In-vitro assessment of fat supplements for ruminants

In-vitro anaerobic incubations were used to assess the degree of metabolism or rumen inertness of different fat supplements containing either triacyglycerols and/or free fatty acids. The extent of triacylglycerol lipolysis and biohydrogenation of the unsaturated fatty acids, oleic acid (C18:1) and linoleic acid (C18:2) was monitored after 24 h incubation in rumen fluid. These studies indicate that the degree of metabolism of different fat sources varies from 15 to 95%. For untreated oil, extruded oil-seed and pelleted (prilled) fat supplements the degradation values were 95, 70, and 65% respectively. The hydrogenation of calcium salts of C18 monounsaturated fatty acids when mixed with predominately C16 and C18 saturated fatty acids was 45%. The lowest degree of metabolism (<20%) occurred with the triacylglycerol embedded in a matrix of aldehyde-treated protein. Therefore, to assist in formulation of rations containing fat supplements, the degree of rumen degradability (metabolism) should be stated.