Absorption of volatile fatty acids from the rumen of lactating dairy cows as influenced by volatile fatty acid concentration, pH and rumen liquid volume

Abstract

The effect of rumen liquid volume, pH and concentration of volatile fatty acids (VFA) on the rates of absorption of acetic, propionic and butyric acids from the rumen was examined in lactating dairy cows. Experimental solutions introduced into the emptied, washed rumen comprised two different volumes (10 or 30 I), four levels of pH (4.5, 5.4, 6.3, 7.2) and three levels of individual VFA concentrations (20, SO or 100 mM-acetic, propionic or butyric acid). All solutions contained a total of 170 mM-VFA and an osmotic value of 400 mOsmol/l. Absorption rates were calculated from the disappearance of VFA from the rumen corrected for passage with liquid phase to the omasum. An increase in initial fluid pH caused a reduction in fractional absorption rates of propionic and butyric acids. Increasing the initial pH from 4 5 to 7.2 reduced fractional absorption rates of acetic, propionic and butyric acids from 0.35, 0.67 and 0.85 to 0.21, 0.35 and 0.28/h respectively. The fractional absorption rates of all VFA were reduced (P < 0.05) by an increase in initial rumen volume. The fractional absorption rate of acetic acid was lower (P < 0.05) a t an initial concentration of 20 mM than of 50 mM. The fractional absorption rate of propionic acid tended (P < 0.10) to decrease as the level of Concentration increased while fractional absorption rate of butyric acid was not affected by butyric acid concentration. These results indicate that relative concentrations of VFA in rumen fluid might not represent relative production rates and that attempts to estimate individual VFA production from substrate digestion must take account of pH and VFA concentration.Volatile fatty acids: Dairy cows -________.

Relative contribution of ruminal buffering systems to pH regulation in feedlot cattle fed either low- or high-forage diets

“…In the current study, ruminal total SCFA concentration, which does not necessarily reflect the rate of production as absorption and passage are not accounted for (Dijkstra et al, 1993), was greater (118 v. 95 mM) in cattle fed LF compared with HF. In addition, the greater ruminal osmolality in LF-than HF-fed cattle reflected the changes in total SCFA concentration that could be attributed to a greater ruminal supply of rapidly fermentable CHO as a result of higher dietary starch content and DMI.…”

In vivo production and molar percentages of volatile fatty acids in the rumen: a quantitative review by an empirical approach

“…This can originate in differences between VFA in their fractional absorption rate (C2 , C3 , C4, Bergman, 1990) and from the differential effect of pH on the absorption rates of the VFA. This effect increases with chain length (Dijkstra et al, 1993), as a function of pKa (Pitt et al, 1996;Noziè re and Hoch, 2006). Despite good within-experiment relationships between the VFA profiles in the production and the VFA profiles in the rumen fluid, inter-experiment variability remained high, particularly for C4.…”

“…Despite good within-experiment relationships between the VFA profiles in the production and the VFA profiles in the rumen fluid, inter-experiment variability remained high, particularly for C4. To assess whether different absorption rates may explain the differences across studies, we performed dynamic simulations of rumen VFA pools, with VFA fractional absorption rates depending on rumen pH (estimated from VFA concentration if not reported in the publications), VFA concentration and rumen volume (Dijkstra et al, 1993;Noziè re and Hoch, 2006). The simulations suggested that the differences in pH, VFA concentrations or rumen volume were insufficient to explain the differences between production and concentration profiles across studies.…”

Foraging behavior and ruminal fermentation of dairy cows grazing ryegrass pasture alone or with white clover

“…Additionally, absorption rates of VFA across the rumen wall may have been increased at night due to a lower rumen fluid volume, resulting in a higher effective surface area for absorption (Dijkstra et al, 1993). Small increases in the VFA pool immediately after the beginning of grazing are expected due to a low efficiency of chewing during eating (Boudon et al, 2006;Acosta et al, 2007).…”