Nutritional evaluation of poultry by-product meal as a protein source for ruminants: small intestinal amino acid flow and disappearance in steers.

Six Angus steers (260+/-4 kg initial BW) fitted with ruminal, duodenal, and ileal cannulas were used in a 6 x 6 Latin square design to evaluate the effect of feeding poultry by-product meal (PBM) on small intestinal flow and disappearance of amino acids. The diets were provided at 2% of BW on a DM basis, formulated to contain 11.5% CP, and consisted of 49% corn silage, 36% cottonseed hulls, and 15% supplement on a DM basis. Supplements were formulated to contain 37% CP with sources of supplemental N being soybean meal (100% SBM) and 0, 25, 50, 75, and 100% PBM, with urea used to balance for N. Duodenal flow of all amino acids increased linearly (P < .07) as PBM increased in the diet and, except for His, increased (P < .09) for 100% PBM compared with 100% SBM. Similar results were observed for duodenal flow of nonbacterial amino acids, which linearly increased (P < .05) with PBM and were greater (P < .05) for 100% PBM than for 100% SBM. Soybean meal increased (P < .09) the duodenal flow of nonbacterial Lys compared with 0% PBM, and 0% PBM increased (P < .04) flow of Val, Ala, and Pro compared with 100% SBM. Duodenal bacterial essential, nonessential, and total amino acid flows were not affected (P > .80) by PBM; however, they were greater (P < .02) for 100% SBM than for 100% PBM. In addition, nonessential and total bacterial amino acid flows were increased (P < .06) for 100% SBM compared with 0% PBM. Small intestinal disappearance of Lys and Pro increased linearly (P < .09) as PBM increased, and 100% PBM increased (P < .07) disappearance of Arg and Ala compared with 100% SBM. Supplemental N source had no effect (P > .31) on apparent small intestinal disappearance of essential, nonessential, and total amino acids. These data suggest that when PBM, SBM, and urea were used as sources of supplemental N, the daily disappearance of amino acids from the small intestine of steer calves consuming a corn silage- and cottonseed hull-based diet was similar.     

Effects of virginiamycin and monensin plus tylosin on ruminal protein metabolism in steers fed corn-based finishing diets with or without wet corn gluten feed

Six ruminally cannulated steers (345 +/- 20 kg initial BW) were used in a 6 x 6 Latin square to evaluate effects of diet and antibiotics on ruminal protein metabolism. Two diets and three antibiotic treatments were arranged factorially. One diet contained (DM basis) 72% dry-rolled corn, 12% soybean meal, 10% alfalfa hay, and 4% molasses (SBM), and the other contained 63% dry-rolled corn, 30% wet corn gluten feed, and 5% alfalfa hay (WCGF). Antibiotic treatments included control, virginiamycin (175 mg/d; VM), and monensin/tylosin (250 and 100 mg/d, respectively; MT). Steers were fed at 12-h intervals at a rate of 2.4% of empty BW daily. Each period included 18 d of adaptation and 3 d of ruminal fluid collections. Samples were collected at 0, 2, 4, 6, 8, and 10 h after the morning feeding on d 19 and 20. On d 21, rumens were dosed 2 h after the morning feeding with 350 g of solubilized casein to evaluate in vivo ruminal protease and deaminase activities. Ruminal fluid samples were collected 1, 2, 3, 4, and 6 h after the casein dose. On d 19 and 20, antibiotics had no effect on ruminal pH or concentrations of VFA, lactate, ammonia, ciliated protozoa, alpha-amino nitrogen (AAN), or peptide N, but VM reduced (P < 0.01) the concentration of isovalerate compared to MT and control. After casein dosing (d 21), peptide N concentration was unaffected by antibiotics, but AAN were higher (P < 0.01) for VM than MT and control. Relative to MT and control, VM reduced ruminal isovalerate (P = 0.05) and increased ruminal propionate (P < 0.01) on d 21. Ruminal pH was lower (P < 0.01) in steers fed SBM than in steers fed WCGF, but lactate concentrations were unaffected by diet. Steers fed SBM had higher (P < 0.05) ruminal concentrations of total VFA and propionate. Ammonia concentrations were lower before feeding and higher after feeding for steers fed WCGF (P < 0.01). Steers fed WCGF had higher counts of total ciliated protozoa than steers fed SBM (P < 0.05) due to greater Entodinium sp. (P < 0.05). Steers fed WCGF had higher (P < 0.01) ruminal AAN and peptide N concentrations than those fed SBM on d 19 and 20. After casein dosing, ruminal peptide N concentrations were similar, but AAN were lower (P < 0.01) for WCGF than SBM. Overall, VM appeared to depress ruminal deaminase activity, and MT had minimal effects on ruminal fermentation products. The protein in WCGF appeared to be more readily degradable than that in SBM.     

Effects of increasing ruminally degraded nitrogen and abomasal casein infusion on net portal flux of nutrients in yearling heifers consuming a high-grain diet.

Seven Meat Animal Research Center (MARC) III heifers (410+/-25 kg) fitted with hepatic portal, mesenteric venous, carotid catheters, and an abomasal cannula were used in a 7 x 5 incomplete Latin square design experiment. The objective was to evaluate the effects of increasing levels of ruminally degradable N (RDN) with or without the addition of abomasally infused casein on portal-drained visceral (PDV) flux of nutrients. Treatments consisted of dietary CP percentage levels of 9.5 (control), control plus .72% dietary urea (11.5U), control plus 1.44% dietary urea (13.5U), control plus abomasally infused casein (250 g/d; 11.5C), or control plus .72% dietary urea and abomasally infused casein (250 g/d; 13.5UC). All diets contained (DM basis) 80% ground corn, 15% corn silage, and 5% dry supplement and were provided for ad libitum consumption. Nitrogen intake increased (linear, P < .001) as CP increased from 9.5 to 13.5%. Portal-drained visceral release of ammonia N increased (linear, P < .10) as RDN increased, and was greater (P < .05) when protein was fed compared with heifers fed control (P < .10). Urea N removal by PDV was not affected ( P > . 10) by level of RDN but was greatest when 11.5C was fed and least when 13.5UC was fed. Net alpha-amino N (AAN) release by PDV was greatest when 13.5UC was fed (309 mmol/h), least when 9.5% CP was fed (112 mmol/h), and intermediate for the other groups (205 to 252 mmol/h). These data suggest that removal of N by the PDV may promote microbial protein synthesis when dietary RDN is low. When RDN needs have been met and amino acids are deficient for the host, escape protein should be fed to increase amino acid absorption.     

Effect of nitrogen source in high-concentrate, low-protein beef cattle diets on microbial fermentation studied in vivo and in vitro

In Exp. 1, four Holstein heifers (112+/-5.5 kg BW) fitted with ruminal cannulas were used in a 4 x 4 Latin square to evaluate the effects of N source on ruminal fermentation and urinary excretion of purine derivatives. A 2 x 2 factorial arrangement of treatments was used; the factors were the type of protein source (soybean meal, SBM, vs a 50:50 mixture of fish meal and corn gluten meal, FMCGM) and the partial substitution of protein source by urea (with vs without). Heifers were allowed to consume concentrate and barley straw on an ad libitum basis. Barley straw:concentrate ratio (12:88) and average ruminal pH (6.25) were not affected (P > 0.05) by treatment. Ruminal NH3 N concentration and urinary excretion of purine derivatives were not affected (P > 0.05) by supplemental N source. In situ CP degradability of supplemented SBM was very low (50%). In Exp. 2, eight dual-flow continuous-culture fermenters were used to study diet effects on microbial fermentation and nutrient flow, using forage:concentrate ratio, solid and liquid passage rates, and pH fluctuation to simulate in vivo conditions. The treatment containing SBM without urea reached the greatest total VFA concentration (P < 0.01), molar percentage of acetate (P < 0.05), and NH3 N concentration (P < 0.05), followed by treatments with partial substitution of protein source by urea, and finally by the treatment containing FMCGM. True OM digestion tended to increase (P = 0.13) in treatments containing SBM. These results suggest that amino N from SBM and NH3 N concentration stimulated nutrient digestion. Microbial protein synthesis was lowest in treatments with FMCGM and without urea, indicating that rapidly available N limited microbial growth. The low CP degradability of SBM observed may have contributed to the limitation in N supply for microbial growth. Efficiency of microbial protein synthesis increased in treatments containing urea (P < 0.05). Protein source affected total (P < 0.05) and essential AA (P < 0.10) flows, which were greater in treatments containing FMCGM. Partial replacement of protein supplements by urea did not affect total and essential AA flows. Because mean dietary protein contribution to total N effluent was 46%, the AA profile of supplemental protein sources had a great impact on total AA flow and its profile.     

Effects of growth hormone-releasing factor and feed intake on energy metabolism in growing beef steers: net nutrient metabolism by portal-drained viscera and liver.

Effects of growth hormone-releasing factor (GRF) and intake on net nutrient metabolism by portal-drained viscera (PDV) and liver were measured in six growing Hereford x Angus steers fed a 75% concentrate diet at two intakes in a split-plot design with 4-wk saline or GRF injection periods within 8-wk intake periods. Daily rations were fed as 12 equal meals delivered every 2 h. Steers were injected s.c. for 21 d with either saline or 10 micrograms/kg of (1-29)NH2 human GRF at 12-h intervals. Six hourly measurements of net nutrient flux (venous-arterial concentration different [VA] x blood flow) across PDV and liver were obtained 8 to 10 d after injections began. Energy and N balances were measured using respiration calorimetry during the last week of injections. Greater intake increased blood flow (P less than .01) and net visceral release or removal of most nutrients (P less than .10). Exceptions included a decrease (P less than .10) in net PDV glucose release with greater intake in saline-treated steers and a decrease (P less than .01) in net liver removal of lactate with greater intake. Treatment of steers with GRF decreased net liver removal of alpha-amino N (AAN; P less than .05) and ammonia N (NH3N; P less than .10) and release of urea N (UN; P less than .05), increased liver release of glutamate (P less than .05), and decreased net PDV release of NH3 N (P less than .10). Decreased liver extraction ratio for AAN in GRF-treated steers (P less than .01) implies a direct effect of GRF treatment on liver metabolism separate from changes in liver AAN supply. Proportions of body N retention not accounted for by net total splanchnic AAN release increased with GRF treatment. This suggests a change in peripheral utilization of dietary AAN supply or an increase in total splanchnic N retention.     

Subclinical ammonia toxicity in steers: effects on hepatic and portal-drained visceral flux of metabolites and regulatory hormones

Four calves (avg wt 161 kg) were surgically fitted with indwelling catheters in the femoral artery and femoral, portal, hepatic and mesenteric veins to study the effects of subclinical ammonia toxicity on portal-drained viscera (PDV) and hepatic (HEP) net flux of key metabolites and pancreatic hormones. Hyperammonemia was induced via administration of ammonium chloride (NH4Cl; 12 mumol.kg BW-1.min-1) via the femoral vein catheter for 240 min; infusions were preceded (PRE) and followed (POST) by 60- and 180-min control periods, respectively. Blood samples were obtained from the arterial catheters, and portal and hepatic vein catheters. Net flux rates were calculated by multiplying venoarterial differences by blood flow. Arterial plasma ammonia N peaked (P less than .01) at 327 micrograms/dl; hepatic ammonia extraction increased (P less than .01) from 10 to 23% during NH4Cl infusion. Arterial plasma glucose concentrations increased (P less than .05) during NH4Cl infusion (90.5 vs 82.6 mg/dl) concomitant with trends toward a reduction in net HEP glucose output. Portal-drained visceral release of insulin did not increase (P greater than .10) during NH4Cl infusion despite the steady rise in circulating glucose concentration; however, cessation of NH4Cl infusion resulted in a 109% increase (P less than .05) in PDV insulin release at +60 min POST. Plasma L-lactate, nonesterified fatty acids, urea N and glucagon concentrations and net fluxes were variable throughout the experiment. Results tend to indicate that hyperammonemia reduced hepatic glucose output and glucose-mediated pancreatic insulin release.     

Effects of energy level and protein source on nitrogen kinetics in steers fed wheat straw-based diets.

A 4 x 4 Latin square metabolism trial with a 2 x 2 factorial arrangement of treatments was conducted to determine N kinetics in steers. Steers were fed either untreated (UNT-WS) or alkaline hydrogen peroxide-treated wheat straw (AHP-WS) based diets supplemented with soybean meal (SBM) or blood meal (BM). Single doses of (15NH4)2SO4 were infused into ruminal pools to determine N kinetics. Ruminal NH3N concentrations (main effects) were 3.81, 1.65, 3.18, and 2.28 mg/dL in steers when fed diets that contained UNT-WS, AHP-WS, SBM, and BM, respectively. Ruminal N pool size was greater (P < .05) for UNT-WS than for AHP-WS diets and also was greater (P < .10) for SBM than for BM diets. Nitrogen flux rate into the rumen was not affected (P > .10) by diet. However, production rate of N from the ruminal pool was greater (P < .05) for UNT-WS than for AHP-WS diets and greater (P < .10) for SBM than for BM diets. Nitrogen recycled into the rumen was 33% greater (P < .05) for AHP-WS than for UNT-WS diets and 26% greater (P < .05) for BM than for SBM diets. Nitrogen recycling (percentage of N intake) was 33, 56, 36, and 49% for UNT-WS, AHP-WS, SBM, and BM diets, respectively. The blood urea N (BUN) concentrations were 10.23, 4.58, 7.15, and 7.65 mg/dL for UNT-WS, AHP-WS, SBM, and BM diets, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Net portal and hepatic flux of nutrients in growing wethers fed high-concentrate diets with oscillating protein concentrations

We hypothesized that oscillating dietary CP would improve N retention by increasing the uptake of endogenous urea N by portal drained viscera (PDV), compared with static dietary CP regimens. Chronic indwelling catheters were surgically implanted in the abdominal aorta, a mesenteric vein, a hepatic vein, and the portal vein of 18 growing Dorset x Suffolk wethers (44.6 +/- 3.6 kg of BW). Wethers had ad libitum access to the following diets in a completely randomized block design: 1) Low (9.9% CP), 2) Medium (12.5% CP), or 3) Low and High (14.2% CP) diets oscillated on a 48-h interval (Osc). Dry matter intake was greater (P = 0.04) for the Osc diet (1,313 g/d) than the Low diet (987 g/d) and was intermediate for the Medium diet (1,112 g/d). Nitrogen intake was not different between the wethers fed the Osc (25.4 g/d) and Medium diets (22.2 g/d), but was lower (P < 0.01) in wethers fed the Low diet (16.0 g/d). Wethers fed the Osc diet (6.7 g/d) retained more (P < 0.04) N than did those fed the Medium diet (4.0 g/d). Hepatic arterial blood flow was not different (P = 0.81) between wethers fed the Osc (31 L/h) or Medium diet (39 L/h) but was greater (P = 0.05) in wethers fed the Low diet (66 L/h). Net release of alpha-amino N by the PDV did not differ (P = 0.90) between the Low (37.8 mmol/h) and Medium diets (41.5 mmol/h) or between the Osc (53.0 mmol/h) and Medium diets (P = 0.29). Net PDV release of ammonia N was less (P = 0.05) for the Low diet than for the Medium diet, and this was accompanied by a similar decrease (P = 0.04) in hepatic ammonia N uptake. Urea N concentrations tended to be (P = 0.06) less in arterial, portal, and hepatic blood in wethers fed the Low diet compared with those fed the Medium diet. Wethers fed the Osc diet tended (P = 0.06) to have a greater PDV uptake of urea N than did those fed the Medium diet, but there was no difference between the Osc and Medium diets (P = 0.72) in hepatic urea N release. Net PDV uptake of glutamine tended to be greater (P < 0.07) in wethers fed the Low diet (6.7 mmol/h) than those fed the Medium diet (2.7 mmol/h). These data indicate that oscillating dietary protein may improve N retention by increasing endogenous urea N uptake by the gastrointestinal tract.     

Effect of ruminal protein degradability on growth and N metabolism in growing beef steers

The objective of two experiments was to correlate plasma levels of urea N (PUN) and the percentage of urine N in the form of urea (UUN) to weight gain in response to different dietary protein regimens for growing Angus steers. In Exp. 1, 60 steers (302 kg BW) were assigned to various levels of dietary N (control plus supplemental N to provide from 100 to 400 g more crude protein daily) within two sources of supplemental N (soybean meal [SBM] or a mixture of two parts corn gluten meal:one part blood meal [CGM:BM]). In Exp. 2, 27 steers (229 kg BW) were fed two levels of SBM, and half of the steers received growth-promoting implants. Steers were housed in groups of 12 and fed individually for 84 d in both experiments. Corn silage was fed at a restricted rate to minimize orts. Jugular blood and urine samples were collected during the experiments. In Exp. 1, maximal ADG of steers fed SBM (1.0 kg) was reached with 671 g/d total crude protein, or 531 g/d metabolizable protein. Maximal ADG of steers fed CGM:BM (0.91 kg) was reached with 589 g/d total crude protein, or 539 g/d metabolizable protein. The DMI was higher (P < 0.07) for steers fed SBM (6.37 kg/d) than for steers fed CGM:BM (6.14 kg/d). Increasing ruminal escape protein from 36% (SBM) to 65% (CGM:BM) of CP decreased (P < 0.05) endogenous production of urea, as evidenced by lower concentrations of urea in blood and lower UUN. In Exp. 2, increasing supplemental protein from 100 to 200 g/d increased (P < 0.05) ADG and PUN. Implants lowered (P < 0.05) UUN, particularly at the higher level of supplemental protein. Protein supplementation of growing steers can be managed to maintain acceptable ADG yet decrease excretion of urea in the urine.     

Splanchnic metabolism of nitrogenous compounds and urinary nitrogen excretion in steers fed alfalfa under conditions of increased absorption of ammonia and L-arginine supply across the portal-drained viscera

Effects of increased ammonia and/or arginine absorption across the portal-drained viscera (PDV) on net splanchnic (PDV and liver) metabolism of nitrogenous compounds and urinary N excretion were investigated in six catheterized Hereford x Angus steers (501 +/- 1 kg BW) fed a 75% alfalfa:25% (as-fed basis) corn-soybean meal diet (0.523 MJ of ME/[kg BW(0.75).d]) every 2 h without (27.0 g of N/kg of dietary DM) and with 20 g of urea/kg of dietary DM (35.7 g of N/kg of dietary DM) in a split-plot design. Net splanchnic flux measurements were obtained immediately before beginning and ending a 72-h mesenteric vein infusion of L-arginine (15 mmol/h). For 3 d before and during arginine infusion, daily urine voided was measured and analyzed for N composition. Feeding urea increased PDV absorption (P < 0.01) and hepatic removal (P < 0.01) of ammonia N, accounting for 80% of increased hepatic urea N output (P < 0.01). Numerical increases in net hepatic removal of AA N could account for the remaining portion of increased hepatic urea N output. Arginine infusion increased hepatic arginine removal (P < 0.01) and hepatic urea N output (P < 0.03) and switched hepatic ornithine flux from net uptake to net output (P < 0.01), but numerical changes in net hepatic removal of ammonia and AA N could not account fully for the increase in hepatic urea N output. Increases in urine N excretion equaled quantities of N fed as urea or infused as arginine. Estimated salivary urea N excretion was not changed by either treatment. Urea cycle regulation occurs via a complex interaction of mechanisms and requires N sources other than ammonia, but the effect of increased ammonia absorption on hepatic catabolism of individual AA in the present study was not significant.     

Effects of ruminal escape proteins and canola meal on nitrogen utilization by growing lambs

The effects of ruminal escape proteins and canola meal (CM) on N utilization by growing lambs were evaluated in two experiments. In both experiments, seven supplemental dietary protein treatments were fed. For each of these protein treatments a 3 x 3 Latin square metabolism trial was conducted, using two sets of three lambs and three periods. Within square treatments were 1.4, 1.7 and 2.0 times maintenance intake levels. In Exp. 1, protein treatments were control (7.0% CP, DM basis), urea fed at 9.5 or 12% dietary CP, CM fed at 9.5 or 12% dietary CP and a 50:50 (N basis) mixture of blood meal/corn gluten meal (BC) fed at 9.5 or 12% dietary CP. In Exp. 2, protein treatments were urea, 64% urea and 36% BC (all mixtures on a N basis), 36% urea and 64% BC, BC, 50% CM and 50% BC (CM/BC), CM and soybean meal (SBM), all at 10.5% CP. In Exp. 1, apparent N digestibility (AND) was lower for CM diets than for urea (P = .13) and BC (P less than .05) diets (49.0 vs 50.6 and 51.3%, respectively). Absorbed N was utilized with similar efficiencies for all supplemental protein sources. Dietary CP and digestible protein (DP) were closely related (DP = .879[CP%] -3.66; r2 = .91), indicating that for urea, CM and BC total tract N digestibility was not influenced by theoretical ruminal degradability. In Exp. 2, N balance and N utilization efficiency indicated that the optimal extent of ruminal protein degradation was about 50%. Nitrogen balance was similar for the CM, CM/BC and SBM treatments.(ABSTRACT TRUNCATED AT 250 WORDS)     

The net portal and hepatic flux of metabolites and oxygen consumption in growing beef steers given postruminal casein

Changes in net portal and hepatic nutrient flux and oxygen consumption in response to 3-d abomasal casein infusions were studied in seven multicatheterized beef steers. Steers were fed 4.3 kg DM/d of a high-concentrate diet in 12 equal meals. Blood flow (para-aminohippurate dilution) and net flux (venoarterial concentration difference x blood flow) across portal-drained viscera (PDV) and hepatic tissues were measured on d 3 of the abomasal infusions. In two experiments, the response to 300 (300C) and 150 (150C) g casein/d were compared, respectively, to a control water infusion. The 300C increased (P less than .05) arterial blood concentrations of alpha-amino N (AAN), urea N and ammonia; 150C increased (P less than .05) arterial urea N. Urinary urea N excretion was increased (P less than .01) by 300C and 150C. Although 300C increased net PDV release of AAN (P less than .07) and alanine (P less than .10), there was no net change in total splanchnic (TSP) flux due to an increased net hepatic uptake of AAN (P less than .01) and alanine (P less than .05). Net PDV glucose flux was decreased (P less than .05) by 300C, but net hepatic glucose flux was not affected by either level of casein. The 150C increased TSP oxygen consumption (P less than .05) and hepatic oxygen extraction (P less than .10). Approximately 26 and 30% of the casein N infused abomasally appeared in the portal blood as AAN for 150C and 300C, respectively. The sum of net PDV ammonia and AAN fluxes accounted for 47 and 88% of the N infused for 150C and 300C, respectively. These data emphasize the importance of intestinal and liver tissues in regulating the flux of nitrogenous compounds absorbed from the diet.     

Effects of heat and alcohol treatments of soybean meal on nitrogen utilization by sheep

Soybean meal (SBM) was treated with aqueous solutions of ethanol or propanol at room temperature or at 80 C to study treatment effects on SBM-N solubility and utilization by sheep. Soybean meal was soaked in an excess of 70% (v/v) ethanol at 80 C (ET-80), 70% ethanol at 23 C (ET-23) or 70% propanol at 80 C (PR-80). Nontreated SBM and nontreated SBM heated at 80 C without alcohol treatment (NT-80) served as controls. Nitrogen solubility in McDougall's buffer was lowest (P less than .05) for PR-80 and ET-80 (2.2 and 4.7% of total N, respectively), intermediate (P less than .05) for ET-23 (9.0%), greater (P less than .05) for nontreated SBM (36.2%) and highest for NT-80 (40.2%). In an situ study using three ruminally cannulated cows and two bags per treatment per animal per removal time, more (P less than .05) N remained in in situ bags after 3, 6, 9 and 12 h incubation for ET-23, ET-80 and PR-80 than for nontreated SBM and NT-80. A lamb metabolism trial, using 15 lambs in each of two periods, compared nontreated SBM, ET-23, ET-80, PR-80 and urea as N supplements. Nitrogen retention was higher (P less than .02) for lambs fed SBM treatments compared with urea. When the same N supplements were fed to wethers in a 5 X 5 Latin square experiment and duodenal N flow was measured, non-ammonia non-bacterial N flow was higher (P less than .07) for wethers fed SBM treatments than for wethers fed urea.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nitrogen metabolism of beef steers fed endophyte-free tall fescue hay: effects of ruminally protected methionine supplementation

Level of nitrogen (N) intake and ruminally protected methionine supplementation were evaluated in eight Angus growing steers (initial BW 253+/-21 kg, final BW 296+/-21 kg) in a replicated 4+/-4 Latin square design. The steers were fed two endophyte-free tall fescue (Festuca arundinacea) hays that contained 2.2 (LO) or 2.8% (HI) of DM as N and were either supplemented or not with ruminally protected methionine (10 g metabolizable methionine/d). Diets were fed to provide adequate energy for 0.5 kg ADG and sufficient protein for maintenance (LO), or protein to support 0.5 kg ADG (HI). Following at least 14 d of adjustment, N balance was measured for 6 d. Isotopic urea was infused (15N15N-urea, 0.164 mmol urea N/h) via a jugular catheter for 56 h and urine was collected from 48 to 56 h to measure urea kinetics. Jugular blood was collected during the balance trial, and serum was analyzed for serum urea N (SUN). By design, daily N intake was greater (P < 0.05) for HI (112 g) than for LO (89 g). Compared with LO, steers when fed HI had greater (P < 0.05) daily DMI (4,217 vs 4,151 g), fecal N (34.4 vs 31.2 g), N digested (77.1 vs 57.7 g), urine N (48.3 vs 37.5 g), urine urea N excretion (34.6 vs 24.8 g), and N retained (29.8 vs 21.1 g). When fed HI steers also had higher (P < 0.05) urine urea N concentration (276 vs 219 mM), SUN (8.7 vs 6.7 mM), N digestibility (69.1 vs 64.9%), percentage of urinary N present as urea (71.5 vs 66.7%, P < 0.053), and rate of urea N production (59.6 vs 49.2 g/d) but lower (P < 0.05) percentage of urea N produced that was returned to the ornithine cycle (15.03 vs 19.2 1%) than when fed LO. Methionine supplementation decreased daily urine N (41.2 vs 44.6 g, P = 0.10) and increased both the amount of N retained daily (27.9 vs 23.7 g, P < 0.089) and the percentage of N digested that was retained (40.4 vs 34.6%, P < 0.094). In summary, supplemental methionine met a specific dietary limitation by increasing the amount of digested N that was retained by the steers.     

Nitrogen utilization and ruminal fermentation in steers fed soybean meal treated with formaldehyde

Four rumen-fistulated steers averaging 400 kg in body weight were used in a 4 X 4 Latin square arrangement with 18-d periods to investigate the effect of treating soybean meal (SBM) with formaldehyde on nitrogen (N) utilization and ruminal fermentation. Experimental diets, on a dry matter basis, consisted of 42% corn silage, 48.5% cracked corn-mineral mixture and 9.5% SBM treated with 0, .3, .6 or .9% formaldehyde by weight. Dry matter and organic matter digestibilities were not affected by treatment. Formaldehyde treatment of SBM resulted in a linear decrease in N digestibility (P less than .005) and urinary N excretion (P less than .01) and a quadratic increase (P less than .05) in N retention. The depression in apparent N digestibility was small when SBM was treated with .3% formaldehyde. This level of formaldehyde treatment also had little effect on in vitro enzymatic hydrolysis of SBM. Ruminal ammonia-N concentrations were lower (P less than .05) in steers fed formaldehyde-treated SBM. Ruminal pH was lower (P less than .05) at 6 and 8 h postfeeding while volatile fatty acid concentrations were higher (P less than .05) at 8 and 12 h postfeeding for steers fed untreated SBM. Propionic acid (mol/100 mol) decreased linearly (P less than .05) with increasing level of formaldehyde treatment. Urea-N concentrations in plasma were decreased (P less than .001) and plasma-free essential amino acid concentrations were increased (P less than .10) by formaldehyde treatment. Ruminal disappearance of N from polyester bags containing the SBM supplements was greatly reduced (P less than .005) by formaldehyde treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Splanchnic nitrogen metabolism by growing beef steers fed diets containing sorghum grain flaked at different densities

The objective of this study was to determine effects of processing method, dry-rolled (DR) vs steam-flaked (SF), and degree of processing (flake density, FD) of SF sorghum grain on splanchnic (gut and liver) N metabolism by growing steers. Diets contained 77% sorghum grain either DR or SF at densities of 437, 360, and 283 g/L (SF34, SF28, and SF22, respectively). Eight crossbred steers (340 kg initial BW), implanted with indwelling catheters into portal, hepatic, and mesenteric veins and the mesenteric artery, were used in a randomized complete block design. Blood flows and net output or uptake of ammonia N, urea N (UN), and alpha-amino N (AAN) were measured across portal-drained viscera, hepatic, and splanchnic tissues. Plasma arterial, portal, and hepatic concentrations of individual amino acids were also measured. Decreasing FD linearly increased (P = .04) net absorption of AAN (51, 73, and 78 g/d for SF34, SF28, and SF22, respectively) and transfer (cycling) of blood UN to the gut (49, 48 and 64 g/d; P = .02). Net UN cycling averaged 38% of N intake across all diets. Hepatic uptake of AAN or UN synthesis, and splanchnic output of AAN and UN, were not altered by FD. Lowering FD linearly increased (P < or = .02) portal-arterial concentration differences for blood AAN and UN and plasma arterial concentrations for alanine. Steers fed SF compared to DR tended to have greater (P = .11) blood UN cycling (percentage of hepatic synthesis; 64 vs 50%) and decreased (P = .03) net splanchnic UN output (30 vs 50 g/d), but other net fluxes of N were not altered across splanchnic tissues. Steam-flaking compared to dry-rolling tended to decrease (P = .12) portal, but not hepatic, blood flow and increased (P < .01) hepatic-arterial concentration differences for blood UN. Except for a decrease (P = .01) in hepatic-arterial concentration differences of glutamine, plasma amino acid concentrations were not altered by feeding SF vs DR sorghum. Processing method (steam-flaking vs dry-rolling) or increasing the degree of processing (by decreasing FD) of SF sorghum grain resulted in greater transfer of blood UN to the gut. Reducing FD also linearly increased the absorption of AAN by growing steers, which explains (in part) published responses of superior performance by steers fed SF grains.     

Net absorption and utilization of nitrogenous compounds across ruminal, intestinal, and hepatic tissues of growing beef steers fed dry-rolled or steam-flaked sorghum grain

Our objectives were to determine effects of grain processing on splanchnic (gut tissues and liver) N metabolism and whole-body N balance by growing steers and to ascertain the relative contributions of ruminal and intestinal tissues to net absorption and utilization of N-containing nutrients. Seven beef steers (348 kg initial BW), surgically implanted with appropriate catheters, were fed diets containing 77% steam-flaked (SF) or dry-rolled (DR) sorghum grain. Blood flows and net output or uptake of ammonia N, urea N, and alpha-amino N (estimate of amino acids) were measured across portal-drained viscera (PDV or gut tissues) and intestinal, ruminal, hepatic, and splanchnic tissues (PDV + hepatic). The experimental design was a crossover between DR and SF diets, with six samplings of blood at 2-h intervals on 2 d for each steer. Nitrogen intake (139 +/- 3 g/d), output in urine (43 +/- 2 g/d), and retention (40 +/- 3 g/d) were similar for both processing treatments. When steers were fed SF sorghum compared to DR sorghum, N retention as a percentage of N intake was numerically greater (P < 0.12), output of fecal N was numerically lower (P < 0.13), and urinary urea N was lower (P < 0.04). For SF vs DR, net uptake of alpha-amino N by liver was higher (P < 0.04; 20 vs 9 g/d) and was numerically lower (P < 0.16) for ruminal tissues (15 vs 33 g/d). Feeding steers SF compared to DR tended to increase net transfer (cycling) of blood urea N to PDV (57 vs 41 g/d; P < 0.07), increased cycling to intestinal tissues (15 vs 6 g/d; P < 0.05), and numerically increased transfer to ruminal tissues (42 vs 32 g/d; P < 0.12) but did not alter other net output or uptake of N across splanchnic tissues. Total urea N transfer (blood + saliva) was similar for both treatments. Net uptake of alpha-amino N by ruminal tissues was about 30% of the net amount of alpha-amino N absorbed across the intestinal tissues. In summary, most of the blood urea N cycled from the liver to gut tissues was transferred to ruminal tissues for potential microbial protein synthesis, and the net ruminal utilization of alpha-amino N was about 30% of that absorbed from intestinal tissues. Feeding growing steers SF compared to DR sorghum diets numerically increased whole-body N retention (percentage of N intake) by about 15% and tended to increase transfer of blood urea N to the gut by about 40%, which could increase the supply of high-quality microbial protein for absorption.     

Alternate day supplementation of corn stalk diets with soybean meal or corn gluten meal fed to ruminants.

Four experiments were conducted to determine the effect of adding corn gluten mean (CGM) or soybean meal (SBM) at 24- or 48-h intervals to diets based on corn stalks. In each experiment corn stalks was the primary diet ingredient fed to wethers or steers. Monensin was also fed to determine whether its effects on ruminal fermentation would improve the efficiency of N utilization under these conditions. Evaluation criteria included ruminal fermentation characteristics, DM intake and utilization, N balance in sheep, and steer feedlot performance. Ruminal ammonia nitrogen (NH3 N) concentrations measured over time were higher (P < .05) when diets contained SBM. Diet did not influence (P > .10) total VFA concentrations in ruminal fluid. Differences in diurnal shifts in ruminal NH3 N and total VFA due to protein source resulted in diet x hour interactions (P < .05). Dry matter intake response to protein source and frequency of supplement feeding was variable. Dry matter digestibility and nitrogen digestibility were not affected (P > .10) by protein source or feeding interval. The 48-h interval feeding of CGM was favorable compared with 24-h interval feeding (P < .05). The opposite response occurred with SBM, resulting in a diet x feeding interval interaction (P < .05). Nitrogen retention was greater (P < .05) when CGM was fed and with alternate day feeding. Diets that contained CGM supported higher (P < .05) ADG and gain/feed than diets that contained SBM when fed to steer calves. Alternate day feeding of supplements that contained monensin was detrimental to steer performance under the conditions of these experiments. Corn gluten meal is an effective substitute for SBM when alternate day protein supplementation is practiced.     

Influence of protein degradability in range supplements on abomasal nitrogen flow, nitrogen balance and nutrient digestibility

Two metabolism trials were conducted with yearling steers fed mature native forage to measure the effect of supplemental protein degradability on selected metabolic variables. Supplements contained 40% crude protein equivalence. In Trial 1, four abomasal-cannulated steers weighing 290 to 379 kg were fed supplements containing the following N sources: (1) 15% corn, 85% urea (U); (2) 100% soybean meal (SBM); (3) 10% corn, 40% soybean meal, 50% urea (SBM-U) and (4) 14% corn, 36% blood meal, 50% urea (BM-U). Equal portions of the daily diet (2.2% of body weight) were fed every 2 h. Treatment differences were not significant for organic matter digestibility, abomasal organic matter flow, nonammonia N flow, feed N flow, bacterial N flow and efficiency of microbial protein synthesis. There was a positive (P less than .05) relationship between quantity of slowly degraded protein fed and nonammonia N flow (r = .97) or feed N flow (r = .98). Escape N was determined to be 21.5, 16.5 and 54.2% in SBM, SBM-U and BM-U supplements, respectively. In the second trial, no supplement, SBM, SBM-U and BM-U were fed in a N balance trial. Dry matter, crude protein and neutral detergent fiber digestibilities were higher (P less than .05) for steers fed supplemented diets. Acid detergent fiber digestibility was higher (P less than .05) for steers supplemented with SBM than steers fed the unsupplemented diets. Nitrogen retention was greater (P less than .05) for cattle fed SBM and BM-U than for cattle fed SBM-U or no supplement.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of acid and alkali treatment of soybean meal on nitrogen utilization by ruminants

Soybean meal (SBM) was treated with acid or alkali to determine effects on N solubility, in vitro NH3-N accumulation, in situ N degradability, and N digestion and retention in growing lambs. The following SBM treatments resulted in decreased (P less than .05) N solubility and in vitro NH3-N accumulation compared with control SBM: spraying with 2.5 or 5% acetic or propionic acid, soaking in .5 N HCl, .5 N NaOH or .5 N propionic acid followed by air drying, and soaking in H2O, .5 N HCl or .5 N propionic acid followed by drying at 100 C. In situ residual N was determined for SBM subjected to the above treatments. Soybean meal sprayed with 2.5 or 5% acetic or propionic acid had greater (P less than .05) in situ residual N after 4, 8 and 12 h of incubation than control SBM. Soybean meal soaked in .5 N HCl or .5 N NaOH and air-dried, and soaked in H2O, .5 N propionic acid or .5 N HCl and dried at 100 C had greater (P less than .05) in situ residual N after 4, 8, 12 and 24 h of incubation than control SBM. In a lamb N balance trial, SBM treated by spraying with 5% acetic or propionic acid or by soaking in .5 N NaOH did not result in reduced N digestion compared to control SBM. Feeding SBM soaked in .5 N NaOH resulted in a 39% increase (P less than .05) in N retention compared with control SBM (5.21 vs 3.74 g/d, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)