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R A Prins

Publications and source records attributed to R A Prins.

13 recordsLinked to original sources
PubMed1979

An analysis of the buffer system in the rumen of dairy cattle.

A method is presented for the analysis of buffer systems in the rumen using the first derivation of titration curves. Bicarbonate and volatile fatty acids (VFA) are the main components of the buffering system in the rumen fluid of dairy cattle under widely different feeding conditions. Phosphate from saliva is of little importance as a buffer, but neutralizes acids produced in the rumen. After studying five cows during the peripartal period a spontaneous and transient increase in the concentrations of VFA and a soluble marker (PEG) as well as a drop in pH and in the bicarbonate concentrations not related to feeding was observed in two animals that were sampled several hours before parturition. The potential risk of provoking rumen disturbances upon feeding animals close to the time of parturition, when buffering capacity may be minimal, is stressed.

Animal Feed↗
PubMed1978

Relative significance of exogenous and de novo synthesized fatty acids in the formation of rumen microbial lipids in vitro.

Mixed rumen microorganisms (MRM) or suspensions of rumen Holotrich protozoa obtained from a sheep were incubated anaerobically with [1-(14)C]linoleic acid, [U-(14)C]glucose, or [1-(14)C]acetate. With MRM, the total amount of fatty acids present did not change after incubation. An increase in fatty acids esterified into sterolesters (SE) and polar lipids at the expense of free fatty acids was observed. This effect was intensified by the addition of fermentable carbohydrate to the incubations. Radioactivity from [1-(14)C]linoleic acid was incorporated into SE and polar lipids with both MRM and Holotrich protozoa. With MRM the order of incorporation of radioactivity was as follows: SE > phosphatidylethanolamine > phosphatidylcholine. With Holotrich protozoa, the order of incorporation was phosphatidylcholine > phosphatidylethanolamine > SE. With MRM the radioactivity remaining in the free fatty acids and that incorporated into SE was mainly associated with saturated fatty acids, but a considerable part of the radioactivity in the polar lipids was associated with dienoic fatty acids. This effect of hydrogenation prior to incorporation was also noted with Holotrich protozoa but to a much lesser extent. Small amounts of radioactivity from [U-(14)C]glucose and [1-(14)C]acetate were incorporated into rumen microbial lipids. With protozoa incubated with [U-(14)C]glucose, the major part of incorporated radioactivity was present in the glycerol moiety of the lipids. From the amounts of lipid classes present, their radioactivity, and fatty acid composition, estimates were made of the amounts of higher fatty acids directly incorporated into microbial lipids and the amounts synthesized de novo from glucose or acetate. It is concluded that the amounts directly incorporated may be greater than the amounts synthesized de novo.

Acetates↗
PubMed1976

On the contribution of the acrylate pathway to the formation of propionate from lactate in the rumen of cattle.

The effect of chloral hydrate, an inhibitor of methanogenesis, on the participation of the acrylate pathway in the formation of propionate from lactate in rumen contents of cattle was studied in vitro. Addition of chloral hydrate resulted in only a small stimulation of the acrylate pathway, much lower than the stimulation of propionate production by chloral hydrate. This means that the flux of carbon through both the acrylate and the dicarboxylic acid pathway is increased during chloral hydrate feeding. The influence of time of sampling after feeding on the contribution of the acrylate pathway was studied in a separate experiment. A marked drop in the participation of the acrylate pathway in propionate formation from lactate during at least 2 h after feeding was observed, whereafter a rapid rise to prefeeding levels occurred.

Acrylates↗
PubMed1975

Some characteristics of Anaerovibrio lipolytica a rumen lipolytic organism.

Strains of Anaerovibrio lipolytica isolated from sheep- and cow-rumen contents on a linseed oil -- rumen fluid -- agar medium fermented ribose, glycerol and DL-lactate. Fermentation products from glycerol were propionate and succinate, while ribose, fructose and DL-lactate were fermented mainly to acetate, propionate and carbon dioxide. Propionate is formed in this organism by the dicarboxylic acid pathway similarly as in propionibacteria. Measurements of the rate of lipolysis by pure cultures suggest that the organism may play an important role in the lipolytic activity of rumen contents of sheep. The demonstrated fact that the cell-free lipase excreted in the culture medium can easily be adsorbed on particulate matter in autoclaved rumen fluid may explain the absence of free lipase in clarified rumen liquor.

Anaerobiosis↗
PubMed1975

Lipid-phase transitions of the strictly anaerobic bacteria Veillonella parvula and Anaerovibrio lipolytica.

As a basis for physicochemical studies on the membranes of the strictly anaerobic bacteria Veillonella parvula, Anaerovibrio lipolytica, and Megasphaera elsdenii, the fatty acyl and alk-1-enyl moieties on the phosphoglycerides of these organism were characterized. Uncommon is the high proportion of a heptadecenoic acyl and alk-1-enyl moiety in these three lactate-fermenting bacteria. In contrast to V. parvula and A. lipolytica, M. elsdenii contains high amounts of branched-chain acyl and alk-1-enyl moieties. Freeze-etching electron microscopy showed that the lipids of the plasma membranes of V. parvula and A. lipolytica go from the liquid crystalline to the gel state upon lowering of the temperature, indicating that the membrane lipids are predominantly in the fluid state. No lipid-protein segregation could be detected in the plasma membrane of M. elsdenii. This can be explained by the abundance of branched-chain fatty acyl and alk-1-enyl residues in the membranes of this organism which may prevent lipid-protein segregation during the lipid-phase transition.

Anaerobiosis↗