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PubMed2006

The production of 10-hydroxystearic and 10-ketostearic acids is an alternative route of oleic acid transformation by the ruminal microbiota in cattle.

The formation of hydroxystearic acid (HSA) and ketostearic acid (KSA) from oleic acid transformation has been documented in a variety of microbial species, including several isolated from the rumen of domesticated ruminant species. However, their ruminal production rates have not been established as influenced by fatty acid source. Dosing continuous cultures of mixed ruminal microorganisms with 1-(13C)-oleic acid increased the 13C enrichment of both HSA and KSA at 24 h postdosing, and showed that the majority (96 and 85%, respectively) of the HSA and KSA present in the 24-h samples originated from oleic acid. Several experiments using batch cultures of ruminal microorganisms showed that production of HSA and KSA was directly related to oleic acid input but was not affected by elaidic acid input, and that HSA was further metabolized to KSA but not to other fatty acids. When continuous cultures of ruminal microorganisms were supplemented with soybean oil or canola oil, production of 10-HSA + 10-KSA was related to oleic acid input but not to linoleic acid input. Daily production of 10-HSA + 10-KSA across treatments was 14.4 micromol/100 micromol oleic acid input into the cultures or 31.1 micromol/100 micromol oleic acid net loss. The results of this study quantify the formation of 10-HSA and 10-KSA from oleic acid transformation by ruminal microorganisms, and show that their accumulation in ruminal contents is directly related to the extent of oleic acid input and biotransformation by the rumen microbiota.

Animals↗
PubMed2005

Moxidectin and ivermectin metabolic stability in sheep ruminal and abomasal contents.

The oral administration of macrocyclic lactones to sheep leads to poorer efficacy and shorter persistence of the antiparasitic activity compared to the subcutaneous treatment. Gastrointestinal biotransformation occurring after oral treatment to ruminant species has been considered as a possible cause of the differences observed between routes of administration. The current work was addressed to evaluate on a comparative basis the in vitro metabolism of moxidectin (MXD) and ivermectin (IVM) in sheep ruminal and abomasal contents. Both compounds were incubated under anaerobic conditions during 2, 6 and 24 h in ruminal and abomasal contents collected from untreated adult sheep. Drug concentrations were measured by high-performance liquid chromatography with fluorescence detection after sample clean up and solid phase extraction. Neither MXD nor IVM suffered metabolic conversion and/or chemical degradation after 24-h incubation in ruminal and abomasal contents collected from adult sheep. Unchanged MXD and IVM parent compounds represented between 95.5 and 100% of the total drug recovered in the ruminal and abomasal incubation mixtures compared with those measured in inactive control incubations. The partition of both molecules between the solid and fluid phases of both sheep digestive contents was assessed. MXD and IVM were extensively bound (>90%) to the solid material of both ruminal and abomasal contents collected from sheep fed on lucerne hay. The results reported here confirm the extensive degree of association to the solid digestive material and demonstrates a high chemical stability without evident metabolism and/or degradation for both MXD and IVM in ruminal and abomasal contents.

Abomasum↗
PubMed1992

GABA receptor-mediated modification of reticulo-ruminal myoelectrical activity in sheep.

The involvement of central and peripheral GABA receptors in the control of the forestomach periodic motor activity was examined in five conscious ewes at rest, chronically fitted with electrodes implanted in the reticular and ruminal wall and a cannula placed in a cerebral lateral ventricle. Intravenous (IV) administration of the GABAA receptor agonist muscimol (5-50 micrograms/kg) did not affect reticulo-ruminal myoelectrical activity, while its intracerebroventricular (ICV) injection (0.05-0.10 micrograms/kg) dose-dependently increased the frequency of reticular and ruminal motor cycles and provoked rumination in 11 trials out of 15. Forestomach responses to ICV muscimol were abolished by a previous ICV treatment of the animals with the GABAA receptor antagonist bicuculline (0.5-4 micrograms/kg), which did not in itself influence reticular or ruminal motility. The GABAB receptor agonist baclofen, given either IV (300-800 micrograms/kg) or ICV (1-3 micrograms/kg), inhibited in a dose-dependent manner both reticular and ruminal activity, with the effects of its ICV administration appearing earlier and lasting longer. The GABAB receptor blocker baclofen given ICV alone (50-300 micrograms/kg) was ineffective, but such a treatment before IV or ICV administration of baclofen in part antagonized the inhibition of the forestomach myoelectrical cyclic activity. These pharmacological data suggest a possible excitatory role of strictly central GABAA and an inhibitory one of mainly central GABAB receptors in the regulation of reticulo-ruminal extrinsic motility in sheep. In this regulation, however, a probable peripheral component of inhibitory GABAB receptors should not be excluded.

Animals↗
PubMed1989

In vitro metabolism of 2,2'-diaminopimelic acid from gram-positive and gram-negative bacterial cells by ruminal protozoa and bacteria.

Bacillus megaterium GW1 and Escherichia coli W7-M5 were specifically radiolabeled with 2,2'-diamino[G-3H]pimelic acid [( 3H]DAP) as models of gram-positive and gram-negative bacteria, respectively. These radiolabeled bacterial mutants were incubated alone (control) and with mixed ruminal bacteria or protozoa, and the metabolic processes, rates, and patterns of radiolabeled products released from them were studied. Control incubations revealed an inherent difference between the two substrates; gram-positive supernatants consistently contained 5% radioactivity, whereas even at 0 h, those from the gram-negative mutant released 22%. Incubations with ruminal microorganisms showed that the two mutants were metabolized differently and that protozoa were the major effectors of their metabolism. Protozoa exhibited differential rates of engulfment (150 B. megaterium GW1 and 4,290 E. coli W7-M5 organisms per protozoan per h), and they extensively degraded [3H]DAP-labeled B. megaterium GW1 at rates up to nine times greater than those of ruminal bacteria. By contrast, [3H]DAP-labeled E. coli W7-M5 degradation by either ruminal bacteria or ruminal protozoa was more limited. These fundamental differences in the metabolism of the two mutants, especially by ruminal protozoa, were reflected in the patterns and rates of radiolabeled metabolites produced; many were rapidly released from [3H]DAP-labeled B. megaterium GW1, whereas few were slowly released from [3H]DAP-labeled E. coli W7-M5. Most radiolabeled products derived from [3H]DAP-labeled B. megaterium GW1 were peptides of bacterial peptidoglycan origin. The ruminal metabolism of DAP-containing gram-positive and gram-negative bacteria, even with the same peptidoglycan chemotype, is thus likely to be profoundly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids, Diamino↗
PubMed1989

Physical degradation of lignified stem tissues by ruminal fungi.

Ruminal bacteria or fungi were selected by the addition of cycloheximide or streptomycin and penicillin, respectively, to ruminal fluid, and the weakening and degradation of lignified tissues in alfalfa and Bermuda grass stems by these treatments and whole ruminal fluid were evaluated in vitro. Dry weight loss in alfalfa was similar for whole ruminal fluid and streptomycin-penicillin treatment, whereas that with streptomycin-penicillin treatment was significantly higher (P </= 0.05) than that with cycloheximide treatment. In Bermuda grass, dry weight loss was significantly higher with streptomycin-penicillin than that with whole ruminal fluid and cycloheximide treatment, which were equal. Both peak load (Newtons) and peak stress were less (P </= 0.05) for streptomycin-penicillin treatment than with other treatments in both forages. Fungi colonized the lignified ring in alfalfa and tended to reduce the width of cell walls in this tissue, but a large number of fungal penetrations through cell walls was not observed. In contrast, fungal rhizoids frequently penetrated into and through cell walls in the lignified ring of Bermuda grass, often expanding the pit fields between the cells. Ruminal fungi disrupt lignified tissues in stems, and their activity results in a weakened residue more amendable to physical degradation. This weakening may allow plant digesta to be more easily broken apart during animal's rumination and thus facilitate digesta flow and fiber utilization.

Journal Article↗
PubMed1996

Use of potassium depletion to assess adaptation of ruminal bacteria to ionophores.

When mixed ruminal bacteria from cattle fed timothy hay were suspended in a medium containing a low concentration of potassium, monensin and lasalocid catalyzed a rapid depletion of potassium from cells. The ionophore-mediated potassium depletion was concentration dependent, and it was possible to describe the relationship with saturation constants. Mixed ruminal bacteria never lost more than 50% of their potassium (Kmax = 46%), and the concentrations of monensin and lasalocid needed to cause half-maximal potassium depletion (Kd) were 178 and 141 nM, respectively. When cattle were fed 350 mg of monensin per day, the ratio of ruminal acetate to propionate decreased from 4.2 to 2.9, and the Kd of monensin was eightfold greater than the value for mixed ruminal bacteria from control animals. Monensin supplementation also caused a twofold increase in the Kd of lasalocid. Lasalocid supplementation (350 mg per day) had no effect on the ruminal acetate-to-propionate ratio, but it caused a twofold increase in the Kd values of monensin and lasalocid. Increases in Kd occurred almost immediately after ionophore was added to the ration, and the Kd values returned to their prefeeding values within 14 days of withdrawal. Ionophore supplementation had no effect on the Kmax values, and approximately 50% of the population was always highly ionophore resistant. Because the Kd values of even adapted ruminal bacteria were low (< 1.5 microM), it appears that a large proportion of the ruminal ionophore is bound nonselectively to feed particles or ionophore-resistant bacteria.

Adaptation, Physiological↗
PubMed2006

Detection of lysergic acid in ruminal fluid, urine, and in endophyte-infected tall fescue using high-performance liquid chromatography.

Ergot alkaloids present in endophyte-infected tall fescue induce fescue toxicosis in livestock consuming the plant. The lysergic acid (LA) ring structure is a common moiety among the ergot alkaloids. Little is known about the bioavailability of LA because of limitations in available analytical protocols. Thus, a high-performance liquid chromatography procedure was developed to analyze biological matrices for LA. The biological matrices of interest were tall fescue straw and seed, and ruminant feces, urine, and ruminal fluid. Lysergic acid was added to each matrix at a high (150 ng/ml) or low (30 ng/ml) level. Using the high-level addition, the greatest recovery of LA was obtained from ruminal fluid, feces, and urine (P < 0.05), with an average 85.1% recovered. At the low level, a greater recovery of added LA was observed in the ruminal fluid, urine, and feces (82.1%; P < 0.05) than that in the other 2 matrices (62.6%). The limit of quantitation (LOQ) in ruminal fluid and urine was 5.5 and 18.4 ng/ml, respectively. Seed, straw, and feces had higher LOQ (24.2, 14.5, and 36.0 ng/g, respectively). Limit of detection (LOD) was 1.64, 10.80, 4.35, 5.52, and 7.26 ng/g for ruminal fluid, feces, urine, seed, and straw, respectively. To test the assay in vivo, samples of ruminal fluid and urine were collected from steers consuming a diet containing 400 ng of ergovaline/g and 30 ng of LA/g. All matrices sampled resulted in levels above the LOD and LOQ for the assay, indicating that this assay is sufficiently sensitive for use in assessing the bioavailability of LA.

Animals↗
PubMed1998

Stress and coping as predictors of children's divorce-related ruminations.

Examined stress and coping variables as predictors of divorce-related ruminations in children whose parents had recently divorced. Simultaneous multiple regression was used to analyze the cross-sectional data of 351 children of divorce. Divorce-related stressful events and threat appraisal were positively related to children's ruminations. A prospective longitudinal design was employed to predict rumination at Time 2 (T2) controlling for Time 1 (T1) rumination. Efficacy of coping was negatively related to T2 rumination after controlling for T1 rumination and all other predictors. This study also provided descriptive data on the frequency of children's divorce-related ruminations.

Adaptation, Psychological↗
PubMed2006

The effects of rumination and distraction on over-general autobiographical memory retrieval during social problem solving.

OBJECTIVES: We examined the effects of rumination and distraction on over-general autobiographical memory (AM) retrieval during social problem solving (SPS), as well as SPS performance in terms of means and effectiveness. DESIGN AND METHODS: After undergoing a rumination or distraction manipulation, dysphoric and non-dysphoric participants performed a SPS task and reported the memories retrieved during SPS. RESULTS: The dysphoric ruminators performed significantly less effectively on the SPS task than the other groups. However, the dysphoric ruminators did not differ from the dysphoric distracters on the numbers of categoric memories retrieved during SPS although they retrieved significantly more categoric memories than the non-dysphoric distracters and non-dysphoric ruminators. For all groups, the effectiveness score was significantly negatively correlated with categoric memories retrieved during SPS. CONCLUSION: The results demonstrated that in a dysphoric sample, rumination impaired SPS performance but did not influence categoric AM retrieval during SPS. The results suggested that in a dysphoric sample, rumination might affect SPS performance by affecting processes like initiation and motivation rather than AM retrieval during SPS.

Affect↗
PubMed1997

Cultural effects: affects following ruminations on success and failure in sports.

Affect following ruminations of success and failure in sport was examined for cultural effects. 66 African-American and 84 Native West African athletes completed questionnaires following ruminations about their most successful athletic experience, and again following ruminations about their worst failure. Analysis suggested that affect following ruminations of successful experiences was more positive than those following failure. Cultural differences were noted in the affective responses following ruminations of success. African athletes tended to be more positive in general and self-related affect following ruminations of success and slightly more negative following ruminations of failure than American athletes.

Adolescent↗
PubMed1990

Effects of the ionophore tetronasin on nitrogen metabolism by ruminal microorganisms in vitro.

The effects of tetronasin on ruminal protein metabolism were investigated in vitro using ruminal fluid from cattle receiving tetronasin in the diet, ovine ruminal fluid from animals not receiving tetronasin and pure cultures of proteolytic ruminal bacteria. Ruminal fluid from cattle receiving tetronasin in a predominantly barley diet had lower proteolytic (76% of control, P less than .10) and deaminative (58% of control, P less than .05) activities than controls after 42 d. The effect of deamination disappeared after 84 d, although the proteolytic activity remained lower (P less than .10) than that of controls. When tetronasin was added in vitro to ruminal fluid from sheep not receiving the ionophore, proteolytic activity (14C-labeled casein hydrolysis) was unaffected, but the rate of ammonia production from amino acids was decreased by 87% (P less than .01). Oligopeptide breakdown was inhibited to a lesser extent (21%, P less than .05). Dipeptidase activity (dialanine hydrolysis) was not affected. The addition of tetronasin to cultures of the ruminal bacteria Ruminobacter amylophilus and Bacteroides ruminicola had no influence on their protease, deaminase or dipeptidase activities. However, when the bacteria were adapted to grow in the presence of tetronasin, deamination of amino acids was severely inhibited (87 to 100%, P less than .01), even when tetronasin was absent from the incubation mixture. Tetronasin had no effect on the proteolytic activity of adapted cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1990

Steam-rolled wheat diets for finishing cattle: effects of dietary roughage and feed intake on finishing steer performance and ruminal metabolism.

Two experiments were conducted to determine the influence of dietary roughage concentration and feed intake on finishing steer performance and ruminal metabolism. In Exp. 1, 126 steers (334 kg) were used in a completely randomized design and fed (120 d) diets of steam-rolled wheat without roughage or containing 5, 10 or 15% roughage (50% alfalfa hay:50% corn silage). Steers fed 5 or 10% roughage gained faster (quadratic, P less than .05) and were more efficient (quadratic, P less than .05) than steers fed 15% or no roughage. In Exp. 2, six ruminally cannulated steers (447 kg) were used in a 6 x 6 latin square design and fed (twice daily) diets of steam-rolled wheat without roughage or containing 5 or 15% alfalfa hay at twice or three times NE required for maintenance. Increasing dietary roughage increased (linear, P less than .01) ruminal liquid passage 38%, indigestible ADF passage 63%, Yb-labeled wheat passage 75% and fiber fill 31%. The rate of in situ starch digestion tended to increase (linear, P = .16), and ruminal VFA concentration was 40 mM higher (P less than .01) at 4 h after feeding with increased roughage. Increased feed intake increased (P less than .05) ruminal starch fill, fiber fill, liquid fill and liquid passage 23%, Yb-labeled wheat passage 50% and Dry-labeled hay passage 20%. It reduced protozoa five- to sixfold (P less than .01) but doubled total bacterial counts (P less than .01). Ruminal NH3N was lower (P less than .01) and total VFA concentration was 50 mM higher (P less than .01) at 4 h after feeding. The acetate:propionate ratio was reduced from 2.3 to 1.3 (P less than .01) with increased intake. Adding roughage to a steam-rolled wheat diet increased passage and tended to increase rate of starch digestion; increased feed intake with its associated effects on ruminal fill and passage dramatically shifted the microbial population and fermentation end products.

Animal Feed↗
PubMed1991

Effect of diet composition and feed intake level on diet digestibility and ruminal metabolism in growing lambs.

Lambs (29 +/- 2.5 kg) were fed three diets at various intakes to determine whether diet composition or level of intake was reflected in changes in diet digestibility or ruminal fluid characteristics. In Exp. 1, a 90% concentrated, pelleted diet or a whole shelled corn diet with a pelleted protein supplement was fed at three levels of intake: ad libitum and 92.5 and 85% of ad libitum (n = 15). Exp. 2 compared the 90% concentrate diet with diets in which the energy density was diluted to 55 or 72.5% concentrate by including alfalfa hay as a possible method of restricting energy intake (n = 6). Lambs were adapted to diets for 13 d; feces were collected for 6 d and ruminal fluid was collected 0, 3, and 6 h after feeding on the day following fecal collection. Restricting intake in Exp. 1 did not affect DM digestibility or digestibility of CP or starch. Digestibility of ADF was increased (P less than .10) by restricting intake. Ruminal fluid pH, ammonia concentration and VFA concentrations were affected little by either restricted intake level. Digestibility of DM was 4% higher (P less than .001) and starch 5% higher (P less than .001) for the whole shelled corn diet than for the pelleted, high-concentrate diet. Ruminal pH of lambs fed the whole shelled corn diet was higher and fluctuated less than the ruminal pH of lambs fed the high-concentrate, pelleted diet. In Exp. 2, diet digestibility was reduced (P less than .01) and ruminal pH was increased (P less than .002) by addition of hay. Restricted feeding of lambs did not seem to increase diet digestibility or alter ruminal conditions.

Ammonia↗
PubMed1991

Effects of cottonseed meal supplementation time on ruminal fermentation and forage intake by Holstein steers fed fescue hay.

Four ruminally cannulated Holstein steers (average BW 303 kg) were used in a 4 x 4 Latin square design digestion trial to study the influence of daily cottonseed meal (CSM; 1.6 g of CP/kg of BW) supplementation time on forage intake and ruminal fluid kinetics and fermentation. Steers were housed individually in tie stalls and were fed chopped fescue hay on an ad libitum basis at 0600 and 1400. Treatments were 1) control, grass hay only (CON) and grass hay and CSM fed once daily at 2) 0600 (EAM) 3) 1000 (MAM), or 4) 1400 (PM). Ruminal NH3 N concentrations reflected a time of supplementation x sampling time interaction (P less than .05); CON steers had the lowest (P less than .05) ruminal NH3 N concentrations at all times other than at 0600, 1000, 1200, and 2400, when they did not differ (P greater than .05) from at least one of the supplemented groups. Forage intake, ratio of bacterial purine:N, rate of DM and NDF disappearance, and ruminal fluid kinetics were not influenced (P greater than .05) by supplementation time. Total ruminal VFA differed (P less than .05) between CON and supplemented steers, as well as among supplemented steers (linear and quadratic effects P less than .05). Acetate, propionate, and valerate proportions were influenced (P less than .05) by a sampling time X supplementation time interaction. Under the conditions of this study, greater peak ammonia concentrations with morning supplementation than with afternoon supplementation did not stimulate ruminal fermentation or rate of NDF disappearance.

Ammonia↗
PubMed1992

Effect of increasing ruminal butyrate on portal and hepatic nutrient flux in steers.

Six Holstein steers (mean +/- SE BW = 344 +/- 10 kg) fitted with hepatic, portal, and mesenteric vein and mesenteric artery catheters and a ruminal cannula were used in a 6 x 6 Latin square design to evaluate the effects of increasing ruminal butyrate on net portal-drained visceral and hepatic nutrient flux. Steers were fed a 40% brome hay, 60% concentrate diet in 12 portions daily at 1.25 x NEm. Water (control) or butyrate at 50, 100, 150, 200, or 250 mmol/h was supplied continuously via the ruminal cannula. Simultaneous arterial, portal, and hepatic blood samples were taken at hourly intervals from 15 to 20 h of ruminal infusion. Portal and hepatic blood flow was determined by continuous infusion of P-aminohippurate, and net nutrient flux was calculated as the difference between venous and arterial concentrations times blood flow. Ruminal and arterial concentrations and total splanchnic flux of butyrate increased (P less than .01) with increased butyrate infusion. Arterial concentrations of acetate (P less than .10), alpha-amino-N (P less than .05), and glucose (P less than .01) decreased with increased butyrate, whereas arterial beta-hydroxybutyrate (P less than .01) and acetoacetate (P less than .05) increased. Increased butyrate produced an increased portal-drained visceral flux of acetoacetate and an increased net hepatic flux of beta-hydroxybutyrate. Urea N and glucose net portal and hepatic fluxes were not affected by ruminal butyrate. Alpha-amino-N uptake by the liver decreased with increased butyrate (P less than .10). Simple linear regression (r2 = .985) indicated that 25.8% of ruminally infused butyrate appeared in portal blood as butyrate. Only 14% could be accounted for as net portal-drained visceral flux of acetoacetate plus beta-hydroxybutyrate.

Ammonia↗
PubMed1993

Effect of diet and folic acid addition on digestibility and ruminal fermentation in growing steers.

Eight ruminally fistulated steers (352 +/- 27 kg BW) were used in a replicated 4 x 4 Latin square design. Treatments were 1) 70% rolled barley +30% timothy hay (HC), 2) HC+folic acid (2 mg/kg BW; HC+F), 3) 30% rolled barley + 70% timothy hay (HF), and 4) HF+F. Total tract apparent digestibility of DM and CP were greater (P < or = .05) in steers fed the HC diet, whereas that of ADF and NDF was greater (P < .001) in steers fed the HF diet. Supplemental dietary folic acid had no effect on either of the forementioned variables, regardless of whether the animal received the HC or the HF diet. To compare ruminal DM disappearance, nylon bags containing either hay or barley were incubated in the rumen of each steer for 4, 8, 12, 24, and 48 h. Ruminal DM disappearance of hay and barley was affected (P < .05) by the type of diet fed but not by the addition of folic acid to either diet. Ruminal fluid was sampled on three consecutive days, at the following postprandial hours: 1, 2, 4, 8, 12, and 23. Differences in ruminal pH and individual VFA among treatments were attributable to the type of diet fed. Changes in ruminal VFA concentrations at various times after feeding were altered with folic acid addition; however, these modifications were not sufficient to affect in a significant way either ruminal or total tract digestibility.

Animal Feed↗
PubMed1993

In vitro ouabain-sensitive respiration and protein synthesis in ruminal epithelial papillae of Hereford steers fed either alfalfa or bromegrass hay once daily.

Seven Hereford steers (457 +/- 8.5 kg BW) with ruminal cannulas were fed either long or short chopped bromegrass (B) or alfalfa (A) hay at 90% of a 3-h ad libitum intake once daily between 0900 and 1200 in a 4 x 4 complete and 3 x 4 incomplete Latin square design. After evacuation of ruminal contents, papillae from the ventral sac of the rumen were excised at 0900, 1200, and 2100 and placed in oxygenated media. Oxygen consumption was determined polarographically, after which either 10(-4) M ouabain or 10(-4) M cycloheximide was added for determination of ouabain-sensitive (OSO2) or cycloheximide-sensitive (CSO2) O2 consumption, respectively. Additionally, protein synthesis was measured by uptake of [3H]phenylalanine. Twenty-four-hour patterns of ruminal fluid pH, osmolality, ammonia N, and VFA were also determined. Steers fed A exhibited a rapid rise in total O2, OSO2, and CSO2 immediately after consumption of a meal; the respiration patterns of ruminal epithelial papillae from animals fed B lagged behind those observed for animals fed A. Patterns of O2 consumption for both diets paralleled those observed for ruminal concentration of products of fermentation; those fed A had a larger magnitude of change in both O2 consumption and fermentation products. Ruminal epithelial O2 consumption seems to be determined by substrate availability and products of fermentation, and Na+,K+ATPase and protein synthetic activity each account for one-fifth of ruminal papillae O2 consumption. Fractional rates of protein synthesis were unaffected by type of forage consumed.

Ammonia↗
PubMed1993

Effect of the protein matrix on the digestion of cereal grains by ruminal microorganisms.

Experiments were conducted to investigate the role of the protein matrix in the digestion of barley and corn by ruminal microorganisms. Grains, ground and collected on sieves as two particle fractions .25 to .89 mm (small particles) and 2.00 to 3.00 mm (large particles), as well as isolated barley and corn starch granules, were incubated with ruminal inocula. For both grains, digestion of starch in small particles was greater (P < .001) than that of large particles. At 16 and 24 h starch digestion was greater (P < .01) in barley than in corn, for small and large particles. Digestion of barley starch granules did not differ (P > .05) from that of corn starch granules at any incubation time. A 4-h preincubation of small-particle corn and barley with protease increased (P < .001) microbial digestion of starch in corn at 16 h but did not affect digestion of barley. When four ruminally cannulated steers were fed diets containing 80% barley, corn, or wheat or 100% alfalfa hay in a 4 x 4 Latin square experiment, amylolytic activity of ruminal inoculum was higher for steers fed grains than for those fed alfalfa. However, when standardized for total viable counts of bacteria, ruminal amylolytic activity did not differ (P > .05) among diet treatments, but proteolytic activity of ruminal inoculum for steers fed alfalfa was higher (P < .01) than that for steers fed cereal grains. Activity of serine proteases in ruminal inoculum was higher (P < .05) for steers fed alfalfa than for steers fed grains.(ABSTRACT TRUNCATED AT 250 WORDS)

Amylases↗