The deep-sea benthic community at the Porcupine Abyssal Plain (NE Atlantic) is a highly food limited system. The annual input of sedimenting phytodetritus, which reaches the sea floor around May/June, is the major input of energy. The relative trophic position of the most abundant components of the benthos (90 species or higher taxonomic groups), including meiofaunal, macrofaunal, and megafaunal organisms, was evaluated by stable isotope analysis. The majority of the macro-and megafaunal organisms investigated were deposit feeders (N=35), less numerous were suspension feeders (N=17) and predators/scavengers (N=29). Stable nitrogen values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of competition for food. Suspension feeders, mainly cnidarians, have a broad trophic spectrum through feeding on resuspended material as well as capturing pelagic prey; thus during the greater part of the year they can compensate for any shortage in sedimenting fresh POM. Benthic deposit feeders use a variety of feeding strategies to exploit their common food resource. The holothurians, the dominant megabenthic group at PAP, included some highly mobile species, which seem to be quite efficient in tracing and exploiting localised patches of nutritious phytodetritus. Other holothurian species, however, forage successfully on more refractory material, possibly assisted by enteric bacteria. Predators/scavengers fall into two groups, representing two major trophic pathways. Firstly, several of the invertebrate predators prey on deposit-feeding organisms and so are the end consumers of an exclusively benthic food web. Secondly, there are highly mobile benthopelagic predators/scavengers, which are a major link with the benthopelagic food web through their feeding on pelagic prey.Generally, within the benthic community at PAP competition for food is reduced by two alternative evolutionary adaptations: (1) specialization on slightly different food sources and (2) vertical expansion of the trophic spectrum. This leads to a rather complex food web, covering a total δ 15 N range of at least 10‰. 

Feeding rumen-protected fat (RPF) is an alternative to increase energy density of the diet and therefore energy intake in dairy cows. To investigate metabolic and endocrine changes in dairy cows fed either a diet containing RPF (FD) or a control diet with an increased amount of cornstarch (SD), 3 Holstein cows (83 +/- 1 d in milk) were fitted with catheters in the portal vein, a mesenteric artery, and 2 mesenteric veins. Cows were fed consecutively SD and FD for 3 wk, respectively. In FD, cornstarch [92 g/kg of dry matter (DM)] was replaced by 50 g of RPF/kg of DM (mainly C16:0 and C18:1). Tracer infusions of NaH(13)CO3 and D-[U-(13)C6]glucose were performed into a jugular vein to measure rate of appearance and oxidation of glucose. Arterial and portal blood samples were collected to measure concentrations of glucose, lactate, volatile fatty acids, nonesterified fatty acids, beta-hydroxybutyrate, triglycerides, AA, insulin, and glucagon. Concomitantly, para-aminohippurate was infused into a mesenteric vein for measurement of portal plasma flow. Although DM intake was slightly lower in FD, protein and energy intakes were unaffected by diets. Milk and lactose yields were higher in FD than SD. Arterial plasma glucose concentration was lower with FD than SD, whereas nonesterified fatty acid and triglyceride concentrations were higher in FD. Glucagon concentration and glucagon-to-insulin ratio were both augmented by FD feeding. When feeding FD, greater milk and lactose yields, but not energy-corrected milk, were associated with elevated lipid status and higher glucagon concentrations but occurred despite lower plasma glucose concentration and were not linked with changes in whole body glucose rate of appearance. This study suggests a glucose-sparing effect allowing an enhanced lactose synthesis when feeding RPF.

Glucose supply markedly changes during the transition to extrauterine life. In this study, we investigated diet effects on glucose metabolism in neonatal calves. Calves were fed colostrum (C; n = 7) or milk-based formula (F; n = 7) with similar nutrient content up to d 4 of life. Blood plasma samples were taken daily before feeding and 2 h after feeding on d 4 to measure glucose, lactate, nonesterified fatty acids, protein, urea, insulin, glucagon, and cortisol concentrations. On d 2, additional blood samples were taken to measure glucose first-pass uptake (FPU) and turnover by oral [U-(13)C]-glucose and i.v. [6,6-(2)H(2)]-glucose infusion. On d 3, endogenous glucose production and gluconeogenesis were determined by i.v. [U-(13)C]-glucose and oral deuterated water administration after overnight feed deprivation. Liver tissue was obtained 2 h after feeding on d 4 and glycogen concentration and activities and mRNA abundance of gluconeogenic enzymes were measured. Plasma glucose and protein concentrations and hepatic glycogen concentration were higher (P < 0.05), whereas plasma urea, glucagon, and cortisol (d 2) concentrations as well as hepatic pyruvate carboxylase mRNA level and activity were lower (P < 0.05) in group C than in group F. Orally administered [U-(13)C]-glucose in blood was higher (P < 0.05) but FPU tended to be lower (P < 0.1) in group C than in group F. The improved glucose status in group C resulted from enhanced oral glucose absorption. Metabolic and endocrine changes pointed to elevated amino acid degradation in group F, presumably to provide substrates to meet energy requirements and to compensate for impaired oral glucose uptake.

Analysis in individual mouse milk samples is restricted by small sample volumes and hindered by high fat contents. Miniaturized methods were developed for the analysis of dry matter (DM), crude fat, crude protein (CP), and lactose in individual samples of

Glucose disposability is often impaired in neonatal calves and even more in preterm calves. The objective of this study was to investigate ontogenic maturation of endogenous glucose production (eGP) in calves and its effects on postnatal glucose homeostasis. Calves (n = 7 per group) were born preterm (PT; delivered by section 9 d before term) or at term (T; spontaneous vaginal delivery), or spontaneously born and fed colostrum for 4 d (TC). Blood samples were taken immediately after birth and before and 2h after feeding at 24h after birth (PT; T) or on d 4 of life (TC) to determine metabolic and endocrine changes. After birth (PT and T) or on d 3 of life (TC), fasted calves were gavaged with deuterium-labeled water to determine gluconeogenesis (GNG) and intravenously infused with [U(13)C]-glucose to measure eGP and glucose oxidation (GOx) in blood plasma. After slaughter at 26h after birth (PT, T) or on d 4 of life (TC), glycogen concentrations in liver and hepatic mRNA concentrations and enzyme activities of pyruvate carboxylase, phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase were measured. Preterm calves had the lowest plasma concentrations of cortisol and 3,5,3'-triiodothyronine at birth. Plasma glucose concentrations from d 1 to 2 decreased more, but plasma concentrations of lactate and urea and glucagon:insulin ratio were higher in PT than in T and TC calves. The eGP, GNG, GOx, as well as hepatic glycogen concentrations and PEPCK activities, were lowest in PT calves. Results indicate impaired glucose homeostasis due to decreased eGP in PT calves and maturation of eGP with ontogenic development.

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Our results in a previous study indicated that the portal absorption of intragastrically fed alpha-ketoglutarate (AKG) was limited in young pigs. Our aim was to quantify the net portal absorption, first-pass metabolism, and whole-body flux of enterally infused AKG. In study 1, we quantified the net portal nutrient absorption in young pigs (n = 9) given an intraduodenal infusion of milk replacer [10 mL/(kg . h)] and either saline (control) or 930 micromol/(kg . h) AKG for 4 h. In study 2, we quantified the luminal disappearance of a duodenal AKG bolus in young pigs (n = 7). In study 3, we quantified the whole-body kinetics of (13)C-AKG metabolism when infused either enterally (n = 9) or intravenously (n = 9) in young pigs. In study 1, when compared with the control group, enteral AKG infusion increased (P < 0.01) the arterial (13.8 +/- 1.7 vs. 27.4 +/- 3.6 micromol/L) and portal (22.0 +/- 1.4 vs. 64.6 +/- 5.9 micromol/L) AKG concentrations and the net portal absorption of AKG [19.7 +/- 2.8 vs. 95.2 +/- 12.0 micromol/(kg . h)]. The mean fractional portal appearance of enterally infused AKG was 10.23 +/- 1.3%. In study 2, the luminal disappearance of AKG was 663 micromol/(kg . h), representing 63% of the intraduodenal dose. In study 3, the whole-body (13)C-AKG flux [4685 +/- 666 vs. 801 +/- 67 micromol/(kg . h)] was higher (P < 0.05) when given enterally than intravenously, but (13)CO(2) recovery was not different (37.3 +/- 1.0 vs. 36.2 +/- 0.7%dose). The first-pass splanchnic (13)C-AKG utilization was approximately 80%, of which 30% was oxidized to (13)CO(2). We conclude that the intestinal absorption of AKG is limited in young pigs largely due to substantial first-pass gastrointestinal metabolism.

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