ARS | Publication request: Glycerol inhibition of ruminal lipolysis in vitro

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 29, 2012
Publication Date: August 23, 2012
Citation: Edwards, H.D., Anderson, R.C., Miller, R.K., Taylor, T.M., Hardin, M.D., Smith, S.B., Krueger, N.A., Nisbet, D.J. 2012. Glycerol inhibition of ruminal lipolysis in vitro. Journal of Dairy Science. 95:5176-5181.

Interpretive Summary: Glycerol is a by-product of biodiesel production, and because of its availability and nutritional properties, it has become an attractive choice for use as a feed supplement for animals. For instance, glycerol is high in energy, and it can also improve the dietary quality of meat and milk produced from cattle and sheep by preventing the bioconversion of healthy fats to unhealthy fats. Feeding too much glycerol, however, can adversely affect beneficial fiber-degrading gut bacteria that may also help prevent the colonization of the animal by unwanted foodborne pathogens. The present study was conducted to determine the safe level of glycerol that can be fed to cattle and sheep. We found that the beneficial effects of glycerol on fat digestion could be achieved with the addition of as little as 6% of this by-product. This level of glycerol feeding is well within the range considered to be safe for fiber digestion. These results provide important, new information to farmers and ranchers so that they can safely feed this by-product without adversely affecting populations of gut bacteria that play an important role in fiber digestion and maintaining good gut health. Ultimately, these results can help farmers and ranchers safely use low cost feed ingredients to produce wholesome meat and milk for the American consumer.

Technical Abstract: Supplemental glycerol inhibits rumen lipolysis, a prerequisite for rumen biohydrogenation, which is responsible for the saturation of dietary fatty acids consumed by ruminant animals. Feeding excess glycerol, however, adversely affects dry matter digestibility. To more clearly define the effect of supplemental glycerol on rumen lipolysis, mixed populations of ruminal bacteria were incubated with 6 or 20% glycerol (vol/vol). After 48 h anaerobic incubation of mixed culture rumen fluid, rates of free fatty acid production (nmol/ml per h) for both glycerol supplemented samples were decreased (P < 0.05) by 80 and 86%, respectively, compared to rates from non-supplemented control cultures (12.4 ± 1.0; mean ± SE). Conversely, assay of prominent ruminal lipase-producing bacteria revealed no effect of glycerol on lipolytic activity by these organisms. These results indicate that supplementing ruminant diets with 6% glycerol will effectively reduce lipolysis. However, the mechanism of glycerol inhibition of ruminal lipolysis remains to be demonstrated.