Effects of dietary fiber content and different fiber-rich ingredients on endogenous loss of fat and fatty acids in growing pigs

Background: Determination of the endogenous loss of fat(ELF) is used to adjust for the estimation of true total tract digestibility(TTTD) of fat in diets and ingredients.Any factor which affected ELF may further affect the digestibility of fat,including sources and concentrations of fat and fiber in the diet.There are some reports of determining the ELF using regression methods based on different levels of fat intake,while reports on effects of dietary fiber content and different fiber-rich ingredients in pig diets on ELF are very limited.Therefore,the objective of this study was to determine the effects of dietary fiber content and different fiber-rich ingredients on endogenous losses of fat and fatty acids at the end of ileum and throughout the entire intestinal tract in growing pigs.Methods: In Exp.1,the effect of fiber content on endogenous loss of fat was determined using six growing pigs(Duroc × Landrace × Yorkshire;27.6 ± 2.4 kg),fitted with a T-cannula at the end of ileum.The experimental design was a 6 × 6 complete Latin square design with six periods of feeding and six diets.The six experimental fat-free diets were formulated to include graded levels of neutral detergent fiber(NDF)(0,40,80,120,160 and 200 g/kg) and soybean hull(SH) was the only fiber source,providing 0,75,150,225,300 and 375 g/kg,respectively.Chromic oxide was included at4 g/kg in all diets as an indigestible marker.In Exp.2,six crossbred growing barrows(27.6 ± 1.6 kg) were used and the experimental design was the same as for Exp.1.The six fat-free diets were formulated to include six common fiber-rich ingredients and the concentration of NDF was 100 g/kg.The six fiber-rich ingredients were defatted rice bran(DRB),sugar beet pulp(SBP),rice hull(RH),corn germ meal(CGM),SH and wheat bran(WB) and they were fed at represented250,270,145,250,170 and 280 g/kg in the diet,respectively.Results: In Exp.1,the endogenous loss of fatty acids profile did not change as dietary NDF increased in growing pigs.The endogenous losses of fat,C16:0,C18:0,C18:1,C18:2,total unsaturated fatty acids(UFA) and total saturated fatty acids(SFA) in growing pigs at the end of ileum and throughout the entire intestinal tract increased linearly as NDF content of diets increased.The endogenous losses of fat,as well as C16:0 and C18:0 throughout the entire intestinal tract also increased quadratically as NDF content of diets increased.The ELF increased from 0.71 to 3.14 g/kg of dry matter intake(DMI) and 0.56 to 8.21 g/kg DMI at the end of ileum and throughout the entire intestinal tract in growing pigs,respectively.The ELF occurred in the hindgut except for the growing pigs fed 0 and 4% NDF in their diets.The endogenous losses of C16:0 and UFA occurred primarily in the upper regions of the gut and the greatest endogenous losses of C18:0 occurred in the hindgut.The endogenous losses of fat,individual SFA and total SFA throughout the entire intestinal tract were much greater than that at the end of ileum.However,the endogenous losses of individual UFA and total UFA were less throughout the intestinal tract than at the end of ileum.In Exp.2,the endogenous losses of fat at the end of ileum were greater in growing pigs fed CGM or WB diets.The endogenous loss of fatty acids profile changed to a slight degree at the end of ileum that the endogenous loss of UFA(particularly C18:1 and C18:2) in growing pigs fed CGM or WB diets were greater(P < 0.01) than that for the other four diets.The greatest(P < 0.01) endogenous loss of SFA(particularly C18:0) was in growing pigs fed the RH diet.The endogenous losses of fat,C16:0,C18:0 and SFA over the entire intestinal tract were much greater in growing pigs fed CGM or WB diets,whereas the lowest values were in growing pigs fed DRB diet.The ELF at the end of ileum in growing pigs fed CGM or WB diets were 3.50 or 4.17 g/kg DMI,respectively,and the ELF over the entire intestinal tract was 7.23 or 7.38 g/kg DMI.The contribution in percentage of ELF in the upper gut was greater than that in the hindgut of growing pigs fed DRB and RH diets,while the ELF in the upper gut and hindgut were equal in growing pigs fed SBP,CGM and WB diets.On the whole,the endogenous losses of C18:1 and C18:2 throughout the entire intestinal tract in growing pigs fed the six fiber-rich ingredients diets were less than losses at the end of ileum,whereas the endogenous loss of fat,C16:0,C18:0 and SFA were greater throughout the intestinal tract than at the end of ileum.Conclusion: The profile of loss in endogenous fatty acids did not change as dietary NDF increased in growing pigs and the endogenous losses of fatty acids(C16:0,C18:0,C18:1 and C18:2) fat,UFA and SFA increased linearly as NDF content increased in the diets of pigs.The endogenous losses of fat or fatty acids at the end of ileum were greater in growing pigs fed RH,CGM or WB diets.The endogenous losses of fat,fatty acids(C16:0 and C18:0) and SFA were greater over the entire intestinal tract in pigs fed CGM or WB diet,while these values were the lowest in growing pigs fed the DRB diet.The contribution in percentage losses of fat in the upper gut were greater than in the hindgut of growing pigs fed DRB and RH diets,while the contribution of losses of fat in the upper gut and hindgut were equal in growing pigs fed SBP,CGM and WB diets.In addition,the endogenous loss of individual or total UFA was less over the entire intestinal tract of growing pigs fed fiber diets than that at the end of ileum,and the greatest endogenous losses of fat,individual or total SFA were over the entire intestinal tract.Therefore,differences in fiber content and the nature of fiber-rich ingredients in diets of pigs have different effects to the endogenous losses of fat or fatty acids.Considering the requirement of fat or fatty acids of pigs,careful attention must be paid that the endogenous losses of fat and fatty acids when fiber ingredients are used in diets of pigs.

Integrative analysis of indirect calorimetry and metabolomics profiling reveals alterations in energy metabolism between fed and fasted pigs

Background: Fasting is a simple metabolic strategy that is used to estimate the maintenance energy requirement where the energy supply for basic physiological functions is provided by the mobilization of body reserves.However, the underlying metabolic components of maintenance energy expenditure are not clear. This study investigated the differences in heat production(HP), respiratory quotient(RQ) and plasma metabolites in pigs in the fed and fasted state, using the techniques of indirect calorimetry and metabolomics.Methods: Nine barrows(45.2 ± 1.7 kg BW) were fed corn-soybean based meal diets and were kept in metabolism crates for a period of 14 d. After 7 d adaptation, pigs were transferred to respiratory chambers to determine HP and RQ based on indirect calorimetry. Pigs were fed the diet at 2,400 k J ME/(kg BW0.6·d) during d 8 to 12. The last 2 d were divided into 24 h fasting and 48 h fasting treatment, respectively. Plasma samples of each pig were collected from the anterior vena cava during the last 3 d(1 d while pigs were fed and 2 d during which they were fasted).The metabolites of plasma were determined by high-resolution mass spectrometry using a metabolomics approach.Results: Indirect calorimetry analysis revealed that HP and RQ were no significant difference between 24 h fasting and 48 h fasting, which were lower than those of fed state(P < 0.01). The nitrogen concentration of urine tended to decrease with fasting(P = 0.054). Metabolomics analysis between the fed and fasted state revealed differences in15 compounds, most of which were not significantly different between 24 h fasting and 48 h fasting. Identified compounds were enriched in metabolic pathways related to linoleic acid metabolism, amino acid metabolism,sphingolipid metabolism, and pantothenate and Co A biosynthesis.Conclusion: These results suggest that the decreases in HP and RQ of growing pigs under fasting conditions were associated with the alterations of linoleic acid metabolism and amino acid metabolism. The integrative analysis also revealed that growing pigs under a 24-h fasting were more appropriate than a 48-h fasting to investigate the metabolic components of maintenance energy expenditure.