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Biomedical subjects

D I Demeyer

Publications and source records attributed to D I Demeyer.

At least 19 recordsLinked to original sources
PubMed1996

Influence of pH on lipolysis and biohydrogenation of soybean oil by rumen contents in vitro.

The effect of different pH values on rumen lipolysis and biohydrogenation was investigated during incubations of the rumen contents with 40 or 80 mg of soybean oil as the sole substrate. Mean pH values studied were 6.8, 6.3, 6.0, 5.6 and 5.2. Lipolysis was calculated from the decrease in fatty acids present in triacylglycerols (TAG), as well as from the accumulation of free fatty acids (FFA) during the incubation. At pH < or = 6.0 lipolysis was low, and the inhibition became greater with decreasing pH. At the same pH value, the inhibition in incubations with 80 mg of soybean oil was more pronounced than with 40 mg. Even at the lowest pH value, after incubation, no free linolenic acid could be detected because of biohydrogenation, whereas linoleic acid hydrogenation was only partially inhibited at pH 5.2. This means that lipolysis is much more sensitive to low pH values than biohydrogenation. Literature data indicate however that, besides pH, other factors must be involved in the decrease of both lipolysis and biohydrogenation in the rumen of animals fed highly concentrated diets.

Animals↗
PubMed1996

Attempted induction of reductive acetogenesis into the rumen fermentation in vitro.

Rumen and caecal contents, obtained from slaughterhouse cattle and rumen contents obtained from a fistulated wether were incubated in vitro with ground hay in the presence and absence of, respectively, casein hydrolysate and mucin. Differences in stoichiometry of rumen and caecal fermentations, indicative of reductive acetogenesis in the caecum, were confirmed, except for incubations with free amino acids. Net fermentation end product production was determined after correction for amounts formed in incubations without the substrate. These determined amounts of hay fermentation end products were compared with the amounts calculated from incubations of hay with added casein hydrolysate or mucin, corrected for amounts formed from the latter added substrates incubated alone. With casein hydrolysate, no differences between the determined and calculated amounts were observed, excluding the occurrence of reductive acetogenesis from hay in the presence of free amino acids. With mucin, the calculated amounts indicated an inhibition of methanogenesis, accompanied by increased amounts of proprionate, butyrate and valerate production. This finding was probably related to the greater availability of easily fermented carbohydrates in the presence of mucins. The absence of an increased acetate production in the incubations with added head space hydrogen gas, also indicate the absence of reductive acetogenesis from hay in the presence of mucin. Stoichiometric considerations also indicate that neither free amino acids, nor mucin, induce reductive acetogenesis in short-term in vitro incubations of rumen contents with hay.

Acetates↗
PubMed1996

In vitro study of the age-dependent caecal fermentation pattern and methanogenesis in young rabbits.

The caecal fermentation pattern, including methanogenesis, was studied in young rabbits using in vitro batch incubations. Six conventional litters of eight rabbits each were used. At the age of 22, 25, 28, 32, 36, 42 and 56 days, an animal was slaughtered from each litter and its caecal contents were used for in vitro batch incubations at 39 degrees C/24 h. The incubated samples were analysed for volatile fatty acids (VFA), methane, hydrogen, ammonia nitrogen (NH3-N) and lactic acid (LA). The net total in vitro VFA production did not differ clearly with age, although a significant decrease was observed on day 36, reflecting the reduced zootechnical performances probably related to an infection with Clostridium spiroforme that occurred in the same period. The molar proportions of butyrate and propionate formed a change in the opposite direction with age, starting with a sudden shift from propionate to butyrate at day 25. In vitro NH3-N production was suggestive of a progressive and significant decrease with age; in vitro LA production was always low. Methane production was almost absent from fermentation until 32 days of age, after which it suddenly shifted from 1.6 to 52.0 mumol/flask/day and increased further with age. A significant litter effect on methanogenesis was observed which suggested the existence of a genetic effect. The hydrogen production was quite low and decreased significantly from day 36 with increasing methanogenesis. The calculated hydrogen recoveries showed a gradual increase from day 32 and were positively correlated (r = 0.92) with methane production. In conclusion, it would seem that in young suckling rabbits, reductive acetogenesis is a major characteristic of caecal fermentation, to be replaced gradually and partially by methanogenesis with the increasing intake of solid feed.

Aging↗
PubMed1996

Effect of pH on biohydrogenation of polyunsaturated fatty acids and their Ca-salts by rumen microorganisms in vitro.

The influence of different pH values on the protection of Ca-salts of polyunsaturated fatty acids (PUFA) against ruminal biohydrogenation was investigated. Ca-salts were prepared from soya bean oil fatty acids (SOH) and incubated in vitro with rumen fluid at different pH values. Biohydrogenation of Ca-salts of the PUFA's and their corresponding free fatty acids in SOH was compared. Two series of incubations were carried out, a first series with pH varying between 6.9 and 5.5, while in the second series, a narrower pH range was studied (6.8-6.3). The experiments showed that between pH 6.9 and 6.3, Ca-salts of PUFA's are partly protected against biohydrogenation. Ca-salt of linoleic acid was protected to a greater extent than Ca-linolenate. Biohydrogenation of the salts is most probably due to dissociation of the solubilized Ca-salts. For efficient protection of Ca-salts of PUFA's against hydrogenation, maintenance of pH values above 6.3 will be necessary.

Animals↗
PubMed1996

Effect of halothane genotype, breed, feed withdrawal, and lairage on pork quality of belgian slaughter pigs.

A total of 434 Belgian Landrace (B) or Piétrain x B (PB) pigs, of known halothane genotype (NN, Nn, and nn), were slaughtered in a commercial abattoir. Pigs were either fed until loading or deprived of food overnight before delivery. Upon arrival at the abattoir, pigs were slaughtered after different lairage times (within 1 h after arrival, after 2 to 3 h lairage, or 4 to 5 h lairage). Meat quality traits were measured on the carcass, as well as on a piece of loin. Halothane genotype was the predominant factor determining meat quality traits related to the PSE condition (P < .001 for pH 40 min after death, internal reflectance, color L value; P < .01 for drip losses, transmission value). For these traits, nn pigs were always significantly different from Nn and NN pigs. Depending on the specific trait, Nn pigs were intermediate between NN and nn pigs, or close to NN pigs. For pH 40 min after death and drip losses, Nn and NN pigs were significantly different, whereas the difference between Nn and NN pigs was not significant for internal reflectance, color L value, and transmission value. Shear force and intramuscular fat content were apparently not related to the PSE condition and were not influenced by the halothane genotype (P > .05). Differences in meat quality between B and PB pigs and between gilts and barrows were rather unimportant compared with the effect of halothane genotype. Overnight feed withdrawal had no effect on meat quality (P > .05 for all PSE-related traits). On the other hand, holding pigs a few hours in lairage improved meat quality compared with immediate slaughtering (P < .05 for pH and temperature in the loin 40 min after death, internal reflectance, color L value, transmission value, drip losses). This effect was more pronounced in stress-susceptible pigs than in stress-resistant pigs.

Abattoirs↗
PubMed1995

Transformations and effects of lipids in the rumen: three decades of research at Gent University.

A survey is given of research results on ruminant lipid digestion obtained at the authors' laboratory. Results are presented in terms of lipid changes occurring in the rumen and in terms of effects on nature, extent and site of digestion. The rumen can be adapted to an extremely high capacity for triglyceride lipolysis, preferentially releasing polyunsaturated fatty acids that are then further hydrogenated with accumulation of oleic acid isomers in vitro only. Evidence was obtained for both microbial incorporation and synthesis of polyunsaturated acids. In vitro lipolysis is inhibited by pH values below 6.3 and by ionophores. Free fatty acids inhibit methanogenesis with associated increases in propionate production and decreases in acetate and butyrate productions; the latter being related to their defaunating effect. Both in the faunated and defaunated rumen, free fatty acids decrease fibre digestion, which is shifted to the hindgut, at least in sheep. Defaunation increases rumen microbial growth efficiency and may result in a higher duodenal flow of both feed and microbial protein, provided these increases are not overcome by a decreased apparent rumen OM digestibility. Considerable between animal variability exists for these effects, associated with variable effects on rumen particle and liquid volumes and outflow rates.

Animals↗
PubMed1995

Lipolysis and biohydrogenation of soybean oil in the rumen in vitro: inhibition by antimicrobials.

This experiment attempted to lower rumen lipolytic activity, biohydrogenating activity, or both using antimicrobial compounds. In vitro incubations were carried out with rumen fluid, 80 mg of soybean oil, and .5 g of commercial concentrates as substrate. Unless stated otherwise, the final concentrations of the additives in the incubation was 20 ppm. Lipolysis and biohydrogenation were determined by separation of triacylglycerols and FFA by TLC; the fatty acid composition of each was determined by GLC before and after incubation and with or without additive. With some of the antibiotics, lipolysis was inhibited 10 to 20%, and the most potent inhibitors were ionophores and amoxicillin. Biohydrogenation (including C18:1) decreased only for lasalocid, but no additive could prevent hydrogenation of linolenic acid liberated from triacylglycerols. Some additives decreased hydrogenation of linoleic acid, but only slightly. Lipolytic activity decreased VFA production more than the other potent additives (amoxicillin, avoparcin, lasalocid sodium, monensin, and salinomycin sodium). This result could indicate a more specific toxic effect on lipolytic microbes. Finally, different antimicrobials influenced fermentation patterns differently (VFA proportions and CH4 production), but shifts were always in accordance with stoichiometric principles.

Animals↗
PubMed1995

[Adaptation of rumen fermentation to monensin].

Adaptation of rumen fermentation to monensin feeding has been studied with rumen-fistulated sheep receiving a daily dose of 30 mg of monensin for a period of 21 d followed by a 28 d period during which 60 mg doses were administered. The ration consisted of 300 g of hay and 300 g of concentrates, fed at 9.00 h and 16.00 h. Monensin was placed in the rumen as an aqueous suspension, just prior to the morning feeding. Monensin infusion was preceded and followed by a period during which no monensin was infused. The following rumen fermentation parameters were determined: methane production, pH, volatile fatty acids (VFA) molar proportions, total volatile fatty acid concentration, lactate and ammonia concentrations and in sacco degradability of hay. Rumen gas expelled through the fistula was collected for 6 h per day and analysed. Total VFA concentration, molar proportions of individual VFA, pH, lactate and ammonia concentration were determined on rumen contents, sampled just prior the administration of monensin and 2 and 6 h later. In vitro incubations of 3 h were carried out with rumen fluid, sampled 1 h after feeding. In vivo and in vitro methane production was decreased by monensin feeding. The molar proportion of propionate in the rumen was increased, while acetate and butyrate percentages were lowered. The total VFA and ammonia concentrations were also decreased by monensin, but pH values were increased. In vitro production of propionate was stimulated by monensin administration and methanogenesis decreased. The organic matter in sacco degradability was not affected, probably because of the time difference between the introduction of bags and monensin in the rumen. These modifications of rumen fermentation persisted as long as monensin was given, indicating that in this experiment, there was no adaptation to the ionophore.

Ammonia↗
PubMed1990

Incorporation of soya oil hydrolysate in the diet of defaunated or refaunated sheep: effect on rumen fermentation in vitro.

The effects of incorporation in the diet of 7% soya oil hydrolysate (SOH) on in vitro incubations of cellobiose + maltose, maize starch and casein by rumen microbes were studied using defaunated and refaunated sheep as rumen fluid donors. Feeding refaunated sheep the SOH supplemented diet lowered the protozoal numbers in the rumen from 1.61 10(6)/ml to 6.1 10(5)/ml. SOH addition reduced in vitro methane production, rather by a depletion of methanogens is than by a simple inhibition of their activity. This reduction seemed to be independent of protozoa depletion. With cellobiose-maltose and maize starch incubations, SOH supplementation increased molar proportion of propionate while acetate decreased. Both variations could be linked to the inhibition of methanogenesis. Volatile fatty acid production from casein was strongly reduced by SOH supplementation with or without protozoa in the rumen of the donors animals.

Animal Feed↗
PubMed1988

Fermentation of methanol in the sheep rumen.

Sheep fed a hay-concentrate diet were adapted to pectin administration and ruminal infusion of methanol. Both treatments resulted in a strong increase in the rate of methanogenesis from methanol. Quantitative data show that methanol was exclusively converted into methane. Treatments did not influence ruminal volatile fatty acid percentages.

Animals↗
PubMed1986

Effect of defaunation and refaunation of the rumen on rumen fermentation and N-flow in the duodenum of sheep.

In order to confirm earlier fragmentary results, the effect of defaunation and refaunation of the rumen on the fermentation pattern and flow of N-components in the proximal duodenum of two sheep was investigated. Defaunation had no effect on acetic acid as a proportion of the total volatile fatty acids in the rumen, while the proportions of propionic acid increased with a concomitant decrease in butyrate. Refaunation resulted in lower acetic acid and higher butyric acid proportions. The concentration of ammonia N in the rumen was clearly decreased after defaunation, already indicating an effect of the elimination of protozoa on nitrogen metabolism in the rumen. Defaunation also increased significantly the flow of total N, non ammonia N and individual and total amino acids in the proximal duodenum. Defaunation resulted in higher bacterial growth efficiency, significantly in one sheep, but the decrease after refaunation was statistically significant for both sheep. Determination of rumen digestibility of organic matter and acid detergent fibre (ADF) revealed lower values in the absence of the protozoa, while total digestibility was only influenced to a much lower extent. This indicated a shift of digestion from rumen to the lower digestive tract. Finally, earlier work is discussed in the light of the present findings.

Ammonia↗
PubMed1985

Effect of monensin on fermentation pattern and soybean protein degradation in the rumen of sheep.

The effect of a daily dose of 30 mg Monensin on rumen fermentation pattern and degradation of the crude protein fraction of soybean meal was investigated with sheep. Degradation parameters for soybean meal were measured by the nylon bag technique. Monensin increased propionic acid percentages in the rumen, with a concomitant decrease in acetic- and butyric acid proportions, thus confirming earlier work. Ammonia N concentration in the rumen was also lowered, indicating an inhibitory effect on rumen protein breakdown. However, no effect on degradation rate, degradability and effective degradability (only with one sheep) could be observed. Possible reasons for these findings are discussed. Amino acid analysis on the residues in incubated bags revealed slight changes in amino acid composition, but these changes were considered to be nutritionally unimportant.

Ammonia↗
PubMed1985

Effect of defaunating the rumen on growth and carcass composition of lambs.

The effect of defaunating the rumen on growth performance and carcass composition of lambs fed a molasses-urea diet was investigated. Before the growth trial, all the animals were defaunated. Based on live weight and daily gain during a preliminar period, the animals were divided in two groups whereafter one group was refaunated. Defaunation caused a decrease in propionic acid percentage in the rumen. Daily gain and food conversion efficiency were better in the defaunated group, but only during the first five weeks. The response over the whole trial (0-9 weeks) remained positive however. There was a trend towards more meat and less fat in the carcass of defaunated lambs. The fact that two animals died during the defaunation procedure indicates the need for a completely harmless and effective defaunating agent.

Animal Feed↗
PubMed1984

Effect of virginiamycin on carbohydrate and protein metabolism in the rumen in vitro.

The effect of virginiamycin in incubations of rumen fluid with carbohydrate or protein substrate was investigated. In carbohydrate incubations, methane production was partially inhibited while propionate proportions increased. Total microbial growth was slightly decreased, but net microbial growth was considerably lower. Protein degradation was slightly lowered after addition of virginiamycin. These effects were compared with results obtained with other rumen manipulating additives.

Animals↗
PubMed1981

Effect of methane inhibitors on the metabolism of rumen microbes in vitro.

In incubations in vitro with rumen fluid, the effect of two methane inhibitors, linseed oil hydrolysate (LOH) and chloral hydrate (CH) on the efficiency of microbiol growth was investigated. Total and net microbial growth were determined from 32PO43- and NH3--N incorporation respectively and expressed as g N incorporated per kg organic matter fermented (gN/kgOMf). In a first series on incubations, it was found that LOH had no influence on overall microbial growth efficiency, while with CH, a small but significant decrease of total and net growth efficiency was measured. Further experiments showed that this was not due to accumulation of hydrogen gas in the CH incubations. Microscopic examination showed a toxic effect of LOH on protozoa, but with CH, no such effect was observed. This observation, together with earlier work where a considerable increase in microbial growth efficiency was found in vitro after defaunation of the rumen suggested the following hypothesis: both inhibitors lowered bacterial growth. In the case of LOH, this effect is marked by the defaunating action of LOH, the latter resulting in an increased growth efficiency of the bacterial fraction. This hypothesis was confirmed by incubations with washed cell suspensions (WCS) of mixed rumen bacteria, where growth efficiency was indeed decreased by both inhibitors. The possible mechanism explaining this phenomenon was discussed.

Animals↗
PubMed1979

Effect of defaunation on the metabolism of rumen micro-organisms.

1. Rumen contents of a fasted fistulated wether, obtained in a faunated, defaunated and refaunated period were incubated in vitro with a mixture of cellobiose and maltose, in the presence of ammonium bicarbonate and 32PO43-. Total synthesis of microbial N (Nt) was calculated from 32P incorporation and N:P determined in microbial matter. The N:P value was not affected by defaunation. Net synthesis of microbial N (Nn) was calculated from ammonia-N incorporation. An estimate of degradation of microbial N was calculated as Nt-Nn. Energetic efficiency of synthesis was calculated from the volatile fatty acids produced during incubation, as g N incorporated per kg organic matter fermented (g N/kg OMf). 2. Defaunation decreased the proportions of acetate, butyrate and methane and increased those of propionate in fermentation end-products. Fermentation rate when expressed per mg microbial N was not affected by defaunation. 3. Expressed per unit volume of rumen contents, Nn was increased by defaunation whereas Nt remained unchanged. Thus, a decrease in degradation can be calculated. Energetic efficiences of total and net synthesis were increased from 35 and 13 to 47 and 30 g N/kg OMf respectively. 4. Specific rates of both total and net synthesis of microbial N were significantly increased by defaunation whereas the specific rate of degradation was not affected.

Animals↗