Digestive tract development in rabbit according to the dietary energetic source: correlation between whole tract digestion, pancreatic and intestinal enzymatic activities

The nutritional strategy of European rabbits is affected by age and sex: Females eat more and have better nutrient optimisation

The ecological interest in the European rabbit (Oryctolagus cuniculus) has grown since it was declared an endangered species. Nutrition is fundamental in its dispersion and the key to its success. This is the main reason why knowledge of their nutritional preferences/requirements could play a fundamental role in rabbit biology and, therefore, in their conservation. The objectives of the work will be to elucidate how age and sex affect both nutritional preferences/requirements, and the nutrient optimisation of European rabbits. To address this gap, 70 wild European rabbits were studied. The rabbits were divided according to their age: adult (n = 43) and young (n = 27). Two groups were differentiated according to the adult rabbits' sex: females (n = 28) and males (n = 15). We analysed the relative (%) and absolute (g) chemical composition of the rabbits' gastric contents: dry matter (DM), ashes (ASH), crude protein (CP), ether extract (EE), neutral detergent fibre (NDF), acid detergent fibre (ADF), and lignin, hemicelluloses and celluloses, highly digestible nonnitrogenous nutrients (HDNN: fat, starch, and soluble fibre), well from the blood was analysed with plasmatic urea nitrogen (PUN), nonesterified fatty acid (NEFA) and glucose (GLU). As a nutrient optimisation measure, the following indices between blood metabolites and stomach content were calculated: PUN/CP total content, NEFA/DM total content and GLU/DM total content ratios. Our works showed that age and sex affected the nutritional strategy of rabbits. Regarding age: adults showed lower CP (-14%; p = 0.0217) and higher HDNN (+21%; p = 0.0399) relative content than young rabbits, and absolute amount of most nutrients: DM (+59%; p = 0.001), OM (+43%; p = 0.0049), ASH (+54%; p = 0.0085), Hemicelluloses (+73%; p = 0.0084), Cellulose (+27%; p = 0.0452), and HDNN (+63%; p = 0.0012). In addition, adults showed better nutrient optimisation. Sex did not affect the relative chemical composition of the gastric content, but it showed a clear higher gastric content by females (+85%; p < 0.0001) and higher intake of most of the absolute chemical components: DM (+64%; p < 0.001), CP (+56%; p = 0.0005), OM (+58%; p = 0.0001), ASH (+44%; p = 0.0123), HDNN (+39%; p = 0.001), NDF (+59%; p = 0.001), ADF (+64%; p = 0.0003), lignin (+82%; p = 0.0036) and cellulose (+58%; p = 0.0002). Finally, we observed that females had better nutrient optimisation than males. This works supports the idea that feeding ecology and nutrition are particularly relevant to reproductive success and fitness in wild animals.

Histomorphological, ultrastructural and morphometrical age-related changes of fundic region of New Zealand rabbits (Oryctolagus cuniculus)

This study investigated the histomorphological, ultrastructural and morphometrical postnatal developmental changes in the rabbit fundic region, especially during changing of the feeding intake. Seventy-two New Zealand rabbits (V-Line breed) at the ages of 1, 7, 15, 23, 30 and 60 days were obtained for light and electron microscopy and morphometric studies of the fundic region. The newborn rabbit's fundic wall was thin and organized into mucosa, submucosa, musclosa and serosa, with a significant increase in thickness with ageing. The fundic glands were few at the first week of life, then increased in length and diameter compared to the preceding age with prominent zonation at 23 days. The gastric pits appeared wide and deep at the first week of life then became typically narrow and shallow at the third week. The mucous cells were the main cell types lining the fundic glands in the first week of life. These cells showed remoulding with a marked increase in Periodic Acid-Schiff reactivity with age. Parietal cells were differentiated earlier (on the first day of life) than the chief cells and distributed at the neck and basal zones. Chief cells differentiated at 15 days old at the base of the glands, followed by an increase in the number and activity. Few active enteroendocrine cells were first seen at 15 days old and then widely distributed throughout the glands. Conclusion: Pronounced histomorphological changes in the fundic mucosal layer, especially the surface and glandular epithelium, correlate with the postnatal rabbit-feeding intake changes.

Plasticity of gut and metabolic limitations of Deoni calves in comparison to crossbred calves on a high plane of nutrition

Plasticity of the digestive system is important for the development and productivity of cows. The objective of the study was to measure the plasticity of the gut in 10 each of Holstein Friesian (HF)-crossbred (Bos taurus; X) and indigenous (Bos indicus, e.g. Deoni breed; D) calves randomly distributed to recommended plane (RN) or 25% higher plane (HN) of nutrition. Body weight (BW) change during a 6-month period in indigenous calve irrespective of the plane of nutrition was 35 kg. Dry matter intake (DMI) in Deoni calves was reduced on a high plane of nutrition but not in HF-crossbred (X) calves. DMI in XHN was 7% more than that in XRN. Compared to crossbred, energy intake, metabolism and energy efficiency of indigenous calves were poor. Significantly higher plasma glucose, triglycerides, cholesterol, AST, ALT and creatinine in DRN or DHN than in XRN or XHN indicated metabolic limitations in indigenous calves. Higher triglycerides and AST, ALT and AST/ALT ratio in indigenous calves may be due to poor insulin sensitivity and hyperlipidaemia. Higher triglycerides in serum may also one of the reasons for the reduced DMI in DHN. Serum creatinine (P < 0.05) in XHN or DHN was higher due to increased crude protein (CP) consumption. The study concluded poor plasticity of the digestive system in indigenous calves on a higher plane of nutrition compared to crossbred calves. Indigenous calves suffer metabolic disturbances like hyperglycaemia, hyperlipidaemia and increased creatinine level because of digestive limitation and slower muscle growth.

Reduced dietary nitrogen with a high Lys:CP ratio restricted dietary N excretion without negatively affecting weaned piglets

We hypothesized that balancing the content of exogenous amino acids, especially lysine, to reduce protein content in swine diets could reduce nitrogen (N) pollution associated with animal husbandry. Two experiments (45 d each experiment) were performed on weaned piglets (Duroc × Landrace × Yorkshire, 28 d of age) to test this and to determine the optimal lysine to crude protein (Lys:CP) ratio in diet. In Exp. 1, 12 piglets (6 replicates [n = 6]) were fed diets containing different levels of CP (17% and 20%) but the same level of Lys. Increased CP content resulted in significant increases (P < 0.05) of average daily gain (ADG), average daily feed intake (ADFI), and body weight (BW), but did not affect the feed to gain ratio. In Exp. 2, 24 piglets (8 replicates [n = 8]) were fed 1 of 3 diets as follows: 1) 20% CP with a regular Lys:CP ratio (6.23%, control); 2) 17% CP with a reduced Lys:CP ratio (6.14%, LL); or 3) 17% CP with a standard Lys:CP ratio (7.32%, SL). The ADG, final BW, serum concentrations of growth hormone and insulin-like growth factor-1, villus height in the jejunum, and villus height to crypt depth ratio were the lowest in piglets fed LL diet, whereas blood urea N concentration was the lowest and the value of lipase activity was the highest in the piglets fed SL diet. The SL diet did not affect growth performance, intestinal morphology, or serum hormone concentrations, indicating that reduced dietary N with a high Lys:CP ratio can efficiently reduce dietary N excretion without negatively affecting weaned piglets.

Plasticity in gastrointestinal morphology and enzyme activity in lactating striped hamsters (Cricetulus barabensis)

In small mammals marked phenotypic plasticity of digestive physiology has been shown to make it easier to cope with the energetically stressful periods, such as lactation. It has been proposed that the capacity of the gut to digest and absorb food is not the factor limiting to sustained energy intake (SusEI) during peak lactation. In this study, plasticity in energy intake and gastrointestinal morphology was examined in striped hamsters at different stages of reproduction and raising litters of different sizes. Mechanisms associated with digestive enzymes and neuroendocrine hormones underpinning the plasticity were also examined. The females significantly increased energy intake, digestibility, masses of digestive tracts and activity of stomach pepsin and maltase, sucrase and aminopeptidase of small intestine in peak lactation compared to the non-productive and post-lactating periods. Further, the females raising large litters significantly increased energy intake, digestibility, gastrointestinal mass and activity of digestive enzymes, and weaned heavier offspring compared with those nursing small and medium litters, indicating that the significant plasticity of digestive physiology increased reproductive performance. The agouti-related protein (AgRP) mRNA expression in the hypothalamus was up-regulated significantly in the females raising large litters relative to those raising small litters. Serum leptin levels, hypothalamus neuropeptide Y (NPY), or anorexigenic neuropeptides (pro-opiomelanocortin / cocaine- and amphetamine-regulated transcript, POMC / CART) mRNA expression did not differ among the females raising small, medium and large litters, indicating that leptin levels in lactation might only reflect a state of energy balance rather than being the prime driver of hyperphagia. Some hypothalamic neuropeptides, such as NPY, POMC and CART, would be involved in the limits to the SusEI during lactation.

Adaptability of the digestive function according to age at weaning in the rabbit: I. Effect on feed intake and digestive functionality

The functional adaptability of the digestive system to the level of feed intake was investigated in the young rabbits by comparing two groups of 12 litters each, weaned at 21 (W21) or 35 (W35) days of age. From 14 days onwards, rabbits were fed a pelleted feed (NDF: 332 g/kg, CP: 177 g/kg, starch: 98 g/kg, as-fed basis). Until 49 days of age, the profile of digestive enzymes was weekly determined in the small intestinal content and mucosa, as well as caecal fermentation traits and fibrolytic activities. In the W21 group, the solid feed intake was increased by 57% between 21 and 35 days (P < 0.01), while the daily body growth was lower from 21 till 42 days (-17%, P < 0.05) when compared with the W35 group. Activities of enzymes of pancreatic origin were only scarcely influenced by the weaning age. In the W21 group, amylase activity tended to be lower at 28 days of age (-36%, P = 0.064), and trypsin activity was decreased by 31% at 49 days of age (P < 0.01). Lipase activity was similar in both weaning groups. Duodenal and jejunal activities of maltase and aminopeptidase N (APN) were higher on day 28 in the W21 group as compared with the W35 group (×1.4 to ×2.4, respectively, P < 0.05). On day 35, duodenal APN activity was twice as higher in the W21 group than in the W35 group (P < 0.01). In caecum, major differences between both weaning groups were observed at 28 days of age with a decrease in ammonia concentration (-43%, P < 0.01) in W21 compared with W35 rabbits. Conversely, the acetate proportion was 5% higher in the W21 group (P < 0.01) on day 28. In conclusion, the digestive tract of early-weaned rabbits showed some adaptative properties in response to nutritional environment changes, but they were insufficient to maintain their growth rate.

Entrapment of Lactobacillus acidophilus into alginate beads for the effective treatment of cold restraint stress induced gastric ulcer

Lactobacillus acidophilus (LAB) loaded alginate floating beads (FBs) were developed with an intent to (i) preserve their viability during manufacture and upon exposure to adverse physiological conditions existing in the stomach, (ii) achieve an increased stay of the system in the stomach for improved pharmacodynamics and to provide for their effective establishment within the gastric mucosa. In vitro characterization of developed beads was performed in terms of entrapment efficiency, buoyancy, and surface as well as cross sectional morphology and viability studies of LAB in a gastric environment. The developed system was evaluated and was found to be significantly better in an experimental model of cold restraint stress (CRS) induced gastric ulcer model in terms of ulcer index, hemorrhagic streak length, histopathological and biochemical markers and their cross talk with reactive oxygen/nitrogen species. The present study emphasizes the advantages and future potential of probiotic loaded FBs in gastric disorders.

Digestive flexibility in females of the subterranean rodent ctenomys talarum in their natural habitat

We studied the occurrence of digestive strategies at different levels in females of the subterranean herbivorous rodent Ctenomys talarum living in their natural habitat. We determined the dimensions of different parts of the gastrointestinal tract and organs along as the activity of key digestive enzymes(sucrase, maltase and N-aminopeptidase) in small intestine in females seasonally caught. Females of C. talarum did not show seasonal variations in the mass of the different parts of the gastrointestinal tract. In nonreproductive females large intestine was longer in autumn, whereas reproductive females did not show seasonal variations in the length of the different parts of the gut. Females of C. talarum exhibited a high sucrose, maltase and N-aminopeptidase activity in small intestine, although these activities were higher in small intestine of females caught in autumn (nonreproductive) than in females caught in winter (reproductive). The results show that C. talarum females exhibit characteristics in the gut at the morphological and biochemical level, which could represent digestive strategies to face the constraints imposed by their costly particular way of life.

Digestive physiology and hindgut bacterial community of the young rabbit (Oryctolagus cuniculus): effects of age and short-term intake limitation

The digestive response of the young rabbit to a short-term (28-53 days) limitation of its voluntary intake (25%) was analysed according to age and in relation to the incidence of digestive troubles. Several physico-chemical parameters of the caecal biotope were studied in relation to the caecal bacterial community structure and diversity, and with other physiological criteria (stomach pH, ileum morphometry and maltase activity). The morphometry of the ileum was significantly affected by age (36 vs. 52 days) but not by the intake level, while the relative maltase activity remained unchanged. In the stomach, the pH of antrum and fundus increased by approximately 1/3 between 36 and 52 days, and was 31% (P=0.003) and 79% (P<0.001) higher for restricted compared to ad libitum rabbits respectively. However the caecal pH remained unchanged (mean: 5.83). The caecal redox potential increased slightly, by 8 units (P=0.02), when intake was limited, but did not change between 36 and 52 days. The caecal bacterial diversity increased with age (4.8 vs. 5.2, P=0.014) while bacterial structure was modified. Limiting the intake for 16 days did not modify the structure or the diversity of the bacterial community.

Thermal and digestive constraints to foraging behaviour in marine mammals

While foraging models of terrestrial mammals are concerned primarily with optimizing time/energy budgets, models of foraging behaviour in marine mammals have been primarily concerned with physiological constraints. This has historically centred on calculations of aerobic dive limits. However, other physiological limits are key to forming foraging behaviour, including digestive limitations to food intake and thermoregulation. The ability of an animal to consume sufficient prey to meet its energy requirements is partly determined by its ability to acquire prey (limited by available foraging time, diving capabilities and thermoregulatory costs) and process that prey (limited by maximum digestion capacity and the time devoted to digestion). Failure to consume sufficient prey will have feedback effects on foraging, thermoregulation and digestive capacity through several interacting avenues. Energy deficits will be met through catabolism of tissues, principally the hypodermal lipid layer. Depletion of this blubber layer can affect both buoyancy and gait, increasing the costs and decreasing the efficiency of subsequent foraging attempts. Depletion of the insulative blubber layer may also increase thermoregulatory costs, which will decrease the foraging abilities through higher metabolic overheads. Thus, an energy deficit may lead to a downward spiral of increased tissue catabolism to pay for increased energy costs. Conversely, the heat generated through digestion and foraging activity may help to offset thermoregulatory costs. Finally, the circulatory demands of diving, thermoregulation and digestion may be mutually incompatible. This may force animals to alter time budgets to balance these exclusive demands. Analysis of these interacting processes will lead to a greater understanding of the physiological constraints within which the foraging behaviour must operate.

Adaptability of the digestive function according to age at weaning in the rabbit: II. Effect on nutrient digestion in the small intestine and in the whole digestive tract

The ability of young rabbits to digest a solid diet was evaluated according to the weaning age: 21 (W21, 12 litters) or 35 (W35, 12 litters) days of age. From 14 days onwards, the rabbits were fed the same pelleted feed. Three methods were compared to estimate the faecal digestibility in the young rabbits, between 24 to 28 and 38 to 42 days. Digestive balance at ileal and faecal levels was determined for the main nutrients provided by milk and solid feed. The W21 rabbits increased their solid feed intake only 2 days after their weaning, when compared with suckling rabbits. Thus, their crude protein (CP) intake remained lower until 26 days compared with the W35 rabbits (from 41%, P < 0.01), as well as their crude fat intake until 28 days (from 72%, P < 0.001). On the contrary, the W35 rabbits increased their solid feed intake without a delay after weaning, quickly reaching the intake level of the W21 rabbits. The amounts of organic matter (OM) and CP reaching the caecum were increased on day 28 by 56% and 42% in the W21 rabbits compared with the W35 rabbits, respectively (P < 0.05), and were similar between groups on day 42. Starch ileal digestibility coefficients were 94·2% and 95·4% in 28- and 42-day-old rabbits, respectively, irrespective of the weaning age. The amount of starch flowing through the ileo-caecal junction was low and only tended to be higher on day 28 in the W21 group (0.20 v. 0.15 g/day in the W35 group, P = 0.10). The digestive balance pointed out that the digestible energy intake was similar between weaned and suckling rabbits from 23 to 27 days, a phenomenon partly explained by a high ability of the W21 rabbits to digest starch (98%) and NDF (36%). Indeed, the amounts of starch and NDF digested by the W21 group were 2.0- and 2.4-fold higher than those of the W35 rabbits at this period (P < 0.001). However, they ate 20% less digestible proteins than still-suckling rabbits (P < 0.001). From 38 till 42 days, only a lower ability of the W21 rabbits to digest lipids was detected (P < 0.05). In conclusion, early-weaned rabbits were able to adapt quickly to digest large amounts of starch and fibres.

Maturation of the intestinal digestion and of microbial activity in the young rabbit: Impact of the dietary fibre:starch ratio

The developmental changes of intestinal digestive potential and caecal microbial activity were described in suckling and weaned rabbits according to two feeding programmes. Two groups of thirteen litters were fed from 18 to 42 days old a "High" or a "Medium" NDF:starch ratio diet (resp. 2.7 vs 2.0, groups HL and ML) with similar protein and lipid levels, and from 42 to 70 days old the two groups were fed a "Low" NDF:starch ratio diet (1.7). From 25 to 32 days (weaning), the milk and solid feed intake were 22% and 41% higher in ML group (P<0.05), and the mortality by diarrhoea was 4 units lower (P<0.01). The whole tract digestive efficiency increased by 10% before weaning, and remained steady (organic matter) or decreased (lipids, protein) after weaning. Energy digestibility was 0.623 and 0.686 for High and Medium diets respectively. From 25 to 42 days, total enzymatic activity in intestinal content increased for chymotrypsin (5-fold, P<0.001), lipase (10-fold, P<0.001), amylase (17-fold, P<0.01) and maltase (11-fold, P<0.001), while trypsin doubled after weaning. The feeding programme only affected the amylase and maltase activities, that were higher in HL group (P<0.05). The volatile fatty acids concentration in the caecum was not significantly different among the groups, but it increased by 44% 10 days after weaning. The bacterial fibrolytic enzymes, increased by 30% after weaning and were similar among the two groups. The study revealed that the intestinal digestive maturation and the caecal microbial activity of the rabbit evolved markedly between 3 and 5 weeks of age, and was weakly affected when the NDF:starch ratio decreased from 2.7 to 2.0.

Disaccharidase activities in camel small intestine: Biochemical investigations of maltase–glucoamylase activity

Disaccharidases (maltase, cellobiase, lactase, and sucrase), alpha-amylase, and glucoamylase in the camel small intestine were investigated to integrate the enzymatic digestion profile in camel. High activities were detected for maltase and glucoamylase, followed by moderate levels of sucrase and alpha-amylase. Very low activity levels were detected for lactase and cellobiase. Camel intestinal maltase-glucoamylase (MG) was purified by DEAE-Sepharose and Sephacryl S-200 columns. The molecular weight of camel small intestinal MG4 and MG6 were estimated to be 140,000 and 180,000 using Sephacryl S-200. These values were confirmed by SDS-PAGE, where the two enzymes migrated as single subunits. This study encompassed characterization of MGs from camel intestine. The Km values of MG4 and MG6 were estimated to be 13.3 mM and 20 mM maltose, respectively. Substrate specificity for MG4 and MG6 indicated that the two enzymes are maltase-glucoamylases because they catalysed the hydrolysis of maltose and starch with alpha-1,4 and alpha-1,6 glycosidic bonds, but not sucrose with alpha-1,2 glycosidic bond which was hydrolyzed by sucrase-isomaltase. Camel intestinal MG4 and MG6 had the same optimum pH at 7.0 and temperature optimum at 50 degrees C and 40 degrees C, respectively. The two enzymes were stable up to 50 degrees C and 40 degrees C, followed by strong decrease in activity at 60 degrees C and 50 degrees C, respectively. The effect of divalent cations on the activity of camel intestinal MG4 and MG6 was studied. All the examined divalent cations Ca(2+), Mn(2+), Mg(2+), Co(2+) and Fe(3+) had slight effects on the two enzymes except Hg(2+) which had a strong inhibitory effect. The effect of different inhibitors on MG4 and MG6 indicated that the two enzymes had a cysteine residue.

Phenotypic flexibility of digestive morphology and physiology of the South American omnivorous rodent Akodon azarae (Rodentia: Sigmodontinae)

We have determined the occurrence of responses at different levels (morphological, physiological and biochemical) in the omnivorous rodent Akodon azarae upon cold acclimation (15 degrees C). A short-term enhancement in food consumption appeared to account for the maintenance of both mass and body composition. At the morphological level, the main response was an increase in the dimensions of small intestine, which constitutes the section of the gut where absorption and secretion take place. An increase in sucrase specific activity was only found in small intestine. Sucrose independent maltase activity was very low since 99.8% of total maltase activity was due to sucrase-isomaltase (SI) complex. Protease specific activities were not affected. The fact that resting metabolic rates determined at 15 and 23 degrees C were similar in cold acclimated animals suggests a change in lower critical temperature. In conclusion, our results show that A. azarae exhibits different strategies to support cold environment that could lead to an enhancement in digestion and absorption efficiency. Furthermore, this work suggests that low temperature is an independent cue of other environmental factors to trigger the strategies allowing the maintenance of body condition in A. azarae.