Apparent Lipid Digestibility Research Articles

Screening of nutrient digestibilities and intestinal pathologies in Atlantic salmon, Salmo salar, fed diets with legumes, oilseeds, or cereals

Ten different plant protein and/or starch sources were studied in a 5-week experiment with triplicate groups of 0.7-kg Atlantic salmon in seawater, pre-adapted to a diet with fish meal, faba beans, sunflower cake, and wheat gluten as sources of protein and starch. The experimental ingredients were corn gluten, defatted soybean, defatted sunflower, dehulled lupin, defatted double-low rapeseed, whole field pea, whole and dehulled faba bean, whole wheat and naked oat, tested one at a time (14–24% inclusion). The diets were balanced by addition of pure wheat starch and/or pure cellulose, to obtain equal macro nutrient compositions. The control diet consisted of fish meal, wheat starch, cellulose and fish oil. The results showed reduced faecal dry matter content in fish fed the soybean diet and to a lesser extent in those fed the sunflower, lupin and rapeseed diets. Diets containing lupin and rapeseed resulted in a moderate increase in the viscosity of the digesta, while diets with wheat and oat increased viscosity of digesta more. Apparent digestibility of lipid decreased linearly with increasing dietary cellulose level. A significant reduction in the digestibility of crude protein was seen for the soybean, sunflower, rapeseed and oat diets, reflecting reduced digestibilities of most amino acids. The salmon fed the corn gluten, lupin, pea, bean and wheat diets had protein digestibilities comparable to the control group. The digestibility of phosphorus was highest for salmon fed the rapeseed diet and lowest for fish fed the oat diet. Faecal excretion of sodium was highly elevated for salmon fed the soybean diet, and moderately elevated for fish fed the corn gluten and sunflower diets. Faecal excretion of zinc was elevated in the fish fed the oat diet. None of these observations were significantly related to the dietary concentration of phytic acid. A histological examination of the stomach, mid- and distal intestine of all groups showed no other irregularities than enteritis in the distal intestine of salmon fed soybean meal. The present study demonstrated a potential for several plant ingredients, such as field pea and faba bean, partly replacing high-quality fish meal in diets for Atlantic salmon, based on nutrient digestibilities and absence of pathologies in the stomach and intestine.

Body composition and selected blood parameters in mice fed a combination of fibre and conjugated linoleic acid

Feeding mice conjugated linoleic acid (CLA) reduces body fat. Soluble fibre decreases apparent lipid digestibility. The objective of the present study was to examine whether a combination of dietary CLA and soluble fibre would further decrease the proportion of body fat than a diet with CLA alone. Therefore, we fed mice diets with CLA and different amounts of Nutrim, containing 10% soluble fibre. CLA was added to the control diet at the expense of high oleic acid sunflower oil (HOSF) component and Nutrim was added at the expense of an isoenergetic combination of starch, dextrose and cellulose. The diets were fed for 28 days. Weight gain after 28 days was less in CLA-fed animals than in HOSF-fed animals. Both CLA and Nutrim increased the body water content. CLA reduced total body fat and epidydymal fat but Nutrim did not. No interaction of CLA and fibre was detected. We, therefore, must conclude that under the present experimental conditions dietary CLA and fibre do not interact to reduce body fat deposition.

Comparative digestion efficiencies in conventional, genetically improved and genetically male Nile tilapia, Oreochromis niloticus (L.)

Apparent digestibility of dry matter, protein, lipid and energy of a ¢shmeal-based feed (41% crude protein, 9% crude lipid and 19 kJ g � 1 gross energy) was compared in genetically improved farmed tilapia (GIFT), genetically male Nile tilapia (GMNT) and conventional Nile tilapia (CNT) (Oreochromis niloticus). The experimental ¢sh were reared individually under standardized conditions in a recirculation system at 27 � 0.1 1C for 10 weeks. Titanium dioxide (TiO2) was used as a marker. Faeces of individual ¢sh were collected daily by siphoning and stored at � 18 1C before analysis. No signi¢cant diierences (Po0.05) were observed in the digestibility coe⁄cients of feed dry matter (78.2 � 3.4%, 77.7 � 4.4% and 76.4 � 3.7%), protein (87.9 � 3.0%, 88.4 � 2.8% and 88.0 � 3.3%), lipid (90.0 � 2.5%, 91.0 � 2.1% and 89.4 � 3.0%) and energy (90.4 � 1.9%, 90.7 � 2.0% and 89.4 � 2.3%) in GIFT, GMNT and CNT respectively. At the end of the experiment, there were no signi¢cant diierences (Po0.05) in average percentage growth (82.2 � 7.2, 87.3 � 7.7 and 74.7 � 4.1 respectively for GIFT, GMNT and CNT), growth rates or feed utilization e⁄ciencies between the three tilapia groups. We conclude that the higher growth claimed for improved GIFT and GMNT as compared with CNT, if ever existing, cannot be attributed to higher nutrients or energy digestibility.

Apparent metabolisable energy and digestibility of shea (Vitellaria paradoxa) fat, cocoa (Theobroma cacao) fat and soybean oil in broiler chicks

1. The objective of this experiment was to determine and compare the apparent lipid digestibility coefficient and apparent metabolisable energy (AME) value of shea nut (Vitellaria paradoxa, Gaertn.) fat in broiler chickens with that of soybean oil and cocoa fat. 2. One hundred and sixty 13-d-old male broiler chicks were used in a randomised complete block design. The fats were added at 30, 60 and 90 g/kg to a basal diet. A tenth dietary treatment was the basal feed with no added fats or oils. The birds were fed on the diets for 8 d and all droppings were collected for the final 4 d. 3. The mean coefficient of apparent lipid digestibility for shea fat (0·58) was similar to that of cocoa fat (0·54) but lower than that of soybean oil (0·95). There was evidence of a lipid × concentration interaction with the 90 g/kg shea fat diet having low lipid digestibility (0·43). 4. There was an interaction between the effects of dietary lipid concentration and test lipid on AME but, at dietary levels of 60 g/kg and below, the AME of shea fat (22·0 MJ/kg DM) and cocoa fat (26·4 MJ/kg DM) was significantly lower than that of soybean oil (39·8 MJ/kg DM).

Digestive function and intestinal integrity in Atlantic salmon ( Salmo salar) fed kernel meals and protein concentrates made from yellow or narrow-leafed lupins

This study assessed the effects of yellow lupin ( Lupinus luteus) and narrow-leafed lupin ( L. angustifolius) kernel meals and protein concentrates on the gastrointestinal integrity, capacity for digestive hydrolysis, and digestibility of nutrients in Atlantic salmon. A basal diet (FM) was made from fish meal, wheat, and fish oil. Six additional diets were formulated by replacing 30% of the FM diet with lupin kernel meal made from L. l. cv. Wodjil (LKM), L. a. cv. Belara (BKM), and L. a. cv. Myallie (MKM), lupin protein concentrates made from the same L. l. (LPC) and L. a. cv. M (MPC), or extracted soybean meal (SBM). All diets were extruded. Each diet was fed to three groups of 176 g salmon kept in 1 m 2 tanks with 5.6 °C saltwater for 3 weeks prior to sampling of blood, intestinal organs, digesta, and faeces. Inclusion of lupin meals in the diets resulted in harder and more condensed feed particles. Ulcer-like lesions were observed in the stomach of fish from all feeding groups, and this was worsened by lupin in the diet, but did not appear to be pellet hardness related. No consistent altered morphology was observed in the distal intestine (DI) of fish fed the FM and lupin diets, while the DI of fish fed SBM showed consistent and typical soybean meal-induced pathomorphological changes. Plasma cholesterol was higher when feeding MKM and LKM than when feeding FM, MPC, and LPC, with intermediate levels when feeding BKM and SBM. Feeding LKM and LPC resulted in a higher weight of the GIT when related to body weight. Trypsin activity and bile acid concentration were generally higher in digesta from the pyloric (PI) and mid (MI) intestine when feeding FM and lupin diets than when feeding SBM, while the opposite was seen for trypsin activity in digesta from DI. There were no effects of diet on leucine aminopeptidase (LAP) and maltase activity in PI and MI, but in DI the activity of these brush border enzymes were significantly lowered when feeding SBM. SBM in the diet resulted in watery faeces and lowered apparent digestibility of lipid, but this was not observed when feeding the lupin diets. To conclude, the tested lupin kernel meals and protein concentrates did not alter the intestinal function in Atlantic salmon when included at 30% of the diet. Dietary lupin was, however, involved in the worsening of ulcer-like gastric lesions.

Effects of chemical hydrogenation of supplemental fat on relative apparent lipid digestibility in finishing swine1,2

Four experiments were conducted to evaluate lipid digestibility in finishing swine fed chemically hydrogenated fats. Dietary chromic oxide was used as an inert marker to measure the apparent digestibility of supplemental fat (SF) that consisted of fully hydrogenated (FH), partially hydrogenated (PH), or PH products blended with other fat sources. In Exp. 1, diets containing 5% SF (as-fed basis) comprising 100, 66.7, 33.3, or 0% FH animal fat (iodine value = 2.5), with the balance contributed by soy oil, were fed to gilts (n = 24). Apparent digestibility increased linearly (-12.0, 26.0, 61.2, and 72.6%; P < 0.001) as the amount of FH fat in the diet decreased, suggesting the digestibility of FH to be near zero. Experiment 2 (2 x 4 factorial; n = 48) evaluated diets containing 5% (as-fed basis) blended fat (FH tallow and yellow grease) to achieve iodine values of 20, 30, 40, or 50 compared with PH tallow with identical iodine values. Digestibility of diets formulated with PH tallow was greater than those containing blended fat (73.4 vs. 67.2%; P < 0.01), especially at lower iodine values (interaction; P < 0.10). In Exp. 3, digestibility was measured in pigs (n = 96) fed 5% (as-fed basis) PH choice white grease with iodine values of 20, 40, 60, or 80. Increasing iodine value did not alter digestibility (66.2, 69.2, 68.2, and 69.7%). Experiment 4 investigated digestibility (n = 32) of diets formulated with 8% (as-fed basis) PH fat (iodine value 20 or 50) with 0.10% lysolecithin as an emulsifier. Lipid digestibility was 14.5% greater in the 8% SF diet with an iodine value of 50 compared with the diet with an iodine value of 20 (79.15 vs. 69.12%; P < 0.001), but lysolecithin was without effect. These experiments indicate that partial hydrogenation is superior to blending unsaturated fat with saturated fat sources and that digestibility is not greatly affected by decreasing the iodine value via partial hydrogenation.

Effects of dietary protein and lipid levels and DP DE-1 ratio on growth, feed utilization and hepatosomatic index of juvenile haddock, Melanogrammus aeglefinus L.

Juvenile haddock, Melanogrammus aeglefinus L. (initial weight, 13.5 ± 0.1 g) were fed practical diets containing digestible protein to digestible energy (DP DE )1 ) ratios of 25– 30 g DP MJ DE )1 as-fed using three protein levels (450, 500 and 550 g kg )1 ) each at two lipid levels (110 and 160 g kg )1 ) for 63 days. The results showed mean weight gain and feed conversion ratio were highest for diets containing 28.5 and 30.2 g DP MJ DE )1 .D P DE )1 ratio had no significant effect on protein efficiency ratio except at the lowest level (24.7 g DP MJ DE )1 ) indicating a protein sparing effect of higher lipid when dietary protein is below the requirement. Haddock appears to preferentially use protein as the prime source of DE. DP DE )1 ratio had little effect on apparent digestibility (AD) of protein while AD of lipid was significantly affected. Significant differences in AD of energy and organic matter were found to be inversely related to the carbohydrate level of the diet. DP DE )1 ratios of 28.5 g DP MJ DE )1 or lower resulted in significantly higher hepatosomatic indexes. The highest whole-body nitrogen gains and energy retention efficiencies were achieved at 28.5 and 30.2 g DP MJ DE )1 , whereas only slight differences in nitrogen retention efficiencies were observed. The highest levels of energy retained in the form of protein were achieved at 28.5 and 30.2 g DP MJ DE )1 . The diet that provided the best growth, feed utilization and digestibility with minimal HSI contained 546 g kg )1 protein (513 g kg )1 DP), 114 g kg )1 lipid, 164 g kg )1 carbohydrate, 17.0 MJ kg DE )1 and a DP DE )1 ratio of 30.2 g DP MJ DE )1 .

Apparent Digestibility Coefficients of Various Feed Ingredients for Grouper Epinephelus coioides

Apparent digestibility coefficients (ADC) of dry matter, crude protein, lipid, gross energy, amino acids, and fatty acids in white fish meal, brown fish meal, soybean meal, peanut meal, and yeast were determined for grouper Epinephelus coioides. Apparent digestibility was determined using a reference diet with 0.5% chromic oxide indicator and test diets that contained 70% reference diet and 30% of the feed ingredient being evaluated. The fish, averaging 12.0 g, were held in 250-L tanks at a density of 30 fish per tank. Feces were collected from three replicate groups-of fish. Apparent dry matter digestibility of ingredients was 78.85 ± 2.43, 79.11 ± 0.61, 69.85 ± 3.60, 73.67 ± 2.30 and 57.70 ± 4.69% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. Apparent gross energy digestibility of ingredients was 93.27 ± 2.90, 89.48 ± 1.78, 70.52 ± 4.01, 73.13 ± 2.41 and 51.67 ± 2.01% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. Apparent protein digestibility of ingredients was 89.82 ± 1.24, 87.34 ± 1.25, 83.97 ± 1.92, 80.79 ± 1.95, and 61.14 ± 0.54% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. White fish meal and brown fish meal showed higher protein digestibility among ingredients tested (P ± 0.01). Lipid digestibility of ingredients was high (90.66-94.48%) and not significantly different except for yeast. Amino acid availability values for test ingredients were similar to values of protein digestibility. Amino acid availability values of white fish meal and brown fish meal were higher than other ingredients. Fatty acid availability values for test ingredients were similar to values of lipid digestibility. In general, the digestibility of most fatty acids was over 80% in all ingredients, except for 14:0 in yeast and 18:0 in peanut meal, PUFA + HUFA > MUFA > SFA. Longer-chain saturated fatty acids were less digestibility, except for 14:0, with digestibilities diminishing as fatty acid chain length increased. Apparent digestibility of dry matter, crude protein, lipid, gross energy, amino acids, and fatty acids in yeast was the lowest among the ingredients.

Apparent Digestible Energy and Nutrient Digestibility Coefficients of Diet Ingredients for Pacu Piaractus brachypomus

AbstractThe digestible energy and apparent nutrient digestibility coefficients of common diet ingredients were determined for pacu Piaractus brachypomus (370.21 ± 17.56 g). Fish were fed with pelleted practical diets to apparent satiation and the feces were collected by siphoning. The digestibility value for each ingredient was determined by comparison of the digestibility of a test diet with a reference diet (24.5% crude protein and 1% chromic oxide). The digestible energy values of soybean meal (SBM), fish meal (FM), corn (CN), and wheat bran (WB) were 2382. 3826, 3353, and 1784 kcal/kg, respectively. The apparent dry matter digestibility coefficients were 83.72, 90.14, 89.13, and 82.05% for SBM, FM, CN, and WB, respectively. The apparent crude protein digestibility coefficients were 75.88, 90.49, 85.06, and 61.62% for SBM. FM, CN, and WB, respectively. The apparent lipid digestibility coefficients were 63.03, 77.00, 83.01, and 82.45% for SBM, FM, CN, and WB, respectively. The digestibility of protein, lipid, and energy from SBM were somewhat low compared to values for other warmwater omnivorous fishes, but similar to values reported for pacu‐caranha P. mesopotamicus. Otherwise, the nutrient and energy availability of the ingredients to P. brachypomus was similar to that of other fish. This information will be useful in formulating nutritious, economical diets for pacus.

Apparent digestibility coefficients of feed ingredients and their prediction in diets for tilapia Oreochromis niloticus x Oreochromis aureus (Teleostei, Cichlidae)

Apparent digestibility of crude protein (CP), lipid, carbohydrate, energy and fatty acids was measured in various feed ingredients fed to hybrid tilapia (Oreochromis niloticus×Oreochromis aureus) including fish and poultry meals, corn gluten, soybean meal, rapeseed meal, sunflower seed meal, wheat, corn, sorghum, barley and wheat bran. Chromic oxide was used as a non-absorbed marker. A diet compounded from a mixture of these ingredients was then used to examine the possibility of predicting the digestibility of formulated diets. In addition, the effect of pelleting or extrusion on digestibility of a compound diet was examined. Apparent digestibility of CP ranged from 75% to 97%, lipids from 72% to 90% and energy from 39% to 89% in the different ingredients. Apparent digestibility of carbohydrates was lower and ranged from 32% to 80%. Digestibility of fatty acids ranged from 75% to 90% with saturated fatty acids exhibiting digestibilities lower than unsaturated fatty acids. In a full-fat soy diet containing 19% fat, digestibility of lipids did not decrease. There were no significant differences in digestibility between a diet that was either pelleted or extruded. Tests conducted using a compound diet indicated that ingredient digestibility was additive for protein, lipids carbohydrates and energy. Diets for the hybrid tilapia may thus be formulated on the basis of digestibility of individual ingredients, for the nutrients examined in this study.

Comparison of two direct bioassays using 3-week-old broilers to measure the metabolisable energy of diets containing cereals high in fibre: Differences between true and apparent metabolisable energy values

1. Nitrogen-corrected apparent and true metabolisable energy contents (AMEN and TMEN) of 12 diets, containing different amounts of maize, wheat, barley and rye, barley with β -glucanase and maize with 0.05 g/kg guar gum were measured using 3-week-old male broilers. 2. The AMEN method involved: 4 d of dietary adaptation, 24 h of starvation, 54 h of ad libitum feeding, 24 h of starvation and daily total droppings collection. TMEN was measured after a 48 h starvation period followed by 2 d of tube-feeding two doses of 15 g of the diets and quantitatively collecting all the droppings after 48 h of starvation. The endogenous energy losses (EELN) were measured after tube-feeding 8 chickens with 30 g of glucose, also over 2 d. 3. The results show that a significant interaction exists between the nature of the diets and the method used to measure metabolisable energy. Differences between TMEN and AMEN values ranged from 1.03 to 1.98 MJ/kg dry matter. These differences were positively correlated with the total pentosan contents of the diet (r = 0.94), the natural logarithm of the viscosities of the water extracts (r = 0.87), the sum of the contents of total pentosans and total β -glucan (r = 0.85), the calculated total non-starch polysaccharide contents (r = 0.79), the neutral detergent fibre contents (r = 0.76) and the total β -glucan contents (r = 0.70). Furthermore, a significant interaction was found between diets and the method used to derive lipid digestibility. The differences between apparent and true lipid digestibility ranged from 0.05 percentage points for the wheat diet to 0.20 percentage points for the rye diet. 4. From the results of this trial, it appears that TMEN overestimates the energy value of high fibre diets.

Lipid and fatty acid digestibility of three oil types in the Australian shortfin eel, Anguilla australis

The lipid and fatty acid digestibilities of three semi-purified, isonitrogenous (48.9–50.8% protein) and isocalorific (19.1–20.8 kJ g −1) diets, in which the lipid source was either cod liver oil (CLO), linseed oil (LO) or sunflower oil (SFO), were estimated in the Australian shortfin eel ( Anguilla australis) using chromic oxide as an external marker. Apparent percent protein and energy digestibilities of the diets were not significantly ( P>0.05) affected by the lipid source, but the lipid digestibility was. The percent apparent lipid digestibility was lowest in the LO diet (90.2±0.6) and highest in the CLO diet (95.6±0.2). Not all the fatty acids present in any one diet were recovered in the faecal samples. In diets with CLO, only three saturates (out of five), five monoenes and six (out of 11) PUFAs were detected in faecal samples. With all the diets, 20:0 and 22:0, and none of the n−6 HUFA were detected in the faecal samples. The digestibility of all the fatty acids, except 18:3 n−3, was lowest in the diet with LO, and significantly so ( P>0.05) from the other diets. In shortfin eel, there was a trend for the digestibility of saturated fatty acids of diets with the animal oil as the lipid source to decrease with increasing chain length, and in diets with vegetable oil to increase initially and then decrease. A somewhat comparable trend was also evident in respect of monoenes. When the digestibility of different categories of fatty acids is considered, the digestibility of saturates, monoenes, unsaturates, n−6, PUFA, HUFA and total fatty acid digestibilities of LO diet were the lowest, and differed significantly ( P<0.05) from those of the CLO and SFO diets, except in the case of n−3 fatty acids.

Review of the lipid and essential fatty acid requirements of rockfish (Sebastes schlegeli )

In order to investigate the effects of dietary lipid and essential fatty acids (EFA) on growth and biochemical change of rockfish (Sebastes schlegeli), a series of studies was conducted. Juvenile rockfish required 0.9% n-3 highly unsaturated fatty acids (n-3HUFA) in the diet. The requirements of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were both 1%, and DHA was superior to EPA as an EFA. Fatty acid compositions in polar lipid of fish were directly reflected from those of dietary fatty acids. The levels of protein, glucose, cholesterol, LDH, GPT and GOT in the serum of rockfish were significantly affected by dietary n-3HUFA levels. Abnormal and necrotic hepatic cells were found in rockfish fed the n-3HUFA-deficient diets. Ca2+-ATPase activities in the liver microsomal membrane were lower in fish fed the n-3HUFA-deficient diets than in those fed the n-3HUFA-sufficient diets. Apparent digestibilities of lipid and saturated fatty acids of rockfish fed the diet were affected by water temperature and fish size, especially in the diet containing beef tallow. These results may be used in developing feed formulation and improving the health of rockfish.

Optimum dietary ratio of digestible protein and energy for juvenile American eel, Anguilla rostrata , fed practical diets

Triplicate groups of juvenile American eel, Anguilla rostrata, initial weight 8.2 ± 0.24 g, were fed to satiation herring meal based diets formulated with digestible protein/digestible energy (DP/DE) ratios of 19, 20, 21, 22 and 23 g DP MJ DE−1 (as-fed basis) for 84 days. Data were collected to determine the effect of dietary DP/DE ratio on feed intake (FI), mean weight (MW), specific growth rate (SGR), feed conversion ratio (FCR), apparent digestibility (AD) of major nutrients, rate of phosphate excretion (RPE) and nutrient retention efficiency (RE). Highest MW, SGR and lowest FCR (P 0.05) with mean AD coefficients for organic matter, protein, energy and phosphorous of 86.3, 94.1, 89.2 and 34.7%, respectively. Lipid AD was significantly higher (P 0.05) on RPE and it averaged 0.05 ± 0.002 g phosphate kg fish−1 day−1. Nitrogen retention efficiency (NRE) significantly (P 0.05) at an average of 31.6 ± 0.67%. Energy retention efficiency (ERE) significantly (P < 0.05) increased to 42.9 ± 1.24% as DP/DE ratio increased to 22 g DP MJ DE−1 and thereafter significantly (P < 0.05) decreased. Lipid retention efficiency (LRE) increased significantly (P < 0.05) to 75.7 ± 0.85% as dietary DP/DE ratio increased to 23 g DP MJ DE−1. Non-linear quadratic regression of ERE against dietary DP/DE ratio yielded an estimated optimum DP/DE ratio for juvenile American eel of 22.1 g DP MJ DE−1.

Impact of different dietary lipid sources on growth, lipid digestibility, tissue fatty acid composition and histology of rainbow trout, Oncorhynchus mykiss

The aim of the present study was to determine the impact of replacing at least 50% of the fish oil by alternative lipid sources in diets for rainbow trout on growth, lipid digestibility, fatty acid profiles of liver and muscle and tissue histology. Four experimental diets were formulated combining two fish oils (capelin and anchovy) with different vegetable oils (soybean, rapeseed, palm and olive) and one type of animal fat (lard), in order to obtain 60% to 80% fish oil replacement. A fifth diet prepared with pure fish oil (capelin oil) served as control. The diets were fed to apparent satiation twice a day to triplicate groups of 30 rainbow trout with an initial weight of 250 g for 64 days at 12 °C. Growth was good (TGC 3 3.7–3.9) and independent of diet. Final body weight was on average 760 g. Feed conversion ratios (FCR) ranged from 0.72 to 0.79. The only significant difference in FCR was found in the group fed an olive oil–lard combination replacing 80% of the fish oil. This diet also had a lower apparent lipid digestibility (79% vs. 91–94% for the rest of the diets). The liver and muscle fatty acid compositions were similar within groups and reflected that of the diets. But, tissue levels of 20:5 n−3 were lower and levels of 22:6 n−3 were higher than their respective dietary percentages. Histologically, a supranuclear accumulation of lipid droplets was observed in the intestinal cells of some of the groups fed diets supplemented with vegetable oils. Similarly, livers from these groups showed large amounts of lipid droplets within the hepatocytes. The present results suggest that most of the fish oil can be replaced by the alternative sources tested without compromising growth and feed utilisation. However, the histological changes observed suggest an impact of dietary lipid source on the transport and/or metabolism of fat in the fish. This requires further investigation.

Nutrient digestibility and intestinal viscosities in broiler chickens fed on wheat diets, as compared to maize diets with added guar gum

1. Three maize diets containing 0, 1 or 3 g of guar gum per kg and 2 wheat diets were given to male broiler chickens for measurements of growth performance and nutrient digestibility. 2. The intestinal viscosities found with wheat diets were within the range of those observed with the 3 maize diets. The correlations between in vivo and in vitro viscosities were higher with real than with potential applied viscosity. 3. The gain:food ratio decreased (P<0.05) with the addition of 3 g guar gum/kg. The mean gain:food ratio observed for wheat diets was lower (P=0.007) than the mean value found for the 3 maize diets. 4. The negative effects of increased intestinal viscosity due to guar gum addition on nutrient digestibility were highest for lipids and lowest for starch. 5. Wheat diets resulted in much lower (P<0.001) starch apparent digestibility compared to maize diets with added guar gum despite similar mean intestinal viscosities in the 2 groups of diets. Apparent lipid digestibility with wheat diets was lower (P<0.01) than the value predicted from intestinal viscosity, the predictive model having been calculated with the guar gum added maize diets. Apparent protein digestibility did not differ between wheat diets and guar gum added maize diets. 6. It was concluded that the low apparent digestibilities of starch and lipid observed with wheats could not be attributed only to intestinal viscosity and that other factors appear to be implicated in the low digestibilities observed with the wheat samples tested in the present experiment.

Long-term protein and lipid growth of Atlantic salmon ( Salmo salar) fed diets with partial replacement of fish meal by soy protein products at medium or high lipid level

This study investigated long-term effects on nutrient digestibility and protein and lipid growth of soy protein and lipid levels used in commercial grower diets for Atlantic salmon. Two series of extruded diets were formulated to contain either 45% protein and 32% lipid (medium fat) or 40% protein and 39% lipid (high fat). Each series consisted of six diets in which a soy protein source partially replaced low-temperature (LT) dried fish meal (FM): FM only (control), soy protein concentrate (SPC, 30% of crude protein, CP); SPC added 0.2% dl-methionine (30% of CP, SPC+met); dehulled, defatted soybean meal (HP-SBM, 20% of CP); full-fat (FF) SBM (10% of CP), and; defatted SBM (10% of CP). Each diet was fed to triplicate groups of 0.56-kg salmon kept in sea pens. The experiment lasted 235 days, during which the salmon reached 2.5 to 2.8 kg. Growth was slower in the FM-control and HP-SBM treatments than in the other treatments. The HP-SBM diet induced enteritis in the distal intestine of the salmon and, at day 215, the apparent digestibilities of nitrogen, lipid and energy were lower in the HP-SBM treatments than in all other treatments. Except a slightly reduced muscle protein concentration in the HP-SBM treatment, no effects of dietary soy were detected on final body composition. Salmon fed the high-fat diets reached on average 122 g higher final weight than those fed the medium-fat diets; however, 91 g of this was in the form of lipid, and corresponded with enlarged deposits of visible fat.

The lowering effect of dietary glucose versus starch on fat digestibility in rats is dependent on the type of fat in the diet.

The aim of the study was to determine whether the type of dietary fat influences the effect of dietary glucose on lipid digestibility. Earlier work had shown that glucose, when compared with starch, reduced fat digestibility in rats fed rations containing animal fat as fat source. Male rats (n = 6/group) were fed for two weeks on purified diets containing either 62% (w/w) starch or glucose and either 8% (w/w) palm oil, coconut fat, soybean oil or medium-chain triglycerides (MCT) as the main source of fat. The diets had no differential effect on growth. Glucose significantly depressed apparent lipid digestibility in rats fed the diets containing either palm oil or coconut fat, but not in rats given the diets containing either soybean oil or MCT. Thus, the inhibitory effect of glucose on lipid digestibility in rats is dependent on the dietary lipid source. This observation may contribute to understanding the mechanism by which dietary glucose inhibits fat digestion.

Ação do tanino na digestibilidade de dietas pela tilápia-do-nilo (Oreochromis niloticus)

This experiment was undertaken to determine the effect of tannin from Stryphnodendron obovatum added to fish diets. The apparent digestibility of dry matter, crude protein and lipid was evaluated. Eighty Nile tilapia juveniles were arranged in five groups (16/aquarium) and fed diets containing 0.00%; 0.21%; 0.42%; 0.63% and 0.84% of total tannin from barbatimao ( Stryphnodendron obovatum ). After three days of acclimatation, feces were collected during 5 days up to reach five replicates/group. The apparent digestibility coefficient was determined based on chemical analyses of feedstuffs and feces using chromic acid as an inert marker. The results of this study indicate that 0.42% of tannin had no effect on dry matter, crude protein and lipid digestibility but 0.63% or higher levels had significant harmful effect on the digestibility of nutrients.

Inhibitory effect of dietary carboxymethylcellulose on fat digestibility in rats fed diets containing either starch or glucose

Dietary carboxymethylcellulose (CMC) inhibits lipid digestibility in broiler chickens by increasing the viscosity of small intestinal digesta. The aim of this study was to investigate the effect of dietary CMC on lipid digestibility in rats fed diets containing either starch or glucose. It was hypothesized that CMC would have a greater inhibitory effect on lipid digestibility when the diet contained starch instead of glucose. Male rats were fed for 2 weeks purified diets containing either 619.2 g starch or glucose per kg and CMC levels of either 0, 20 or 40 g/kg. The experimental diets had no differential effect on growth of the rats. CMC significantly lowered the apparent lipid digestibility coefficient by more than 0.1, this effect being independent of the type of carbohydrate in the diet. Lipid digestibility was significantly reduced by glucose when compared with starch, but the mechanism is unknown.