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The objective of this study was to determine whether supplementing organic acids can prevent incidences of subacute ruminal acidosis (SARA) in beef heifers fed a diet consisting of 8% barley silage and 92% barley grain-based concentrate (DM basis). Ten ruminally cannulated Hereford crossbred heifers (484 ± 25 kg BW) were used in a replicated 5 × 5 Latin square design with 14-d periods including 10 d for dietary adaptation and 4 d for measurements. Dietary treatments included no supplementation (Control), low fumaric acid (61 g/d), high fumaric acid (125 g/d), low malic acid (59 g/d), and high malic acid (134 g/d). Organic acid supplementation had no effect on DMI ( = 0.77). Similarly, no effects were observed on mean ( = 0.74), minimum ( = 0.64), and maximum ( = 0.27) ruminal pH measured continuously for 48 h. Moreover, area under the curve for pH thresholds 6.2 ( = 0.97), 5.8 ( = 0.66), 5.5 ( = 0.55), and 5.2 ( = 0.93) was similar for all treatments. However, malic acid supplementation lowered the amount of time that ruminal pH was <6.2 compared with the Control ( = 0.02) and fumaric acid treatments ( < 0.01). No effects were observed on total VFA concentrations with organic acid supplementation ( = 0.98) compared with the Control, but greater total VFA concentrations were observed with fumaric acid compared with the malic acid treatments ( = 0.02). The population of total culturable bacteria 3 h after feeding was reduced with supplemental malic acid compared with the Control ( = 0.03) and fumaric acid treatments ( = 0.03). However, no effects were observed with organic acid supplementation on lactic acid-utilizing bacteria ( = 0.59). In conclusion, under the conditions of the present study, organic acid supplementation did not have any significant effects on ruminal fermentation parameters compared with the Control and were not effective in preventing SARA in beef cattle fed high-grain diets.

A slow-release form of nitrate (encapsulated nitrate [EN]) was investigated for effects on risk of toxicity, feed consumption rates, and feed sorting behavior in 2 experiments. In Exp. 1, 5 beef heifers (806 ± 72 kg BW) were fed once daily at 75% of ad libitum intake. Supplementary EN (85.6% DM; 71.4% NO3(-) on a DM basis) was increased by 1% every 4 d from 0 to 1.0, 2.0, 2.9, 3.9, 4.8, and 5.8% of dietary DM (from 10.3 to 15.6% CP and 0.11 to 4.8% total NO3(-)). During the study, a heifer was removed due to nitrate poisoning with 59% blood methemoglobin (MetHb; % of total hemoglobin) at 2.9% EN and another due to refusal to eat the 2% EN diet. When dietary EN increased from 0 to 5.8%, DMI (8.8 to 7.6 kg/d; P < 0.001) and feed consumption from 0 to 3 h were decreased (70.3 to 48.6% of total feed offered on an as-is basis; P = 0.001) and feed consumption from 12 to 24 h was increased (0.6 to 22.6%; P < 0.001). Blood MetHb at 1% EN was negligible (<1.5% of total hemoglobin). However, MetHb levels were greater (average 9.8 vs. 3.1% and maximum 23.6 vs. 13.6% at 3 h) at 2.0 and 2.9% EN than at 3.9, 4.8, and 5.8% EN. In Exp. 2, 8 beef heifers (451 ± 21 kg BW) were used in a replicated 4 × 4 Latin square design and fed for ad libitum intake, once daily, diets containing 0, 1, 2, and 3% EN (isonitrogenous, 12.7% CP, and 0.15 to 2.5% total NO3(-) in dietary DM). Each period consisted of 14 d for adaption and 14 d for sampling followed by a 7-d washout. During adaptation, EN was provided to heifers in a stepwise manner (an increase by 1% every 4 d). In Exp. 2 with ad libitum feeding, feed consumption rates were not different (41.8% of total feed consumed from 0 to 3 h; P = 0.56) among EN levels, but DMI tended to decrease linearly (0 to 3% EN; 10.4 to 10.1 kg/d; P = 0.06) and feed was sorted (linear, P < 0.05) against concentrates (containing EN) with EN inclusion. Potential toxicity of nitrate based on blood MetHb was not observed (all samples <2.0% of total hemoglobin). In both studies, ruminal pH increased numerically (Exp. 1) and significantly (Exp. 2; linear, P = 0.04) with EN. In conclusion, studies indicated that the organoleptic properties of diets containing >3% EN may have caused lower feed intake, reduced feed consumption rates, and feed sorting. In addition, feed consumption rate, which was altered by restrictive or ad libitum feeding, was an important factor affecting the potential toxicity of nitrate (e.g., MetHb). Ad libitum feeding minimized risks of nitrate toxicity.

The objectives were to characterize the effects of supplemental CP concentration and ruminal degradability in barley-based finishing diets on microbial protein synthesis, ruminal fermentation and nutrient digestion, and route and chemical form of N excretion in beef cattle. Four Angus heifers (564 ± 18 kg BW) with ruminal and duodenal cannulas were used in an experiment designed as a 4 × 4 Latin square with four 28-d periods (9 d for diet adaptation and 19 d for measurements). The basal diet consisted of 9% barley silage and 91% barley-based concentrate (DM basis). Dietary treatments included the basal diet with no added protein (13% CP) or diets containing 14.5% CP by supplementation with urea (UREA), urea and canola meal (UREA+CM), or urea, corn gluten meal, and xylose-treated soybean meal (UREA+CGM+xSBM). Nutrient digestion was determined using Yb as a digesta flow marker and purine N as a microbial marker with the collection of ruminal, duodenal, and fecal samples over 5 d. The next week, total collections of feces and urine were performed for 5 d to quantify route and chemical form of N excretion. Feed offered was restricted (95% of ad libitum) and there was no effect of the dietary treatments on DMI (P = 0.55); therefore, N intake was less (P < 0.05) in heifers fed the 13% CP diets than the 14.5% CP diets. Supplemental RDP and RUP had no effect on ruminal NH3-N (P = 0.17), peptide N (P = 0.46), and VFA (P = 0.62) concentrations, flow of microbial (P = 0.69) and feed (P = 0.22) N, and ruminal and total tract nutrient digestibility (P ≥ 0.18). Nutrient digestion in the rumen and total tract averaged 75.4 ± 3.8% and 84.6 ± 0.9% for OM, 80.8 ± 3.6% and 95.8 ± 0.8% for starch, and 41.2 ± 7.9% and 60.4 ± 3.3% of intake for NDF, respectively. Daily output of N in feces (P = 0.91) and urine (P = 0.14) were not affected by the dietary treatments. Fecal N output averaged 19.9 ± 1.9% (P = 0.30) and urine N output averaged 44.1 ± 2.8% (P = 0.63) of N intake. Urea N output, however, was greater (P < 0.05) in heifers fed the 14.5% CP than the 13% CP diets and was the major form of N in urine (68.3% in heifers fed the 13% CP diet and 78.7 ± 2.9% in heifers fed the 14.5% CP diets; P < 0.10). Beef cattle fed barley-based finishing diets containing 13% CP do not require additional RDP or RUP to meet microbial or host N requirements. Barley-based finishing diets with no supplemental CP minimized urea N excretion and the potential loss of N from the system.

The objectives of the study were to characterize the effects of CP concentration and ruminal degradability of barley-based backgrounding diets on route and chemical form of N excretion, ruminal fermentation, microbial protein synthesis, and nutrient digestion in beef cattle. Four Angus heifers (479 ± 14.6 kg average BW) with ruminal and duodenal cannulas were used in an experiment designed as a 4 × 4 Latin square. The basal diet consisted of 54% barley silage and 46% barley grain-based concentrate (DM basis). Dietary treatments included the basal diet with no added protein (12% CP) or diets formulated to contain 14% CP by supplementation with urea (UREA), urea and canola meal (UREA+CM), or urea, corn gluten meal, and xylose-treated soybean meal (UREA+CGM+xSBM). The amount of feed offered was restricted to 95% of ad libitum intake. There was no effect of the diets on DMI (P = 0.38), and therefore, N intake was less (P < 0.05) in heifers fed the 12% CP diets than the 14% CP diets. Fecal N output was not affected by the diet (P = 0.15), but urine N (P < 0.10) and urea N output were greater (P < 0.05) in heifers fed the 14% CP than the 12% CP diets. There was no effect of CP degradability (P > 0.10) on the amount of urine N output. Urine N output was 38.9 and 45.1 ± 5.50% of N intake in heifers fed the 12% CP and 14% CP diets (P < 0.05), respectively. Urea N, the form of N most susceptible to NH3-N volatilization and loss, was the major form of N in urine (75.5% in heifers fed the 12% CP diet and 81.4 ± 1.7% in heifers fed the 14% CP diets; P < 0.05). Supplemental RDP (UREA+CM) and RUP combined with urea (UREA+CGM+xSBM) to provide 14% CP increased (P < 0.05) ruminal NH3-N but had no effect on ruminal peptide N (P = 0.62) and free AA N (P = 0.18) concentration, the flow of microbial (P = 0.34) and feed (P = 0.55) N, and ruminal (starch, P = 0.11; NDF, P = 0.78) and total tract nutrient digestibility (OM, P = 0.21; starch, P = 0.16). Supplementation of barley-based backgrounding diets containing 12% CP with NPN alone or combined with ruminally degradable and undegradable true protein to attain 14% CP had no effect on fecal N output, but urine N and urea N increased irrespective of protein source. In addition, the ruminal degradability of the protein sources did not influence the composition of protein flowing to the intestine and site and extent of nutrient digestibility.

Three groups of five wethers with ruminal and duodenal cannulas and maintained as either fauna-free (FF) or inoculated with total mixed fauna (TF) or Entodinium caudatum as a single-species monofauna (EN) were used in an experiment with two 28 d periods. In the first period, the sheep were fed a control barley-based diet (40:60 concentrate to silage DM) and in the second period the diet was supplemented with 187 g DM of Enterolobium cyclocarpum for the last 12 d of the period. The diets of period 1 and 2 were isonitrogenous. There was no effect of fauna on apparent ruminal and total tract organic matter and fibre digestion, but bacterial and microbial N flow and efficiency were improved in FF sheep compared to TF sheep. In period 2, protozoal numbers were reduced between 31 and 88 % 2 h after feeding E. cyclocarpum for the third to twelfth day of supplementation and by an average of 25 % in samples collected over the 24 h feeding cycle. Supplementation of the diet with E. cyclocarpum and the consequent protozoal reduction in TF and EN sheep improved the flow of non-ammonia N and bacterial N to the small intestine and the efficiency of microbial synthesis. However, E. cyclocarpum reduced ruminal organic matter digestion, especially in faunated sheep, and total tract organic matter, N and fibre digestion. Thus, a reduction in the protozoal cell numbers of 25 % was sufficient to achieve the beneficial effects of reduced fauna on the bacterial protein supply, but diet digestibility was reduced.

Ruminal escape of various amounts of methionine hydroxy analog [D,L-2-hydroxy-4-(methylthio)-butanoic acid (HMB)] was measured in an experiment designed as a 4 x 4 Latin square using four lactating dairy cows with cannula in the rumen and duodenum. The cows were fed a diet composed of corn silage, alfalfa haylage, rolled barley grain, canola meal, and blood meal, three times per day. The cows were fed the liquid analog each day for 1 wk before the experiment was started. On the day of the experiment, each cow received an intraruminal bolus dose of 0, 25, or 50 g of the liquid analog (Alimet feed supplement, 88% HMB) or 51.2 g of a dry calcium salt of the analog (86% HMB; MHA) mixed with 0.5 kg of ground barley grain. A liquid phase marker (Co-EDTA) was administered as a bolus dose into the rumen at the time of administration of the methionine hydroxy analogs. Rumen and duodenal contents, and blood serum were collected at 0, 1, 3, 6, 9, 12, and 24 h relative to the time of dosing. Rumen and duodenal samples were analyzed for Co and HMB, and serum was analyzed for free methionine. Fractional rate constants for the passage of the liquid marker (k(p)) and the decline of HMB concentration in the rumen (k(rHMB)) were determined by nonlinear regression. Liquid passage from the rumen was similar among the four analog treatments (0.136 +/- 0.012/h; mean +/- SEM). Ruminal escape of HMB as a percentage of the dose (100% x k(p)/k(rHMB)) did not differ between cows receiving 25, 50, and 51.2 g of the methionine analogs (42.5, 41.0, and 34.9 +/- 9.0%, respectively) and averaged 39.5%. Duodenal appearance of HMB as a percentage also did not differ between cows receiving 25, 50, and 51.2 g of the methionine analogs (16.2, 26.8, and 22.7%, respectively) and averaged 22%. Omasal absorption of HMB was variable ranging from 12.3 to 26.3% and averaged 17.6%. Serum methionine concentration peaked at 3 and 6 h after dosing and increased in proportion to the amount of the analog administered. It was concluded that 39.5% of the methionine hydroxy analog escaped rumen degradation, the percentage of the dose that escaped the rumen was not affected by the amount or form of the methionine analog fed, and the analog that escaped ruminal degradation was likely absorbed and metabolized to methionine.

Bioavailability of Met from a rumen-protected Met product was evaluated in two experiments using three ruminally and duodenally cannulated lactating (experiment 1) and nonlactating (experiment 2) dairy cows. In the first experiment, the ruminal in situ and mobile bag technique was used to assess ruminal degradability and intestinal disappearance of Met from the protected Met product. Effective ruminal degradability of Met at a ruminal outflow rate of 0.11/h was 21.7%. Combining effective ruminal degradability with intestinal digestibility yielded an estimate of Met availability of 25%. In the second experiment, designed as a 3 x 3 Latin square, Met availability was assessed by determining the response of plasma Met to supplementation of the protected Met product relative to that of duodenally administered Met. The periods were 1 wk with cows fed a meal containing 0, 20, or 63 g of protected Met on d 1 and infused intraduodenally with 10.7 g of Met on d 4. Blood was collected at various times relative to the time of oral dosing and the commencement of the duodenal infusion. Plasma Met response measured as area under the curve increased linearly with increasing protected Met. The response of plasma Met increased by 33 and 65.5% of the control values for 20 and 63 g of protected Met, respectively. Intestinal bioavailability of Met in the protected Met product ranged from 22 to 34%.

The effects of protozoa on ruminal NH3-N kinetics and bacterial N recycling were measured in five sheep (57.6+/-7.1 kg BW, x +/- SD) with ruminal and duodenal cannulas in naturally faunated, defaunated, and refaunated periods. The sheep were fed a diet of 239 g of alfalfa haylage and 814 g of barley concentrate per day (DM basis) divided into 12 equal portions and allocated at 2-h intervals. A pulse dose of 300 mg of 15N as [15N]NH4Cl was administered into the rumen (on d 1 and 15) and 300 mg of 15N as [15N]urea was administered intravenously to the blood (d 8). Enrichment of 15N was measured in ruminal NH3-N, bacterial N, and plasma urea N over a period of 35 h. Total collection of urine was made for 5 d and analyzed for purine derivatives to calculate the flow of microbial N. Ruminal parameters and nutrient digestibilities were also measured. Sheep were defaunated using a rumen washing procedure 50 d prior to measurements in the defaunated period. Sheep were refaunated with ruminal contents from a faunated sheep receiving the same diet. Measurements began 26 d following refaunation, at which time protozoal numbers had returned to those in the originally faunated sheep. Data reported in parentheses are for faunated, defaunated, and refaunated sheep, respectively. Total culturable and cellulolytic bacterial numbers were unaffected by defaunation, but there was an increase in flow of microbial N from the rumen (10.8, 17.3, and 11.1 g N/d; P < .05) in the defaunated period. Flux, irreversible loss, and intraruminal recycling of NH3-N and recycling of NH3-N from plasma urea N were not affected by defaunation. Defaunation had no effect on reducing the absolute amount (13.8, 10.0, and 11.3 g N/d; P > .20) of bacterial N recycling and the percentage of N flux through the bacterial N pool. Total-tract digestion was reduced in defaunated compared with faunated sheep by 8, 17, 15, and 32% for OM, N, NDF, and ADF, respectively. In conclusion, defaunation improved ruminal N metabolism through the enhancement of bacterial protein synthesis, and improvement in the flow of microbial protein to the host animal.

Availability of liquid methionine hydroxy analog [D,L-2-hydroxy-4-(methylthio)-butanoic acid] was evaluated in two experiments using four cannulated lactating dairy cows. The first experiment was designed as a 4 x 4 Latin square. Each cow received a pulse dose of 0, 30, 60, or 90 g of the methionine analog in the rumen each day for 10 d. Duodenal samples were collected at 16, 20, and 24 h after dosing for the last 5 d and pooled. The methionine analog was not detected in duodenal contents because it passed rapidly from the rumen relative to the sampling protocol. In the second experiment, cows were offered 90 g of the methionine analog and 600 ml of Cr-EDTA (3.5 g of Cr) mixed with ground corn for a period of 20 min after which any remains of the treatment were placed in the rumen. The concentration of the analog peaked in ruminal and duodenal fluid at 1 and 3 h, respectively. Based on the fractional rate constants for ruminal and duodenal disappearance of the methionine analog and passage of the liquid, it was determined that 50.0 +/- 2.8% of the methionine analog escaped ruminal degradation and became available for intestinal absorption (44.6 +/- 5.7%) or was absorbed from the omasum (5.4 +/- 3.3%). Serum methionine concentration peaked 6 h after analog dosing at a level that was three times the predose level, indicating that the methionine analog that escaped ruminal degradation was absorbed and metabolized to methionine.