Misalignment of day/night and feeding rhythms has been shown to increase fat deposition and the risk for metabolic disorders in humans and rodents. In most studies, however, food intake and intake patterns are not controlled. We studied the effects of circadian misalignment on energy expenditure in pigs while controlling for food intake as well as intake patterns. Twelve groups of five male pigs were housed in respiration chambers and fed either during the day (10.00–18.00 hours; DF) or night (22.00–06.00 hours; NF), bihourly the same sequential meals, representing 15, 10, 25, 30 and 20 % of the daily allowance. Paired feeding was applied to ensure equal gross energy intake between treatments. Apparent total tract digestibility, energy balances and heat partitioning were measured and analysed using a mixed linear model. Apparent total tract energy and DM digestibility tended to be lower for NF-pigs than DF-pigs (P < 0·10). Heat production was 3 % lower for NF-pigs than DF-pigs (P < 0·026), increasing fat retention by 7 % in NF-pigs (P = 0·050). NF-pigs were less active than DF-pigs during the feeding period, but more active during the fasting period. RMR was greater for DF-pigs than NF-pigs during the fasting period. Methane production was 30 % greater in NF-pigs than DF-pigs (P < 0·001). In conclusion, circadian misalignment has little effect on nutrient digestion, but alters nutrient partitioning, ultimately increasing fat deposition. The causality of the association between circadian misalignment and methane production rates remains to be investigated.

Physicochemical properties of diets are believed to play a major role in the regulation of digesta transit in the gastrointestinal tract. Starch, being the dominant nutrient in pig diets, strongly influences these properties. We studied transport of digesta solids and liquids through the upper gastrointestinal tract of ninety pigs in a 3 × 3 factorial arrangement. Dietary treatments varied in starch source (barley, maize and high-amylose maize) and form (isolated starch, ground cereal and extruded cereal). Mean retention times (MRT) of digesta solids ranged 129–225 min for the stomach and 86–124 min for the small intestine (SI). The MRT of solids consistently exceeded that of liquids in the stomach, but not in the SI. Solid digesta of pigs fed extruded cereals remained 29–75 min shorter in the stomach compared with pigs fed ground cereals (P < 0·001). Shear stress of whole digesta positively correlated with solid digesta MRT in the stomach (r 0·33, P < 0·001), but not in the SI. The saturation ratio (SR), the actual amount of water in stomach digesta as a fraction of the theoretical maximum held by the digesta matrix, explained more variation in digesta MRT than shear stress. The predictability of SR was hampered by the accumulation of large particles in the stomach. In addition, the water-holding capacity of gelatinised starch leads to a decreased SR of diets, but not of stomach digesta, which was caused by gastric hydrolysis of starch. Both of these phenomena hinder the predictability of gastric retention times based on feed properties.

This study aimed to examine in vivo starch digestion kinetics and to unravel the mechanisms of starch hydrolysing enzymes. Ninety pigs (23 (sd 2·1) kg body weight) were assigned to one of nine treatments in a 3×3 factorial arrangement, with starch source (barley, maize, high-amylose (HA) maize) and form (isolated, within cereal matrix, extruded) as factors. We determined starch digestion coefficients (DC), starch breakdown products and digesta retention times in four small-intestinal segments (SI1–4). Starch digestion in SI2 of pigs fed barley and maize, exceeded starch digestion of pigs fed HA maize by 0·20–0·33 DC units (P<0·01). In SI3–4, barley starch were completely digested, whereas the cereal matrix of maize hampered digestion and generated 16 % resistant starch in the small intestine (P<0·001). Extrusion increased the DC of maize and HA maize starch throughout the small intestine but not that of barley (P<0·05). Up to 25 % of starch residuals in the proximal small intestine of pigs was present as glucose and soluble α(1–4) maltodextrins. The high abundance of glucose, maltose and maltotriose in the proximal small intestine indicates activity of brush-border enzymes in the intestinal lumen, which is exceeded by α-amylase activity. Furthermore, we found that in vivo starch digestion exceeded our in vitro predictions for rapidly digested starch, which indicates that the role of the stomach on starch digestion is currently underestimated. Consequently, in vivo glucose release of slowly digestible starch is less gradual than expected, which challenges the prediction quality of the in vitro assay.

The passage rate of solids and liquids through the gastrointestinal tract differs. Increased dietary nutrient solubility causes nutrients to shift from the solid to the liquid digesta fraction and potentially affect digesta passage kinetics. We quantified: (1) the effect of three levels of dietary nutrient solubility (8, 19 and 31 % of soluble protein and sucrose in the diet) at high feed intake level (S) and (2) the effect of low v. high feed intake level (F), on digesta passage kinetics in forty male growing pigs. The mean retention time (MRT) of solids and liquids in the stomach and small intestine was assessed using TiO2 and Cr-EDTA, respectively. In addition, physicochemical properties of digesta were evaluated. Overall, solids were retained longer than liquids in the stomach (2·0 h, P<0·0001) and stomach+small intestine (1·6 h, P<0·001). When S increased, MRT in stomach decreased by 1·3 h for solids (P=0·01) and 0·7 h for liquids (P=0·002) but only at the highest level of S. When F increased using low-soluble nutrients, MRT in stomach increased by 0·8 h for solids (P=0·041) and 0·7 h for liquids (P=0·0001). Dietary treatments did not affect water-binding capacity and viscosity of digesta. In the stomach of growing pigs, dietary nutrient solubility affects digesta MRT in a non-linear manner, while feed intake level increases digesta MRT depending on dietary nutrient solubility. Results can be used to improve predictions on the kinetics of nutrient passage and thereby of nutrient digestion and absorption in the gastrointestinal tract.

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.

The aim was to evaluate under protein-limiting conditions the effect of different supplemental energy sources: fermentable NSP (fNSP), digestible starch (dStarch) and digestible unsaturated fat (dUFA), on marginal efficiency of fat deposition and distribution. A further aim was to determine whether the extra fat deposition from different energy sources, and its distribution in the body, depends on feeding level. A total of fifty-eight individually housed pigs (48 (sd 4) kg) were used in a 3 × 2 factorial design study, with three energy sources (0·2 MJ digestible energy (DE)/kg0·75 per d of fNSP, dStarch and dUFA added to a control diet) at two feeding levels. Ten pigs were slaughtered at 48 (sd 4) kg body weight and treatment pigs at 106 (sd 3) kg body weight. Bodies were dissected and the chemical composition of each body fraction was determined. The effect of energy sources on fat and protein deposition was expressed relative to the control treatments within both energy intake levels based on a total of thirty-two observations in six treatments, and these marginal differences were subsequently treated as dependent variables. Results showed that preferential deposition of the supplemental energy intake in various fat depots did not depend on the energy source, and the extra fat deposition was similar at each feeding level. The marginal energetic transformation (energy retention; ER) of fNSP, dStarch and dUFA for fat retention (ERfat:DE) was 44, 52 and 49 % (P>0·05), respectively. Feeding level affected fat distribution, but source of energy did not change the relative partitioning of fat deposition. The present results do not support values of energetic efficiencies currently used in net energy-based systems.

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.