright © 1968. American Society of Animal Science . Copyright 1968 by American Society of Animal Science