Black rhinoceros (Diceros bicornis) and domestic horse (Equus caballus) hindgut microflora demonstrate similar fermentation responses to grape seed extract supplementation in vitro.

The domestic horse is used as a nutritional model for rhinoceros maintained under human care. The validity of this model for browsing rhinoceros has been questioned due to high prevalence of iron overload disorder (IOD) in captive black rhinoceros (Diceros bicornis), which is associated with high morbidity and mortality. Iron chelators, such as tannins, are under investigation as dietary supplements to ameliorate or prevent IOD in prone species. Polyphenolic compounds variably affect microbial fermentation, so the first objective of this experiment was to evaluate the effects of grape seed extract (GSE; a concentrated source of condensed tannins; CT) on black rhinoceros hindgut fermentation. Equine nutrition knowledge is used to assess supplements for rhinoceros; therefore, the second objective was to evaluate the domestic horse model for black rhinoceros fermentation and compare fermentation responses to GSE using a continuous single-flow in vitro culture system. Two replicated continuous culture experiments were conducted using horse and black rhinoceros faeces as inoculum sources comparing four diets with increasing GSE inclusion (0.0%, 1.3%, 2.7% and 4.0% of diet dry matter). Diet and GSE polyphenolic compositions were determined, and sodium sulphite effect on neutral detergent fibre extraction of CT-containing forages was tested. Increasing GSE inclusion stimulated microbial growth and fermentation, and proportionally increased diet CT concentration and iron-binding capacity. Horse and black rhinoceros hindgut microflora nutrient digestibility and fermentation responses to GSE did not differ, and results supported equine fermentation as an adequate model for microbial fermentation in the black rhinoceros. Interpretation of these results is limited to hindgut fermentation and further research is needed to compare foregut digestibility and nutrient absorption between these two species. Supplementation of GSE in black rhinoceros diets up to 4% is unlikely to adversely affect hindgut nutrient digestibility or microbial viability and fermentation.

Effect of corn inclusion on soybean hull-based diet digestibility and growth performance in continuous culture fermenters and beef cattle.

Two experiments were conducted using soybean hull (SH) diets with increasing corn proportions to determine increasing corn inclusion effects on fermentation characteristics, diet digestibility, and feedlot performance. The hypothesis was that fiber digestibility would quadratically respond to starch proportion in the diet with a break point where starch inclusion improved fiber digestion and feedlot performance. Proportionately, the diets contained 100:0 (SH100), 90:10 (SH90), 80:20 (SH80), 60:40 (SH60), or 20:80 SH:corn (SH20). In Exp. 1, diets were randomly distributed over 24 continuous culture fermenters and fed for 7 d. In Exp. 2, forty steers (347 ± 29 kg BW) and 50 heifers (374 ± 24 kg BW) were blocked by gender, stratified by BW, and distributed across diets. Cattle were fed for 70 d with titanium dioxide included in the diet for the final 14 d and fecal samples collected to measure digestibility. Individual DMI was measured using GrowSafe Feed Intake system. Data were analyzed using the MIXED procedure of SAS with diet evaluated as the fixed effect. In Exp. 1, NDF digestibility (NDFd) linearly decreased ( = 0.04) and ADF digestibility (ADFd) tended to linearly decrease ( = 0.09) as corn increased. Dry matter digestibility (DMd) was cubic ( = 0.01) and OM digestibility (OMd) was quadratic ( = 0.03), and among the 4 SH-based diets, DMd and OMd were greatest for SH90. Acetate:propionate ratio and pH were quadratic ( < 0.01) and greatest for SH80. In Exp. 2, ADG and G:F linearly increased ( < 0.01) as corn inclusion increased. Among the 4 SH-based diets, ADG was numerically greatest for SH80. There was no DMI difference ( ≥ 0.4) due to diet. As corn inclusion increased, DMd tended to linearly increase (P = 0.06), as did OMd ( = 0.05). Both NDFd and ADFd were quadratic ( = 0.04) and greatest for SH80. Overall, feedlot performance increased and fiber digestibility decreased as corn inclusion increased. However, based on continuous culture digestibility and VFA values as well as feedlot digestibility and performance, optimal corn inclusion for growth and diet utilization in the 4 SH-based diets fell between SH80 and SH90, or 0.4 and 0.2% BW corn supplementation. In this study, providing 0.4% BW corn supplementation in fiber-based diets (SH80) provided greater improvement in performance compared with 0.2% BW corn supplementation (SH90).

Integrating bermudagrass into tall fescue-based pasture systems for stocker cattle.

The daily BW gain of stocker steers grazing tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbysh. = Schedonorus arundinaceus (Schreb.) Dumort.]-based pastures typically declines during summer. To avoid these declines, in part to mitigate the effects of tall fescue toxicosis, it is commonly advised to move cattle to warm-season forage during this period. A 3-yr (2006, 2007, and 2008) grazing study was conducted to evaluate the effect of replacing 25% of the area of a tall fescue/clover (81% endophyte-infected) pasture system with "Ozark" bermudagrass [Cynodon dactylon (L.) Pers.] overseeded with clover (Trifolium spp.) to provide summer grazing for stocker steers (TF+BERM). The TF+BERM treatment was compared with a grazing system in which tall fescue/clover (TF) pastures were the only type of forage available for grazing. Our objective was to determine if replacement of 25% of the land area in a fescue system with bermudagrass would increase annual beef production compared with a system based solely on tall fescue. The study was conducted at the Southwest Research and Education Center of the University of Missouri near Mt. Vernon. Each treatment was rotationally stocked with 5 steers (248 ± 19.3 kg) on 1.7 ha. Fertilizer applications were applied at rates recommended for each respective forage species. Total forage production, BW gain per hectare, and season-long ADG of steers was greater (P < 0.06) for TF+BERM than for TF in 2006, but none of these measures differed (P > 0.19) in 2007 or 2008. In vitro true digestibility of pastures was greater (P = 0.01) for TF (84.4%, SEM = 0.64%) compared with TF+BERM (80.6%, SEM = 0.79%), even in summer. The decreased in vitro true digestibility of the bermudagrass pastures likely negated any benefit that animals in TF+BERM had in avoiding the ergot-like alkaloids associated with endophyte-infected tall fescue. Renovating 25% of the pasture system to bermudagrass provided some benefit to the system in years when summertime precipitation was limited (2006) but provided no value in wetter years (2007 and 2008). Although renovating endophyte-infected tall fescue pastures to a warm-season forage is a widely used practice to mitigate tall fescue toxicosis, the benefits of this practice are limited if forage quality of the warm season component is poor.

Fructooligosaccharide supplementation in the yearling horse: effects on fecal pH, microbial content, and volatile fatty acid concentrations.

Short-chain fructooligosaccharides (FOS) were supplemented to the diets of nine quarter horses ranging in age from 489 to 539 d with initial BW averaging 400.6 +/- 21.2 kg. The objectives of this study were to determine the effects of dietary FOS on the fecal responses in terms of pH, the microbial population, and VFA concentrations. The horses were used in a 3 x 3 replicated Latin square design, fed according to NRC requirements, and their individual diets were supplemented with no FOS (CON), 8 g of FOS/d (LOW), or 24 g of FOS/d (HIGH) over three 10-d feeding periods. On the last 3 d of each 10-d feeding period, a single fecal sample was collected between 0730 and 0930. Fecal pH decreased linearly (P = 0.01) from 6.48 with the CON diet to 6.38 with the HIGH diet, but there was no change (P = 0.19 for linear effect) in fecal consistency among treatments. A quadratic effect (P < 0.01) was observed for fecal Escherichia coli population, but no difference (P = 0.88 for linear effect) was found in fecal Lactobacilli enumeration among treatments. The presence of fecal Bifidobacteria was unable to be confirmed and was therefore not reported. Fecal acetate concentrations increased linearly (P = 0.03), with means of 2.13, 2.18, and 2.52 mg/g of wet feces for CON, LOW, and HIGH treatments, respectively. Similarly, fecal propionate concentrations increased linearly (P = 0.01), with means of 0.58, 0.64, and 0.73 mg/g for CON, LOW, and HIGH treatments, respectively. Fecal butyrate concentrations also increased linearly (P = 0.02), with means of 0.40, 0.46, and 0.54 mg/g for CON, LOW, and HIGH treatments, respectively. Total VFA (P = 0.01) and lactate (P = 0.02) concentrations increased linearly, with total VFA means of 3.47, 3.69, and 4.25 mg/g for CON, LOW, and HIGH treatments, respectively, and lactate means of 0.36, 0.41, and 0.47 mg/g for CON, LOW, and HIGH treatments, respectively. Supplementing FOS in diets fed to yearling horses altered fecal microbial populations, fecal VFA concentrations, and pH.

Level of supplemental protein does not influence the ruminally undegradable protein value.

Two experiments were conducted to determine whether elevating the percentage of ruminally undegradable protein (RUP) in the diet would influence the RUP value of the protein feedstuff. A single-effluent, continuous-culture study was designed to test the effect of RUP inclusion rate in the diet on ruminal degradability of the protein. Treatments consisted (DM basis) of a control diet with no supplemental protein, control + 2.5% bloodmeal (BM-L), control + 5% bloodmeal (BM-H), control + 4.45% soybean meal (SBM-L), and control + 8.89% soybean meal (SBM-H). Proteolytic activity and total VFA concentration were not affected (P = 0.73 and P = 0.13) by treatment. Within protein source, dietary RUP value was not affected (P = 0.94) by level of inclusion. When corrected for control diet RUP flow, the RUP value of the blood meal (BM) protein was higher (P = 0.01) than soybean meal (SBM); however, level of supplementation did not affect (P = 0.07) the RUP value of BM or SBM. In Exp. 2, 32 British x Continental crossbred steers (276 +/- 26.3 kg) were fed for 72 d to examine the effects of balancing the AA:energy ratio, using BM as a RUP source, on ADG, G:F, and lean tissue deposition. Diets were formulated to provide increasing levels of arginine, while ruminally degradable protein and energy were held constant. Four dietary treatments provided 0.5, 1, 1.5, and 2x the required amount of arginine, whereas the control diet had no BM included. Daily DMI averaged 7.6 kg/steer and did not differ (P = 0.71) among treatments. Steers gained an average of 1.9 kg/d and average G:F was 0.260, with no differences (P = 0.60 and P = 0.97, respectively) among treatments. There was no difference (P = 0.48) in the change in 12th-rib fat depth during the study; however, change in LM area was affected quadratically as the level of BM increased in the diet, with the greatest increase in LM area occurring in steers fed the 1x and 1.5x required arginine treatments. Balancing the AA:energy ratio did not affect G:F, DMI, or ADG; however, it increased deposition of lean in the LM quadratically. Level of dietary inclusion of BM as an RUP source does not affect its RUP value or efficacy of providing postruminal AA in growing steers.

Evaluation of ruminally protected methionine and lysine or blood meal and fish meal as protein sources for lactating Holsteins.

Forty lactating Holstein cows averaging 55 days in milk were used in a randomized block designed experiment to evaluate the effectiveness of ruminally protected Met and Lys compared with that of ruminally undegradable protein for supporting lactation. Cows were fed total mixed diets for 15 wk. Diets were formulated to be isonitrogenous with the same base ingredients resulting in base crude protein percentage of 15.5. Supplemental crude protein supplied by urea, soybean meal, or a 50:50 (wt/wt) mixture of fish and blood meal increased total dietary nitrogen to 18.0% of diet DM. Two additional diets consisted of the basal diets soybean meal and urea, which were supplemented with ruminally protected DL-Met and Lys-HCL at 10 and 25 g/d, respectively (soybean meal + amino acids (AA), urea + AA). Mean measures of dry matter intake, milk yield, milk protein percentage, and milk fat percentage were not affected by protein supplement. Milk protein yield, milk fat yield, casein yield, and casein percentage also were not affected by source of supplemental protein. Results indicate that at the level of crude protein intake relative to milk production in this experiment, the source of protein did not affect lactational performance.

Amino acid and energy interrelationships in growing beef steers: II. Effects of energy intake and metabolizable lysine supply on growth.

We conducted three experiments to determine the optimal metabolizable Lys:net energy ratio for growth of beef calves. The single basal diet fed contained corn (56.1%), soybean hulls (18%), cottonseed hulls (15%), animal fat (4.25%), and corn gluten meal (5.6%). In Exp. 1, 54 steers were individually fed the basal diet at 1.5, 2.25, and 3.0 times NEm requirement; rations were top-dressed with 3.4 g of rumen-stable (RS) Met and either 0, 2, 4, 6, 8, or 12 g of RS-Lys daily. An additional 18 steers were fed the same three levels of energy and supplemented with 125 g of blood meal per steer. In Exp. 2, 68 crossbred steers were subjected to the same experimental protocol, with the exception that only the two highest levels of energy were used. Of these steers, 48 were fed individually and received the RS-Lys treatments; the remaining 20 steers received 125 g of blood meal per steer. No interaction (P > .10) was detected between level of supplemental Lys and energy intake in Exp. 1 or 2. Supplementation with RS-Lys improved (P < .01) ADG in Exp. 1, but it had no effect (P > .10) on growth in Exp. 2. The Lys requirement estimates were 44.3 and 51.3 g/d, corresponding to maximal growth rates of 1.21 and 1.64 kg/d for the 2.25 and 3.0 times maintenance treatments, respectively. Comparing the growth rates of steers fed supplemental Lys with those of steers fed blood meal in Exp. 1 and 2 revealed an ADG advantage (P < .03) with blood meal supplementation. To confirm the blood meal response, Exp. 3 used 75 crossbred steers fed the basal diet at 3.0 times NEm requirement plus either 3.4 g RS-Met, 3.4 g RS-Met and 12 g RS-Lys, or 125 g of blood meal per steer. Blood meal supplementation improved (P < .01) growth of steers over those fed supplemental Met or Met plus Lys. Although a distinct relationship between amino acid requirements and energy supply may exist, Lys and Met were not first-limiting in these experiments, or selective supplementation with undegradable protein may have provided some factor that enhanced performance beyond that detected with Lys and Met alone.

Amino acid and energy interrelationships in growing beef steers: I. The effect of level of feed intake on ruminal characteristics and intestinal amino acid flows.

Five cannulated Holstein steers (538 +/- 35 kg) were used in a 4 x 4 Latin square design experiment with extra observations to examine the influence of level of feed intake on postruminal flow and intestinal disappearance of N and amino acids (AA). Treatments consisted of a single diet fed at four levels of energy intake (1.5, 2.0, 2.5, and 3.0 times NEm requirement). The diet was formulated on a DM basis to contain 13.25% CP using cracked corn (56.1%), soybean hulls (18%), cottonseed hulls (15%), soybean oil (4.25%), and corn gluten meal (5.6%). Increasing feed intake linearly increased (P < .0001) the quantity of OM truly digested in the stomach but tended to decrease (P = .11) OM digestion as a percentage of intake. Level of feed intake had no effect (P > .10) on ruminal pH, NH3 N, or peptide concentration or on particulate and fluid passage rates. However, total VFA concentration increased linearly (P < .0001) and the acetate: propionate ratio decreased linearly (P < .0001) as feed intake increased. Flows of microbial and nonmicrobial N at the duodenum linearly increased (P < .002) with increasing intake but did not differ (P > .10) as a percentage of intake. Level of feed intake did not affect (P > .10) microbial efficiency, N disappearance from the small intestine, or total tract N digestibility. With the exception of tryptophan, flows of all individual AA increased linearly (P < .01) with increasing intake. As a percentage of duodenal flow, AA digestion in the small intestine did not differ (P > .10), leading to a linear increase (P < .10) in the net quantity of individual (with the exception of tryptophan) and total AA disappearing from the small intestine as feed intake increased. Likewise, the profile of AA (except tryptophan) disappearing from the small intestine was unaffected (P > .10) by level of feed intake. When compared with predicted requirements for a 227-kg growing beef steer, Arg, Met, His, and Lys were suggested to be the most limiting AA for growth when this diet is fed. We conclude that altering energy intake by restricting intake of a single diet has only minor effects on the profile of digestible AA or other nutrients presented to the animal.

Supplemental protein and energy for beef cows consuming endophyte-infected tall fescue.

Effects of energy and protein supplementation of endophyte (Acremonium coenophialum)-infected (E+) and noninfected (E-) tall fescue (Festuca arundinacea Schreb.) on forage intake, digestibility, N flow to the small intestine, and cow-calf productivity was evaluated in two experiments. In Exp. 1, 10 ruminally and duodenally cannulated steers were fed either E- or E+ hay with four supplements or E- or E+ hay unsupplemented. Four supplements formulated with either cracked corn or soybean hulls with 100 or 200 g/d of ruminally undegraded intake protein (UIP) were compared. Levels of UIP were varied by adding soybean meal or blood meal. Hay OM intake was not affected (P > .20) by source of energy of level of UIP; however, intake of E- was greater (P < .05) than that of E+. True ruminal OM digestion tended to be greater (P < .12) for steers fed 200 g/d of UIP than for steers fed 100 g/d. Steers receiving 200 g/d of UIP had increased (P < .10) total N flow to the duodenum compared with steers receiving 100 g/d but similar (P > .20) microbial efficiencies. In Exp. 2, 30 cows (average initial BW 459 +/- 26 kg) and their calves (average initial BW 74 +/- 5 kg and 74 +/- 5 d of age) grazed an 8.1-ha E+ pasture from late May to late July. Cows were individually fed supplements used in Exp. 1 each day. Cows that received cracked corn lost .10 kg/d when fed 100 g/d of UIP but gained .33 kg/d when fed 200 g/d. Cows fed soybean hulls and 100 g/d of UIP gained .07 kg/d, whereas cows provided 200 g/d lost .10 kg/d. Calves nursing cows supplemented with 100 g/d of UIP gained more (P < .08) BW because of increased (P < .07) milk consumption and slightly greater (P < .19) forage intake than calves nursing cows supplemented with 200 g/d of UIP.

Effect of increasing the dietary level of rapeseed meal on intake by growing beef steers.

Three experiments were conducted to determine the effects of rapeseed meal on intake by cattle. In the first experiment, the effect of increasing rapeseed meal level on intake, growth, and performance of growing beef steers was evaluated. In the second experiment, the effect of extrusion (glucosinolate reduction) on supplement intake by steers was evaluated. In the third experiment, the effect of increasing dietary rapeseed meal level on supplement intake was evaluated. In the first experiment, rapeseed meal replaced soybean meal at 0, 33, 67, or 100% of the supplemental protein. Dry matter intake, crude protein intake, and serum thyroxine levels were decreased linearly (P < .01) with increasing level of rapeseed meal in the supplement. Protein sources used in Exp. 2 were soybean meal, rapeseed meal, extruded rapeseed meal, and soybean meal containing rapeseed oil at the same level as the rapeseed meal. In Exp. 3, the protein sources were composed of different combinations of rapeseed meal and soybean meal (100% rapeseed meal; 67% rapeseed meal and 33% soybean meal; 33% rapeseed meal and 67% soybean meal; and 100% soybean meal). Supplement intake was measured at .5, 4, and 24 h after feeding in both experiments. Extrusion treatment, which reduced glucosinolate content in rapeseed meal 75%, did not improve (P > .10) supplement intake. Rapeseed meal resulted in lower supplement intakes at .5 and 4 h than the soybean meal and soybean meal+rapeseed oil supplements (P = .003).(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of the ruminal escape value and duodenal amino acid flow of rapeseed meal.

A 4 x 4 Latin square metabolism trial was conducted to evaluate protein escape potential, duodenal amino acid (AA) flows, and ruminal digestion effects of rapeseed meal (RSM) when fed with non-endophyte-infected tall fescue (Festuca arundinacea) hay. Four Holstein steers (average BW = 400 +/- 6.5 kg), each equipped with ruminal and duodenal cannulas, were fed twice daily at 0700 and 1900. Protein supplements compared with RSM, soybean meal (SBM), blood meal (BM), and a negative control based on urea (U). Diets were formulated to contain 14% CP. Rapeseed meal-supplemented steers had lower (P < .01) ruminal NDF and OM digestibilities than steers fed SBM. Based on in situ data, the lower NDF, DM, and OM digestibilities that occurred when RSM was fed than when SBM and BM were fed were possibly due to the reduced digestibility of the hulls in the RSM. Ruminal pH was not different (P > .05) among treatments. Blood meal supplementation decreased (P < .01) ruminal and total tract CP digestibilities compared to all other supplements. Ruminal liquid and particulate passage rates were not changed (P > .05) by supplement source. Urea supplementation resulted in the highest (P < .01) ruminal ammonia concentration, whereas BM supplementation resulted in the lowest ruminal ammonia concentration (P < .01). Blood meal resulted in greater (P < .01) dietary protein flow to the duodenum than the other treatments. However, microbial efficiencies, as well as microbial DM and protein flows to the duodenum were not different (P > .05) among treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of endophyte-infected tall fescue consumption and use of a dopamine antagonist on intake, digestibility, body temperature, and blood constituents in sheep.

Two experiments were conducted with lambs that consumed endophyte-infected (Acremonium coenophialum) tall fescue diets under elevated temperature and humidity and supplemented with the dopamine antagonist metoclopramide (M). In Exp. 1, 12 ruminally cannulated wethers (average weight 49 kg) were allotted by weight to either an endophyte-free diet (E-) or endophyte-infected diet (E+; 1,170 ppb of ergovaline), or E+ supplemented with M (15 mg/kg of lamb BW; E+M). Ad libitum DM intake and digestibility were lower (P < .05) for E+ than for E- diet. Supplementation of E+ with M increased (P < .05) DM intake by 27.6% but did not change DM digestibility. Body temperature increased (P < .05) when lambs consumed E+ and was further increased when M was supplemented. For Exp. 2, 19 wether lambs (average weight 24 kg) were allotted to treatments to evaluate the effects of endophyte consumption (0 vs 2,430 ppb of ergovaline) and supplementation with M (0 vs 20 mg/kg BW). An interaction (P < .05) of main effects was measured for DM intake. Lambs that consumed E+M consumed more DM than did lambs fed only E+, but lambs offered the E- diet and supplemented with M did not increase DM consumption. Diet DM digestibility was not different among treatments. Skin vaporization decreased (P < .05) due to E+ consumption and M supplementation. The concentration of prolactin in plasma was decreased (P < .05) by consumption of E+ (8 vs 136 ng/mL) and did not increase due to M supplementation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of grass maturity and legume substitution on large particle size reduction and small particle flow from the rumen of cattle.

Five ruminally and abomasally cannulated heifers (average weight 365 kg) were fed 6 kg/d of early (EOG) or late (LOG) maturity orchardgrass (OG) hay with or without replacement of EOG or LOG by 1.5 kg/d red clover hay (RC) in a 5 x 5 Latin square design. A fifth treatment, of LOG supplemented with 100 g/d casein (LOG + C), was used to evaluate the effect of supplemental protein. In situ fiber digestion, in vivo nutrient digestion and rate of passage from the rumen of large (retained on a 1.68-mm screen; labeled with La) and small (passed a 1.68-mm screen; labeled with Sm) EOG and LOG particles were determined in heifers fed these diets. Early maturity OG hay had 20% and 62%, respectively, greater (P less than .05) rates, and 61% and 73%, respectively, greater (P less than .05) extents of in situ NDF and ADF disappearance than LOG. Red clover substitution for OG increased (P less than .05) in situ extent of NDF disappearance by 6%. Early maturity OG large and small particles had 40% and 36%, respectively, greater (P less than .05) rates of passage than LOG. Large and small particle ruminal pool sizes were increased (P less than .05) by 115% and 33%, respectively, with LOG. Red clover substitution for OG increased (P less than .10) large and small particle output (kg/d) from the rumen by 15% and large particle rate of passage by 20%. Grass maturity may be affecting intake through rate of large particle size reduction and passage and small particle passage, although legume supplementation of OG may influence intake by increasing rate of large particle size reduction and passage.

Effects of treating wheat straw with pH-regulated solutions of alkaline hydrogen peroxide on nutrient digestion by sheep.

An experiment using a 4 X 4 Latin square design was to determine effects of treating wheat straw with pH-regulated (pH = 11.5) solutions of hydrogen peroxide on site and extent of nutrient digestion in multiple-fistulated sheep. Regulating reaction pH at 11.5 prevented solubilization of some cell wall hemicelluloses, resulting in improved retention of DM. Diets fed to sheep contained 33 or 70% wheat straw either untreated or treated with alkaline hydrogen peroxide. Sheep fed diets of treated wheat straw digested more DM, NDF, ADF, and cellulose anterior to the duodenum and in the total tract than when fed diets of untreated wheat straw. Apparent CP digestion before the duodenum was highest when sheep were fed the treated 33% wheat straw diet and untreated 70% wheat straw diet. Treatments did not affect apparent nutrient digestibilities in the large intestine. Ruminal pH was lower when sheep were fed the alkaline hydrogen peroxide-treated or diets containing 33% wheat straw. Ruminal ammonia concentrations were highest when sheep were fed the untreated 70% wheat straw diet. Molar proportions of ruminal acetic and propionic acids were unaffected by diet. Alkaline hydrogen peroxide treatment substantially increased susceptibility of structural carbohydrates of wheat straw to microbial degradation in the gastrointestinal tract of sheep.