Glycerol till mjölkkor : effekter på våmmetabolismen

Abstract: Glycerol is essential for the lipid metabolism of both plants and animals. Glycerol is formed in the rumen by hydrolysis of lipids from the feed. Glycerol is also a by-product from the production of biodiesel from rapeseed oil and other fat sources. Glycerol might be used as a dietary glucose precursor for dairy cows in similar ways as propylene glycol. Due to increased production of biodiesel more glycerol has been available to a lower price. There are different qualities of glycerol on the market representing different stages of processing. Crude glycerol also contains water, fat, minerals and methanol while refined glycerol often contains >99.5% glycerol. This study was divided in two different parts. In the first part three rumen fistulated non-lactating, nonpregnant cows were used. Fractional disappearance of glycerol from the rumen was determined by means of a combination of in vivo and in vitro methods. Furthermore the effects of glycerol on rumen fluid volatile fatty acids (VFA) concentration and osmolality were analysed. In the second part four rumen fistulated lactating cows received two different glycerol qualities or as a control no glycerol during three two week periods. The effect of the two glycerol qualities on digestibility of dry matter (DM), neutral detergent fiber (NDF) and crude protein CP) was determined. Furthermore the effect of the different glycerol qualities on rumen fluid VFA concentration and osmolality was investigated. Glycerol appeared to be readily absorbed from the rumen and while the digestion rate of glycerol in the rumen was low. The rumen micro flora apparently did not adapt to glycerol since the rate of glycerol digestion was not affected when the coes were fed glycerol for two weeks. Glycerol did not have any marked effect on the digestibility of silage DM, NDF or CP. Glycerol changed the rumen fluid VFA pattern towards more butyrate and less acetate while the effect on propionate varied. The total concentration of VFA rumen fluid was reduced by glycerol. There appeared to be no difference between the two glycerol qualities regarding rumen metabolism.