Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Tool for evaluation initiatives aiming at reducing overweight in order to generate best practices
    Schreurs, M.H.G.M. ; Raaij, J.M.A. van; Bemelmans, W. ; Schuit, J. - \ 2007
    Measuring intestinal blood flow in group-housed weaner pigs using Physiogear TM I: A pilot study
    Berkeveld, M. ; Hendriksen, S.W.M. ; Beers-Schreurs, H.M.G. van; Koets, A.P. ; Langendijk, P. ; Essen, G.J. van; Taverne, M.A.M. ; Verheijden, J.H.M. - \ 2007
    Livestock Science 108 (2007)1-3. - ISSN 1871-1413 - p. 159 - 162.
    The objective of this study was to determine whether intestinal blood flow can be measured adequately in group-housed animals using the recently developed Physiogear (TM) I wireless flowmeter. We used the weaner pig as one of many possible animal models. Four 7-kg piglets were instrumented with a 3-mm flowprobe around the superior mesenteric artery (SMA) and SMA flow was measured pre- and post-weaning. During measurements, behavior was recorded. The piglets did not show any abnormal behavior and were not restrained by the flowmeter. Severe reductions (> 75%) in SMA flow coincided with nursing (pre-weaning) and aggressive behavior (post-weaning) and were only short-lived. Our results demonstrate that the Physiogear (TM) I flowmeter can be used to measure flow in group-housed animals without any human contact, providing the opportunity to relate flow measurements to undisturbed animal behavior. (c) 2007 Elsevier B.V. All rights reserved.
    Mathematical analysis of human [13CO2]-breath test results: post prandial fate of amino acids is related to their ditary form.
    Schreurs, V.V.A.M. ; Nolles, J.A. ; Krawielitzki, K. ; Bujko, J. - \ 2007
    In: 2nd International Symposium on Energy and Protein Metabolism and Nutrition, EAAP publication 124, Vichy, France, 9 - 13 Septenber, 2007. - Wageningen, The Netherlands : Wageningen Academic Publishers - ISBN 9789086860418 - p. 237 - 238.
    Energetic and metabolic consequences of aerobic and an-aerobic ATP-production.
    Schreurs, V.V.A.M. ; Aarts, M.J. ; IJssennagger, N. ; Hermans, J. ; Hendriks, W.H. - \ 2007
    Agro Food Industry Hi-Tech 18 (2007)5. - ISSN 1722-6996 - p. 25 - 28.
    high-altitude - exercise - protein
    ATP, the currency of cellular energy metabolism, can be produced during aerobic and an-aerobic oxidation of metabolic substrates. The aerobic oxidation yields CO2 + H2O as metabolic end products while ATP is produced by oxidative phosphorylation in the mitochondria. Carbohydrate, protein and fat provide a similar amount of 12-13 ATP/MJ ME when the ME is based on their value as body constituent. The energetic efficiency is 42-43 percent. In the anaerobic mode, for glucose only, ATP is produced by substrate level phosphorylation during cytoplasmic glycolysis, the normal first step in the aerobic oxidation of glucose. However, under an-aerobic conditions cytoplasmic glycolysis produces lactate which requires one of two ways of aerobic clearance to avoid lactic acidosis. The 'ketogenic clearance' re-channels the lactate in aerobic oxidation of glucose, but elsewhere in the body. This ketogenic clearance can contribute to the normal ATP-requirement of the whole body, but causes a move to carbohydrate as energy substrate. If necessary these carbohydrates can be produced from body protein, with a decrease in the energetic efficiency to 29 percent. The "glucogenic clearance" re-cycles the lactate to glucose. This glucogenic pathway (Cori cycle) further lowers the energetic efficiency of ATP-production for peripheral use to 14.1 percent. The Cori cycle requires extra ATP and causes a move to fat as energy substrate. This desk study shows that the energetic efficiency of ATP-production for peripheral use will range between 14-43 percent depending on the need and availability of glucose. It is suggested that these results could be used to develop specific nutritional, physiological and environmental strategies to benefit physical fitness and weight management in daily practice.
    Postweaning growth check in pigs is markedly reduced by intermittent suckling and extended lactation
    Berkeveld, M. ; Langendijk, P. ; Beers-Schreurs, H.M.G. van; Koets, A.P. ; Taverne, M.A.M. ; Verheijden, J.H.M. - \ 2007
    Journal of Animal Science 85 (2007)12. - ISSN 0021-8812 - p. 258 - 266.
    feed-intake characteristics - digestive enzyme-activity - housed weanling pigs - early-weaned pig - small-intestine - boar exposure - crypt depth - performance - sows - consumption
    The objective of this study was to determine whether intermittent suckling (IS) combined with an extended lactation can reduce postweaning growth check in pigs. Three weaning regimens [ conventional weaning (CW), IS with 6-h separation intervals (IS6), and IS with 12-h separation intervals (IS12)] were compared. In CW (n = 17 litters), litters had continuous access to the sow until weaning (d 21, d 0 = farrowing). In IS6 and IS12, litters were separated from the sow for 12 h/d, beginning at d 14 and lasting until weaning (d 41 to 45). Litters were with the sow from 1400 to 2000 and from 0200 to 0800 (IS6, n = 14) or between 2000 and 0800 (IS12, n = 14). Litter size was standardized within 2 d after farrowing by crossfostering, resulting in an average litter size of 10.9 +/- 1.8 piglets. Piglets had ad libitum access to creep feed from d 7 onward. One week after the onset of IS (d 20), creep feed intake was increased in litters from both IS groups compared with CW litters (P <0.05). Both IS groups consumed considerable amounts of creep feed before weaning (d 41 to 45). Total feed intake before weaning was greater (P = 0.004) in IS12 (3,808 +/- 469 g/ piglet) than in IS6 (2,717 +/- 404 g/ piglet). In comparison, CW litters consumed 18 +/- 9 g/ piglet before weaning (d 21). Irrespective of weaning regimen, total feed intake of litters before weaning was highly correlated with postweaning feed intake (P <0.001). Furthermore, in all treatment groups, total preweaning feed intake was correlated with postweaning growth (P <0.10). Irrespective of treatment, piglets suckling anterior teats grew faster than piglets suckling middle or posterior teats during the first 2 wk of lactation. Body weights at the end of the experiment (d 55) were similar among weaning regimens. Onset of IS induced a growth check in both IS groups (34% for IS12 and 22% for IS6). Only a mild growth check was observed after weaning of IS litters (14% for both IS groups). However, a serious growth check (98%) was observed after weaning of CW litters. Results of the current study indicate that IS stimulated feed intake during lactation, providing a more gradual transition to weaning. Because the IS6 regimen did not prevent the growth check after the onset of IS and is rather laborious, we suggest that IS12 might be preferable for a practical implementation of IS.
    Does a time interval for methionine supplementation favour weight gain and body composition? A model study with growing rats.
    Gas, M. ; Bujko, J. ; Chudobinska, E. ; Verstegen, M.W.A. ; Koopmanschap, R.E. ; Schreurs, V.V.A.M. - \ 2007
    In: Energy and protein metabolism and nutrition, EAAP publication No. 124, Vichy, France, 9 - 13 September, 2007. - Wageningen, The Netherlands : Wageningen Academic Publishers - ISBN 9789086860418 - p. 95 - 96.
    Addition of chromic oxide to creep feed as a fecal marker for selection of creep feed-eating suckling pigs
    Kuller, W.I. ; Beers-Schreurs, H.M.G. van; Soede, N.M. ; Taverne, M.A.M. ; Kemp, B. ; Verheijden, J.H.M. - \ 2007
    American Journal of Veterinary Research 68 (2007)7. - ISSN 0002-9645 - p. 748 - 752.
    weanling pigs - performance - consumption
    Objective-To determine whether the addition of chromic oxide (Cr2O3) to creep feed could be used as a visual marker in feces for selection of creep feed-eating suckling pigs. Animals-20 suckling pigs. Procedures-Via syringe, 5 pigs (2 to 3 days old on day 0; 1 pig/treatment) from each of 4 litters received oral administrations of 10, 20, 30, or 40 g of creep feed containing 10 g of Cr2O3 center dot kg(-1) on each of 2 consecutive days (days 20 and 21) or 30 g of creep feed containing 10 g of Cr2O3 center dot kg(-1) on day 20 and 30 g of Cr2O3 free creep feed on day 21. On days 21 through 24, 6 fecal samples were collected from each pig at regular intervals between 8:00 Am and 6:00 Pm. Green-colored feces were considered indicative of creep feed consumption (eaters). Data analyses were based on single and multiple fecal samples. Results-On day 22, evaluation of 1 fecal sample/pig and multiple fecal samples per pig resulted in identification of as many as 40% and only 15% of the feed-treated pigs wrongly as noneaters, respectively. Repeated sampling over multiple days would identify 99% of eaters accurately. Pigs erroneously identified as noneaters were those administered either low amounts of Cr2O3 supplemented creep feed for 2 days or Cr2O3 supplemented creep feed on only 1 day. Conclusions and Clinical Relevance-Data suggest that addition of Cr2O3 to creep feed enables selection of individual creep feed-eating suckling pigs via examination of feces, provided that repeated fecal samples are evaluated.
    Creep feed intake during lactation enhances net absorption in the small intestine after weaning
    Kuller, W.I. ; Beers-Schreurs, H.M.G. van; Soede, N.M. ; Langendijk, P. ; Taverne, M.A.M. ; Kemp, B. ; Verheijden, J.H.M. - \ 2007
    Livestock Science 108 (2007)1-3. - ISSN 1871-1413 - p. 99 - 101.
    performance - pigs
    The aim of the study was to measure the effect of creep feeding during lactation on net absorption in the small intestine at 4 days after weaning. Intermittent suckling was used to increase creep feed intake during lactation. Creep feed containing chromic oxide was provided. Based on the colour of the faeces, piglets were classified as `eaters¿ or `non-eaters¿, respectively. At day 4 after weaning, an in vivo small intestine segment perfusion test was performed at 5 sites along the small intestine in 24 piglets (12 eaters and 12 non-eaters). At both sides of each intestinal segment a tube was fitted to perfuse and drain fluid in order to assess net absorption. Net absorption was higher in eaters than in non-eaters (P <0.001). Net absorption varied greatly between and within piglets and was highest in the caudal segments of the small intestine (P <0.001). These data suggest that creep feeding could be a useful tool in the prevention of post-weaning diarrhoea.
    Effects of intermittent suckling and creep feed intake on pig performance from birth to slaughter
    Kuller, W.I. ; Soede, N.M. ; Beers-Schreurs, H.M.G. van; Langendijk, P. ; Taverne, M.A.M. ; Kemp, B. ; Verheijden, J.H.M. - \ 2007
    Journal of Animal Science 85 (2007). - ISSN 0021-8812 - p. 1295 - 1301.
    reproductive-performance - lactating sows - weanling pigs - consumption - estrus - fertility - piglets
    An experiment was conducted to determine if the improved creep feed intake observed during intermittent suckling (IS) is important for postweaning performance. Therefore, creep feed intake of litters was assessed, and within litters, eaters and noneaters were distinguished using chromic oxide as an indigestible marker. Batches of sows were suckled intermittently (IS, 7 batches; n = 31) or continuously (control, 7 batches; n = 31). In the IS group, litters were separated from the sow for a period of 12 h/d (0930 to 2130), beginning 11 d before weaning. Litters were weaned at 4 wk of age. Litters had free access to creep feed from 1 wk of age onward. Five days after weaning, the piglets were moved as a litter to weanling pens. At 8 wk of age, 2 barrows and 2 gilts were randomly chosen from each litter and moved to a finishing facility. Feed intake was improved by IS during the last 11 d of lactation (IS, 284 ± 27 vs. control, 83 ± 28 g/piglet; P <0.001) and after weaning during the first (IS, 201 ± 24 vs. control, 157 ± 25 g·piglet¿1·d¿1; P <0.05) and second (IS, 667 ± 33 vs. control, 570 ± 35 g·piglet¿1·d¿1; P <0.05) wk. Thereafter, no differences were found to slaughter. Weaning BW was lower in IS litters (IS, 7.1 ± 0.01 vs. control, 8.1 ± 0.01 kg/piglet; P <0.05), but 7 d after weaning BW was similar (IS, 8.5 ± 0.2 vs. control, 8.7 ± 0.2 kg/piglet; P = 0.18), and no differences were found to slaughter. The percentage of eaters within a litter was not increased by IS during lactation (IS, 23 ± 4.5% vs. control, 19 ± 4.1%; P = 0.15). Weaning BW did not differ between eaters and noneaters (eater, 7.7 ± 0.1 vs. noneater, 7.5 ± 0.08 kg/piglet; P = 0.63). From 1 until 4 wk after weaning, piglets that were eaters during lactation had heavier BW than noneaters (eater, 20.3 ± 0.3 kg vs. noneater, 18.2 ± 0.2 kg; P <0.05). The influence of eating creep feed during lactation on BW and ADG and the influence of suckling treatment never showed an interaction. We conclude that IS increases ADFI during lactation on a litter level and improves ADG in the first week and ADFI in the first and second weeks after weaning. No long-term effects on ADFI or ADG were observed throughout the finishing period. In the current experiment, in which creep feed intake was low, the percentage of eaters within a litter was not increased, suggesting that creep feed intake of piglets that were already eating was stimulated by IS. Further, piglets that were eaters during lactation had heavier BW up to 4 wk after weaning.
    Application of a [13CO2] breath test to study short-term amino acid catabolism during the postprandial phase of a meal
    Bujko, J. ; Schreurs, V.V.A.M. ; Nolles, J.A. ; Verreijen, A.M. ; Koopmanschap, R.E. ; Verstegen, M.W.A. - \ 2007
    The British journal of nutrition 97 (2007)5. - ISSN 0007-1145 - p. 891 - 897.
    humans - proteins
    A [13CO2] breath test was applied as a non-invasive method to study the catabolism of ingested amino acids shortly after a meal. This test requires the ingestion of a [1-13C]-labelled amino acid and the analysis of expired air for [13C] enrichment and CO2. The recovery of label as [13CO2] reflects the catabolism of the [1-13C]-labelled substrate. Such a non-steady state approach provides information that is complementary to the information obtained by steady-state methods using a primed continuous infusion of tracer amino acids during the fed state. In a model study with twenty adult male rats, two groups of animals were fed twice a day with one of two semi-synthetic iso-energetic diets. One diet contained egg white protein (EW) as the sole amino acid source. The second diet contained a mixture of free amino acids with a pattern similar to that of the EW diet. On day 5 of the dietary treatment, l-[1-13C]leucine, either bound in EW protein or in free form, was ingested as part of the morning meal. The expired air was sampled at 30 min intervals for 5 h. The rate of recovery ranged from 0 % to 6 % of the dose/h. Up to 120 min after the onset of the meal, the recovery values for the free amino acid diet were higher than those for the EW diet. Differences in recovery reflect differences in postprandial utilisation. The differences in label recovery were mainly determined by the [13C] enrichment of the expired air. As a consequence, CO2 measurements are not mandatory when CO2 production is comparable.
    Ingrediënten voor een energieneutrale belichte glastuinbouw in 2020: Position Paper Licht
    Ruijter, J.A.F. de; Marcelis, L.F.M. ; Schreurs, M. - \ 2007
    Arnhem/Wageningen : KEMA/Wageningen UR Glastuinbouw - 110
    kassen - energiegebruik - duurzaamheid (sustainability) - energiebehoud - milieubeheersing - belichting - gebruiksefficiëntie - glastuinbouw - biobrandstoffen - warmtekrachtkoppeling - biobased economy - greenhouses - energy consumption - sustainability - energy conservation - environmental control - illumination - use efficiency - greenhouse horticulture - biofuels - cogeneration - biobased economy
    De glastuinbouw heeft de ambitie geformuleerd in 2020 energieneutraal te telen in nieuw te bouwen kassen. Die ambitie geldt ook voor de belichte glastuinbouw. Een kas (of glastuinbouwbedrijf) is energie-neutraal als er op jaarbasis nette geen fossiele primaire energie wordt verbruikt. Dat wil zeggen dat de kas (minimaal) evenveel benutbare energie exporteert als deze aan primaire (fossiel) energie importeert.
    Effect of weaning on intestinal blood flow : a pilot study
    Berkeveld, M. ; Langendijk, P. ; Beers-Schreurs, H.M.G. van; Hendriksen, S.W.M. ; Essen, G.J. van; Koets, A.P. ; Taverne, M.A.M. ; Verheijden, J.H.M. - \ 2006
    In: Proceedings of the 19th International Pig Veterinary Congress, Copenhagen, Denmark, 16-19 July 2006. - - p. 538 - 538.
    Effect of weaning on intestinal blood flow: a pilot study
    Berkeveld, M. ; Beers-Schreurs, H.M.G. van; Langendijk, P. ; Hendriksen, S.W.M. ; Essen, G.J. van; Koets, A.P. ; Taverne, M.A.M. ; Verheijden, J.H.M. - \ 2006
    Effect of creep feed intake before weaning on the small intestine of intermittently or continuously suckled pig
    Kuller, W.I. ; Beers-Schreurs, H.M.G. van; Soede, N.M. ; Taverne, M.A.M. ; Kemp, B. ; Verheijden, J.H.M. - \ 2006
    Intermittent suckling prevents weaning induced growth check
    Berkeveld, M. ; Langendijk, P. ; Beers-Schreurs, H.M.G. van; Koets, A.P. ; Taverne, M.A.M. ; Verheijden, J.H.M. - \ 2006
    Intermittent suckling prevents weaning induced growth check
    Berkeveld, M. ; Langendijk, P. ; Beers-Schreurs, H.M.G. van; Koets, A.P. ; Taverne, M.A.M. ; Verheijden, J.H.M. - \ 2006
    Comparison of different methods of body fat measurement in non-obese young adults
    Bujko, J. ; Kasprzak, J. ; Hulshof, P.J.M. ; Schreurs, V.V.A.M. - \ 2006
    Polish Journal of Food and Nutrition Sciences 15/56 (2006)S12. - ISSN 1230-0322 - p. 139 - 144.
    Dietary amino acids fed in free form and as protein components do not differently affects postprandial plasma insulin, glucagon, growth hormone and corticosterone responses in rats
    Nolles, J.A. ; Straten, E.M.E. van; Bremer, B.I. ; Koopmanschap, R.E. ; Verstegen, M.W.A. ; Schreurs, V.V.A.M. - \ 2006
    Journal of Animal Physiology and Animal Nutrition 90 (2006)7-8. - ISSN 0931-2439 - p. 289 - 299.
    skeletal-muscle - neonatal pigs - humans - ingestion - leucine - carbohydrate - metabolism - retention - mixtures - nitrogen
    This study examined, whether the postprandial fate of dietary amino acids from different amino acid sources is regulated by the responses of insulin, glucagon, corticosterone and growth hormone (GH). Male Wistar rats were cannulated in the vena jugularis and assigned to dietary groups. The diets contained 21% casein or the same amino acids in free form. In the free amino acid diets, methionine level was varied between the groups. The feed was supplied in two distinct meals. In previous experiments it was established that oxidative amino acid losses of the free amino acid diets and protein diets were different. After 3 weeks on those diets, it appeared that the differences in postprandial oxidative losses had been diminished. GH was measured every 12 min, from 144 min before the start of the experimental meal over the following 144 min. Insulin and corticosterone were measured six times from the start of the meal until 270 min after the meal. No differences have been observed between the hormonal responses to both meals at day 5 and at day 26. In conclusion, it has been found that the differences in the oxidative losses between protein and free amino acid meals are not mediated by the combined action of the insulin, glucagon, corticosterone and GH. Postprandial catabolism of amino acids is most probably regulated by substrate induction.
    Postprandial fate of amino acids: adaptation to molecular forms
    Nolles, J.A. - \ 2006
    Wageningen University. Promotor(en): Martin Verstegen, co-promotor(en): Victor Schreurs. - S.l. : S.n. - ISBN 9789085043423 - 120
    ratten - diermodellen - aminozuren - diëten - diervoeding - oxidatie - metabolisme - adaptatie - darmabsorptie - voedingsfysiologie - rats - animal models - amino acids - diets - animal nutrition - oxidation - metabolism - adaptation - intestinal absorption - nutrition physiology

    During the postprandial phase dietary proteins are digested to peptides and amino acids and absorbed. Once absorbed the peptides are further hydrolyzed to amino acids and transported to the tissues. These amino acids are largely incorporated into body proteins. Not all amino acids are, however, incorporated into body proteins part of these amino acids are oxidized, and can, thus, no longer be utilized to support protein metabolism in the body. The objective of this thesis was to increase the understanding of those processes that determine the utilization efficiency of dietary proteins. The studies described in this thesis, focused on the appearance rate of dietary amino acids in the free amino acid pool of the body. The rate of appearance of dietary amino acids in this pool has been shown to modulate the postprandial oxidation of amino acids and thereby also their utilization efficiency for physiological purposes. As a consequence postprandial oxidative losses influence the nutritional protein status of the body. This thesis aimed to elucidate whether the body is able to cope with diets in which the amino acid appearance rate is high and what mechanisms are involved in this process.

    First an effort was made to establish the metabolic consequences of amino acid sources with a high appearance rate in a rat and a human model. Postprandial oxidation of free or protein derived [1-13C]- leucine was determined in a [13CO2]-breath test, using both a diet consisting of only free amino acids including [1-13C]-leucine and a diet consisting of proteins in which [1-13C]-leucine was incorporated, and 1:1 mixtures of both diets. In those mixed diets either the protein part or the free amino acid part was labeled. The postprandial oxidative losses of dietary leucine after 5 days being fed these diets (short-term adaptation) appeared to be significantly higher for the free amino acid diet compared to the protein diet. These differences between dietary free amino acids and dietary protein persisted in the mixed diets, as measured by the [13CO2] breath-test. It was concluded that amino acids derived either from a free amino acid or a protein diet, were handled independently even when ingested simultaneously during the same meal. Results obtained in rats were comparable to the results obtained in humans.

    The differences in oxidation between a free amino acid and a protein diet had largely disappeared after long-term adaptation (after 26 to 30 days on the diet). An adaptive decrease in the oxidation of free amino acids was observed. In the second study it was examined to which extent increasing levels of methionine supplements in a diet (50, 100 or 200% methionine supplement relative to casein) were retained in body protein. This was thus far not clear since a higher appearance rate in the free pool has been reported to have a negative influence on the efficiency of utilization of amino acids from the diet. Moreover, only specific patterns of amino acids are supposed to be deposited in body protein. Higher dietary methionine levels resulted in higher postprandial oxidative losses of methionine. The groups, which were fed the diets with the highest methionine levels, showed the lowest methionine retention as part of intake but the highest retention in absolute terms. After long term adaptation, however, to the free amino acid diets, methionine retention was increased in all groups. It was concluded that postprandial retention of dietary amino acids is, at least in part, driven by the amino acid composition of the diet.

    In third study it was examined whether the postprandial fate of different dietary amino acid was regulated by hormonal responses to the diet. It has been observed that the differences in oxidative losses between diets consisting of free amino acids or protein were not mediated by the combined action of insulin, glucagon, corticosterone and GH. Hence, postprandial catabolism of amino acids is probably regulated by other mechanisms. As stated above, the amino acid appearance rate plays a crucial role in determining the postprandial utilization of amino acids. In the fourth study it was, therefore, investigated, whether the amino acid absorption rate can adapt to dietary free amino acids. Rats were kept on a free amino acid diet for 0 (nonadapted), 5, or 26 to 30 days (long-term adaptation). The methionine absorption of long-term adapted rats was lower than that of the non-adapted rats. It was concluded that the absorption of amino acid by the intestine plays a crucial role in minimizing the postprandial oxidative losses.

    Consequences of different strategies of free amino acid supplementation to dietary proteins for physiological utillization
    Gas, M. - \ 2006
    Wageningen University. Promotor(en): Martin Verstegen, co-promotor(en): Victor Schreurs; J. Bujko. - s.n. : S.n. - ISBN 9789085043355 - 150
    ratten - diermodellen - diëten - voer - vrije aminozuren - voedersupplementen - voedingseiwit - katabolisme - oxidatie - voedingsfysiologie - rats - animal models - diets - feeds - free amino acids - feed supplements - dietary protein - catabolism - oxidation - nutrition physiology
    The efficiency of using free amino acids (AAs) as dietary constituent is sometimes lower than that of AAs derived from intact protein. The aim of the project was to evaluate dietary management conditions, which can determine the efficiency of utilization of crystalline AAs in animal diets or in clinical nutrition. The studies in this thesis were focused mainly on differences in short-term catabolism between protein bound and free AAs during the post prandial phase of a meal. The stable isotope technique was used in model studies with laboratory Wistar (WU) rats. In different experiments, so-called [ 13 CO 2 ]-breath test studies were used to compare the metabolic fate of free and protein-bound [1- 13 C]-labeled AAs in a meal in various nutritional situations. The influence of free AA supplementation strategies on weight gain development was also studied. Moreover, protein and fat content in the liver and carcass were analysed.

    The results of the present study confirm literature that showed a higher post prandial catabolic losses of the tracer when dietary protein is replaced with crystalline AAs. In some, but not all situations a lower weight gain was observed for growing animals. Our results showed that short-term catabolic losses of endogenous leucine were modulated by exogenous AA supply. It increased or decreased depending on the adequacy of the dietary supply.

    The common practice for free AA supplementation is to mix it with the deficient protein. In our study we showed that during the post prandial period the best utilization of methionine deficient protein did not occur when methionine supplement was given simultaneously with methionine deficient meal. The best utilisation occurred when there was a delay between the supply of deficient meal and free methionine. Therefore, introducing time interval of free amino acid supplementation to poor quality protein should be considered as a factor with potential to improve physiological utilization of dietary amino acids.A 1h time interval for free methionine supplementation influenced the weight gain, but differently depending on the protein level. Animals fed very deficient protein diet (5%) showed higher weight gain when supplementation of the deficient free methionine was provided with a 1h delay (1h interval). With protein deficient diets and less than 7.5 % protein we found fatty livers in our experiment. We concluded that post prandial AA oxidation influences the post absorptive AA catabolism. This does not always mean effect on growth. For growth in rats lysine deficiency is most limiting but it seems that even a 34% methionine deficiency below the NRC recommendation did not limit growth. We found that methionine deficiency influenced fat metabolism and from the literature we concluded that the mechanism probably works via choline and carnitin
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