Fractionation of plasma triglyceride-rich lipoproteins of the dairy cow: evidence of chylomicron-size particles.

Electron micrographs of bovine triglyceride-rich lipoproteins demonstrated spherical particles with diameters up to 3000 A. Chylomicron-size particles (larger than 750 A) were isolated specifically by rate zonal centrifugation. Subfractionation by rate zonal centrifugation, isopycnic centrifugation, and gel filtration chromatography all indicated a wide range of bovine triglyceride-rich lipoproteins from chylomicrons to very low density lipoproteins. Chemical analysis of subfractions from gel filtration showed changes in the ratio of triglyceride/protein characteristic of chylomicrons versus very low density lipoproteins. Electrophoretic analysis on agarose gels of bovine chylomicrons obtained by centrifugation and gel filtration showed migrating bands similar to very low density lipoproteins, unlike human chylomicrons. Evidence of bovine chylomicrons provides support for the concept of a significant contribution to milk fat from intestinally absorbed lipid in the dairy cow.