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The effects of protozoa on ruminal [NH.sub.3] N kinetics and bacterial N recycling were measured in five sheep (57.6 [+ or -] 7.1 kg BW, [bar]x [+ or -] 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 [.sup.15]N as [[.sup.15]N][NH.sub.4]Cl was administered into the rumen (on d 1 and 15) and 300 mg of [.sup.15]N as [[.sup.15]N]urea was administered intravenously to the blood (d 8). Enrichment of [.sup.15]N was measured in ruminal [NH.sub.3]-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 [is less than] .05) in the defaunated period. Flux, irreversible loss, and intraruminal recycling of [NH.sub.3]-N and recycling of [NH.sub.3]-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 [is greater than] .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. Key Words: Bacterial Protein, Nitrogen Balance, Protozoa, Ruminant Flora, Sheep

Crossbred beef steers (« = 312) were used in an experiment with a completely randomized design during the growing (235 ± 1.6 kg initial BW) and fin-ishing (363 ± 2.7 kg) phase to determine the effects of dietary CP concentration and rumen degradability on NH3-N emissions, growth performance, and carcass traits. Diets were barley based and consisted of 55% silage and 45% concentrate in the backgrounding phase and 9% silage and 91% concentrate in the finishing phase. For each phase, there were 4 dietary treatments (6 pens of 13 cattle per diet): the basal diet with no protein supplementation (12% CP backgrounding and 12.6% CP finishing) or supplemented (14% CP) with urea (UREA), urea and canola meal (UREA+CM), or urea, corn gluten meal, and xylose-treated soybean meal (UREA+CGM+xSBM). Feed intake and BW of cattle were measured at 3-wk intervals. One pen of steers fed the 12 or 12.6% CP and 1 pen fed 1 of the 14% CP diets were housed in 2 isolated pens to quantify NH3-N emis-sions using the integrated horizontal flux technique with passive NH3 samplers. In the backgrounding phase final BW, ADG, and G:F were less (P < 0.05) in cattle fed the 12% CP and UREA compared with the UREA+CM and UREA+CGM+xSBM diets. Nitrogen-use efficiency of cattle fed UREA+CM and UREA+CGM+xSBM was equal to that of cattle fed 12% CP and averaged 19.8%. In the finishing phase, there was no effect (P > 0.10) of CP supplementation on BW, DMI, ADG, G:F, N-use efficiency, and carcass traits. The NH3-N emissions from December to February during the backgrounding phase ranged from 4.3 to 25.6 g N/(steerd) and 3.8 to 16.3% ofN intake and from April to July during the fin-ishing phase ranged from 9.7 to 76.4 g N/(steer-d) and 4.4 to 26.7% of N intake. Differences in NH3-N emis-sions between the pens of cattle fed the backgrounding diets with 12 and 14% CP were not detected. For cattle fed the 12.6 and 14% CP finishing diets, NH3-N emis-sions tended (P < 0.16) to be less for 2 of the 5 periods and averaged 14.4 and 28.1 g N/(steer-d) and 7.7 and 12.7% of N intake, respectively. The NH3-N emitted as a % ofN intake averaged 42% less for cattle fed 12.6% compared with 14% CP. Feeding the barley-based con-centrate diet to finishing cattle with 12.6% compared with 14% CP diets reduced NH3-N emissions with no effect on performance. Feeding tbe barley-based forage diet to backgrounding cattle with 12% CP, however, reduced performance compared with growing cattle fed supple-mentary degradable and undegradable true protein. [ABSTRACT FROM AUTHOR]

Four ruminally cannulated and four ruminally and duodenally cannulated beef heifers (476 ± 25 kg, initial BW) were used in a replicated 4 × 4 Latin square to determine the effects of feeding condensed and hydrolysable tannin extracts with a high protein diet containing wheat distillers grains on ruminal fermentation, digestibility, and route of nitrogen (N) excretion. Periods were 4 wk and included a 1-wk washout, 2 wk for adaptation to the tannin extracts, and 1 wk for measurements. Dietary treatments were control (CON, basal diet), 2.5% Acacia mearnsii (ACA), 2.5% quebracho (QUE), and 2.5% chestnut (CHE; DM basis). The basal diet was composed of 71% barley grain concentrate, 20% wheat distillers grains and solubles, and 9% barley silage and contained 16.8% CP (DM basis). Diets were fed as total mixed rations once per day for ad libitum intake. Feed offered and refused were measured daily. Total collection of urine and feces were made for 6 d. Plasma was collected at 3 h and rumen fluid was collected at 0, 3, 6, 9, 12, 15, and 18 h after feeding at the end of the collection period. Data were analyzed using a mixed linear model with square, period, and treatment as fixed effects and animal within square as a random effect. Dry matter intake tended (P = 0.10) to be lower when heifers were fed the CHE compared to the CON and QUE, and was intermediate for the ACA. Total tract digestibility of DM was similar among heifers fed the tannin extracts (78.1, 77.4, and 77.6% for ACA, QUE, and CHE, respectively), however, all tannin extracts reduced DM digestibility compared to the CON (80.8%, SEM 0.98%; P < 0.05). Plasma urea-N and ruminal NH3-N were also similar among heifers fed the tannin extracts and were reduced (P < 0.05) compared to the CON. There was no effect of the dietary treatments on total N output (P > 0.05), but fecal N output was increased (P < 0.05) and conversely urinary N output was decreased (P < 0.05) for heifers fed ACA and QUE compared to the CON. Fecal and urinary N outputs were intermediate for the CHE. Feeding tannins to beef cattle fed high protein diets containing wheat distillers grains reduced ruminal NH3-N and plasma urea-N and shifted the route of N excretion from labile forms in urine to feces although there was a 4% decrease in DM digestibility. [ABSTRACT FROM AUTHOR]

In situ and in vitro experiments were conducted to determine the nitrate (NO3 -) release rate from encapsulated NO3 - (EN; 71% NO3 -) in the rumen and to examine metabolism of ENNO 3 - in conjunction with methane (CH4), hydrogen (H2), and nitrous oxide (N2O) production. Three ruminally-cannulated beef heifers were used to incubate the following substrates in the rumen for 72 h: soybean meal, EN, and unencapsulated NO3 - (UEN). Because of immediate solubilization, the soluble nitrogen (N) fraction of UEN was assumed to be 100%. A non-linear regression model fitted to N disappearance of EN (r2 = 0.93, P < 0.01) indicated 35.4% and 54.7% of soluble and slowly degradable N fraction, respectively. Two in vitro experiments were conducted where UEN and EN were incubated for 24 h in buffer alone or with buffered-rumen fluid with substrates containing urea, UEN, or EN as sole N sources. When UEN was incubated with buffer, 99.9% of UEN-NO3 --N was recovered as NO3 --N in the buffer over 24 h. However, recovery of EN-NO3 - as NO3 --N gradually increased over 24 h up to 58%. When urea, EN or UEN were incubated with buffered-rumen fluid, total gas production decreased (P = 0.022) for UEN compared with urea and EN. Methane production decreased (10.7 and 13.3 vs 19.6 mL; P < 0.01) for UEN and EN, respectively, compared with urea. Hydrogen production increased (0.2 vs 0.07 and 0.08 mL; P < 0.01) for UEN compared with urea and EN, respectively. Nitrous oxide production was greater for UEN (20.8, 7.5 and 0.02 μL, respectively; P < 0.05) followed by EN and urea. During the incubation with buffered-rumen fluid, 100% of UEN-NO3 - was recovered as NO3 --N in the medium until 6 h and then the recovery gradually decreased to 18% at 24 h while recovery as nitrite (NO2 -)-N increased up to 22% at 24 h. However, recovery of EN-NO3 --N as NO3 --N in the medium increased by 20% at 12 h and then gradually decreased to 5% at 24 h without accumulation of NO2 --N in the medium. In conclusion, EN released NO3 - comparatively slowly in the rumen and decreased CH4 production without negatively affecting microbial fermentation. Increases in H2 and N2O production and accumulation of NO3 - and NO2 - in the medium were not observed for EN compared with UEN, indicating that EN could be a promising NO3 - source to lower CH4 production with less risk of NO3 -/NO2 - toxicity. [ABSTRACT FROM AUTHOR]

A finishing feedlot study was conducted with beef steers to determine effects of encapsulated nitrate (EN) on growth performance, carcass characteristics, methane production, and nitrate (NO3-) residues in tissues. The 132 crossbred steers were backgrounded in a feedlot and transitioned to the high concentrate diets evaluated in the present study. The steers were initially assigned to 22 pens (6 animals per pen) in a randomized complete block design with BW (18 pens) and animals designated for methane measurement (4 pens) as blocking factors. Five animals in each pen designated for methane measurement were monitored for methane emissions in respiratory chambers twice during the finishing period. Pens received 3 dietary treatments (7 pens each): Control, a finishing diet supplemented with urea (0.03% NO3- and 0.9% urea in dietary DM); 1.25% EN, the control diet supplemented with 1.25% EN (1.1% NO3-) which partially replaced urea; 2.5% EN, the control diet supplemented with 2.5% EN (2.0% NO3-) fully replacing urea. The final pen designated only for methane measurement received a fourth dietary treatment, 2.3% UEN; control diet supplemented with unencapsulated NO3- (UEN; 2.0% NO3- in dietary DM) fully replacing urea. The cattle weighed 449 ± 32 kg at the start of the finishing period. The 2.5% EN diet decreased DMI (9.9 vs 10.7 and 10.7 kg/d; P < 0.01) compared with Control and 1.25% EN. Feeding EN tended to increase ADG (1.41 vs 1.36 kg/d; P = 0.09) and increased gain:feed (0.137 vs 0.127 kg/kg; P < 0.01) for EN compared with Control. No differences in methane production and yield were observed among treatments. Inclusion of EN in the diets increased (P  0.03) sorting in favor of large and medium particles and against small and fine particles. Plasma NO3- and NO2 - concentrations were elevated (0.06 to 3.68 mg/L of NO3- and 1.47 to 9.23 g/L of NO2 -; P < 0.01) with EN in a dose response manner, but blood methemoglobin levels for all treatments were below 1%. Feeding EN increased (P < 0.01) NO3- concentrations in muscle, fat, liver, and kidney and NO3- concentrations of those were similar between 1.25% EN and 2.3% UEN. In conclusion, including up to 2.5% of EN on a DM basis in a finishing diet did not cause NO3- toxicity or health problems in a long term study. In comparison with supplemental urea, feeding EN improved feed efficiency despite increases in sorting against dietary EN. [ABSTRACT FROM AUTHOR]

A backgrounding feedlot study was conducted to examine the effects of feeding encapsulated calcium ammonium nitrate (EN) on growth, enteric methane production, and nitrate (NO3 -) toxicity in beef cattle. A total of 108 crossbred steers (292 ± 18 kg) were blocked by BW and randomly assigned to 18 pens. The pens (experimental unit; 6 animals per pen) received 3 dietary treatments: Control, a backgrounding diet supplemented with urea (0.2% NO3 - and 0.9% urea in dietary DM); 1.25% EN, control diet supplemented with 1.25% EN (1.2% NO3 -) in dietary DM, which partially replaced urea; or 2.5% EN, control diet supplemented with 2.5% EN (2.3% NO3 -) in dietary DM, fully replacing urea. Twenty four steers were allocated to additional 4 pens and randomly assigned to 1 of the above 3 dietary treatments plus a fourth treatment: 2.3% UEN, control diet supplemented with 2.3% unencapsulated NO3 - (UEN; 2.4% NO3 -) fully replacing urea. Animals in the additional 4 pens were used for methane measurement in respiratory chambers and the pens (except UEN) were also part of the performance study (i.e., n = 7 pens/treatment). The experiment was conducted for 91 d in a randomized complete block design. During the experiment, DMI was not affected by inclusion of EN in the diet. Changes in BW, ADG, and gain:feed were not observed (P ≥ 0.57) by feeding EN. Methane production (g/d) tended to decrease (P = 0.099) by NO3 -(188, 174, 156, and 152 g/d for Control, 1.25%, 2.5% EN, and UEN, respectively), but yield (g/kg DMI) did not differ (P=0.56) among treatments. Inclusion of EN in the diet increased (P ≤ 0.02) sorting of the diets in favor of large and medium particles and against small and fine particles resulting in considerable increases in NO3 - concentrations of orts without affecting DMI. Plasma NO3 - and NO2 - concentrations increased (P ≤ 0.05) for EN compared with Control in a dose response manner, but blood methemoglobin levels were below the detection limit. Nitrate concentration in fecal samples slightly increased (from 0.01% to 0.14%; P < 0.01) with increasing levels of EN in the diet. In conclusion, EN can be used as a feed additive replacing urea in beef cattle diets during the backgrounding phase without NO3 - intoxication or any negative effects on growth performance. In addition, the study confirmed that feeding EN tended to decrease enteric methane production in the long term. [ABSTRACT FROM AUTHOR]

Selenium is an essential trace mineral for dairy cattle and can be provided in the diet in various forms that may differ in bioavailability. The objective of this study was to determine how source of Se affects animal performance, Se status, retention, and apparent and true absorption. Multiparous Holstein cows (n = 24; 597 ± 49 kg of BW) were blocked by DIM (161 ± 18) and randomly assigned to receive 0.3 mg Se/kg of DM (100% of National Academies of Sciences, Engineering, and Medicine requirements) of either organic Se (ORG; selenized yeast) or inorganic Se (INO; sodium selenite). The Se premix was top dressed on a common TMR fed daily and mixed into the top 15 cm directly before feeding. Following an 11-wk adaptation period, cows received simultaneous infusions of an intraruminal isotope dose of 77 Se in the same chemical form as the premix, and an intravenous dose of 82 Se in an inorganic form. Infusions were followed by a 4-d period of blood and rumen fluid sampling, and total collection of feces, urine, and milk. Daily DMI (23 ± 0.6 kg), milk yield (35 ± 1.2 kg), and serum Se (0.11 ± 0.003 µg/g) were not different between treatments during the adaptation period, but milk Se concentrations were greater for ORG compared with INO. Serum 77 Se maximum concentration and area under the curve (AUC) were not different between treatments for 72 h following infusion, but rumen fluid 77 Se AUC was higher for ORG than INO. Apparent absorption (64% ± 1.4%), and retention (44% ± 1.5%) of the 77 Se dose did not differ between treatments. True absorption was calculated using 82 Se enrichment in serum and feces and was determined to be 69% ± 1.3% and did not differ between treatments. Fecal excretion of the 77 Se dose was not different between treatments (36% ± 1.4%), but ORG had lower urinary excretion and higher milk excretion compared with INO. These results indicate that organic Se resulted in greater Se concentration of milk and lower urinary Se excretion into the environment, but absorption, Se status, and performance of the cow were not affected by Se source at this supplementation level., (© 2024, The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

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%.

We investigated the effects of two new hollow-fiber membrane oxygenators, the Capiox SX10 and the Lilliput 901, on pulsatile versus nonpulsatile perfusion in an in vitro model designed to simulate a 3 kg infant. The experiments were divided into eight groups (six pulsatile and two nonpulsatile), according to the equipment and settings used. Each group included six tests. In all experiments, the pseudo-patient's mean arterial pressure was 40 mmHg, and the pump flow rate was 550 ml/min. During pulsatile cardiopulmonary bypass, the pump's base flow was set at 30%, and the pump rate was set at 80, 100, 120, 140, or 150 beats/min. The PUMP START and PUMP STOP timing points were adjusted to produce different pulse-width settings. We were especially interested in evaluating the pre- and postoxygenator extracorporeal circuit pressure (ECP), the oxygenator pressure drop, and the precannula ECP. When used with a pulsatile roller pump, the Capiox produced a significantly lower preoxygenator ECP than the Lilliput (p < 0.001); moreover, the Capiox yielded a significantly lower oxygenator pressure drop (p < 0.001). During nonpulsatile perfusion, the Capiox again produced a lower preoxygenator ECP than the Lilliput (p < 0.001). These results suggest that the Capiox may be more suitable than the Lilliput when the pulsatile flow is employed, and pulsatile flow does not increase the ECP with either oxygenator.

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.

Six lactating, cannulated Holstein cows were used in a double 3 x 3 Latin square design to compare the effects of hull-less barley with barley and corn on ruminal fermentation, rate of passage, flow of nutrients to the duodenum, and milk production. Diets consisted of 60% concentrate, 30% barley silage, and 10% alfalfa hay (dry matter basis). Concentrates contained steam-rolled grains: hull-less barley, barley, or corn. Dry matter intake was unaffected by grain source, but starch intake tended to be greatest when hull-less barley or corn was fed. The barley diet was more degradable in the rumen than was the hull-less barley or corn diet, and, therefore, flow of microbial organic matter to the duodenum was greatest for cows fed the barley diet. Flow of microbial N to the duodenum was greater (50 g/d) for cows fed the barley diet than for cows fed the other diets, and the flow of ruminally undegradable N was greater (43 and 28 g/d) for cows fed the hull-less barley and corn diets, respectively, than for cows fed the barley diet. As a result, flow of nonammonia N to the duodenum was unaffected by grain source. Total tract apparent digestibility was highest for cows fed the barley and corn diets. Despite its low digestibility, cows fed the hull-less barley diet produced a similar amount of milk as did cows fed the barley and corn diets. Further studies are needed to evaluate the effects of processing hull-less barley on its utilization by dairy cows.

An inductively coupled plasma mass spectrometer with a newly designed continuous flow hydride generator was used for the determination of Se in biological materials. The design of the hydride generator was important in minimizing interference from HCl and in maximizing analytical sensitivity. Two sample preparation procedures incorporating either 3.8 or 7.2 M HCl in the final sample solutions were compared. Interference from Cu was eliminated by the addition of 0.2 M NaI to the sodium borohydride solution (3.8 M method) or by maintaining a high concentration of HCl in the sample solution (7.2 M method). The 3.8 M method had the advantage of minimizing exposure of expensive equipment to corrosive HCl fumes, whereas the 7.2 M method did not contaminate equipment with I and had no measurable sample-to-sample cross-contamination. In practice, cross-contamination from sample to sample in both methods was negligible during analysis. An important factor in minimizing cross-contamination from sample to sample was the elimination of the air bubble normally entrained between samples. Determination of isotopic tracer enrichment was linear from 0 to 320% enrichment, which provided a broad range for isotope dilution analysis. A detection limit of 6.4 pg of Se was observed under optimum conditions, whereas a detection limit of 1.3 ng of Se was found for routine analysis of 1-g samples of plant material. Selenium was accurately determined by isotope dilution analysis in a variety of biological reference materials.