Dietary Starch Level Research Articles

Effect of dietary carbohydrate on non-specific immune response, hepatic antioxidative abilities and disease resistance of juvenile golden pompano (Trachinotus ovatus)

The present study was conducted to investigate the effects of dietary carbohydrate (CHO) levels on non-specific immune responses, hepatic antioxidative status and disease resistance of juvenile golden pompano. Fish were fed six isonitrogenous and isoenergetic diets containing various CHO levels for 8 weeks. After the feeding trial, fish were challenged by Vibrio harveyi and survival rate was recorded for the next 12 days. Plasma total protein and albumin content, respiratory burst activity, alkaline phosphatase, slightly increased with dietary starch level from 0% to 16.8%, but significantly decreased at dietary starch levels of 16.8%–28%. Plasma lysozyme, complement 3 and complement 4 levels increased with increasing dietary carbohydrate up to 11.2% and then declined (P < 0.05). Contrary to glutamic-oxalacetic transaminase and triiodothyronine, plasma cortisol content increased with increasing dietary carbohydrate up to 22.4%, and then levelled off. The hepatic total antioxidative capacity, reduced glutathione and catalase levels reached the peak at the fish fed diet with 16.8% carbohydrate (P < 0.05). This also held true for hepatic superoxide dismutase activities, whereas the hepatic malondialdehyde content of fish fed dietary starch level of 16.8% was significantly lower than that of fish fed no CHO diet, but showed little difference (P > 0.05) with those of the other treatments. After challenge, fish fed 11.2% and 16.8% dietary CHO showed higher survival rate than that of fish in 0% CHO group (P < 0.05). However, survival rate showed little difference among 0%, 5.6%, 22.4% and 28% CHO groups (P > 0.05). The results of this study suggest that ingestion of 11.2–16.8% dietary CHO can enhance the non-specific immune responses, increase the hepatic antioxidant abilities, and improve resistance to V. harveyi infection of juvenile golden pompano.

Adipose tissue and liver metabolic responses to different levels of dietary carbohydrates in gilthead sea bream (Sparus aurata)

This study analyzes the effects of replacing dietary lipids by carbohydrates and carbohydrates by fiber on gilthead sea bream growth, as well as lipid and glucose metabolism in adipose tissue and liver over the course of a 15-week feeding trial. Six different diets were formulated and fish were classified into two experimental groups sharing one diet. In the first group (LS), fish were fed four diets where lipids were reduced (23%–17%) by increasing carbohydrates (12%–28%) and, the second group (SF) consisted on three diets where the amount of carbohydrates (28%–11%) was exchanged at expenses of fiber (1%–18%). Differences in growth were not observed; nevertheless, the hepatosomatic index was positively related to dietary starch levels, apparently not due to enhanced hepatic lipogenesis, partly supported by unchanged G6PDH expression. In the LS group, lipogenic activity of adipose tissue was stimulated with low-lipid/high-carbohydrate diets by up-regulating G6PDH expression and a tendency to increase FAS, and promoted carbohydrate utilization versus fatty acid oxidation by modulating the transcription factors LXRα, PPARα and PPARβ expression. In the SF group, PPARs and LXRα increased parallel to fiber levels in adipose tissue. Furthermore, an adaptation of hepatic GK to dietary starch inclusion was observed in both groups; however, the lack of effects on G6Pase expression indicated that gluconeogenesis was not nutritionally regulated under the conditions examined. Overall, metabolic adaptations directed to an efficient use of dietary carbohydrates are present in gilthead sea bream, supporting the possibility of increasing carbohydrate or fiber content in diets for aquaculture sustainability.

Carbohydrate utilization by herbivorous and omnivorous freshwater fish species: a comparative study on gibel carp (Carassius auratus gibelio. var CAS III) and grass carp (Ctenopharyngodon idellus)

Two 8-week feeding trials were conducted to evaluate dietary carbohydrate utilization by omnivorous gibel carp (Carassius auratus gibelio) (2.4 ± 0.1 g) and herbivorous grass carp (Ctenopharyngodon idellus) (6.5 ± 0.1 g). Five isonitrogenous (370 g kg−1) and isolipid (70 g kg−1) diets were formulated with increasing corn starch levels (60, 140, 220, 300 and 380 g kg−1). Results showed that specific growth rate (SGR), feed efficiency (FE) and protein retention efficiency (PRE) of gibel carp significantly increased from dietary starch of 60 to 300 g kg−1 and then decreased from 300 to 380 g kg−1, but those of grass carp showed no significant differences between treatments. Independent of dietary starch levels, grass carp gained significantly higher FE and PRE than gibel carp. Feeding rate (FR) of gibel carp was significantly higher than that of grass carp. In two fish species, high dietary starch (300 and 380 g kg−1) tended to obtain higher hepatosomatic index (HSI), serum triglyceride, hepatic lipid and body lipid contents. Serum glucose concentration of grass carp was not affected, while that of gibel carp fed the starch of 300 g kg−1 diet was significantly lower than those of the fish fed other four diets (60, 140, 220 and 380 g kg−1). Grass carp showed high tolerance to dietary starch while dietary corn starch should be no more than 300 g kg−1 for gibel carp. High starch contents may cause lipid accumulation in the liver and body.

Effect of varying dietary starch and fiber levels and inoculum source (mule deer vs. dairy cow) on simulated rumen fermentation characteristics

This study measured starch and fiber digestion and microbial fermentation of three commercial exotic animal feeds using mule deer (MD) or dairy cow (DC) rumen inoculum. Diets were formulated to provide either high starch/low fiber (based on neutral detergent fiber fraction; NDF) with either alfalfa (diet A) or grain and oilseed byproducts (diet B) as the major fiber sources or low starch/high NDF (diet C). An initial batch culture incubation was run with diets inoculated with each rumen inoculum (n = 6; N = 36) over a 48 hr period with samples taken at different hour points for ammonia, pH, lactate, and volatile fatty acids (VFA). A second experiment was conducted where two continuous culture incubations (MD or DC) were run with six single-flow polycarbonate fermentation vessels per dietary treatment. Diets were fed two times a day over an 8-day period and sampled for ammonia, pH, and VFA before and after feeding on the last 3 days. On day 8, fermenter and effluent contents were collected and analyzed for nitrogen, dry matter digestibility (DMD), and organic matter digestibility (OMD). OMD was greater in MD (P = 0.02) and DMD tended to do the same (P = 0.06), but there were no differences due to diet (P > 0.05). Ammonia concentration was greater in DC (P < 0.01), and diets A and B had greater concentrations than diet C (P < 0.01). The greater digestibility, higher acetate:propionate (A:P) ratio and increased lactate levels prior to feeding likely led to diet C having a lower pH than diet A (6.59 vs. 6.66, respectively; P < 0.01) and led the tendency of A to be lower than C after feeding (P = 0.08). A:P ratio was greater in DC than MD before and after feeding (P < 0.01) and was greater in diet C than diets A or B (P < 0.01). Total VFA production tended to be greater in diets B and C in DC (P = 0.06). Rumen fluid source did affect fermentation. Increasing fiber level did not negatively affect fermentation and may increase OMD by removal of negative associative affects by starch on cellulolytic bacteria.

Central Role of the PPARγ Gene Network in Coordinating Beef Cattle Intramuscular Adipogenesis in Response to Weaning Age and Nutrition

Adipogenic/lipogenic transcriptional networks regulating intramuscular fat deposition (IMF) in response to weaning age and dietary starch level were studied. The longissimus muscle (LM) of beef steers on an early weaning (141 days age) plus high-starch diet (EWS) or a normal weaning (NW, 222 days age) plus starch creep-feed diet (CFS) was biopsied at 0 (EW), 25, 50, 96 (NW), 167, and 222 (pre-slaughter) days. Expression patterns of 35 target genes were studied. From NW through slaughter, all steers received the same high-starch diet. In EWS steers the expression of PPARG, other adipogenic (CEBPA, ZFP423) and lipogenic (THRSP, SREBF1, INSIG1) activators, and several enzymes (FASN, SCD, ELOVL6, PCK1, DGAT2) that participate in the process of IMF increased gradually to a peak between 96 and 167 days on treatment. Steers in NW did not achieve similar expression levels even by 222 days on treatment, suggesting a blunted response even when fed a high-starch diet after weaning. High-starch feeding at an early age (EWS) triggers precocious and sustained adipogenesis, resulting in greater marbling.

Effect of Dietary Starch Inclusion Rate on Digestibility and Amylase Activity in Arctic charr (Salvelinus alpinus) and Eurasian perch (Perca fluviatilis)

This study investigated digestibility and amylase activity in Arctic charr and Eurasian perch fed different dietary levels of wheat starch. Eurasian perch (190 ± 0.5 g) and Arctic charr (102 ± 0.5 g) were fed one of six iso-nitrogenous diets containing 0, 10, 15, 20, 25 and 30% wheat starch. Each diet was fed to four replicate groups of fish to determine the impact of diet on the apparent digestibility (AD) of dry matter (DM), crude protein, starch, crude fat and energy. At the end of the experiment, tissue samples were collected for assessment of amylase activity in the proximal and distal intestine. The AD of DM, crude protein, starch, crude fat and energy differed between fish species (P 0.05) of dietary starch level on the AD of DM, crude protein, crude fat and energy. Overall, α-amylase activity correlated with the trends obtained for starch digestibility. The inclusion of wheat starch did not affect amylase activity within species.

Urea-N recycling in lactating dairy cows fed diets with 2 different levels of dietary crude protein and starch with or without monensin

Rumensin (monensin; Elanco Animal Health, Greenfield, IN) has been shown to reduce ammonia production and microbial populations in vitro; thus, it would be assumed to reduce ruminal ammonia production and subsequent urea production and consequently affect urea recycling. The objective of this experiment was to determine the effects of 2 levels of dietary crude protein (CP) and 2 levels of starch, with and without Rumensin on urea-N recycling in lactating dairy cattle. Twelve lactating Holstein dairy cows (107±21d in milk, 647kg ± 37kg of body weight) were fed diets characterized as having high (16.7%) or low (15.3%) CP with or without Rumensin, while dietary starch levels (23 vs. 29%) were varied between 2 feeding periods with at least 7d of adaptation between measurements. Cows assigned to high or low protein and to Rumensin or no Rumensin remained on those treatments to avoid carryover effects. The diets consisted of approximately 40% corn silage, 20% alfalfa hay, and 40% concentrate mix specific to the treatment diets, with 0.5kg of wheat straw added to the high starch diets to enhance effective fiber intake. The diets were formulated using Cornell Net Carbohydrate and Protein System (version 6.1), and the low-protein diets were formulated to be deficient for rumen ammonia to create conditions that should enhance the demand for urea recycling. The high-protein diets were formulated to be positive for both rumen ammonia and metabolizable protein. Rumen fluid, urine, feces, and milk samples were collected before and after a 72-h continuous jugular infusion of 15N15N-urea. Total urine and feces were collected during the urea infusions for N balance measurements. Milk yield and dry matter intake were improved in cows fed the higher level of dietary CP and by Rumensin. Ruminal ammonia and milk and plasma urea nitrogen concentrations corresponded to dietary CP concentration. As has been shown in vitro, Rumensin reduced rumen ammonia concentration by approximately 23% but did not affect urea entry rate or gastrointestinal entry rate. Urea entry rate averaged approximately 57% of total N intake for cattle with and without Rumensin, and gastrointestinal rate was similar at 43 and 42% of N intake for cattle fed and not fed Rumensin, respectively. The cattle fed the high-protein diet had a 25% increase in urea entry rate and no effect of starch level was observed for any recycling parameters. Contrary to our hypothesis, Rumensin did not alter urea production and recycling.

Effects of dietary fiber and starch levels on the non-specific immune response of growing rabbits

The effects of dietary fiber and starch on the non-specific immune response were studied using four different experimental diets (I, II, III, and IV) on 200 growing rabbits. The following parameters were assessed: the number of membranous epithelial (M) cells in the appendix, total SIgA titers in the gut, total IgG levels in the serum and the CD4+/CD8+ T cell ratio in the peripheral blood; as these measures were taken to determine the effect of diet with age, samples were obtained at 52, 62, 72 and 82 days of age. The number of M cells was increased with dietary fiber enhancement and starch reduction at 52 and 62 days of age (P<0.001). However, at 72 and 82 days of age, there was no difference (P>0.05) in M cell number among the four diets. Using immunohistochemistry, the high fiber/low starch diet (Diet I) resulted in an increase in M cell size and number when compared with the other diets. The only differences(P<0.001) in SIgA titers from gut tissues were detected between animals that received a high fiber (Diet I) and a low fiber (Diet IV) diet at an early stage (52 d and 62 d). Serum IgG titers were only affected (P=0.05) at 82 days of age. The ratio of CD4+/CD8+ T cells in the peripheral blood was not affected. The study revealed that increased levels of fiber might improve mucosal functionality, but only during the early stage of growth of rabbits. The effect of dietary fiber and starch levels on intestinal immunity was greater than their effect on humoral immunity in the peripheral blood.

Substitution of starch by soluble fiber and Saccharomyces cerevisiae dose response on nutrient digestion and blood metabolites for precision-fed dairy heifers

The objective of this experiment was to determine the effects of 2 levels of dietary starch and the dose at which the effects of yeast culture (YC) derived from Saccharomyces cerevisiae (Yea-Sacc1026, Alltech Inc., Nicholasville, KY) were maximized based on nutrient total-tract digestibility (AD), N utilization, and blood metabolites of precision-fed dairy heifers. A split-plot design with starch level as the whole plot and YC dose as subplot was administered in a 4-period (21 d), 4×4 Latin square. Eight Holstein heifers (432.49±6.81kg of body weight) were allocated to 2 starch treatments (28% starch, high starch, HS, or 17% starch, low starch, LS) and to a sequence of YC doses (0, 10, 30, and 50g/d). Dry matter (DM) and neutral detergent fiber (NDF) AD were not different between HS and LS; however, HS decreased acid detergent fiber (ADF) and increased hemicellulose AD. Digestibility of DM and organic matter (OM) increased quadratically in response to increasing YC dose. Hemicellulose, NDF, and ADF AD increased or tended to increase quadratically with increasing YC dose. No significant effects were noted on fecal or urine output between dietary starch concentrations; YC decreased wet and dry fecal output corresponding to the effect in DM and OM. Apparent N digestibility was greater in the LS group. As YC dose increased, fecal N output decreased quadratically and was lowest at 30g/d YC. A corresponding quadratic increase was observed for N retention expressed as a percentage of N digested: N output in urine tended to increase with increasing YC dose, resulting in no differences in retained N (g/d). Dietary starch concentration did not affect blood glucose, triglyceride, creatinine, or lactate concentration. However, HS increased plasma urea N concentration. Glucose concentration tended to increase quadratically with daily YC dose in both starch treatments, with the greatest response at 30g/d. For triglycerides, dietary starch concentration and YC dose interacted, decreasing quadratically in the LS group and increasing in the HS group (lowest and highest value for 10g/d respectively). We observed a significant time effect for all blood metabolites measured. We conclude that starch level did not affect DM AD, but influenced ADF and hemicellulose AD. Yeast culture had the greatest effect on DM, NDF, ADF, and hemicellulose AD when added at 30g/d. Addition of YC influenced glucose and triglyceride concentrations differently according to the dietary starch concentration of the diet.

Dietary protein requirement of sharpsnout sea bream (Diplodus puntazzo, Cetti 1777) juveniles

A trial was undertaken to estimate the protein requirement of sharpsnout sea bream (Diplodus puntazzo) and the protein sparing of dietary lipids. Ten diets were formulated to contain 5 protein levels (ranging from 15 to 55%) and two lipid levels (12 and 18%). Each diet was assigned to duplicate groups of 15 fish with a mean individual body weight of 49.3g. A quadratic model was used to adjust weight gain and N retention (gkgABW−1day−1) to dietary protein levels. Based on that model, optimum dietary protein requirement was estimated to be 42.9% for maximum weight gain and 43.8% for maximum N retention, corresponding to a protein intake of 7.68gkgABW−1day−1. Protein requirement for maintenance was estimated to be 0.71gkgABW−1day−1. Dietary lipid level improved protein utilization efficiency but did not affect protein requirement. Whole-body protein content increased with dietary lipids and protein content, but no other relevant differences in body composition were noticed. Hepatosomatic index increased with dietary starch and lipid levels and was directly correlated to liver glycogen content. Diet composition affected plasma glucose clearance and cholesterolaemia but not plasma protein and triglyceride levels.

Effect of Protein and Starch Level in Practical Extruded Diets on Growth, Feed Utilization, Body Composition, and Hepatic Transaminases of Juvenile Grass Carp, Ctenopharyngodon idella

Six practical extruded diets were formulated to investigate the effect of graded levels of starch (17, 22, and 26%) associated with either 30 or 34% protein level on growth, feed utilization, body composition, and hepatic transaminases of juvenile grass carp, Ctenopharyngodon idella. Over an 8‐wk growth trial, survival rates (99–100%) were not significantly affected (P &gt; 0.05) by dietary treatments. Independent of dietary starch level, weight gain (WG, %), specific growth rate (SGR, %/d), and feed efficiency ratio (FER) showed significant better response (P &lt; 0.05) of fish fed 34% protein diet than those of fish fed 30% protein diet. Protein productive value (PPV) was only affected by dietary protein level, with higher values in the 34% protein level than their 30% counterparts. Irrespective of dietary protein level, lipid productive value (LPV), energy productive value (EPV), viscerosomatic index (VSI, %), intraperitoneal fat ratio (IPF, %), and whole body, liver, and muscle lipid level increased with increasing starch supply. At the same protein level, plasma triacylglycerol (TG), cholesterol (CHO), and low density lipoprotein‐cholesterol (LDL‐C) increased when dietary starch level increased from 17 to 26%. Neither dietary protein level nor starch level affected activities of hepatic alanine aminotransferase (ALAT) and aspartate transferase (ASAT). The overall results in this study suggested that the higher 34% protein was superior for juvenile grass carp and an increase in dietary starch level did not improve growth or protein utilization but enhanced whole‐body lipid deposition and liver, viscera and muscle lipid level. The diet containing 34% protein and 17% starch was optimal for practical production of juvenile grass carp.

Effect of Dietary Starch Level and Kind on the Growth and Body Composition of Juvenile Olive Flounder Paralichthys olivaceus

A 7-week feeding trial was conducted to investigate the effect of dietary starch level and kind on the growth and body composition of juvenile olive flounder. Triplicate groups of fish (average weight: 1.5 g) were fed iso-nitrogenous (48% crude protein) and isocaloric (4.8 kcal/g diet) diets containing 15-25% <TEX>${\alpha}$</TEX>-potato starch and 15% <TEX>${\beta}$</TEX>-potato starch. Survival was not affected by dietary starch level and kind. The weight gain of fish fed the diet containing 20% <TEX>${\alpha}$</TEX>-potato starch was significantly higher than that of fish fed the diets containing 15% and 25% <TEX>${\alpha}$</TEX>-potato starch levels. The feed efficiency and protein efficiency ratios of fish fed the diets containing 15% <TEX>${\beta}$</TEX>-potato starch were significantly lower than those of the other groups (P < 0.05). The protein efficiency ratio tended to increase with increasing <TEX>${\alpha}$</TEX>-potato starch. The daily feed intake of fish fed the diet containing 15% <TEX>${\beta}$</TEX>-potato starch was significantly higher than that of the other groups (P < 0.05). The hepatosomatic index, condition factor, and proximate composition of the whole body were not affected by the dietary starch level and kind. These results indicate that up to 20% <TEX>${\alpha}$</TEX>-potato starch could be incorporated into the juvenile flounder diet for optimum growth.

The effect of dietary starch level on postprandial glucose and insulin concentrations in cats and dogs

A charge made against feeding dry foods to cats is that the high carbohydrate (i.e. starch) content results in high blood glucose levels which over time may have detrimental health effects. The present study determined the post-meal concentrations of plasma glucose and insulin in adult cats (seven males and four females) and dogs (Labrador retrievers; four males and five females) fed dry diets with low-starch (LS), moderate-starch (MS) or high-starch (HS) levels. In a cross-over design with at least 7 d between the test meals, plasma glucose and insulin concentrations were measured following a single meal of a LS, MS and HS diet (209 kJ/kg bodyweight). Only the HS diet resulted in significant post-meal increases in plasma glucose concentration in cats and dogs although the time-course profiles were different between the species. In cats, plasma glucose concentration was significantly increased above the pre-meal concentration from 11 h until 19 h after the meal, while in dogs, a significant increase above baseline was seen only at the 7 h time point. Plasma insulin was significantly elevated in dogs 4-8 h following the MS diet and 2-8 h after the HS diet. In cats, plasma insulin was significantly greater than baseline from 3-7 and 11-17 h after the HS diet. The time lag (approximately 11 h) between eating the HS diet and the subsequent prolonged elevation of plasma glucose concentration seen in cats may reflect metabolic adaptations that result in a slower digestive and absorptive capacity for complex carbohydrate.

Effects of dietary phosphorus and starch levels on growth performance, body composition and nutrient utilization of grass carp (Ctenopharyngodon idellaVal.)

Six iso-nitrogenous (410 g kg−1) diets with three levels of total phosphorus (P4, P10 and P18 g kg−1) and two levels of starch (S200 and S350 g kg−1) were fed to triplicate groups of 30 fish to evaluate whether the high level of dietary phosphorus could improve the utilization of starch. Over 8-week-growth trial, best weight gain (WG) and specific growth rate (SGR) (P < 0.05) were observed in fish fed the P10/S200 and P18/S200 diets. WG and SGR significantly decreased as starch levels increased whereas for P4, while lipid contents of liver and whole body, hepatosomatic index and intraperitoneal fat ratio (IPF) significantly increased. These results suggested that high dietary starch will depress the growth performance and cause lipid accumulation. Within both starch levels, fish fed diet with P4 tended to produce lower (P < 0.05) WG and SGR, and had higher (P < 0.05) values of IPF. The whole body lipid, ash, calcium, phosphorus and iron contents were significantly affected by dietary phosphorus levels. Supplied phosphorus could improve the growth and decrease the whole body lipid, but there is no more effect after the phosphorus requirement was met at 10 g kg−1.

Influence of dietary starch and cellulose levels on the metabolic profile and apparent digestibility in penaeoid shrimp

The present study compared the effect of different starch/cellulose ratios (30/0, 20/10, 10/20, 0/30) on the metabolic response and apparent digestibility in two species of penaeoids: Artemesia longinaris and Pleoticus muelleri . Adult animals were used in order to obtain sufficient quantities of haemolymph and faecal material for analysis. No significant differences were found in levels of plasma metabolites in P. muelleri , but in A. longinaris , a significant increase was observed in glucose, total protein, and cholesterol in correlation with increased dietary starch. The apparent digestibility coefficients decreased from 83.7% to 51.2% ( A. longinaris ) and from 71.9% to 7.6% ( P. muelleri ) as the dietary starch levels increased. The ratio of amylase activity to protease activity (A/P ratio) declined in A. longinaris when the percentage of dietary starch increased. In contrast, the A/P ratio for P. muelleri increased with higher starch concentrations. These results demonstrated a close relationship between the feeding habits and digestive physiology of the two species studied; they also suggest a more herbivorous behavior for A. longinaris and more omnivorous habits for P. muelleri .

Influence of dietary starch and cellulose levels on the metabolic profile and apparent digestibility in penaeoid shrimp

Influence of dietary starch and cellulose levels on the metabolic profile and apparent digestibility in penaeoid shrimp

Temperature and dietary starch level affected protein but not starch digestibility in gilthead sea bream juveniles

A study was carried out with gilthead sea bream juveniles to assess the effect of water temperature (18 and 25°C) and dietary pregelatinized starch level (10, 20 and 30%) on digestibility of protein and starch and on the activity of proteolytic and amylolytic enzymes. ADC of pregelatinized starch was very high (>99%) irrespectively of dietary inclusion level, and it was not affected by water temperature. ADC of protein was also high (>90%) but improved at the higher water temperature. Dietary starch interacted with protein digestibility, which decreased as dietary starch level increased. Temperature affected both acid and basic protease activities, with acid protease activity being higher at 25°C and basic protease activity being higher at 18°C. However, total proteolytic activity and amylase activities were not affected by water temperature. Dietary carbohydrate exerted no effect on proteolytic or amylolitic activities. It is concluded that gilthead sea bream juveniles digest pregelatinized starch very efficiently irrespective of water temperature, due to adjustments of amylase activity to cope with temperature differences. Pregelatinized starch interacts negatively with protein digestibility, with the ADC of protein decreasing as dietary starch levels increase.

Effects of different dietary wheat starch levels on growth, feed efficiency and digestibility in grass carp (Ctenopharyngodon idella)

An experiment was conducted to determine the effect of dietary wheat starch on grass carp (Ctenopharyngodon idella) in terms of growth performance, feed efficiency and digestibility. Five isoproteic (23.5%) and isolipidic (5.7%) diets with five supplemented levels of wheat starch (D20, D26, D33, D40 and D47 with 20, 26, 33, 40 and 47%, respectively) were fed to triplicate groups of grass carp (mean initial wet weight 6.9 ± 0.1 g) for 8 weeks. Results showed that weight gain (WG, %), feed efficiency (FE, %) and protein efficiency ratio (PER) in D20, D26 and D33 treatments were significantly higher than those in D40 and D47 treatments (P 33%) despite fish ate increasing levels of dietary digestible energy. Furthermore, excess digestible carbohydrate was to some extent converted to lipid that was deposited in various tissues. Most importantly, grass carp could endure high levels of cellulose without any negative effect on growth and digestibilities of dietary protein and carbohydrate.

Pancreatic and Intestinal Carbohydrases Are Matched to Dietary Starch Level in Wild Passerine Birds

Evolutionary shifts in diet composition are presumably accompanied by simultaneous changes in digestive physiology. The adaptive modulation hypothesis predicts that activities of digestive enzymes should match the relative levels of their substrates in an animal's diet so that available membrane space and synthetic energy are not wasted on enzymes in excess of need. However, previous studies on captive passerine birds showed high intraspecific phenotypic flexibility only in proteases but not in carbohydrases in response to varying diet composition. In this study, we measured the activities of pancreatic, intestinal, and hepatic enzymes in six wild-caught passerine species. We predicted that if the adaptive modulation hypothesis holds during evolutionary shifts in diet composition in birds, then mass-specific activities of digestive enzymes should be correlated positively with the content of their relevant substrates in species' diets. Whereas mass-specific activities of proteases (aminopeptidase-N, trypsin, chymotrypsin, alanine aminotransferase) were not correlated with estimated dietary protein content, mass-specific activities of all studied carbohydrases (amylase, maltase, sucrase) were positively correlated with estimated dietary starch content. We conclude that activities of carbohydrases but not proteases are evolutionarily matched to diet composition in passerine birds. We hypothesize that the need for nitrogen and essential amino acids can prevent the evolution of a low activity of proteases, even in species feeding on a low-protein diet.

Technical note: Health status and growth performance of rabbits fed diets with different starch level during the post-weaning period.

A total of 240 rabbits (Hyplus®), weaned at 35 days of age, were used for growth rate and health status evaluation. Rabbits were divided into two groups (group S14 and group S12), and fed diets S14 (diet Starch 14%) and S12 (diet Starch 12%) formulated according to the most recent recommendations for rabbit feeding. The study was performed on a commercial farm. The diets were similar in the level of crude protein, fibre fractions and fat, but differed in the level of starch (14.4 vs. 11.9% in the S14 and S12 diets, respectively) and consequently digestible energy (10.0 vs. 9.6 MJ/kg), as well as in the digestible protein/digestible energy ratio. Rabbits of the S14 group received diet S14 from weaning to slaughter (77 days of age). Those in the S12 group received diet S12 from weaning to 49 days of age and were then fed with the S14 diet till slaughter. No significant differences were observed in feed intake between groups. For the entire fattening period, the weight gain values observed for the rabbits of the S12 group, were lower than those observed of the S14 group, but non significant differences were recorded (39.9 vs. 41.3 g/d, P=0.10). Rabbit mortality was relatively low and no significant differences were recorded between groups, either during post-weaning or in the finishing period. However, both morbidity (P=0.01) and health risk index (P=0.03) were observed to be significantly higher in rabbits of the S12 group than in those of the S14 group. The highest number of sick rabbits in the S12 group was recorded before the change of diet. Similar morbidity was subsequently observed in both groups. It can be concluded that i) a lower dietary starch level did not prevent digestive troubles in weaned rabbits and ii) a 14% dietary starch level is suitable for both growth and good health status in the post-weaning and finishing period.