Reflux of 15N-labeled uric acid after intracloacal infusion in broiler chickens fed low- or high-protein diets.

Reflux of urine from the cloaca into the ceca provides chickens with a mechanism for recycling of urinary-Nitrogen (N) in a way analogous to urea recycling in mammals. However, it is unknown if reflux has substantial relevance in current poultry husbandry, where birds are fed ad libitum and have high protein intake. To evaluate the fate of urinary-N in ad libitum-fed broiler chickens, 15-day-old broilers were assigned to a high (21.9% CP, n = 22) or low (10.2 % CP, n = 22) protein diet. At 25 d of age, 20 broilers per dietary treatment were infused into the cloaca with a pulse dose of 107 mg [1,3-15N]-uric acid. N-contents and 15N-enrichment in digesta, blood plasma, and body tissues were measured at 5, 30, 60, 90, 150, 300, 450, 600, 1,200, or 1,800 min after administration (n = 2 /time-point /diet). Two broilers per dietary treatment were infused with saline and served as control to analyze background 15N-enrichment. The average total recovery (% of infused (w/w)) of 15N from infused uric acid in all body tissues was low (2.9 ± 0.62 %), of which the largest proportion was found in carcass tissue (2.5 ± 0.60%). 15N-enrichment was greatest in intestinal tissues. Even at 1,200 min, 15N-enrichment of ceca (0.46 ± 0.169 APE) and colon (0.13 ± 0.159 APE) digesta was considerably exceeding background enrichment. 15N-enrichment in excess of background enrichment in cecum and colon digesta (10-fold, P < 0.05), and 15N recovery in intestinal tissues (4-fold, P < 0.01) were greater in birds fed the low protein diet compared with the high protein diet, speculatively pointing out differences in the occurrence of reflux, incorporation of uric acid-N derivatives in intestinal tissues by first-pass metabolism, and a prolonged digesta retention time in protein deficient birds. In conclusion, these data confirm that uric acid-N infused in the cloaca can be refluxed and used for body N-deposition, but its contribution to whole body protein metabolism in broilers is probably limited.

The use of metabolic profiling to identify insulin resistance in veal calves.

Heavy veal calves (4-6 months old) are at risk of developing insulin resistance and disturbed glucose homeostasis. Prolonged insulin resistance could lead to metabolic disorders and impaired growth performance. Recently, we discovered that heavy Holstein-Friesian calves raised on a high-lactose or high-fat diet did not differ in insulin sensitivity, that insulin sensitivity was low and 50% of the calves could be considered insulin resistant. Understanding the patho-physiological mechanisms underlying insulin resistance and discovering biomarkers for early diagnosis would be useful for developing prevention strategies. Therefore, we explored plasma metabolic profiling techniques to build models and discover potential biomarkers and pathways that can distinguish between insulin resistant and moderately insulin sensitive veal calves. The calves (n = 14) were classified as insulin resistant (IR) or moderately insulin sensitive (MIS) based on results from a euglycemic-hyperinsulinemic clamp, using a cut-off value (M/I-value <4.4) to identify insulin resistance. Metabolic profiles of fasting plasma samples were analyzed using reversed phase (RP) and hydrophilic interaction (HILIC) liquid chromatography-mass spectrometry (LC-MS). Orthogonal partial least square discriminant analysis was performed to compare metabolic profiles. Insulin sensitivity was on average 2.3x higher (P <0.001) in MIS than IR group. For both RP-LC-MS and HILIC-LC-MS satisfactory models were build (R2Y >90% and Q2Y >66%), which allowed discrimination between MIS and IR calves. A total of 7 and 20 metabolic features (for RP-LC-MS and HILIC-LC-MS respectively) were most responsible for group separation. Of these, 7 metabolites could putatively be identified that differed (P <0.05) between groups (potential biomarkers). Pathway analysis indicated disturbances in glycerophospholipid and sphingolipid metabolism, the glycine, serine and threonine metabolism, and primary bile acid biosynthesis. These results demonstrate that plasma metabolic profiling can be used to identify insulin resistance in veal calves and can lead to underlying mechanisms.

Dietary Protein Intake and Distribution Patterns of Well-Trained Dutch Athletes.

Dietary protein intake should be optimized in all athletes to ensure proper recovery and enhance the skeletal muscle adaptive response to exercise training. In addition to total protein intake, the use of specific proteincontaining food sources and the distribution of protein throughout the day are relevant for optimizing protein intake in athletes. In the present study, we examined the daily intake and distribution of various proteincontaining food sources in a large cohort of strength, endurance and team-sport athletes. Well-trained male (n=327) and female (n=226) athletes completed multiple web-based 24-hr dietary recalls over a 2-4 wk period. Total energy intake, the contribution of animal- and plant-based proteins to daily protein intake, and protein intake at six eating moments were determined. Daily protein intake averaged 108±33 and 90±24 g in men and women, respectively, which corresponded to relative intakes of 1.5±0.4 and 1.4±0.4 g/kg. Dietary protein intake was correlated with total energy intake in strength (r=0.71, p <.001), endurance (r=0.79, p <.001) and team-sport (r=0.77, p <.001) athletes. Animal and plant-based sources of protein intake was 57% and 43%, respectively. The distribution of protein intake was 19% (19±8 g) at breakfast, 24% (25±13 g) at lunch and 38% (38±15 g) at dinner. Protein intake was below the recommended 20 g for 58% of athletes at breakfast, 36% at lunch and 8% at dinner. In summary, this survey of athletes revealed they habitually consume > 1.2 g protein/kg/d, but the distribution throughout the day may be suboptimal to maximize the skeletal muscle adaptive response to training.

Dietary Amino Acid Deficiency Reduces the Utilization of Amino Acids for Growth in Growing Pigs after a Period of Poor Health.

BACKGROUND: During immune system activation, partitioning of amino acids (AAs) changes between protein gain and use by the immune system. OBJECTIVE: We determined the effects of health status and dietary AA deficiency on nitrogen retention and AA utilization in pigs. METHODS: Barrows (55 d of age) were obtained from good health (GH, n = 14) or poor health (PH, n = 14) status farms and allocated to a diet either adequate in essential amino acids (Adq) or 25% deficient in Met + Cys, Thr, and Trp (Def). Nitrogen balance was measured and AA irreversible loss rates (ILRs) were measured after an intravenous bolus of U-(13)C-labeled L-AAs. RESULTS: On arrival at the experimental facilities, the PH pigs had 14% lower serum albumin and 50% greater serum haptoglobin and blood leukocyte counts than the GH pigs (P < 0.01), but the PH pigs showed signs of recovery during the trial. Total tract nitrogen digestibility was 3 percentage points lower in the PH pigs (P < 0.01). The PH-Adq pigs had compensatory body weight gain after arrival, coinciding with 7% greater nitrogen retention (P < 0.01) in the PH pigs than in the GH pigs. The PH pigs had a 24% greater ILR for Lys. Health status × diet interactions for Lys (P = 0.07), Val (P = 0.03), and Leu (P = 0.10) pool sizes and a greater urea pool size in the PH pigs (P = 0.01) support the observation that the increase in the ILR of Lys in the PH pigs was related to oxidation when feeding the Def diet, but to synthesis when feeding the Adq diet. Feeding Def diets increased monocyte counts by 30% (P < 0.01). CONCLUSIONS: This study illustrates how the competition for AAs between protein synthesis associated with immune system activation and body protein deposition is greater when the dietary supply of Met + Cys, Thr, and Trp is limited in pigs during and after a period of poor health.

Fermentation in the small intestine contributes substantially to intestinal starch disappearance in calves.

BACKGROUND: The proportion of starch disappearing from the small intestinal lumen is generally lower in ruminants than in monogastric animals, and there are indications that the starch digestion capacity in ruminants is limited. OBJECTIVES: Milk-fed calves were used to study the rate-limiting enzyme in starch hydrolysis and to quantify starch fermentation in ruminants. METHODS: Forty male Holstein-Friesian calves were fed milk replacer containing either lactose (control) or 1 of 4 corn starch products. The following starch products differed in the enzyme ratios required for their complete hydrolysis to glucose: gelatinized starch [α-amylase and (iso)maltase], maltodextrin [(iso)maltase and α-amylase], maltodextrin with α-1,6-branching (isomaltase, maltase, and α-amylase), and maltose (maltase). In the adaptation period, calves were stepwise exposed to an increasing dose of the starch product for 14 wk to allow maximal adaptation of all enzyme systems involved. In the experimental period, apparent total tract and ileal starch product disappearance, total tract starch product fermentation, and α-amylase, maltase, and isomaltase activities were determined at 18% inclusion of the starch product. RESULTS: Maltase and isomaltase activities in the brush border did not increase for any of the starch product treatments. Luminal α-amylase activity was lower in the proximal (3.9 ± 3.2 and 2.7 ± 1.7 U/mg Co for control and starch product calves, respectively) but greater in the distal small intestine of starch-fed calves than in control calves (0.0 ± 0.0 and 6.4 ± 1.5 U/mg Co for control and starch product calves, respectively; means ± SEs for control and means ± pooled SEMs for starch product treatments). Apparent ileal (61.6% ± 6.3%) and total tract (99.1% ± 0.4%) starch product disappearance did not differ between starch product treatments, suggesting that maltase activity limits starch digestion in ruminants. Total tract starch product fermentation averaged 414 ± 43 g/d, corresponding to 89% of intake, of which half was fermented before the terminal ileum, regardless of starch product treatment. CONCLUSION: Fermentation, rather than enzymatic digestion, is the main reason for small intestinal starch disappearance in milk-fed calves.

Induced lung inflammation and dietary protein supply affect nitrogen retention and amino acid metabolism in growing pigs.

It is hypothesised that during immune system activation, there is a competition for amino acids (AA) between body protein deposition and immune system functioning. The aim of the present study was to quantify the effect of immune system activation on N retention and AA metabolism in growing pigs, depending on dietary protein supply. A total of sixteen barrows received an adequate (Ad) or restricted (Res) amount of dietary protein, and were challenged at day 0 with intravenous complete Freund's adjuvant (CFA). At days - 5, 3 and 8, an irreversible loss rate (ILR) of eight AA was determined. CFA successfully activated the immune system, as indicated by a 2- to 4-fold increase in serum concentrations of acute-phase proteins (APP). Pre-challenge C-reactive protein concentrations were lower (P< 0·05) and pre- and post-challenge albumin tended to be lower in Res-pigs. These findings indicate that a restricted protein supply can limit the acute-phase response. CFA increased urinary N losses (P= 0·04) and tended to reduce N retention in Ad-pigs, but not in Res-pigs (P= 0·07). The ILR for Val was lower (P= 0·05) at day 8 than at day 3 in the post-challenge period. The ILR of most AA, except for Trp, were strongly affected by dietary protein supply and positively correlated with N retention. The correlations between the ILR and APP indices were absent or negative, indicating that changes in AA utilisation for APP synthesis were either not substantial or more likely outweighed by a decrease in muscle protein synthesis during immune system activation in growing pigs.

Urea recycling contributes to nitrogen retention in calves fed milk replacer and low-protein solid feed.

Urea recycling, with urea originating from catabolism of amino acids and hepatic detoxification of ammonia, is particularly relevant for ruminant animals, in which microbial protein contributes substantially to the metabolizable protein supply. However, the quantitative contribution of urea recycling to protein anabolism in calves during the transition from preruminants (milk-fed calves) to ruminants [solid feed (SF)-fed calves] is unknown. The aim of this study was to quantify urea recycling in milk-fed calves when provided with low-protein SF. Forty-eight calves [164 ± 1.6 kg body weight (BW)] were assigned to 1 of 4 SF levels [0, 9, 18, and 27 g of dry matter (DM) SF · kg BW(-0.75) · d⁻¹] provided in addition to an identical amount of milk replacer. Urea recycling was quantified after a 24-h intravenous infusion of [¹5N2]urea by analyzing urea isotopomers in 68-h fecal and urinary collections. Real-time qPCR was used to measure gene expression levels of bovine urea transporter B (bUTB) and aquaglyceroporin-3 and aquaglyceroporin-7 in rumen wall tissues. For every incremental gram of DM SF intake (g DM · kg(0.75)), nitrogen intake increased by 0.70 g, and nitrogen retention increased by 0.55 g (P < 0.01). Of this increase in nitrogen retention, 19% could be directly explained by urea recycling. Additionally, part of the observed increase in nitrogen retention could be explained by the extra protein provided by the SF and likely by a greater efficiency of postabsorptive use of nitrogen for gain. Ruminal bUTB abundance increased (P < 0.01) with SF provision. Aquaglyceroporin-3 expression increased (P < 0.01) with SF intake, but aquaglyceroporin-7 expression did not. We conclude that in addition to the increase in digested nitrogen, urea recycling contributes to the observed increase in nitrogen retention with increasing SF intake in milk-fed calves. Furthermore, ruminal bUTB and aquaglyceroporin-3 expression are upregulated with SF intake, which might be associated with urea recycling.

High environmental temperature increases glucose requirement in the developing chicken embryo.

Environmental conditions during the perinatal period influence metabolic and developmental processes in mammals and avian species, which could impact pre- and postnatal survival and development. The current study investigated the effect of eggshell temperature (EST) on glucose metabolism in broiler chicken embryos. Broiler eggs were incubated at a high (38.9°C) or normal (37.8°C) EST from day 10.5 of incubation onward and were injected with a bolus of [U-(13)C]glucose in the chorio-allantoic fluid at day 17.5 of incubation. After [U-(13)C]glucose administration, (13)C enrichment was determined in intermediate pools and end-products of glucose metabolism. Oxidation of labeled glucose occurred for approximately 3 days after injection. Glucose oxidation was higher in the high than in the normal EST treatment from day 17.6 until 17.8 of incubation. The overall recovery of (13)CO2 tended to be 4.7% higher in the high than in the normal EST treatment. An increase in EST (38.9°C vs 37.8°C) increased (13)C enrichment in plasma lactate at day 17.8 of incubation and (13)C in hepatic glycogen at day 18.8 of incubation. Furthermore, high compared to normal EST resulted in a lower yolk-free body mass at day 20.9 (-2.74 g) and 21.7 (-3.81 g) of incubation, a lower hepatic glycogen concentration at day 18.2 (-4.37 mg/g) and 18.8 (-4.59 mg/g) of incubation, and a higher plasma uric acid concentration (+2.8 mg/mL/+43%) at day 21.6 of incubation. These results indicate that the glucose oxidation pattern is relatively slow, but the intensity increased consistently with an increase in developmental stage of the embryo. High environmental temperatures in the perinatal period of chicken embryos increased glucose oxidation and decreased hepatic glycogen prior to the hatching process. This may limit glucose availability for successful hatching and could impact body development, probably by increased gluconeogenesis from glucogenic amino acids to allow anaerobic glycolysis.

A diet high in resistant starch modulates microbiota composition, SCFA concentrations, and gene expression in pig intestine.

Resistant starch (RS) is highly fermentable by microbiota in the colon, resulting in the production of SCFAs. RS is thought to mediate a large proportion of its health benefits, including increased satiety, through the actions of SCFAs. The aim of this study was to investigate the effects of a diet high in RS on luminal microbiota composition, luminal SCFA concentrations, and the expression of host genes involved in SCFA uptake, SCFA signaling, and satiety regulation in mucosal tissue obtained from small intestine, cecum, and colon. Twenty adult female pigs were either assigned to a digestible starch (DS) diet or a diet high in RS (34%) for a period of 2 wk. After the intervention, luminal content and mucosal scrapings were obtained for detailed molecular analysis. RS was completely degraded in the cecum. In both the cecum and colon, differences in microbiota composition were observed between DS- and RS-fed pigs. In the colon these included the stimulation of the healthy gut-associated butyrate-producing Faecalibacterium prausnitzii, whereas potentially pathogenic members of the Gammaproteobacteria, including Escherichia coli and Pseudomonas spp., were reduced in relative abundance. Cecal and colonic SCFA concentrations were significantly greater in RS-fed pigs, and cecal gene expression of monocarboxylate transporter 1 (SLC16A1) and glucagon (GCG) was induced by RS. In conclusion, our data show that RS modulates microbiota composition, SCFA concentrations, and host gene expression in pig intestine. Combined, our data provide an enhanced understanding of the interaction between diet, microbiota, and host.

Effects of dietary fibers with different fermentation characteristics on feeding motivation in adult female pigs.

Dietary fibers can be fermented in the colon, resulting in production of short-chain fatty acids (SCFA) and secretion of satiety-related peptides. Fermentation characteristics (fermentation kinetics and SCFA-profile) differ between fibers and could impact their satiating potential. We investigated the effects of fibers with varying fermentation characteristics on feeding motivation in adult female pigs. Sixteen pair-housed pigs received four diets in four periods in a Latin square design. Starch from a control (C) diet was exchanged, based on gross energy, for inulin (INU), guar gum (GG), or retrograded tapioca starch (RS), each at a low (L) and a high (H) inclusion level. This resulted in a decreased metabolizable energy intake when feeding fiber diets as compared with the C diet. According to in vitro fermentation measurements, INU is rapidly fermentable and yields relatively high amounts of propionate, GG is moderately rapidly fermentable and yields relatively high amounts of acetate, and RS is slowly fermentable and yields relatively high amounts of butyrate. Feeding motivation was assessed using behavioral tests at 1h, 3h and 7h after the morning meal, and home pen behavioral observations throughout the day. The number of wheel turns paid for a food reward in an operant test was unaffected by diet. Pigs on H-diets ran 25% slower for a food reward in a runway test than pigs on L-diets, and showed less spontaneous physical activity and less stereotypic behavior in the hours before the afternoon meal, reflecting increased interprandial satiety. Reduced feeding motivation with increasing inclusion level was most pronounced for RS, as pigs decreased speed in the runway test and tended to have a lower voluntary food intake in an ad libitum food intake test when fed RS-H. In conclusion, increasing levels of fermentable fibers in the diet seemed to enhance satiety in adult pigs, despite a reduction in metabolizable energy supply. RS was the most satiating fiber, possibly due to its slow rate of fermentation and high production of butyrate.

The effects of bulking, viscous and gel-forming dietary fibres on satiation.

The objective was to determine the effects of dietary fibre with bulking, viscous and gel-forming properties on satiation, and to identify the underlying mechanisms. We conducted a randomised crossover study with 121 men and women. Subjects were healthy, non-restrained eaters, aged 18-50 years and with normal BMI (18.5-25 kg/m²). Test products were cookies containing either: no added fibre (control), cellulose (bulking, 5 g/100 g), guar gum (viscous, 1.25 g/100 g and 2.5 g/100 g) or alginate (gel forming, 2.5 g/100 g and 5 g/100 g). Physico-chemical properties of the test products were confirmed in simulated upper gastrointestinal conditions. In a cinema setting, ad libitum intake of the test products was measured concurrently with oral exposure time per cookie by video recording. In a separate study with ten subjects, 4 h gastric emptying rate of a fixed amount of test products was assessed by ¹³C breath tests. Ad libitum energy intake was 22 % lower for the product with 5 g/100 g alginate (3.1 (sd 1.6) MJ) compared to control (4.0 (sd 2.2) MJ, P< 0.001). Intake of the other four products did not differ from control. Oral exposure time for the product with 5 g/100 g alginate (2.3 (sd 1.9) min) was 48 % longer than for control (1.6 (sd 0.9) min, P= 0.01). Gastric emptying of the 5 g/100 g alginate product was faster compared to control (P< 0.05). We concluded that the addition of 5 g/100 g alginate (i.e. gel-forming fibre) to a low-fibre cookie results in earlier satiation. This effect might be due to an increased oral exposure time.

Asynchronous supply of indispensable amino acids reduces protein deposition in milk-fed calves.

A balanced supply of indispensable amino acids (AA) is required for efficient protein synthesis. Different absorption kinetics (e.g., free vs. protein-bound AA) may, however, create asynchrony in postabsorptive availability of individual AA, thereby reducing the efficiency of protein deposition. We studied the effects of AA asynchrony on protein metabolism in growing, milk-fed calves. In 2 experiments, each with a change-over design including 8 calves, a milk replacer deficient in Lys and Thr was used. In Expt. 1, L-Lys and L-Thr were parenterally supplemented, either in synchrony (SYN), asynchrony (ASYN), or partial asynchrony (PART) with dietary AA. In Expt. 2, l-Lys and l-Thr were orally supplemented, either in SYN or ASYN with dietary AA. In Expt. 1, digested protein was used less efficiently for growth for ASYN (31.0%) than for SYN (37.7%), with PART being intermediate (36.0%). Indicator AA oxidation tended (P = 0.06) to be higher for ASYN. In Expt. 2, the efficiency of protein utilization was lower for ASYN (34.9%) than for SYN (46.6%). Calves spared AA from oxidation when the limiting AA were provided in excess after a short period (<24 h) of deprivation. Restoring AA balance by parenteral supplementation resulted in a 19% lower efficiency of digestible protein utilization than by oral supplementation, likely caused by splanchnic oxidation of imbalanced AA in excess to Thr. In conclusion, asynchronous availability of individual indispensable AA reduces the efficiency by which digested protein is retained in milk-fed calves. Furthermore, an AA imbalance in the splanchnic tissues may result in disproportionate AA oxidation.

Effects of pretreatment of wheat bran on the quality of protein-rich residue for animal feeding and on monosaccharide release for ethanol production.

The effects of hydrothermal conditions for pretreating wheat bran on the quality of residual protein for animal feeding, and on monosaccharide release for ethanol production were studied according to a 4×2×2 design with the factors, temperature (120, 140, 160, and 180°C), acidity (pH 2.3 and 3.9), and retention time (5 and 10 min). Temperature affected the quality of residual protein for animal feeding. Pretreatment at 120 and 140°C did not affect O-methylisourea-reactive lysine in protein-rich wheat bran residue, although total lysine decreased with increasing temperature at pH 2.3. At temperatures higher than 140°C, reactive lysine decreased and melanoidins, furfural and 5-HMF increased. Lower acidity during pretreatment at 120 and 140°C increased the digestibility of the residual wheat protein in vitro by 36%. Pretreatment conditions did not substantially affect the release of monomeric xylose and arabinose by hemicellulases, which suggests that arabinoxylans in wheat bran are well accessible for enzymes.

Effects of dietary fibers with different physicochemical properties on feeding motivation in adult female pigs.

The satiating effects of dietary fiber may depend more on physicochemical properties of the fiber than on total fiber intake. These properties are expected to affect satiety feelings and feeding motivation due to different effects in the gastrointestinal tract. The aim of the current study was to assess the effects of fibers with varying physicochemical properties (bulkiness, viscosity and fermentability) on feeding motivation in adult female pigs. Sixteen pair-housed pigs received four diets: lignocellulose (LC), pectin (PEC), resistant starch (RS), and control (C) without fiber, in four periods in a Latin square design. Each fiber was fed at a low (L) followed by a high (H) inclusion level (7 days each). At 1h, 3h, and 7h after the morning meal, feeding motivation was assessed in an operant test, where turning a wheel yielded multiple food rewards, and in a runway test, where walking a fixed U-shaped track yielded one food reward. Pigs were observed in their home pen for 6h, using 90-s instantaneous scan sampling. In the operant test, throughout the day feeding motivation was higher for pigs on PEC compared with pigs on LC. In the runway, feeding motivation increased particularly at 1h after the meal for pigs on PEC compared with pigs on RS. Also at 7h, feeding motivation tended to decrease for pigs on RS compared with pigs fed other diets. In their home pen, pigs on PEC showed more feeder-directed behavior compared with pigs on RS. In conclusion, PEC was the least satiating fiber. LC and RS, despite a lower supply of available energy, were the most satiating fibers, possibly due to their bulky and fermentation properties, respectively.

Quantifying resistant starch using novel, in vivo methodology and the energetic utilization of fermented starch in pigs.

To quantify the energy value of fermentable starch, 10 groups of 14 pigs were assigned to one of two dietary treatments comprising diets containing 45% of either pregelatinized (P) or retrograded (R) corn starch. In both diets, a contrast in natural ¹³C enrichment between the starch and nonstarch components of the diet was created to partition between enzymatic digestion and fermentation of the corn starch. Energy and protein retention were measured using indirect calorimetry after adapting the pigs to the diets for 3 wk. Fecal ¹³C enrichment was higher in the R-fed pigs (P < 0.001) and 43% of the R resisted enzymatic digestion. Energy retained as protein was unaffected and energy retained as fat was 29% lower than in P-fed pigs (P < 0.01). Prior to the morning meal, end products of fermentation substantially contributed to substrate oxidation in the R-fed pigs. During the 3-4 h following both meals, heat production was higher (P < 0.05) in P-fed pigs, but this was not preferentially fueled by glucose from corn starch. Digestible energy intake, metabolizable energy intake, and energy retention were reduced (P < 0.05) in R-fed pigs compared with P-fed pigs by 92, 54, and 33 kJ/(kg°·75 · d), respectively. Therefore, the energy values of fermented resistant starch were 53, 73, and 83% of the digestible, metabolizable, and net energy values of enzymatically degradable starch, respectively. Creating a contrast in natural ¹³C enrichment between starch and nonstarch dietary components provides a promising, noninvasive, in vivo method for estimating the proportion of dietary starch fermented in the gastrointestinal tract.

Oxidation of dietary stearic, oleic, and linoleic acids in growing pigs follows a biphasic pattern.

We used the pig as a model to assess the effects of dietary fat content and composition on nutrient oxidation and energy partitioning in positive energy balance. Pigs weighing 25 kg were assigned to either: 1) a low fat-high starch diet, or 2) a high saturated-fat diet, or 3) a high unsaturated-fat diet. In the high-fat treatments, 20% starch was iso-energetically replaced by 10.8% lard or 10.2% soybean oil, respectively. For 7 d, pigs were fed twice daily at a rate of 1200 kJ digestible energy · kg(-0.75) · d(-1). Oral bolus doses of [U-(13)C] glucose, [U-(13)C] α-linoleate, [U-(13)C] stearate, and [U-(13)C] oleate were administered on d 1, 2, 4, and 6, respectively, and (13)CO(2) production was measured. Protein and fat deposition were measured for 7 d. Fractional oxidation of fatty acids from the low-fat diet was lower than from the high-fat diets. Within diets, the saturated [U-(13)C] stearate was oxidized less than the unsaturated [U-(13)C] oleate and [U-(13)C] linoleate. For the high unsaturated-fat diet, oxidation of [U-(13)C] oleate was higher than that of [U-(13)C] linoleate. In general, recovery of (13)CO(2) from labeled fatty acids rose within 2 h after ingestion but peaked around the next meal. This peak was induced by an increased energy expenditure that was likely related to increased eating activity. In conclusion, oxidation of dietary fatty acids in growing pigs depends on the inclusion level and composition of dietary fat. Moreover, our data suggest that the most recently ingested fatty acids are preferred substrates for oxidation when the direct supply of dietary nutrients has decreased and ATP requirements increase.

Tissue methionine cycle activity and homocysteine metabolism in female rats: impact of dietary methionine and folate plus choline.

Impaired transfer of methyl groups via the methionine cycle leads to plasma hyperhomocysteinemia. The tissue sources of plasma homocysteine in vivo have not been quantified nor whether hyperhomocysteinemia is due to increased entry or decreased removal. These issues were addressed in female rats offered diets with either adequate or excess methionine (additional methyl groups) with or without folate and choline (impaired methyl group transfer) for 5 wk. Whole body and tissue metabolism was measured based on isotopomer analysis following infusion with either [1-(13)C,methyl-(2)H3]methionine or [U-(13)C]methionine plus [1-(13)C]homocysteine. Although the fraction of intracellular methionine derived from methylation of homocysteine was highest in liver (0.18-0.21), most was retained. In contrast, the pancreas exported to plasma more of methionine synthesized de novo. The pancreas also exported homocysteine to plasma, and this matched the contribution from liver. Synthesis of methionine from homocysteine was reduced in most tissues with excess methionine supply and was also lowered in liver (P<0.01) with diets devoid of folate and choline. Plasma homocysteine concentration (P<0.001) and flux (P=0.001) increased with folate plus choline deficiency, although the latter still represented <12% of estimated tissue production. Hyperhomocysteinemia also increased (P<0.01) the inflow of homocysteine into most tissues, including heart. These findings indicate that a full understanding of hyperhomocysteinemia needs to include metabolism in a variety of organs, rather than an exclusive focus on the liver. Furthermore, the high influx of homocysteine into cardiac tissue may relate to the known association between homocysteinemia and hypertension.

Body fat deposition does not originate from carbohydrates in milk-fed calves.

Milk-fed heavy calves utilize dietary protein with a low efficiency and often develop hyperglycemia and insulin resistance. Distributing the daily nutrient intake over an increasing number of meals increases protein deposition and improves glucose homeostasis. Therefore, we examined effects of feeding frequency (FF) and feeding level (FL) on the diurnal pattern of substrate oxidation and on the fate of dietary carbohydrates in milk-fed heavy calves. Eighteen milk-fed calves weighing 136 +/- 3 kg were assigned to FF (1, 2, or 4 meals daily) at each of 2 FL (1.5 or 2.5 times maintenance), except for calves at FF1 (only at a low FL). Urea, leucine, and glucose kinetics were assessed for each treatment by use of [(13)C]urea, [1-(13)C]leucine, [U-(13)C], and [2-(13)C]glucose, respectively. FF altered the diurnal pattern, but not the total, of urea production production. Although urea production correlated well with nitrogen retention, oxidation of oral l-[1-(13)C]leucine did not. Dietary glucose was almost completely oxidized (80% based on [(13)C]glucose and 94% from indirect calorimetry measurements) regardless of FL. Fatty acid synthesis from glucose appeared to be negligible based on similar recoveries of (13)CO(2) from orally supplied [U-(13)C]glucose and [2-(13)C]glucose. The increased fat deposition at the higher FL originated almost exclusively from greater transfer of fatty acids to body lipid stores. These findings contrast with both glucose and lipid metabolism in growing pigs and indicate that alternative adaptive mechanisms operate in heavy milk-fed calves.

Whole body and muscle energy metabolism in preruminant calves: effects of nutrient synchrony and physical activity.

The effects of asynchronous availability of amino acids and glucose on muscle composition and enzyme activities in skeletal muscle were studied in preruminant calves. It was hypothesized that decreased oxidative enzyme activities in muscle would explain a decreased whole body heat production with decreasing nutrient synchrony. Preruminant calves were assigned to one of six degrees of nutrient synchrony, step-wise separating the intake of protein and lactose over the two daily meals. Calves at the most synchronous treatment received two identical meals daily. At the most asynchronous treatment, 85% of the daily protein and 20% of the daily lactose supply were fed in one meal and the remainder in the other meal. Daily intakes of all dietary ingredients were identical for all treatments. Oxidative enzyme activities and fat content increased with decreasing nutrient synchrony in M. Rectus Abdominis (RA), but not in M. Semitendinosus. Cytochrome-c-oxidase activity was positively correlated with fat content in RA (r 0.49; P < 0.01). Oxidative enzyme activities in both muscles were not correlated with average daily heat production, but citrate synthase activity in RA was positively correlated (P < 0.01) with the circadian amplitude (r 0.53) and maximum (r 0.61) of heat production associated with physical activity. In conclusion, this study indicates that muscle energy stores are regulated by nutrient synchrony. The lack of correlation between muscle oxidative enzyme activities and average daily heat production was in contrast with findings in human subjects. Therefore, oxidative enzyme activity in muscle should not be used as an indicator for whole body heat production in growing calves.

Synchronizing the availability of amino acids and glucose decreases fat retention in heavy preruminant calves.

Effects of synchronizing the availability of amino acids and glucose within a day on protein and energy metabolism were studied in heavy preruminant calves. Thirty-six preruminant calves (148 +/- 1.6 kg body weight) were assigned to 1 of 6 degrees of nutrient synchrony (SYN, 1-6) and to 1 of 2 meal sequences (i.e., the high-protein meal in the morning or in the evening). Calves at SYN 1 received 2 balanced meals: one at 0600 and one at 1800. Nutrient synchrony decreased stepwise from SYN 1 to SYN 6 in which calves received 85% of the daily protein supply in 1 meal. The digestible energy intakes at 0600 and 1800 were equal between treatments. Daily intakes of all nutrients and dietary ingredients were identical for all treatments. Calves were housed individually in respiration chambers. Apparent fecal nutrient digestibility and nitrogen and energy balances were measured. Apparent nutrient digestibility decreased when >71% of the dietary protein was fed in one meal. Nutrient synchrony did not affect the efficiency of digestible protein utilization in calves at a identical digestible nutrient intake. Heat production decreased from 691 to 629 kJ/(kg(0.75) x d) (P < 0.05) and energy retained as fat increased from 116 to 184 kJ/(kg(0.75) x d) (P < 0.01) with decreasing nutrient synchrony. Meal sequence did not affect any of the traits. In conclusion, synchronizing the availability of amino acids and glucose within a day did not increase the efficiency of protein utilization but substantially decreased fat retention in heavy preruminant calves.