Does release of encapsulated nutrients have an important role in the efficacy of xylanase in broilers?

The non-starch polysaccharides (NSPs) in cell walls can act as a barrier for digestion of intracellular nutrients. This effect is called "cage effect." Part of the success of fibrolytic enzymes in broiler feed is assumed to be attributed to cage effect reduction. Further, changes in viscosity and potential prebiotic action should also be considered. The aim of this study was to gain insight into the relative importance of the cage effect in xylanase efficacy in broilers. Using a 2×2 factorial design, 24 pens with 30 Ross 308 male chicks were fed corn-soy based diets consisting of normal and freeze-thawed (5 d at -18°C) corn, both with and without xylanase. The freeze-thaw method was used to eliminate the cage effect, whereas a corn-based diet was used to exclude viscosity effects. Body weights (BW), feed intake (FI), and feed conversion ratio (FCR) were determined at d 13, 26, and 39. A balance study was executed at the end of the growing phase. These birds were euthanized at d 34 (non-fasted) to determine the viscosity of digesta, blood metabolites, intestinal morphology, and microbiota composition. During the finisher period, there was a significant interaction between enzyme supplementation and freeze-thawing for FCR, in which FCR was improved by freeze-thawed corn and tended to be improved by normal corn+enzyme compared with the control group. The improvement in performance (finisher period) of freeze-thawed corn and xylanase coincided with increased gut absorption of glucose (based on postprandial plasma concentrations) and increased number of Clostridiumcluster IV in the caecum, and agreed with the higher gut villus height. In addition, xylanase inclusion significantly increased the postprandial plasma glycine and triglycerides concentration, and led to elevated bacterial gene copies of butyryl CoA:acetate CoA-transferase, suggesting a prebiotic effect of xylanase addition through more than just the cage effect reduction. The applied model managed to rule out viscosity by using corn, and it was possible to isolate the cage effect by freeze-thawing the dietary corn.

Changes in egg quality traits during the last phase of production: is there potential for an extended laying cycle?

1. A field study was conducted to investigate the deterioration of eggshell quality at the end of lay and examine the potential to extend the production cycle. A total of 1200 eggs were assessed originating from commercial farms in Belgium: eggs were random sampled at the collection belt at 57-65 weeks of age and at the end of the production cycle (74-92 weeks). 2. Based on a linear mixed model, egg quality was estimated for an average flock at 60 weeks of age and changes in quality traits were predicted until the end of the laying cycle. 3. Egg weight increased by 0.07 g every week from 60 weeks of age onwards and shape index decreased by 0.04 unit weekly (P < 0.001). Haugh unit values decreased weekly by 0.38 units whereas relative yolk weight was unaffected after 60 weeks of age. Relative albumen weight showed a weekly increase of 0.02% and relative shell decreased by 0.02% weekly until the end of lay. 4. Shell quality traits were also influenced by age: shell index decreased by 0.013 g weekly, shell thickness was calculated to be 0.23 µm thinner every week, deformation increased by 0.06 µm weekly from 60 weeks to the end of the laying cycle. Variability of the deformation of eggs indicated more heterogeneous shell quality at the end of the production cycle. Dynamic stiffness increased from 60 weeks of age on. 5. Laying hens were depopulated on average at 80 weeks of age (varying from 74-92 weeks). Although ageing had a significant effect on most of the egg quality traits, egg quality was still acceptable at the end of lay, indicating the potential to extend the laying cycle.

Effects of Xylo-Oligosaccharides on Broiler Chicken Performance and Microbiota.

In broiler chickens, feed additives, including prebiotics, are widely used to improve gut health and to stimulate performance. Xylo-oligosaccharides (XOS) are hydrolytic degradation products of arabinoxylans that can be fermented by the gut microbiota. In the current study, we aimed to analyze the prebiotic properties of XOS when added to the broiler diet. Administration of XOS to chickens, in addition to a wheat-rye-based diet, significantly improved the feed conversion ratio. XOS significantly increased villus length in the ileum. It also significantly increased numbers of lactobacilli in the colon and Clostridium cluster XIVa in the ceca. Moreover, the number of gene copies encoding the key bacterial enzyme for butyrate production, butyryl-coenzyme A (butyryl-CoA):acetate CoA transferase, was significantly increased in the ceca of chickens administered XOS. In this group of chickens, at the species level, Lactobacillus crispatus and Anaerostipes butyraticus were significantly increased in abundance in the colon and cecum, respectively. In vitro fermentation of XOS revealed cross-feeding between L. crispatus and A. butyraticus. Lactate, produced by L. crispatus during XOS fermentation, was utilized by the butyrate-producing Anaerostipes species. These data show the beneficial effects of XOS on broiler performance when added to the feed, which potentially can be explained by stimulation of butyrate-producing bacteria through cross-feeding of lactate and subsequent effects of butyrate on gastrointestinal function.

Consequences of phosphorus interactions with calcium, phytase, and cholecalciferol on zootechnical performance and mineral retention in broiler chickens.

The objective was to determine the effect of calcium (Ca), total phosphorus (Ptot), cholecalciferol, and phytase level in the diet on the performance, tibia ash percentage, and Ca and P retention in broilers until slaughter age. Broilers were randomly assigned to 12 treatments, each with 6 replicates, comprising 3 diets differing in Ca and P level: 1) normal Ca and Ptot level (NN); 2) normal Ca and low Ptot level (NL), 3) low Ca and Ptot level (LL). Broilers were also given 2 levels of cholecalciferol and 2 levels of phytase. The normal levels of Ca and Ptot for the starter, grower, and finisher phases were 0.90, 0.82, 0.74% and 0.67, 0.62, 0.57%, respectively. The low Ca and Ptot levels for the 3 phases were 0.67, 0.60, 0.52% and 0.57, 0.51, 0.46%, respectively. Broilers of the NL treatment obtained the lowest BW, whereas BW of the NN and LL groups were comparable. Cholecalciferol significantly affected the BW, with differences up to 2.6 and 1.2% for the starter and grower phases, respectively. The highest cholecalciferol effect was found in combination with the NN treatment. The percentage of retained Ca increased from 33% to 41% and 48% when the imbalanced diet was replaced by the NN and LL balanced diets, respectively. P release from phytate was 64 and 67% for the NL and LL diets, respectively. Phytase and cholecalciferol had significantly favorable effects on retention values but these effects were dependent on Ca and Ptot levels and their ratio. In conclusion, both diets with the balanced Ca/Ptot ratio resulted in the best performance, highest tibia ash percentage and P release from phytate. A reduction of the Aviagen (2009) recommended P requirements by 25 to 30% and Ca by 15 to 20% over the various phases did not negatively affect performance, bone development, and improved Ca and Ptot retention. The effects of supplementing cholecalciferol and phytase were additive but not significant and no synergism between both was present.

Supplementation of guanidinoacetic acid to broiler diets: effects on performance, carcass characteristics, meat quality, and energy metabolism.

Creatine, (CREA) a central constituent in energy metabolism, is obtained from dietary animal protein or de novo synthesis from guanidinoacetic acid (GAA). Especially in all-vegetable diets, supplemental CREA or GAA may restore the CREA availability in tissues, and hence, improve performance. In this study, 768 one-d-old male Ross 308 broilers were assigned to 1 of 4 diets: negative control, all-vegetable corn-soybean-based; negative control supplemented with either 0.6 or 1.2 g of GAA per kilogram of feed; and positive control (60, 30, and 30 g/kg of fish meal in the starter, grower, and finisher diets, respectively). Each treatment was replicated in 6 pens of 32 birds each. At the end of the grower period (d 26), 2 birds per pen were euthanized for metabolic measurements. Four broilers per pen were selected at slaughter age (d 39) to determine carcass characteristics and meat quality. Compared with the negative control, GAA supplementation resulted in an improved gain:feed ratio (P < 0.05) and ADG (P < 0.05; + 2.7 and + 2.2% for GAA at 0.6 and 1.2 g/kg, respectively) throughout the entire period. Breast meat yield was higher for the GAA diets compared with that of the negative control birds (P < 0.05; 30.6 vs. 29.4%) and was comparable with that of the positive control birds (30.2%). With regard to meat quality, lower ultimate pH values, higher cooking and press fluid losses, and higher color L* values were observed for the GAA diets compared with those of the negative control diet (P < 0.05). These effects were small, however. The GAA and CREA levels in breast meat were lower and higher, respectively, in GAA-fed birds compared with those of the control birds (P < 0.01). The diets did not affect plasma metabolic traits, except that plasma insulin-like growth factor I concentrations were almost twice as high in animals fed 1.2 g/kg of GAA compared with those of all other treatments. The GAA included in all-vegetable diets improved animal performance for the whole rearing period and increased breast meat yield.

Quality and lipid composition of spermatozoa in rabbits fed DHA and vitamin E rich diets.

The effects of fish oil (FO) and vitamin E (vE) dietary supplementation on semen quality, sperm susceptibility to lipid peroxidation, tocopherols content and fatty acid profiles were studied in rabbits. Fifty-two rabbit bucks randomly divided in four groups received a control diet and enriched diets containing either FO (1.5%, w/w), vE (200mg/kg) or both. Semen volume, concentration, motility and viability were analysed at various time-points and the lipid composition was assessed on sperm cells. The phospholipid fatty acid profile was determined: n-6 PUFA were the major fatty acids found, with a proportion of 42%, whereas the n-3 PUFA accounted for nearly 1%, mainly represented by C22:6n-3 (docosahexaenoic acid, DHA). FO supplementation produced a seven-fold increase in the content of DHA in sperm phospholipids and a comprehensive rearrangement of the phospholipid fatty acid composition, while an unexpected negative effect of feeding high level of vE on the proportion of total PUFA was found. Despite the remarkable changes observed in sperm lipid composition, semen quality parameters were not affected by the dietary treatments and the interaction between the two dietary supplements had a significant effect only on sperm concentration. An increase in semen production by ageing and a concomitant rise in sperm susceptibility to in vitro peroxidation was found. alpha- and delta-tocopherol, present in rabbit sperm in similar amount, were not affected by dietary treatment. delta-tocopherol content had a significant linear negative regression with age and showed a significant negative correlation with the susceptibility to peroxidation values.

Can choice feeding improve performances and N-retention of broilers compared to a standard three-phase feeding schedule?

1. An experiment was conducted to investigate if broilers can improve their performances and N-retention using choice feeding (CF). 2. Treatment 1 consisted of a standard three-phase feeding regime (SF). Treatments 2-7 were CF treatments with a high (HP) and a low protein (LP) feed offered simultaneously to the birds. Choice feeding started at day 1 or 8 and feeds were offered in mash form or as pellets. 3. When choice feeding was started at day 1 and the HP diet was mash, growth rates were increased (+4.2%) compared to SF, whereas all other CF treatments showed similar or significantly lower final body weights compared to SF. Feed conversion was increased for all CF strategies. 4. Highest yield and breast meat percentages were obtained if the low protein diet was pelleted. The amount of N excreted was increased for most choice feeding treatments as a result of the increased N-intakes and the less efficient growth. 5. Broilers were able to make a choice between two feeds differing in protein/amino acid contents starting as early as day 1, but choices were influenced by feed form. The results confirmed that very high protein/amino acid concentrations in the starter period are desirable to improve growth rates in fast-growing chickens.

Effect of feed restriction timing on live performance, breast myopathy occurrence, and muscle fiber degeneration in 2 broiler chicken genetic lines.

During recent years, research on meat quality in poultry has aimed to evaluate the presence and consequences of breast myopathies as well as the factors which can affect their occurrence by modifying the growth rate. A total of 900 broiler chickens were reared until slaughter (48 D) to evaluate the effect of 2 genetic lines (A vs. B) and feeding plans (ad libitum [AL], early restricted [ER], from 13 to 23 D of age, and late restricted [LR], from 27 to 37 D of age; restriction rate: 80%) on performance, meat quality, and breast muscle myopathies. Calsequestrin and vascular endothelial growth factor (VEGF) expressions, and muscle fiber degeneration (MFD) were recorded at 22, 36, and 48 D. Chickens in the AL treatment had greater final live (P < 0.01) and carcass weights and proportion of pectoralis major muscle (P = 0.04) compared to chickens in the LR treatment, whereas chickens in the ER treatment had intermediate final live (3,454 g) and carcass weights, and proportion of pectoralis major muscle (25.6%). Chickens of line A were heavier than chickens of line B (P < 0.001), and had a greater feed conversion rate. Chickens of line A also had a greater dressing out percentage (P < 0.001), but a lower proportion of pectoralis major muscle (P = 0.04), as well as a greater meat pH (P < 0.001), meat cooking losses (P < 0.01), and shear force of the pectoralis major muscle (P = 0.03). Calsequestrin and VEGF mRNA were significantly lower in ER and LR chickens compared to AL chickens after feed restriction and during refeeding (P < 0.05). MFD scores increased with chicken age (P < 0.001) and differed between genetic lines (P < 0.001). Neither feeding plan nor genetic line affected the occurrence of white striping or wooden breast condition.

Effect of different split-feeding treatments on performance, egg quality, and bone quality of individually housed aged laying hens.

In order to try to combat the effect of age on eggshell quality in aged laying hens, 5 split-feeding treatments were compared with conventional feeding between 75 and 92 wk of age. In the conventional treatment (T1), the same morning (M) and afternoon (A) diet was fed containing fine (FL) and coarse (CL) limestone at a 50:50 ratio. In the split treatments, the ratio of FL and CL was 50:50 or 30:70, and time of administration (M/A) differed. The following treatments were given: T2 = 50FL-M:50CL-A, T3 = 50CL-M:50FL-A, T4 = 30FL-M:20FL-A+50CL-A, T5 = 30FL-M:70CL-A, and T6 = 0M:30FL-A+70CL-A. A total of 12 individually housed Dekalb white hens was used per treatment. Feed intake, nutrient intake, and laying % was lower in T1 compared to all split treatments (P ≤ 0.001). Due to this low performance in T1, split feeding could not be compared to the conventional system in this trial. By the end of the trial, eggshell quality was improved in T1 as a result of low laying % and more frequent and longer laying pauses. In the split treatments, laying % and feed intake were similar, except in T3 in which a decrease was observed after 81 wk (P ≤ 0.05). Egg weight was higher in T5 and T6 due to higher total and morning protein intake compared to T3 (P ≤ 0.05). Feeding only 50FL-A in T3 not only resulted in lower performance but also in consistently lower shell thickness, indicating a negative effect of suboptimal limestone supplementation. In the split-feeding system, the most optimal combination of morning and afternoon diet was a morning diet with only FL and an afternoon diet with only CL (T2), which both provided ∼50% of the total daily Ca intake. Shell breaking strength and dynamic stiffness could be maintained on this diet between 75 and 92 weeks. Decreasing the amount of Ca in the morning and increasing it in the afternoon did not improve shell quality traits. Bone quality was not affected by limestone particle size or inclusion level in the split-feeding system.

Supplementation of fine and coarse limestone in different ratios in a split feeding system: Effects on performance, egg quality, and bone strength in old laying hens.

Different ratios of fine- (FL) and coarse limestone (CL) were compared (50FL:50CL, 30FL:70CL, 0FL:100CL) in conventional (C) and split feeding (S) for their effects on performance, egg quality traits, and bone quality of old, brown laying hens (72 to 83 wk). Each treatment consisted of 42 hens (7 hens × 6 replicates). In the C system diets supplemented with limestone were provided during the whole day, whereas in the S system a morning diet was fed without added limestone, and only the afternoon diet was supplemented with different limestone ratios. Highest laying %, egg mass, and lowest feed conversion were found in the C system with 50FL:50CL and 0FL:100CL and in the S system with 30FL:70CL between 76 and 79 wk (P ≤ 0.001). Reduced cracked egg % was found when 0FL:100CL was supplemented in the C system and 30FL:70CL in the S system between 72 and 83 wk (P ≤ 0.001). Tibia ash content was higher in the S system compared to the C system (P = 0.005); tibia breaking strength, however, did not differ between feeding systems. Egg quality traits were not improved by S feeding. However, at 83 wk, S feeding resulted in higher breaking strength, but lower shell thickness compared to the C system (P = 0.036, P ≤ 0.001, respectively). Therefore, hens in the S feeding system might have been able to form a structurally superior shell compared to the C system. For further investigation, instead of restricting limestone supplementation solely to the afternoon, it might be a better approach to provide FL and CL at a different time of the d in a split feeding system to improve shell quality in old, brown laying hens in an extended production cycle.

Cutaneous staphylococcosis in rabbits.

An outbreak of cutaneous staphylococcosis caused high mortality among newborn and very young rabbits. The most typical lesions were exudative dermatitis in the youngest, subcutaneous abscesses in rabbits of all ages and mastitis in lactating does. Generalised staphylococcosis was a frequent secondary manifestation of the disease.

Evaluation of the energy value of rabbit feeds: a critical review.

An analysis is given of the methods actually used for the determination and calculation of the energy value of rabbit feeds and feedstuffs. The apparent digestible energy (DE) system is recommended. Standardization of the applied methodology for in vivo determination is emphasized. Four to six ad libitum fed growing rabbits are necessary to obtain sufficiently accurate results. The reliability of the estimation of the feeds' energy content, based on the table values of the ingredients, is discussed. The importance of using recently and properly determined data is stressed. Multiple regression equations, based on the results of the chemical analysis of feeds, explain 85-90% of the variability of DE content. The first attempts with in vitro techniques are encouraging.

Effect of double nursing on some anatomical and physiological properties of the digestive tract of rabbits between 23 and 44 days of age.

Anatomical and physiological properties of the digestive tract were examined and compared in young rabbits nursed either by one (SS) or by two does (DD) daily up to the age of 35 days. At the age of 23, 30, 37 and 44 days, 8 young per treatment were euthanised. Double suckling and the subsequent higher level of solid feed intake after weaning were found to exert a stronger influence on the weight of the entire gastrointestinal tract and that of its individual parts (the stomach, small intestine, caecum and colon) than on its length. The quantity of the gastric content was found to rise with advancing age in both groups (from 36 to 70 g and from 37.5 to 79 g). In both groups the pH of the stomach was higher during the suckling period (4.5-5.3) than subsequent to weaning (1.6-2.4). The quantity of the caecal content also increased with age (from 4 or 8 g), but on the 37th day significantly higher quantities of caecal content were recorded in DD rabbits (50.5 g compared with 35 g). The pH of the caecal content decreased more slowly from an initial high value (6.0 and 6.5 in SS and DD rabbits, respectively), and by the 37th day had settled at a low value (5.7-5.8) in both groups. The dry matter content of the caecal content decreased from 270-273 g to 188-207 g in both groups. Total volatile fatty acid (tVFA) and acetic acid (C2) concentration, which amounted to 66-88% of tVFA, rose; in SS rabbits they were at higher levels by the 30th day (53.6 and 42.2 mmol/L, respectively), and remained at an increased level until the 44th day (P < 0.05). The ratio of C3: C4 was high on the 23rd day (2.5 and 2.4), but dropped at the age of 30 days (0.5 in SS and 1.7 in DD, P < 0.05) and, further, by the 37th day (0.2 in SS). In SS rabbits coliform count proved significantly lower (10(5)) on the 23rd day than in DD rabbits (10(6)). By the 37th day this count had decreased in both groups and subsequently remained at a low level (< 10(4)). By the 23rd day Bacteroides were present in large quantities (10(8)) in the caecum and showed no change with advancing age or feeding regime.

Effects of semi-group housing and floor type on pododermatitis, spinal deformation and bone quality in rabbit does.

The most common housing system for reproduction rabbits, individual cage housing on a wire floor, is increasingly scrutinized because of its potential detrimental impact on animal welfare. We compared three types of housing: (1) individual cage housing on a wire floor (3952 cm2/doe, maximum roof height 63 cm, one 1000 cm2 plastic footrest/doe), (2) semi-group housing on a wire floor (5000 cm2/doe, roofless, one 1000 cm2 plastic footrest/doe) and (3) the same semi-group housing, but with a fully plastic slatted floor. In all housing systems, does had free access to an elevated platform. In the semi-group housing pens, four does were housed communally during 21 days of the reproduction cycle (to allow more space for locomotion and to increase opportunities for social contact), and individually during the other 21 days of the cycle (to minimize doe-doe and doe-kit aggression that peaks around kindling). In all, 24 Hycole does were included per system. The does entered the experiment at 203 days of age (after their first parity). The experiment consisted of four reproductive cycles, ending at 369 days of age. Pododermatitis was scored in cycles 1, 2 and 4. At the end of the 4th cycle the does were euthanized and X-rays were taken to assess spinal deformation. Tibia and femur length, width and cortical thickness were determined and bone strength was assessed using a shear test, as a measure of bone quality. Although severe pododermatitis was absent, the prevalence of plantar hyperkeratosis (hair loss and callus formation) at the end of the 4th cycle was much greater on the wire floor (65% and 68% for semi-group housing and individual cages, respectively) than on the plastic floor (5%, P<0.0001), even though the wire floors were equipped with a plastic footrest known to decrease hyperkeratosis. In contrast to our expectations, semi-group housing did not affect the prevalence of spinal deformations (P>0.10), but in line with our expectations bone quality was affected favourably by semi-group housing. The tibial cortex (and to a lesser extent the femoral cortex) was thicker in semi-group housing than in individual cages (1.45, 1.46 and 1.38 mm for semi-group housing on wire, semi-group housing on plastic and individual housing on wire, respectively, P=0.045). What this increase in cortical thickness means in terms of doe welfare requires further study, as it may reflect an increase in activity resulting either from increased space for locomotion, or from fleeing aggressive pen mates.

Measuring fluctuating asymmetry in fattening rabbits: a valid indicator of performance and housing quality?

Fluctuating asymmetry (FA) has been advocated as the preferred measure of developmental instability and a reliable indicator of the quality of an animal (performance/fitness) and of its environment during its growing life. Empirical studies, however, are too scant or equivocal to consider this assumption adequately validated, which is partly due to the lack of a robust methodological framework for collecting and analyzing FA data. Therefore, we conducted an experiment in which 306 weaned rabbits were housed either in welfare-friendly pens (n = 6) or barren pens (n = 6). The size of both types of pen was similar (1.91 m2), but the welfare-friendly pens were equipped with suitable enrichment material (gnawing stick, elevated platform, and hiding box) and were stocked with one-half of the number of rabbits compared with the barren pens (17 vs. 34 rabbits per pen). Performance data (BW gain, ADFI, and G:F) were collected every 14 d. After slaughter (d 63 to 72), we measured twice the left- and right-hand side of 11 presumed bilateral traits on intact carcasses and 50 traits on fleshed bones. Using a stringent decision process, an optimal combination of morphological traits for estimating FA in fattening rabbits was determined. This combination consisted of five traits (fleshed bones) that showed no directional asymmetry or antisymmetry and showed a high level of FA relative to the measurement error; also, these traits were not correlated in their signed FA values. Measurements on intact carcasses seemed inappropriate for estimating FA. Using this robust FA measuring protocol, rabbits housed in the welfare-friendly pens were less asymmetric than were rabbits from the barren pens. Except for a greater daily BW gain in the welfare-friendly pens during the first 14 d after weaning, there were no effects of housing conditions on performance traits. The FA was negatively correlated with BW gain in rabbits from the barren pens, whereas in the welfare-friendly pens, there was no correlation. These results support the application of FA as an indicator of animal welfare and performance; however, FA seems to be a more reliable estimator of the underlying developmental instability when living conditions are suboptimal.

Age dependent variation of caecal contents composition of young rabbits.

In order to study the age dependent variation of caecal contents composition, a young rabbit was slaughtered out of 6 conventional litters at the age of 22; 25; 28; 32; 36; 42 and 56 days. Rabbits were fed a standard diet before and after weaning (at 28 days of age). Daily growth and caecum size were determined. Caecal contents were analyzed for dry matter (DM), pH, crude protein (CP), neutral detergent fibre (NDF), ribonucleic acid (RNA), lactate, ammonia nitrogen and volatile fatty acids (VFA). Between 22 and 25 days of age, a highly significant drop in CP content was found, associated with an increase in NDF content. RNA values tended to decrease with age, but it is striking that the RNA/CP ratio suggests that about 50% of CP is microbial N, very early in the development (22 days). No significant changes of ammonia nitrogen concentration with age were observed, and lactic acid concentration showed some significant changes, suggestive of a decrease after weaning. Total VFA concentration is suggestive of a progressive and significant (P < 0.01) increase reaching a plateau after 42 days (83.7 mmoles/kg). Molar proportions of propionate and butyrate varied significantly (P < 0.001) and inversely with age. Propionate drops by nearly 50% while butyrate proportion doubles between 22 and 56 days of age. The shift from a propionic to a butyric pattern occurs already at day 25. Correlation analysis revealed significant associations between CP-NDF and RNA. The significant negative correlation between pH and daily weight gain reflects the relation caecal pH-animal health. PH was correlated with lactate and VFA concentration.

In vitro study of the age-dependent caecal fermentation pattern and methanogenesis in young rabbits.

The caecal fermentation pattern, including methanogenesis, was studied in young rabbits using in vitro batch incubations. Six conventional litters of eight rabbits each were used. At the age of 22, 25, 28, 32, 36, 42 and 56 days, an animal was slaughtered from each litter and its caecal contents were used for in vitro batch incubations at 39 degrees C/24 h. The incubated samples were analysed for volatile fatty acids (VFA), methane, hydrogen, ammonia nitrogen (NH3-N) and lactic acid (LA). The net total in vitro VFA production did not differ clearly with age, although a significant decrease was observed on day 36, reflecting the reduced zootechnical performances probably related to an infection with Clostridium spiroforme that occurred in the same period. The molar proportions of butyrate and propionate formed a change in the opposite direction with age, starting with a sudden shift from propionate to butyrate at day 25. In vitro NH3-N production was suggestive of a progressive and significant decrease with age; in vitro LA production was always low. Methane production was almost absent from fermentation until 32 days of age, after which it suddenly shifted from 1.6 to 52.0 mumol/flask/day and increased further with age. A significant litter effect on methanogenesis was observed which suggested the existence of a genetic effect. The hydrogen production was quite low and decreased significantly from day 36 with increasing methanogenesis. The calculated hydrogen recoveries showed a gradual increase from day 32 and were positively correlated (r = 0.92) with methane production. In conclusion, it would seem that in young suckling rabbits, reductive acetogenesis is a major characteristic of caecal fermentation, to be replaced gradually and partially by methanogenesis with the increasing intake of solid feed.

Age and incubation time effects on in vitro caecal fermentation pattern in rabbits before and after weaning.

The caecal fermentation pattern was studied in four litters of rabbits. Rabbits were sequentially slaughtered at the age of 4 (before weaning), 6, 8 and 11 weeks. Their caecal contents were analyzed and incubated in vitro at 39 degrees C for 6 and 12 h. Net productions of short-chain fatty acids (SCFA), hydrogen and methane were determined. The average caecal weight increased three-times within two weeks after weaning, from 31.4 to 93.7 g. At the end of the experiment, the caecal weight was on average 134.4 g. A large variability of the SCFA concentration observed before weaning decreased after weaning. Measurements of caecal metabolite profiles and results of in vitro experiments indicated a certain decrease of propionate in favour of butyrate, associated with the weaning. The establishment of methanogens in rabbits was slow. Methanogenesis started in one out of four rabbits at the age of 6 weeks. Five weeks later, one of four rabbits still did not produce methane. The hydrogen recovery decreased between the 4th and the 6th week of age, due to the increase of the butyrate/propionate ratio. After the 6th week, the hydrogen recovery increased with age, apparently because of the increase in methane production. Hydrogen recovery tended to increase during incubation, suggesting a decrease of reductive acetogenesis. This increase was observed both in methanogenic and non-methanogenic rabbit caecal cultures. In former cultures, the ratio CH4/SCFA rose with time of incubation.