Meta-analysis of 0 to 8 h post-prandial evolution of ruminal pH.

The objective of this study was to identify relevant descriptors of ruminal pH post-prandial evolution that can replace the mean pH (considered unsatisfactory). These descriptors are to be used in the attempts to predict ruminal pH from dietary characteristics, in order to quantify the potential of a diet to induce subacute ruminal acidosis from its intrinsic characteristics. A total of 219 pH curves, reported as graphics in 48 published articles describing the post-prandial evolution of ruminal pH (first 8 h), were digitized by image analysis then summarized in 15 pH variables. Relationships among pH variables and the principal components (PCs) of pH variability were analyzed in order to identify possible alternatives to mean pH, as the average value of all pH data the curve is composed of. Two groups of pH variables were identified according to their relationship with the most important principal components. A first group, including mean pH, was closely related to PC1, which accounted for 78% of data variability; hence, correlations between variables of this group were generally high. Of these, threshold-related variables were distinct as their within-study correlations with mean pH were rather moderate (0.69 on average). This suggests they might carry supplementary information that could explain the variation in ruminal pH induced by within-study factors, e.g. diet characteristics. However, caution should be taken in their use because of their truncation at 0 h and their non-normal distribution. Variables from the second group were independent of the PC1, and thus of the first group of variables, whereas they were mostly related to PC2 and PC3. This implies they are complementary to mean pH. Of this second group, the rate of pH decreases or the time period when pH reaches its minimum might be useful to better describe the ruminal status, from the point of view of the risk of subacute ruminal acidosis.

Effect of corn hybrid and chop length of whole-plant corn silage on digestion and intake by dairy cows.

The objectives of this experiment were to study the effects of corn hybrid and chop length of whole-plant corn silage (WPCS) on intake, and to quantify ruminal digestive processes that could help to identify factors limiting dry matter intake (DMI). Eight lactating cows and 4 dry cows fitted with a ruminal cannula were randomly assigned to 4 treatments in a 4 x 4 Latin square design with replications for lactating cows and without for ruminally cannulated cows. Treatments were fed in a total mixed ration (TMR) containing 75% WPCS and 25% concentrate. The 4 WPCS differed in the characteristics of 2 conventional hybrids, less degradable vs. more degradable in the rumen and in the chop length, fine vs. coarse. The DMI was measured for all cows, and digestion measurements and chewing activities were recorded with the cannulated cows. With lactating cows, DMI and milk yield varied with corn hybrids but not with chop length. The less degradable hybrid in the rumen was the less ingested. Dry matter intake of dry ears followed the same trend, but the differences between hybrids were lower than that observed with the lactating cows and not significant. Dry matter digestibility in the total tract and rumen fill were not different between hybrids. Ruminal mean retention time was greater for the least degradable hybrid. The rumen fill capacity could explain intake differences between hybrids. Ingestive mastication strongly reduced particle size, and the efficiency of particle size reduction was more important with the coarsely chopped WPCS than the finely chopped ones. The small differences in particle size of material entering the rumen after mastication of WPCS during eating might explain the lack of response for decreasing chop length. Because the rumen fill decreased with the decrease in chop length, rumen fill could not be the only factor responsible for DMI control of WPCS.

Effect and stability of gliotoxin, an Aspergillus fumigatus toxin, on in vitro rumen fermentation.

Aspergillus fumigatus is a toxicogenic fungus usually found in contaminated animal feeds, especially in conserved forages where it can produce several mycotoxins. Gliotoxin, one of the most important toxic metabolites produced by this fungus, has antibacterial, immunosuppressive and apoptotic effects. Ruminants due to the high proportion of forages they receive in the ration would be particularly exposed to gliotoxin. The objective of this work was (1) to assess the effect of gliotoxin on in vitro rumen fermentation and (2) to determine the effect of fermentation on gliotoxin stability. Gliotoxin did not affect rumen fermentation at concentrations found in naturally contaminated feeds. No effects were observed up to a concentration of 20 microg toxin ml(-1) and an extremely high toxin concentration (80 microg ml(-1)) was necessary to affect dry matter degradation, gas and total volatile fatty acids production by 24, 37 and 18%, respectively (p < 0.01). In addition, the toxin was unstable in the rumen environment with 90% disappearance at 6 h of incubation (p < 0.05). In contrast, extracts of A. fumigatus cultures containing gliotoxin at concentrations several times lower than that used for experiments with pure toxin had a negative effect on fermentations indicating the toxicity and possible synergism of other metabolites produced by this fungus. Extracts containing 8.8 microg gliotoxin ml(-1) decreased dry matter degradation, gas and volatile fatty acids production by 28, 46 and 35%, respectively (p < 0.01). Identification of these toxic metabolites and assessment of the rate of passage of gliotoxin to the lower intestinal tract is necessary to evaluate the potential risk of these toxins to ruminants.

A comparison of enzymatic and molecular approaches to characterize the cellulolytic microbial ecosystems of the rumen and the cecum.

We used RNA probes and enzyme activities to compare the cellulolytic microbial ecosystems of the rumen and the cecum. Four rumen- and cecum-cannulated wethers were fed a diet of barley plus hay (60:40). Digesta samples were collected 1 h before feeding and 3, 6, and 9 h after feeding for measurements on microbial populations, and 1 h before feeding and 3 and 6 h after feeding for digestion measurements, pH, and VFA. Polysaccharidase and glycosidase specific activities of solid-adherent microorganisms were measured respectively by the amount of reducing sugars released from xylan or avicel or p-nitrophenol from the p-nitrophenol derivatives of xylose and glucose. The distribution and amounts of the three main cellulolytic bacterial species (Fibrobacter succinogenes, Ruminococcus albus, and Ruminococcus flavefaciens) were determined by dot-blot hybridization using specific 16SrRNA-targeting probes. Enzyme activities were higher in the rumen than in the cecum and before feeding than at 3 h after feeding. The sum of the three cellulolytic bacterial species represented, on average, 4.5% of the total bacterial RNA in the two compartments and did not vary with sampling time. The cellulolytic bacterial community structure was different in the two compartments, with F. succinogenes as the main species in the rumen and R. flavefaciens in the cecum. The lower cellulolytic activity in the cecum than in the rumen could not be ascribed to any difference in the structure of the cellulolytic bacterial community between these two compartments, and other hypotheses related to digestion are proposed.

Fibrolytic activities and cellulolytic bacterial community structure in the solid and liquid phases of rumen contents.

Four sheep were fed an alfalfa hay diet. Rumen content samples were collected three hours after feeding in order to total microorganism population (TP), solid attached population (SAP) and solid attached firmly population (SAFP). Fibrolytic specific activities (xylanase, CMCase and beta-glycosidases) were estimated by the amount of reducing sugars or p-nitrophenol released from the appropriate substrate. The distribution of the three main cellulolytic bacterial species (Fibrobacter succinogenes, Ruminococcus albus and Ruminococcus flavefaciens) was quantified by dot-blot hybridisation using specific 16S-rRNA-targeting probes. Specific activities of polysaccharidase enzymes were higher in SAP than in TP, and in SAFP than in SAP. The sum of RNA of the three cellulolytic bacterial species represented on average 9% of the total bacterial RNA, and increased after filtration. In all samples, the relative population size of F. succinogenes was higher than that of R. albus and of R. flavefaciens. These results demonstrate that the most active enzymes are secreted by the particle-associated microorganisms. The differences in composition of the microflora between the solid and liquid phase suggest that bacteria are not equally distributed throughout the rumen content: the cellulolytic species are present in a higher proportion in the solid phase of rumen contents.

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.

Cereal supplementation modified the fibrolytic activity but not the structure of the cellulolytic bacterial community associated with rumen solid digesta.

4 ruminally cannulated cows were fed a forage diet (93% hay + 7% straw) and a mixed diet (33 % hay + 7% straw + 40% barley) in a 2 x 2 crossover experimental design. In sacco degradation of forage, fibrolytic activities (polysaccharidases and glycosidases) of the solid-associated bacteria (SAB), and distribution of the 3 main cellulolytic bacterial species (Fibrobacter succinogenes, Ruminococcus albus, Ruminococcus flavefaciens) were determined for both diets. Barley supplementation decreased the hay degradation rate and mainly the polysaccharidase activities of the SAB (30% on average). The sum of rRNA of the 3 cellulolytic bacterial species represented on average 17% of the total bacterial signal and R. albus was the dominant cellulolytic bacterial species of the 3 studied. Barley supplementation did not modify the proportion of the 3 cellulolytic bacteria attached to plant particles. The negative effect of barley on the ruminal hay degradation rate is due to a decrease in fibrolytic activity of the SAB, and not to a modification of the balance of the three cellulolytic bacterial species examined.

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.

Influence of sampling site on concentrations and carbohydrate-degrading enzyme activities of protozoa and bacteria in the rumen.

Four ruminally cannulated cows were used to assess the distribution of the concentrations and carbohydrate-degrading enzyme activities of the liquid-associated protozoa (LAP) and solid-associated bacteria (SAB) in the rumen. The cows were fed diets (7 kg of DM/d) of 100% hay (Diet F) or 60% barley plus 40% hay (Diet C) in a 2 x 2 crossover experimental design. Samples of ruminal digesta were collected successively from the dorsal (DS), ventral (VS), and anterior (AS) sacs 1h before and 3 h after the morning feeding on two sampling days with a 2-d interval. Irrespective of diet and sampling time, the greatest proportion of entodiniomorphs, representing the main population of protozoa, was found in the DS (40% mean; P < .05). Low pH values observed in the DS (P < .05) indicated higher fermentative activity in this site than in the other parts of the rumen. Protozoa may contribute more than previously thought to the high digestive potential present at the top of the rumen that has classically been attributed to bacteria. The specific activity of plant cell wall polysaccharide-degrading enzymes in the LAP was correspondingly greater (P < .05) for DS than for VS or AS. For the two diets and sampling times, specific activity of fibrolytic enzymes in the SAB tended to be less in the upper than in the lower parts of the rumen, and less in the VS than in the AS. This tendency became significant (P < .05) for total fibrolytic enzyme activity. Differences in bacterial colonization of particles among the three sampling sites may explain such differences in fibrolytic activity of the SAB. Data suggest a spatio-temporal complementary action of the bacteria and protozoa in ruminal plant cell wall degradation, at least with the barley diet, for which the number of protozoa was highest.

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.

Influence of sampling time and diet on amino acid composition of protozoal and bacterial fractions from bovine ruminal contents.

Four ruminally cannulated cows were used to compare amino acid (AA) composition of protozoal and bacterial fractions as affected by sampling time and diet. Cows were given once a day restricted feed (80% of ad libitum intake) of 7 kg DM with two successive diets. Diet HB was 65% Cocksfoot hay and 35% pelleted ground barley, and Diet H was 100% Cocksfoot hay. Samples of whole ruminal contents were taken 2, 5, 8, 11, and 23 h after feeding for Diet HB and 2 h after feeding for Diet H to isolate the liquid-associated protozoa and bacteria (LAP, LAB) and particle-associated bacteria (PAB). At each sampling time, the AA compositions of the different microbial populations were determined. The AA profiles of the LAP were different from those of the bacteria for 13 AA out of 17 studied. Differences between AA compositions of LAB and PAB were also observed for 10 AA out of 17 studied. Irrespective of the microbial population, AA composition did not vary with sampling time after feeding diet HB (P > .05; except for arginine, glutamate, and glycine). The AA contents of none of the three microbial populations were affected (P > .05) by the diet except for leucine and glutamate (P < .01). The differences in AA profiles between LAP and bacteria and between LAB and PAB confirm the importance of the representativeness of the microbial reference sample for correctly estimating microbial AA flow into the small intestine.

Influence of barley and buffer supplements on quantitative aspects of ruminal fiber digestion of cows.

Four Jersey cows, fitted with ruminal and duodenal cannulas, were used to assess the specific effects of changes in ruminal pH that were induced by barley addition to a hay diet on ruminal fiber digestion. Cows received successively 100% unchopped cocksfoot hay (diet H), 65% hay and 35% pelleted ground barley (diet HB), and HB plus a continuous intraruminal infusion of bicarbonate salt solution (diet HBB). Cows were limit-fed once daily at 7 kg of DM day-1. The ruminal fractional passage rate of the liquid and hay was respectively estimated from a single administration of Cr-EDTA and Eu labeled on hay fiber. Duodenal fiber flow was estimated both by the double marker method (Yb-acetate/Cr-EDTA) and by multiplying the fractional passage rate of Eu-labeled hay by ruminal pool size. Barley supplement decreased ruminal NDF and ADF digestion compared with diet H, but passage rates of the solid and fluid fractions in the rumen were not affected. The depressive effect of barley supplement on in situ degradability of hay NDF and ADF decreased the degradation rates and increased the 72-h undegradable fraction. Compared with diet HB, ruminal NDF and ADF digestion was improved with buffer supplementation but was less than that of diet H, even though ruminal pH was similar to that of diet H. Passage rates of the fluid and particle fractions were depressed and unaffected, respectively, with buffer addition. Higher in situ degradability of hay with the buffer supplement resulted in an increase in the 72-h undegradable fraction, but the fractional degradation rate was unaffected.

Isolation and characteristics of the protozoal and bacterial fractions from bovine ruminal contents.

Four cows were fed once a day either a Cocksfoot hay diet (H) or a diet consisting of 65% hay and 35% pelleted ground barley (HB). 15(NH4)2SO4 was continuously infused into the rumen as a microbial marker and ruminal digesta samples were collected during the 24-h postprandial period for the isolation of liquid-associated protozoa and bacteria (LAP, LAB) and particle-associated bacteria (PAB). There were marked differences between ruminal pH diurnal variations with diets H and HB. Irrespective of the diet and sampling time, the chemical composition (OM, N, DAPA, 15N) of the protozoa was clearly different from that of the bacteria (P < .001). The LAP contained more OM but less N and 15N than the bacterial fractions. The DAPA used to validate the isolation technique for the mixed ciliate population was not detected in protozoal fractions. The OM content of LAB was lower than that of PAB, whereas the N, DAPA, and 15N contents were higher. The observed effects of diet (P < .01) on LAP mean N contents were due to the different N contents of the LAP samples isolated 23 h after feeding and were correlated with the variation in the number of Endodiniomorphid protozoa (r = .72; P < .05). The N content of LAB was not affected (P > .05) by diet but that of the PAB was increased on diet HB (P < .05). The diet did not affect the 15N content of any of the three microbial populations. However, the 15N content of the bacteria decreased shortly after feeding (P < .001).

Effect of extraction method on activities of polysaccharide-depolymerase enzymes in the microbial population from the solid phase in the rumen.

Samples of rumen digesta were collected from 2 cows fed with a 100:0 or 40:60 forage/concentrate diet 1 h before and 2 h after feeding. Enzymes from particle-associated microorganisms were extracted by 5 different methods, including physical (freezing, grinding and sonication) or chemical and enzymatic (autolysis in a buffer, lysozyme and CCl4) treatments. Hydrolytic enzyme activities were measured on 3 polysaccharidic substrates: xylan, carboxymethylcellulose and Avicel cellulose. Contamination of enzyme preparations by feed proteins was evaluated. For the 3 substrates, the effect of feeding (sampling time and diet) on enzyme activities was independent of extraction method. Maximal activities were obtained with treatments including lysozyme and CCl4 or grinding in liquid nitrogen. Contamination of enzyme preparations by feed proteins was higher with chemical and enzymatic methods than with physical treatments.

Degradation in the rumen of proteins of 2 legumes: soybean meal and field pea.

Ruminal protein degradation of soybean meal and field pea were compared using 2 analytical methods: in situ and a laboratory analysis with a proteolytic enzyme extracted from Streptomyces griseus. The degradation of total nitrogen in nylon bags of the feeds was measured between 0 and 48 h in the rumen of 2 cows (theoretical degradability: 70.0% for soybean meal and 94.7% for field pea). Electrophoresis of proteins of feeds and in situ residues, in sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) showed that both species have the same type of proteins (7S and 11S) which were degraded in a similar manner in the rumen. The 7S fraction was degraded rapidly whereas the 11S fraction was more resistant. The electrophoretic profiles showed that protein components were less degraded after enzymatic than in situ degradation. In the supernatant after enzymatic hydrolysis, protein and peptides were found in large concentrations and alpha-amino nitrogen and ammonia in low concentrations. It was difficult to simulate the in vitro activity of enzyme complexes in the rumen and the results must be confirmed by direct measurement of the rumen liquid.

Influence of hay making on in situ nitrogen degradability of forages in cows.

The influence of hay making on in situ N degradability of forages was assessed by comparing the degradability of nine hays with that of standing forages at the time of harvest. Three ryegrass, two cocksfoot, and three alfalfa forages were used. The N degradability of hays was related closely to that of the corresponding standing forages (R = .91) and was, on average, lower (-2.5 points). This decrease in degradability after hay making was not constant; it increased when the degradability of the standing forage was high and when harvesting conditions were poor.

In situ starch degradation of different feeds in the rumen.

The in situ starch degradation of 5 feeds (barley, maize, pea, oats and wheat bran) has been measured (trial 1), and the influence of particle size on starch degradation investigated with 3 feeds (barley, maize, pea) (trial 2). The starch degradability of barley, oats and wheat bran was found to be higher than that of pea, and higher again than that of maize: 98, 97, 96, 90 and 58% respectively. For barley, oats and wheat bran, starch was degraded more rapidly than the other dry matter (pm) components. Maize and pea starches were degraded at the same rate as non-starchy components. The particle size variations between feeds ground on the same screen may partly explain variations in starch degradability. When the particle size increased from 0.8 to 6.0 mm screen grinding, in situ starch degradability decreased; the decrease was higher for maize (13.8 points) than for barley (7.4 points) or pea (10.4 points).