Comparative fibre-degrading capacity in foals at immediate and late post-weaning periods.

Total tract apparent digestibility of dietary fibrous components and parameters of the faecal digestive ecosystem were compared at immediate and late post-weaning periods using five foals. The foals were abruptly weaned (day 0) from their mares at 6 months of age. Immediately (day 0 to day 14) and later (day 131 to day 194) after weaning, foals received the same basal diet consisting of hay and pellets. Pellets were fed at 0.36% BW. Hay was offered ad libitum and corresponded to 120% of the average voluntary hay intake measured individually during the immediate (days 1 to 4) and late (days 180 to 183) post-weaning periods. Total feed intake was measured during the two post-weaning periods (from days 7 to 10 and from days 187 to 190). Total tract apparent digestibility of DM, organic matter (OM), NDF and ADF was assessed using a 4-day partial collection of faeces (from days 8 to 11 and from days 188 to 191). Major bacterial groups in faeces, Fibrobacter succinogenes, DM, pH and volatile fatty acids were quantified at days -1, 1, 3, 7, 14 and 180. During the post-weaning period, minor changes were observed in the composition and activity of the faecal microbiota. The amylolytic count in faeces decreased immediately after weaning (between days 1 and 7) (P<0.05). Later (from days 14 to 180), the molar proportion of propionate decreased (P=0.03). The limited alteration seen in the hindgut ecosystem was probably due to the fact that the foals had undergone a gradual dietary transition from milk to solid feed before weaning. Such conclusions have also been reported in other animal species. Between the immediate and late post-weaning periods, the average daily feed intake and the digestibility coefficients of DM, OM, NDF and ADF increased (P<0.05). These results could suggest an increase in the fibre-degrading capacity of foals after weaning.

Effects of bacterial direct-fed microbials on ruminal characteristics, methane emission, and milk fatty acid composition in cows fed high- or low-starch diets.

This study investigated the effects of bacterial direct-fed microbials (DFM) on ruminal fermentation and microbial characteristics, methane (CH4) emission, diet digestibility, and milk fatty acid (FA) composition in dairy cows fed diets formulated to induce different ruminal volatile fatty acid (VFA) profiles. Eight ruminally cannulated dairy cows were divided into 2 groups based on parity, days in milk, milk production, and body weight. Cows in each group were fed either a high-starch (38%, HS) or a low-starch (2%, LS) diet in a 55:45 forage-to-concentrate ratio on a dry matter (DM) basis. For each diet, cows were randomly assigned to 1 of 4 treatments in a Latin square design of (1) control (CON); (2) Propionibacterium P63 (P63); (3) P63 plus Lactobacillus plantarum 115 (P63+Lp); (4) P63 plus Lactobacillus rhamnosus 32 (P63+Lr). Strains of DFM were administered at 1010 cfu/d. Methane emission (using the sulfur hexafluoride tracer technique), total-tract digestibility, dry matter intake, and milk production and composition were quantified in wk 3. Ruminal fermentation and microbial characteristics were measured in wk 4. Data were analyzed using the mixed procedure of SAS (SAS Institute Inc., Cary, NC). The 2 diets induced different ruminal VFA profiles, with a greater proportion of propionate at the expense of acetate and butyrate for the HS diet. Greater concentrations of total bacteria and selected bacterial species of methanogenic Archaea were reported for the HS diet, whereas the protozoa concentration in HS decreased. For both diets, bacterial DFM supplementation raised ruminal pH (+0.18 pH units, on average) compared with CON. Irrespective of diet, P63+Lp and P63+Lr increased ruminal cellulase activity (3.8-fold, on average) compared with CON, but this effect was not associated with variations in ruminal microbial numbers. Irrespective of diet, no effect of bacterial DFM on ruminal VFA was observed. For the LS diet, supplementing cows with P63+Lr tended to decrease CH4 emission (26.5%, on average, when expressed per kilogram of milk or 4% fat-corrected milk). Only P63 supplementation to cows fed the HS diet affected the concentration of some milk FA, such as cis isomers of 18:1 and intermediates of ruminal biohydrogenation of polyunsaturated FA. Overall, bacterial DFM could be useful to stabilize ruminal pH. Their effects on CH4 production mitigation and milk FA profile depended on DFM strain and diet and should be confirmed under a greater variation of dietary conditions.

Faecal parameters as biomarkers of the equine hindgut microbial ecosystem under dietary change.

Faeces could be used for evaluating the balance of the equine hindgut microbial ecosystem, which would offer a practical method for assessing gut health and how this relates to disease. However, previous studies concluded that faeces microbial ecosystem was not representative of the proximal hindgut (caecum and ventral colon). This study aimed to evaluate if variations of the faecal microbial ecosystem were similar to those observed in the proximal hindgut. Six horses, fistulated in the caecum and right ventral (RV) colon, were subjected to a gradual change of diet, from a 100% hay (high fibre) diet (2.2 DM kg/day per 100 kg BW) to a 57% hay+43% barley (high starch) diet (0.8 DM kg/day per 100 kg BW hay and 0.6 DM kg/day per 100 kg BW barley). The two diets were iso-energetic and fed over a 3-week trial period. Samples of digesta from the caecum, RV colon and faeces were collected two times on the 10th and 20th day of the trial, for each diet to assess the microbial ecosystem parameters by both classical culture technics and biochemical methods. The variations observed in the caecal and colonic bacterial composition (increase in total anaerobic, amylolytic and lactate-utilizing and decrease in cellulolytic bacteria concentrations) and microbial activity (changes in volatile fatty acids concentrations and increase in lactate concentrations) demonstrated that the hay+barley diet caused changes in the hindgut microbial ecosystem. Similar variations were observed in the faecal microbial ecosystem. Feeding the hay+barley diet resulted in higher concentrations of faecal lipopolysaccharides. The functional bacterial group concentrations (cellulolytics, amylolytics and lactate utilizers) were significantly correlated between caecum and faeces and between colon and faeces. From analyses of the metabolites produced from microbial activity, only valerate concentration in the caecum and the proportion of propionate were significantly correlated with the same parameters in the faeces. Results of the principal component analysis performed between all the caecal/faecal and colonic/faecal parameters revealed that the total anaerobic and cellulolytic bacteria concentrations, as well as valerate, l-lactate and lipopolysaccharide concentrations were strongly correlated with several microbial parameters in the caecum (P|0.45|) and in the colon (P|0.50|). This demonstrated that faecal samples and their bacterial analyses could be used to represent caecum and RV colon hindgut microbial ecosystem in terms of variations during a change from a high-fibre to a high-starch diet, and thus could be markers of particular interest to diagnostic proximal hindgut microbial disturbances.

Effect of concentrate feeding sequence on equine hindgut fermentation parameters.

Feeding a diet with a small amount of hay and a high proportion of concentrate given in large meals entails a risk of colic to horses as this can impact the hindgut microbial ecosystem. To counteract this potential negative effect, one feeding strategy is to modify the distribution sequence of concentrate and hay. The purpose of the present study was to assess the impact of feeding the concentrate meal before or with the hay meal on fermentative parameters postprandial variations in caecum and right ventral colon contents and faeces. We focused on the comparison of pH value and volatile fatty acid (VFA) concentrations between the three compartments. Four horses fitted with two cannulas in the caecum and right ventral colon were fed a 100% hay diet (H) for a 3-week period, and then a 40% concentrate-60% hay diet for two consecutive periods of 3 weeks each. Concentrate and hay were offered simultaneously in two equal meals at 0800 and 1700 h (HC1) during one period, or separately in two equal meals at 0800 and 1600 h for the concentrate and at 1000 and 1730 h for hay (HC2) during the second one. During the 2nd week of each diet period (H, HC1, HC2), caecal, right ventral colonic and faecal samples were collected before (0) and at 2, 4, 6 and 8 h after the morning meal. pH values and VFA concentrations were measured. Adding concentrate to the hay was associated with a decrease of pH value in the caecum, right ventral colon and faeces and an increase of faecal VFA concentrations (P<0.01). An impact of the concentrate feeding sequence was observed on caecal pH and faecal propionate concentration (P<0.001) but none on the other parameters investigated. In the caecum and right ventral colon, pH values decreased and VFA concentrations increased within the range of 4 to 8 h after the morning meal. Our data suggested that the variation of faecal pH could be an indicator of those of the caecal and right ventral colonic pH with a delay of 2 h. The present study showed that hay and commercial pelleted could be safely distributed simultaneously, thus making easier every day horse feeding.

Impact of barley form on equine total tract fibre digestibility and colonic microbiota.

This study aimed at assessing the impact of four barley forms on total tract apparent digestibility of dietary fibre in horses fed a large amount of starch in the morning meal (0.27% BW). Processed barley forms had a greater pre-caecal starch digestibility than the whole form. Based on this result, we hypothesised that using barley-processing methods would limit the potential dumping of undegraded starch in the hindgut of horses and, consequently, the potential negative effect on fibre degradation in the hindgut. In a 4×4 latin square design, four mature geldings fitted with a right ventral colon-fistula were fed a meadow hay : concentrate (62 : 38; dry matter (DM) basis) diet at 1.7% BW. The concentrate was made of 80% barley distributed either as whole grain or as processed forms: 2.5 mm ground, pelleted or steam-flaked. For each period, total tract apparent digestibilities of DM, NDF and ADF were determined over 3 consecutive days by total faecal collection, whereas pH, volatile fatty acids (VFA) concentrations and cultural functional bacteria counts (total anaerobic, cellulolytic bacteria, lactic acid producers, amylolytic bacteria and lactic acid utilisers) in colonic content were evaluated on 1 day 4 h after the morning meal. Total tract apparent digestibility of DM and dietary fibre was influenced (P<0.05) by barley form. Diets including thermo-mechanically treated barley forms led to a higher (P<0.05) total tract apparent digestibility of NDF than those constituted of ground barley and also led to a greater (P<0.05) total tract apparent digestibility of ADF than those made of whole or ground barley forms. However, no significant difference was observed in colonic pH, VFA concentrations and cultural bacteria concentrations. Owing to a high starch supply in the morning meal, the concentration of the functional bacteria in the colonic content averaged 7.8 log CFU/ml, 5.9 NPM/ml, 6.9 and 7.3 CFU/ml for total anaerobic, cellulolytic, amylolytic and lactic acid-utilising bacteria, respectively. Consequently, providing horses with pelleted or steam-flaked instead of ground barley forms may limit the negative impact of starch on fibre digestibility in horses fed a high level of starch in the morning meal (0.27% BW). Moreover, the fibre-to-starch ratio fed in this experiment did not cause any digestive upset.

Comparison of the bacterial community structure within the equine hindgut and faeces using Automated Ribosomal Intergenic Spacer Analysis (ARISA).

The horse's hindgut bacterial ecosystem has often been studied using faecal samples. However few studies compared both bacterial ecosystems and the validity of using faecal samples may be questionable. Hence, the present study aimed to compare the structure of the equine bacterial community in the hindgut (caecum, right ventral colon) and faeces using a fingerprint technique known as Automated Ribosomal Intergenic Spacer Analysis (ARISA). Two DNA extraction methods were also assessed. Intestinal contents and faeces were sampled 3 h after the morning meal on four adult fistulated horses fed meadow hay and pelleted concentrate. Irrespective of the intestinal segment, Principal Component Analysis of ARISA profiles showed a strong individual effect (P<0.0001). However, across the study, faecal bacterial community structure significantly (P<0.001) differed from those of the caecum and colon, while there was no difference between the two hindgut communities. The use of a QIAamp(®) DNA Stool Mini kit increased the quality of DNA extracted irrespective of sample type. The differences observed between faecal and hindgut bacterial communities challenge the use of faeces as a representative for hindgut activity. Further investigations are necessary to compare bacterial activity between the hindgut and faeces in order to understand the validity of using faecal samples.

Effect of physical training on nutrient digestibility and faecal fermentative parameters in Standardbred horses.

This study aimed at evaluating, in previously inactive Standardbreds horses, the effect of 5 weeks of an exercise training programme on nutrient digestibility and faecal fermentative parameters (FFPs). As an increase in digestibility had previously been reported in trained endurance horses, we hypothesized that similar results would be found in horses being trained for other types of exercise on a different type of diet. After 3 weeks of dietary adaptation, a digestibility trial (DT1) was undertaken, over 3 days, in eight untrained Standardbreds with a fresh faecal sample being collected on the second day for FFP determinations. Six of the eight horses undertook a training programme, and after 5 weeks of exercise, the DT and the FFP measurements were then repeated (DT2). DT2 began after 3 days of inactivity. The same natural meadow hay (H) and pelleted complementary feed (CF) were fed throughout. For 5 days before the DTs, horses were fed 2.1% BW on a dry matter basis (55:45 ratio H:CF). Body weight and body condition score remained constant. Apparent digestibility of dry matter, organic matter, neutral detergent fibre, hemicellulose, crude protein and gross energy, as well as faecal total volatile fatty acids (VFA), acetate and propionate concentrations were significantly (p < 0.05) higher at DT2 than at DT1. A 5-week exercise programme had a positive impact on nutrient digestibility and FFP. Training may improve dietary energy supply, in particular via increased hindgut VFA production. The potential improvement of digestive efficiency with training should be taken into account when formulating nutritional recommendations for the exercising horse, particularly when performing light work, which is low-intensity exercise for 1-3 h per week.

Mobile bag starch prececal disappearance and postprandial glycemic response of four forms of barley in horses.

To determine prececal starch digestibili-ty and estimate glucose uptake from the digestion of 4 forms of barley in the small intestine, 4 mature cecally fistulated geldings (449 ± 41 kg BW) fed a 62:38 (wt/wt) meadow hay:concentrate diet at 1.7 kg DM/100 kg BW were included in a 4 × 4 Latin square design experiment. During each period, horses received 80% DM of their concentrate as 1 of the 4 forms of a same batch of barley, whole grain, 2.5 mm ground, steam flaked, and pelleted. Hay was offered in 2 equal meals and concentrate in 2 unequal meals. The starch supply in the morning meal amounted 2.7 g starch/kg BW. At each period, mobile bag DM and starch disappearance was determined. Except for ground barley, each form of barley was 4 mm ground before being introduced in the bag. Nylon bags containing each substrate were intubated in the horse receiving the pelleted barley. Bags were collected in the cecum for 10 h postintubation. At each period, postprandial glycemia was measured on blood samples collected on the 4 horses via an indwelling jugular catheter just before the concentrate morning meal and for 8 h. No hay in the morning meal was given the day of the measurements. Whole blood glucose was analyzed with a portable blood glucose meter. Mobile bag prececal DM disappearance and starch disappearance depended (P < 0.01) on barley form. Prececal starch disappearance of whole barley was the lowest but no difference (P > 0.05) was detected among the 3 processed grains. No significant effect of barley form was found whatever the glycemic parameters. No significant correlation was reported between glycemic parameters and the amount of prececal mobile bag disappeared starch calculated as the starch intake in the morning meal by the mobile bag starch disappearance. To conclude, the whole form of barley exhibited the lowest prececal mobile bag starch disappearance whereas, in relationship with large individual variations, no significant variation has been shown in glycemic parameters. Further investigations should be performed to improve methods for estimating prececal starch digestion of processed cereals in the different digestive segments of horses.

Long-term effects of endurance training on total tract apparent digestibility, total mean retention time and faecal microbial ecosystem in competing Arabian horses.

REASONS FOR PERFORMING STUDY: In endurance horses, commonly fed 80% forage, energy is provided mainly by VFA produced in the hindgut during cell wall degradation, but cell wall digestibility has been reported to be impaired by exercise. OBJECTIVES: To assess the influence of a long-term endurance conditioning on cell wall digestion in horses. METHODS: The total tract apparent digestibility of dry matter, organic matter and fibrous constituents, solid and liquid total mean retention time and the faecal microbial ecosystem of purebred Arabian horses were measured for 2 years in 2 longitudinal experiments. MEASUREMENTS: Performed at the beginning of each year for control level and after conditioning periods corresponding to incremental endurance racing levels: 60, 90 (year 1) and 120 (year 2) km. During the 5 measurement periods, feed intake and diet composition were similar. RESULTS: In year 1, digestibility of DM, OM and NDF was higher after 10 weeks of training (P = 0.008, P = 0.010 and P = 0.031, respectively), corresponding to the 90 km level, compared to the pretraining level. In year 2, NDFd and (NDF-ADF)d tended to be higher (P = 0.06 and P = 0.07, respectively) after the 17 weeks conditioning necessary to reach 120 km level, than before training. These variations were not systematically associated to a longer total MRT, neither to an increase in the microbial fibrolytic activity. CONCLUSIONS: Digestibility of DM, OM and NDF appeared to be higher after endurance conditioning. Such an increase could be beneficial for endurance horses as it would provide more energy from forage degradation. Additional experiments are needed to elucidate the mechanisms, understand some contradictory results and investigate methodological aspects.

Isolation and quantitation of zeins in waxy and amylose-extender and wild flint and dent maize endosperm using a new solvent sequence for protein extraction.

Protein distribution in endosperm of maize grains differing by their texture, flint or dent, and by their genotype, wild or waxy or amylose-extender, was examined by the successive use of 0.5 M NaCl, 0.5 M NaCl plus 0.6% 2-mercaptoethanol (2ME) at neutral and then alkaline pH, and 55% 2-propanol plus 0.6% 2ME as extractants. Proteins extracted in the presence of 2ME were characterized by their size polymorphism and amino acid composition. Proteins isolated with NaCl plus 2ME at neutral pH corresponded with a mixture of gamma-zein (27 kDa) and glutelin-like proteins. Proteins isolated with NaCl plus 2ME at pH 10 were a mixture of gamma-zeins (27 and 16 kDa) and beta-zeins (14 kDa). Alcohol-soluble proteins consisted of alpha-, beta-, and delta-zeins, alpha subunits being predominant. Zein quantitation was improved by weighing the nitrogen percentage of extracts by their zein content, as estimated from the data on amino acid composition. The data reported by Wolf et al. (Cereal Chem. 1975, 52, 765) were integrated to the results of this work to suggest the occurrence of an inverse correlation between amylose in starch and zeins in proteins.

Effect of wheat and corn variety on fiber digestion in beef steers fed high-grain diets.

Six Salers steers, fitted with ruminal and duodenal cannulas, were used in a double 3x3 Latin square design to assess the depressive effect of the nature of wheat, flint corn, and dent corn on fiber digestion in animals fed high-concentrate diets, and to determine the mechanisms involved in these negative digestive effects. Diets were balanced to be equal in starch content (47.7+/-2.3%). The three cereals were characterized by ruminal starch digestibilities of 86.6, 60.8, and 34.8% for the wheat, dent corn, and flint corn, respectively. Ruminal digestion of NDF was lower with wheat- than with corn-based diets (49.4 vs. 55.2%; P<.001), and with dent corn than with flint corn (53 vs. 57.3%; P<.01). Degradability of hay in nylon bags was not affected by the grain source in the diet (P>.1). The mean retention time of forage particles in the rumen was similar between wheat and corn diets (P>.1), but it was lower for steers fed dent corn than for those fed flint corn (P<.05). Most fibrolytic activities of the solid-associated microorganisms were lower (P<.05) in animals fed wheat than in those fed corn. Differences in fibrolytic activities of the solid-associated microorganisms between the two corn genotypes were not statistically significant (P>.1), but activities of all fibrolytic enzymes were lower (P<.05) with the dent than with the flint corn diet. Protozoal number in ruminal fluid was lower in animals receiving wheat than in those fed corn (177 vs. 789x10(3)/mL; P<.001) and was related to the high ruminal acidity (P<.01) of the wheat diet. Large modifications in the rumen microbial ecosystem between the two corn genotypes were not visible in protozoal numbers or pH. Total-tract digestion of NDF was the same for wheat and for corn diets, averaging 55% for the three diets. A postruminal compensation of NDF digestion (14% of the total tract NDF digestion) seemed to occur with the wheat diet. The lack of any postruminal NDF digestion (0%) with the two corn diets may suggest negative digestive interactions in the hindgut similar to those in the rumen.

Influence of grain source on ruminal characteristics and rate, site, and extent of digestion in beef steers.

Six cannulated Salers steers (305 +/- 17 kg initial BW) were used in a double 3 x 3 Latin square design to compare the effects of the nature of the cereal (wheat vs corn) and the corn genotype (dent vs flint) on rate, site, and extent of digestion of high-concentrate diets. The cereals were coarsely cracked, and the diets were balanced to have the same percentage of starch (47.7 +/- 2.3%) and CP (14.6 +/- .7%). Differences in ruminal starch digestion were observed between wheat- and corn-based diets (86.6 vs 47.8%; P < .001) and between corn genotypes (60.8 vs 34.8% for dent and flint corns; P < .001). For flint corn, more than half the starch was digested in the hindgut. Total tract digestion of starch was greater (P < .001) by steers fed wheat than by those fed corn and did not differ (P > .1) between the two corn genotypes. Ruminal mean pH (P < .01) was lower and total VFA concentration (P < .1) was higher for wheat- than for corn-based diets. Ruminal acetate:propionate tended to increase with the decrease in the amount of starch degraded in the rumen, but differences were not significant (P > .1). When wheat replaced corn, nonammonia, nonmicrobial N duodenal flow decreased (P < .01), and microbial duodenal flow increased (P < .05), so there were no differences in the duodenal flow of nonammonia N duodenal flow (P > .1). The lower nonammonia N duodenal flow for the dent corn- than for the flint corn-based diet (P < .05) was related to a lower passage of nonammonia, nonmicrobial N into the duodenum. Efficiency of microbial protein synthesis was inversely correlated with the amount of starch degraded in the rumen. Nature of the cereal, wheat vs corn, and genotype of the corn, dent vs flint, alter the site and extent of starch digestion.

Relationship between ruminal starch degradation and the physical characteristics of corn grain.

The objectives of this study were to determine the range of variation in the rate and extent of in situ ruminal starch degradation of 14 corns differing in vitreousness and to predict ruminal starch degradability by physical characteristics of corn grains. This study was conducted with eight dent and six flint corns. Ruminal starch degradability was determined by an in situ technique on 3-mm ground grains. Physical characteristics of corn grain were measured: hardness by grinding energy and particle size distribution, apparent and true densities, and specific surface area. Ruminal DM and starch degradabilities averaged 50 and 55.1% and varied from 39.7 to 71.5% and from 40.6 to 77.6%, respectively. Ruminal starch degradability averaged 61.9 and 46.2% in dent and flint types, respectively. The proportion of coarse particles (61.9 vs. 69.6% for dent and flint, respectively), the apparent density (1.29 vs. 1.36 g/cm3 for dent and flint, respectively), and the specific surface area (.13 vs. .07 m2/g for dent and flint, respectively) varied with the vitreousness. Ruminal starch degradability could be predicted accurately by vitreousness (r2 = .89) or by the combination of apparent density and 1,000-grain weight (R2 = .91), a measurement faster than the vitreousness determination.

Influence of genotype and ensiling of corn grain on in situ degradation of starch in the rumen.

This trial was conducted to determine the influence of genotype and ensiling of corn grain on the rate and extent of ruminal starch degradation. Two cultivars of corn that differed in texture of the endosperm, dent (Zea mays ssp. indentata) or flint (Zea mays ssp. indentura) were harvested at 30% whole-plant dry matter (DM). After separation from stover and cob, the kernels were coarsely chopped and ensiled or not ensiled. Grains were oven-dried at 40 degrees C and either ground through a 3-mm sieve or left unground. Ruminal DM and starch degradabilities were determined using the in situ technique. The proportion of starch lost through the pores of the bag without degradation was also determined. Mean ruminal DM and starch degradabilities were higher for ground grains than for chopped grains, which could be related to the proportion of DM and starch lost through the pores of the bag. For unensiled, chopped grain, ruminal starch degradability was higher for dent corn than for flint corn (72.3% vs. 61.6%). The ensiling process increased ruminal starch degradability, averaging 5.8 percentage units. The difference in ruminal starch degradability between dent corn and flint corn remained constant whether the corn was unensiled or ensiled (10.7 vs. 11.6 percentage units).

In situ and in vitro ruminal starch degradation of untreated and formaldehyde-treated wheat and maize.

Ruminal starch degradation of untreated and formaldehyde-treated wheat and maize was measured in situ (trial 1) and in vitro (trial 2). The in situ starch degradability was higher for wheat than for maize (82.1 vs 52.3%), for untreated cereals than for cereals treated with 1% formaldehyde (77.3 vs 67.0%) and for cereals treated with 1% formaldehyde than those treated with 5% formaldehyde (67.0 vs 57.2%). The in vitro results were similar. The treatment of cereals by formaldehyde decreased starch degradability more for wheat than for maize, suggesting that the treatment was more efficient when cereal starch and/or nitrogen was highly degradable. Formadehyde treatment of wheat was more effective at decreasing the rate of wheat protein degradability than starch degradability. The difference of response to treatment between the two cereals may be due to differences in properties of the protein matrix of these two cereals.