Histological measurement of fat content of liver of dairy cows.

A total of 275 liver biopsies were performed on dairy cows in 6 Friesian and one Guernsey herd during the first 2 weeks after calving. Liver samples were processed by 2 independent histological procedures: (a) formalin-fixed frozen sections were stained with oil-red O (ORO), or (b) samples fixed in glutaraldehyde-osmium tetroxide were embedded in plastic and sections stained with toluidine blue (TOLB). The sections were then subjected to stereological point-counting procedures to assess the quantities of stainable fat present within the liver cells. Estimates of liver cell fat by the 2 techniques were highly correlated, although those obtained by the TOLB method were consistently lower than those obtained by the ORO method. The analytical sampling error was slightly lower in the TOLB method. The simpler ORO method should prove an acceptable alternative in the routine histology laboratory to the tedious and technically demanding TOLB method.