Research note: Investigation on the metabolism of glycerol in the rumen of bulls

Abstract

Two bulls, each fitted with rumen and duodenal cannulas, received (in addition to a hay-grain diet) twice daily an infusion of 200 g glycerol into the rumen over a period of six days. During this preliminary in vivo investigation, the influence of a glycerol application on the rumen environment over a six-day adaptation period was examined. Samples of rumen fluid were collected daily, two hours after glycerol infusion. An additional 15N-urea application into the rumen was given on days 1 (without glycerol infusion), 3 and 7 (with glycerol infusion). Extra samples of rumen fluid and blood plasma (from puncture of vena jungularis) were taken through the 12th hour following urea application. Rumen fluid pH was reduced due to glycerol intake from 6.3 (day 1, without glycerol) to 5.4 by day 7. Molar proportion of acetic acid to propionic acid decreased from 3.5 (day 1) to 2.1 (days 6 and 7). Average glycerol disappearance rate from the rumen was 4.7 gl-1 h-1 for the first hour. Only small amounts of glycerol could be detected in the duodenal digesta. Blood plasma glycerol content was significantly higher after glycerol application (0.061 mmol l-1 vs. 0.019 mmol l-1). The incorporation of 15N into the rumen bacteria and the proportion of bacterial N (as percent of TCA-precipitable N in the rumen fluid) were lower after glycerol influsion. These results, coupled with the lower concentration of iso-acids (isobutyric and isovaleric acids) in the rumen fluid, indicate that the high amount of glycerol infusion (10% of DMI) reduced protein metabolism of rumen bacteria throughout the experimental period.

Evaluation of feeding glycerol on free-fatty acid production and fermentation kinetics of mixed ruminal microbes in vitro

“…The retention of glycerol within the rumen will depend on the absorption as well as the microbial fermentation and fluid passage rate of this compound. The observed effects of glycerol on ruminal VFA accumulations (Donkin and Doane 2007;Kijora et al, 1998) suggest that glycerol is not absorbed so fast as to preclude appreciable microbial fermentation. These finding suggests that long-term feeding of glycerol may ultimately select and enrich the populations of glycerol-fermenting microbes such as Megasphaera elsdenii and Selenomonas rumiantium.…”

Effect of replacement of barley meal with crude glycerol on lactation performance of primiparous dairy cows fed a grass silage-based diet

“…This was not observed in the present trial. However, other studies found that glycerol supplementation decreased rumen pH (Kijora et al, 1998;Mach et al, 2009;Wang et al, 2009b). One reason for these seemingly contradictory findings could have been the high content of starch in the maize silage that was fed in these other studies, which is known to decrease the rumen pH.…”

Effects of Dietary Crude Glycerin Supplementation on Nutrient Digestibility, Ruminal Fermentation, Blood Metabolites, and Nitrogen Balance of Goats

“…Similarly, Chung et al (2007) reported that feeding glycerol to dairy cows increased circulatory glucose concentrations. In ruminants, glycerol can be rapidly converted to propionic acid and readily absorbed through the ruminal wall (Johns, 1953; Kijora et al, 1998). Therefore, the glycerol component can be converted to glucose by the liver and kidneys (Krebs and Lund, 1966) to provide energy for cellular metabolism.…”