Influence of urea calcium mixture supplementation on ruminal fermentation characteristics of beef cattle fed on concentrates containing high levels of cassava chips and rice straw

The purpose of this study was to evaluate the effects of various N sources in concentrates containing high levels of cassava chips, with rice straw as the basal forage, on rumen ecology, rumen microbial counts, microbial crude (CP) protein synthesis, and digestibility of nutrients. Four ruminally fistulated crossbred (Brahman × native) beef steers with initial body weight (BW) of 400 ± 40.2 kg were randomly assigned according to a 4 × 4 Latin square design. The dietary treatments were different sources of N in the concentrates and were: T1 = urea (control; urea); T2 = soybean meal (SBM); T3 = urea CaCl₂ mixture (U-Cal); T4 = urea CaSO₄ mixture (U-Cas). All steers were kept in individual pens and supplemented with concentrate at 5 g/kg of BW daily. The experiment was 4 periods, and each lasted 21 d. During the first 14 d, all steers were fed their respective diets ad libitum and for during the last 7 d, they were moved to metabolism crates for total urine and fecal collection. Dry matter intake ranged from 9.8 to 10.5 kg daily and was not altered by diet, while digestibility of NDF differed among treatments and was highest with U-Cas supplementation (P<0.05). Ruminal NH₃ N and plasma urea N with U-Cal, U-Cas, and SBM diets were lower compared with the urea supplemented group (P<0.05). Ruminal volatile fatty acid concentrations were not altered by treatments. Total viable, and cellulolytic bacteria, differed among treatments and were highest with U-Cas (9.1 × 10¹¹, and 4.0 × 10⁹ cfu/mL, respectively). In addition, efficiency of rumen microbial CP synthesis based on organic matter (OM) truly digested in the rumen was increased by SBM or U-Cal supplementation, and was highest with U-Cas supplementation (18.2 g of N/kg of OM truly digested in the rumen). Supplementation of U-Cas to a concentrate containing a high level of cassava chips improved rumen ecology and microbial CP synthesis in beef cattle, suggesting that urea calcium mixtures can replace soybean meal or urea in beef cattle diets without adverse affects on rumen fermentation and other rumen parameters.     

Effects of oilseed meals and grain–urea supplements fed infrequently on digestion in sheep: 2. Cereal straw diets

An experiment examined the intake, growth responses and rumen digestion of young sheep fed ad libitum oat or barley straws alone or supplemented with approximately isonitrogenous amounts of barley grain and urea (Bar/N), safflower seed meal (SAF) or linseed meal (LIN) supplements provided at 3 day intervals. The supplements comprised 15–22% of total dry matter (DM) intake. Sheep offered either of the straws alone consumed 35.0–37.2 g DM/kg liveweight (LW^0.75) per day of straw and an estimated 2.03–2.07 MJ metabolizable energy (ME) per day, and lost 85–97 g LW per day. Supplements increased (P<0.05 or <0.001) voluntary intake of straw and of total DM, and the organic matter (OM) digestibility of the entire diet. Each of the supplements increased (P<0.001) the estimated ME intake to a similar extent and changed the rapid LW loss of sheep fed straw alone to approximate LW maintenance. Rumen ammonia concentrations in sheep fed barley and oat straws alone (12 and 24 mg NH₃/l, respectively) were expected to be deficient for microbial activity, but were increased (P<0.001) by provision of the supplements. Digestion of straw in synthetic fibre bags incubated in the rumen was markedly increased (P<0.01 or <0.001) when supplements were provided. Rumen pH was depressed briefly to pH <6.0 by the Bar/N, but not by the LIN or SAF, supplements. In young sheep fed cereal straws and losing LW rapidly the oilseed meal supplements increased wool growth more than the barley grain–urea supplements, but both types of supplement increased ME intake similarly and were equally effective to reduce the extent of LW loss.     

Effect of elevated systemic concentrations of ammonia and urea on the metabolite and ionic composition of oviductal fluid in cattle

High dietary protein leads to elevated systemic concentrations of ammonia and urea, and these, in turn, have been associated with reduced fertility in cattle. The effect of elevating systemic concentrations of ammonia and urea on the concentrations of electrolytes and nonelectrolytes in bovine oviductal fluid were studied using estrus-synchronized, nulliparous heifers (n = 25). Heifers were randomly assigned to 1 of 3 treatments consisting of jugular vein infusion with either ammonium chloride (n = 8), urea (n = 8), or saline (n = 9). Oviducts were catheterized, and fluid was recovered over a 3-h period on either Day 2 or 8 of the estrous cycle. No difference (P > 0.05) was found in the concentrations of any electrolyte or nonelectrolyte between oviducts ipsi- or contralateral to the corpus luteum. Plasma and oviductal concentrations of urea were increased by infusion with urea (P < 0.001) and ammonium chloride (P < 0.05) but not by saline (P > 0.05). Plasma and oviductal concentrations of ammonia were elevated by infusion with ammonium chloride (P < 0.001) but not by infusion with urea or saline (P > 0.05). No effect (P > 0.05) of treatment was found on oviductal or plasma concentrations of glucose, lactate, magnesium, potassium, or sodium or on plasma concentrations of insulin or progesterone. The concentration of calcium in oviductal fluid was reduced by urea infusion and was negatively associated with systemic and oviductal concentrations of urea. Oviductal concentrations of sodium were higher on Day 8 than on Day 2 (P < 0.05). No effect of sample day was found on any of the other electrolytes or nonelectrolytes measured (P > 0.05). Elevated systemic concentrations of ammonia and urea are unlikely to reduce embryo survival through disruptions in the oviductal environment.     

Effects of supplemental urea sources and feeding frequency on ruminal fermentation,fiber digestion,and nitrogen balance in beef steers

The objective of two experiments was to evaluate non-protein N supplementation with protected urea sources in terms of rumen fermentation products, nutrient digestibility, and N balance in ruminally fistulated beef steers (initial bodyweight 239 ± 18 kg) fed switchgrass hay. Experiment 1 compared urea with Optigen II^®, and Experiment 2 compared urea with RumaPro^®. In both experiments, supplements (400 g/kg of daily dietary dry matter) were fed once daily or every 2 h in a balanced design. Supplements contained soybean hulls, corn grain, vitamins, and minerals as well as non-protein N sources. Non-protein N provided 0.18 g/g of dietary N. Switchgrass hay was fed once daily, at the same time as the supplement in the once-daily treatments. Dry matter intake (4.1 kg/d in Experiment 1, 4.5 kg/d in Experiment 2), dry matter digestibility (P<0.25, 0.58 ± 0.014 g/g in Experiment 1, 0.58 ± 0.010 g/g in Experiment 2), N balance (P<0.83, 11.3 ± 1.9 g/d in Experiment 1, 11.8 ± 3.6 g/d in Experiment 2), ruminal ammonia concentrations (P<0.29, 15.2 ± 1.4 mM in Experiment 1, 11.8 ± 0.6 mM in Experiment 2), and ruminal short-chain fatty acid concentrations (P<0.13, 77.7 ± 3.0 mM in Experiment 1, 75.4 ± 3.0 mM in Experiment 2) were not affected by feeding protected urea sources. Providing a steady supply of ruminally degradable N by feeding supplement every 2 h vs once daily decreased ruminal ammonia concentrations by approximately one-half by 4 h after feeding hay (P<0.01 in both experiments) and increased (P<0.02 in Experiment 1, P<0.08) in Experiment 2) apparent digestibility of dry matter (0.58–0.62 in Experiment 1, 0.56–0.61 in Experiment 2) and dietary fiber components.     

Effect of the proportions of neutral detergent fibre and starch, and their degradation rates, on in vitro ruminal fermentation

Effects of proportions of neutral detergent fibre (aNDFom) and starch, as well as their degradation rates, on rumen fermentation were tested using an in vitro rumen simulation system (SIMCO). The in vitro system was designed to simulate selective particle retention and had an average fluid volume of 1150 ml with a liquid dilution rate of approximately 0.07 h⁻¹. Two types of hay (aNDFom sources) and two types of starch were each included at two different levels in the diet and were examined in an experiment following a 2×2×2 factorial arrangement of treatments (eight diet combinations). The hay was either late-cut timothy (Phleum pretense L.) or early cut meadow grass (Poa pratensis L.), with ruminal in situ aNDFom digestion rates of 0.03–0.04 and 0.07–0.08 h⁻¹, respectively. The two starch types were raw (R) and cooked (C) potato starch with previously determined in vitro ruminal digestion rates of 0.04 and 0.20 h⁻¹, respectively. The starch levels were 300 and 600 g/kg diet dry matter (DM) with the remaining being hay (282–682 g/kg DM) and peptone (14–111 g/kg DM). The aNDFom level varied among the diets with different starch levels and hay types. The peptone acted as a source of peptides and, together with ammonia salts from buffer, was used to balance the N contents of the diets. The feeding level for each of the eight vessels was 28 g DM/d. Two 10-day simulations were made with the system. The average pH was higher (P<0.05) for all treatments with raw potato starch (6.19) versus cooked starch (6.07). Protozoa scores, on a qualitative scale, declined faster at the higher starch level. The aNDFom digestibility was, as expected, higher (P<0.001) for meadow hay (0.57) than timothy (0.32), and was also higher (P<0.001) at the lower starch level (0.54) versus the higher (0.35). Microbial protein production efficiency (mg microbial N/g organic matter truly digested) was higher for the faster degrading aNDFom (P<0.01) and starch (P<0.05) sources, but was not affected by starch level. Cooked starch resulted in a lower acetate proportion (449 mmol/mol versus 591 mmol/mol VFA; P<0.001) but higher proportions of propionate (297 mmol/mol versus 236 mmol/mol VFA; P<0.001), and butyrate (169 mmol/mol versus 127 mmol/mol VFA; P<0.01). Butyrate increased with starch level (127 mmol/mol versus 169 mmol/mol VFA; P<0.01), and was also higher for meadow hay versus timothy (168 mmol/mol versus 128 mmol/mol VFA; P<0.01). Interactions between the treatments demonstrate that the response in VFA pattern to starch level is dependent on starch and aNDFom sources. Substrates such as starch and aNDFom are fermented differently depending on their rates of ruminal degradation.     

Rumen and post-abomasal disappearance in lactating cows of amino acids and other components of barley grain treated with sodium hydroxide, formaldehyde or urea

Four rumen and duodenum cannulated, Holstein lactating cows were used in a change-over design to determine the effects of NaOH, formaldehyde (HCHO) or urea treated barley on disappearance of dry matter (DM), crude protein (CP), amino acids (AA), NDF, ADF and starch of barley in the rumen, post-abomasal (PAT) and total tract by the mobile nylon bag technique. Experimental treatments were coarse milled barley, barley treated with 35 g NaOH/kg, barley treated with 4 g formaldehyde/kg and barley treated with 35 g urea/kg, in which all chemical treated barley was milled coarse before feeding.

NaOH treatment reduced concentrations of lysine and cystine in the barley grain. All chemical treatments decreased rumen disappearances of barley CP but only NaOH and formaldehyde treatments also decreased total AA and some of the AA disappearances in the rumen. All chemical treatments increased DM, OM, CP, starch, NDF and ADF disappearance of barley in the PAT, but only NaOH and formaldehyde treatments increased total AA and most individual AA disappearances in the PAT. Chemical treatments increased disappearance of starch, methionine and glycine in the total tract (P<0.05).

Rumen disappearance of TAA was lower than for CP but PAT disappearance of TAA was more than for CP and finally total tract disappearance of TAA was more than for CP. Individual AA in barley disappeared at different rates in the rumen and PAT. Consequently, the proportion of digesta CP and AAs of barley, entering the intestine were changed by the chemical treatments. We concluded that, appropriate treatment of barley with NaOH or HCHO were provided substantial protection of CP and individual AA from rumen digestion and increased disappearance of most of barley nutrients in PAT, but, NaOH treatment reduced the AA quality of barley. Consequently, formaldehyde can therefore be considered better than NaOH and urea for treatment of barley grain.     

Interaction Between Nickel and Protein Source in the Ruminant

Eighty growing steers were used to determine the effect of nickel supplementation on performance and metabolic parameters of steers fed corn silage-based diets supplemented with different crude protein sources. Crude protein sources examined included: (1) soybean meal, (2) blood meal, (3) urea, and (4) blood meal-urea (two-thirds of supplemental nitrogen from blood meal and one-third from urea). The protein sources differed in ruminal degradability, nitrogen solubility, and nickel content. Nickel was added within each protein treatment to supply either 0 or 5 ppm of supplemental nickel. The experiment was 84 d in duration and rumen fluid and blood samples were collected on days 42 and 80. Average daily gain and feed efficiency were not affected by nickel supplementation. The addition of 5 ppm supplemental nickel greatly increased rumen bacterial urease activity regardless of protein source. When samples were collected prior to feeding on day 80, nickel increased serum urea nitrogen concentrations in steers fed urea, but decreased circulating urea concentrations in animals fed blood meal or the blood meal-urea combination.Ad libitum intake of trace mineral salt was greatly reduced in steers receiving 5 ppm supplemental nickel. The present study suggests that the source of protein may influence ruminant responses to dietary nickel.     

Effects of oilseed meal and grain-urea supplements fed infrequently on digestion in sheep: 1. Low quality grass hay diets

An experiment examined intake, growth response and rumen digestion of young sheep fed ad libitum low quality grass hay alone or supplemented with approximately isonitrogenous amounts of barley grain and urea (Bar/N), safflower meal (SAF) or linseed meal (LIN) provided at 3 days intervals. Supplements comprised 13–20% of total DM intake. Sheep fed grass hay alone consumed 60.2 g DM/kg LW^0.75/day of hay and an estimated 6.09 MJ metabolizable energy (ME)/day, and were in liveweight (LW) maintenance. Hay intake was decreased (P<0.05) by the Bar/N supplement with a substitution rate of 0.9, but was not changed by the oilseed meal supplements. Each of the supplements increased (P<0.05) estimated ME intake to a similar extent, but LW gain and wool growth were lower (P<0.05) in sheep supplemented with Bar/N than those supplemented with LIN. Rumen degradabilities of the SAF and LIN CP were estimated to be 0.72 and 0.62, respectively. Rumen ammonia concentrations in sheep fed hay alone (average 97 mg NH₃/l) were expected to be adequate for microbial activity. Fractional outflow rate (FOR) of liquid from the rumen measured with Co-EDTA (mean 0.109 h⁻¹) was greater than that of Cr-mordanted supplements (mean 0.056 h⁻¹), which was in turn greater than the FOR of Cr-mordanted hay (mean 0.031 h⁻¹). Diet did not affect these FOR. Supplemented sheep accommodated increased DM intake on Day 1 of the 3 day supplementation cycle by increasing rumen digesta load rather than by increasing rate of passage of digesta. Results show that the LW gain of young sheep fed low quality hay was increased more by either oilseed meal than by equivalent amounts of barley grain/urea supplement, apparently due to more efficient utilization of ME for LW gain.     

Appearance of intraportally infused [15N]urea in blood and urine of domestic fowl

The time course of the occurrence of intraportally infused [15N]urea in blood and urine was investigated in chickens. The infused urea appeared in ureteral urine, mostly in the form of urea, as early as 30 min after the start of infusion and the excretion further increased up to the end of 2 hr infusion. Blood urea concentration rapidly increased and reached about three times the initial level at the end of the experiment (P < 0.05 after 20 min), but no significant effects were observed on uric acid, ammonia and glutamine concentrations. Fifty-seven percent of blood urea N and 3% of blood glutamine-amide N and 1% of blood ammonia N, which were determined at the end of experiment, were derived from the infused urea N. It is concluded that urea, which is rapidly increased in blood and urine after feeding urea to chickens, is mostly derived from dietary urea.     

The stimulatory effect of the organic sulfur supplement, mercaptopropane sulfonic acid on cellulolytic rumen microorganisms and microbial protein synthesis in cattle fed low sulfur roughages

Two metabolism trials (experiments 1 and 2) were conducted to examine the effect of the organic S compound, sodium 3-mercapto-1-propane sulfonic acid (MPS) on feed intake, fiber digestibility, rumen fermentation and abundance of cellulolytic rumen microorganisms in cattle fed low S (<0.11%) roughages. Urea was provided in all treatments to compensate for the N deficiency (<0.6%) in the roughages. In experiment 1, steers (333 ± 9.5 kg liveweight) were fed Angleton grass (Dicanthium aristatum) supplemented with S in equivalent amounts as either MPS (6.0 g/day) or sodium sulfate (9.56 g/day). Supplementation of Angelton grass with either sulfate or MPS resulted in an apparent increase in flow of rumen microbial protein from the rumen. Sulfur supplementation did not significantly change whole tract dry matter digestibility or intake, even though sulfate and MPS supplementation was associated with an increase in the relative abundance of the fibrolytic bacteria Fibrobacter succinogenes and anaerobic rumen fungi. Ruminal sulfide levels were significantly higher in the sulfate treatment, which indicated that the bioavailability of the two S atoms in the MPS molecule may be low in the rumen. Based on this observation, experiment 2 was conducted in which twice the amount of S was provided in the form of MPS (8.0 g/day) compared with sodium sulfate (6.6 g/day) to heifers (275 ± 9 kg liveweight) fed rice straw. Supplementation with MPS compared with sulfate in experiment 2 resulted in an increase in concentration of total volatile fatty acids, and ammonia utilization without a change in feed intake or whole tract fiber digestibility even though S and N were above requirement for growing cattle in both these treatment groups. In conclusion, supplementation of an S deficient low-quality roughage diet with either MPS or sodium sulfate, in conjunction with urea N, improved rumen fermentation, which was reflected in an increase in urinary purine excretion. However, MPS appeared to have a greater effect on stimulating short-chain fatty acid production and ammonia utilization when provided at higher concentrations than sulfate. Thus, the metabolism of MPS in the rumen needs to be investigated further in comparison with inorganic forms of S as it may prove to be more effective in stimulating fermentation of roughage diets.     

Association between blood plasma urea nitrogen levels and reproductive fluid urea nitrogen and ammonia concentrations in early lactation dairy cows

Two experiments were conducted to study the relationship of blood plasma urea nitrogen (PUN) concentrations with NH3, urea nitrogen, K, Mg, P, Ca, and Na concentrations in fluid of preovulatory follicles (experiment 1) and the relationships of PUN concentration and stage of estrus cycle with ammonia and urea nitrogen concentrations in uterine fluids (experiment 2) in early lactation dairy cows. Mean PUN levels were used to distribute cows into two groups: cows with PUN>or=20 mg/dl (HPUN), and cows with PUN<20 mg/dl (LPUN). In experiment 1, blood and follicular fluids from preovulatory follicles of 38 early lactation dairy cows were collected on the day of estrus (day 0) 4h after feed was offered. Follicular fluid NH3 was higher (P<0.01) in HPUN cows (339.0 micromol/L+/-72.2) compared to LPUN cows (93.9 micromol/L+/-13.1). Follicular fluid urea N was higher (P<0.001) in HPUN cows (22.4 mg/dl+/-0.4) compared to LPUN cows (17.0 mg/dl+/-0.3). PUN and follicular fluid urea N were correlated (r2=0.86) within cows. In experiment 2, blood and uterine fluids were collected from 30 cows on day 0 and on day 7. Uterine fluid NH3 was higher (P=0.05) in HPUN cows (1562 micromol/L+/-202) than in LPUN cows (1082 micromol/L+/-202) on day 7, but not on day 0. Uterine fluid urea N was higher (P<0.001) in HPUN cows than in LPUN cows on day 0 (26.9 mg/dl+/-1.3 and 20.4 mg/dl+/-0.7) and day 7 (26.5 mg/dl+/-1.1 and 21.4 mg/dl+/-1.1). There was a correlation (r2=0.17) between PUN and uterine fluid urea N within cows. The results of this study indicate that high PUN concentrations were associated with elevated NH3 and urea N concentrations in the preovulatory follicular fluids on the day of estrus and in the uterine fluid during the luteal phase of the estrous cycle in early lactation dairy cows. Elevated NH3 or urea N concentrations in the reproductive fluids may contribute to reproductive inefficiency in dairy cows with elevated plasma urea nitrogen due to embryo toxicity.     

Effect of level and origin of rumen degradable nitrogen on rumen microbial growth and nitrogen utilisation efficiency of animals fed maize silage at maintenance.

Isoenergetic maize silage diets, fed at maintenance to 24 suckling cows (Exp. 1) and to 3 (Exp. 2) or 4 (Exp. 3) rumen fistulated sheep, were compared with a urea and controlled release NPN diet (Exps. 1 and 2) and with a protein-N supplemented diet (Exp. 3). Supplementation increased blood urea concentrations (44.7 +/- 22.3 vs. 97.6 +/- 23.7 mg urea-N x L(-1)) (Exp. 1) and renal urea excretion (2.5 +/- 1.1 vs. 7.6 +/- 1.8 g urea-N x d(-1)) (Exps. 2 and 3), whereas blood allantoin concentrations (286.7 +/- 77.0 micromol x L(-1)) (Exp. 1) and renal excretion of purine derivatives (357.6 +/- 90.7 mg purine-N x d(-1)) (Exps. 2 and 3) were not affected, indicating additional N supplementation did not improve rumen microbial growth. However, some deficiency of rumen degradable N might occur in non supplemented diets as suggested by the reduced rumen NH3-N and RNA concentrations (868 +/- 270 vs. 1466 +/- 466 mg RNA x kg(-1) rumen contents).     

持续施用缓/控释尿素条件下水田土壤NH3挥发与N2O排放特征

以持续9年施用不同缓／控释尿素的水田棕壤为试验对象,以普通大颗粒尿素为对照,研究了持续施用不同缓／控释尿素条件下水田土壤NH₃挥发与N₂O排放特征.结果表明: 与普通大颗粒尿素(U)相比,除1% 3,4－二甲基吡唑磷酸盐(DMPP)+U处理 NH₃挥发增加了25.8%外,其他缓／控释尿素肥料处理对NH₃有明显的减排效果.树脂包膜尿素(PCU)对NH₃减排效果最明显,为73.4%,硫包膜尿素(SCU)为72.2%,0.5% N-丁基硫代磷酰三胺(NBPT)+1% DMPP+U为71.9%,1% 氢醌(HQ)+3% 双氰胺(DCD)+U为46.9%,0.5% NBPT+U为43.2%,1% HQ+U为40.2%,3% DCD+U为25.5%, 1% DMPP均与施用普通大颗粒尿素差异显著;所有缓／控释尿素处理与对照相比均可显著减少N₂O排放.1% DMPP+U对N₂O减排效果最明显,为74.9%,PCU为62.1%,1% HQ+3% DCD+U为54.7%,0.5% NBPT+1% DMPP+U为42.2%,3% DCD+U为35.9%,1% HQ+U为28.9%,0.5% NBPT+U为17.7%,SCU为14.5%,均与施用普通大颗粒尿素差异显著.比较0.5% NBPT+1% DMPP+U、SCU、PCU对NH₃和N₂O减排的综合效果,3种肥料作用相近,且均明显优于其他处理,但包膜材料的成本较抑制剂高数倍.因此,同时添加脲酶和硝化抑制剂的缓释尿素是减少水田氮素损失及环境污染的首选氮肥.     

The feeding value for ruminants of straw and wholecrop barley and oats treated with anhydrous or aqueous ammonia or urea

Ammonia-treated or untreated barley straw supplemented with urea was given as the only feed to two groups of Friesian heifers weighing approximately 550 kg. The digestibility of dry matter (DM) was 58.8 and 49.9%, daily feed intake was 5.88 and 3.87 kg and daily liveweight change was +324 and -447 g for the ammonia-treated and control barley straw diets, respectively.Anhydrous or aqueous ammonia (NH₃) was injected into large round straw bales covered with plastic. The rates of degradation of barley straw in nylon bags and digestibility in vivo were the same for both ammonia treatments. The distribution of N in the bales was also similar and uniform with both treatments. No differences were recorded in the rate of degradation in nylon bags if the plastic was removed 2 or 8 weeks after treatment.Anhydrous or aqueous ammonia or isonitrogenous amounts of urea were injected into large round bags containing whole-crop barley or oats collected with a forage harvester. The digestibility of starch by steers was about 92% for ammonia-treated samples and 78% for the urea-treated samples. Urea and ammonia efficiently preserved the whole-crop materials but untreated control samples and samples treated with NaOH deteriorated during storage.     

Effect of harvesting period on the nutritive value of rice grass (Echinochloa sp.) hay given as sole diet to lambs

Data regarding the influence of maturity within the vegetative stage of tropical grasses on forage quality are limited and conflicting. The change in chemical composition of rice grass (Echinochloa sp.) hay harvested at 32, 46, 72 and 90 days of regrowth, and its effect on intake, digestibility, ruminal fermentation, rumen microbial protein synthesis (Experiment 1) and splanchnic oxygen uptake (Experiment 2) by lambs was evaluated. Except intake of indigestible neutral detergent fibre (NDF) which was similar for all treatments, intake of all hay components and the apparent digestibility of dry matter, organic matter (OM), NDF, N, as well as OM and N true digestibility, N retention and rumen microbial protein synthesis decreased linearly (P < 0.05) with increased regrowth age. Rumen fluid pH, ammonia N and peptide concentrations were similar for all treatments while sugars and amino acid concentrations decreased linearly with increased regrowth age of rice grass (P < 0.05). Passage rate of particles through reticulum-rumen (PRrr) was quadratically related (P < 0.05) to regrowth age. The highest PRrr and, consequently, the lowest retention time in the reticulum-rumen were obtained at 72 days of regrowth. There was a quadratic effect (P < 0.05) on net portal-drained viscera (PDV) flux of oxygen and heat production, while OM intake, portal blood flow and heat production as proportion of digestible energy (DE) intake were not affected by the increased regrowth age of rice grass. The highest means of oxygen uptake and heat production by PDV tissues were in 72 days treatment. In the whole splanchnic metabolism assay neither hay intake nor blood flow, oxygen uptake or heat production were affected by forage regrowth age. In conclusion, the nutritive value of rice grass hay decreased as regrowth age increased from 32 to 90 days due to decrease both OM intake and digestibility.     

Influence of the diet and grazing on adipose tissue lipogenic activities and plasma leptin in steers

The objectives of the two experiments were to determine the respective effects and interactions of diet type (grass v. maize diets) and physical activity (grazing v. zero grazing) on lipogenic enzyme activities and adipose cell size in subcutaneous, perirenal and intermuscular adipose tissues and on plasma metabolites and hormones in Charolais steers. After weaning, the steers were assigned to two (Experiment 1, n = 24) or three (Experiment 2, n = 24) groups, with steers in Experiment 1 grazed grass or indoors maize-silage-fed and steers in Experiment 2 grazed grass, indoors cut grass- or indoors maize-silage-fed. Both experiments lasted for 23 months. All grass-fed animals were fed grass silage during the two winter seasons. During the two summer seasons, steers fed on grass were rotationally grazed on a perennial rye-grass pasture while steers fed on cut grass were fed indoors on freshly cut grass alone. Steers fed on maize silage were fed maize silage indoors during the entire experiment. All animals were reared for similar body weight and growth rates and slaughtered at the same age (31 to 32 months). Activities of lipogenic enzymes were significantly lower in the three adipose tissue sites of steers fed cut grass compared with maize silage, although there were less-marked effects in intermuscular adipose tissue. Plasma insulin and glucose concentrations were also lower in steers fed cut grass whereas plasma leptin concentration was similar. As body fat content was not affected by nutritional treatment, it is suggested that the decrease in potential lipogenic activity was associated with the nature of the diet and not to differences in available net energy. In other respects, grazed grass compared with eating cut grass did not affect lipogenic enzyme activities but decreased plasma leptin concentrations in the older steers and increased plasma non-esterified fatty acids and glucose concentrations without affecting adipose tissue weight and adipose cell size.     

Trace mineral source influences digestion,ruminal fermentation,and ruminal copper,zinc, and manganese distribution in steers fed a diet suitable for lactating dairy cows

High solubility of certain trace minerals (TM) in the rumen can alter nutrient digestibility and fermentation. The objectives of the present studies were to determine the effects of TM source on 1) nutrient digestibility and ruminal fermentation, 2) concentrations of soluble Cu, Zn, and Mn in the rumen following a pulse dose of TM, and 3) Cu, Zn, and Mn binding strength on ruminal digesta using dialysis against a chelating agent in steers fed a diet formulated to meet the requirements of a high producing dairy cow. Twelve Angus steers fitted with ruminal cannulae were adapted to a diet balanced with nutrient concentrations similar to a diet for a high producing lactating dairy cow for 21 d. Steers were then randomly assigned to dietary treatments consisting of 10 mg Cu, 40 mg Mn, and 60 mg Zn/kg DM from either sulfate (STM), hydroxychloride (HTM) or complexed trace minerals (CTM). The experimental design did not include a negative control (no supplemental Cu, Mn, or Zn) because the basal diet did not meet the National Research Council requirement for Cu and Zn. Copper, Mn, and Zn are also generally supplemented to lactating dairy cow diets at concentrations approximating those supplied in the present study. Following a 14-d adaptation period, total fecal output was collected for 5-d. Following the fecal collection period, rumen fluid was collected for Volatile fatty acid (VFA) parameters. On the following day, the same diet was provided for 14 d, without supplemental Cu, Zn, and Mn. This period served as a wash-out period. A pulse dose of 100, 400, and 600 mg of Cu, Zn, Mn, respectively, from either STM, HTM, or CTM, was administered via ruminal cannulae to the steers on day 15. Over a 24-h period ruminal samples were obtained every 2-h. Following centrifugation, the supernatant was analyzed for Cu, Mn, and Zn. Ruminal solid digesta samples from times 0, 12, and 24 h after bolus dosing were exposed to dialysis against Tris-EDTA. Digestibility of NDF and ADF were lesser in STM vs. HTM and vs. CTM supplemented steers. Steers receiving HTM and CTM had greater total VFA concentrations than STM, and molar proportions of individual VFA were not affected by treatment. Ruminal soluble Cu and Zn concentrations were greater post dosing in STM and CTM supplemented steers at 2, 4, and 6 h for Cu and 4, 6, 8, 10 and 12 h for Zn when compared to HTM supplemented steers. The release of Cu and Zn from ruminal solid digesta following dialysis against Tris-EDTA at 12 and 24 h postdosing was greater for steers receiving HTM compared to those receiving STM or CTM. Results indicate trace mineral source impacts: 1) how tightly bound Cu and Zn are to ruminal solid digesta; 2) fiber digestion; 3) and ruminal total VFA concentrations.     

The effect of protein content of the diet on the rate of urea formation in sheep liver

1. In the livers of six sheep given a high-protein diet, the concentrations of certain urea-cycle enzymes [ornithine transcarbamoylase, arginine synthetase (combined activity of argininosuccinate synthetase and argininosuccinase) and arginase] were significantly greater than when the sheep were given a low-protein diet. Alkaline phosphatase activity/mg. of liver protein was not significantly affected by diet. 2. Three sheep previously given the high-protein diet showed no significant rise in the concentration of ammonia in the blood after the administration of urea (0·5g./kg. body wt.). The concentration of ammonia in the blood of the three sheep given the low-protein diet rose exponentially with time after dosing with urea and all sheep died. 3. It is suggested that tolerance to ammonia toxicity in the sheep is at least partly a function of the activity of the urea-cycle enzymes in the liver.     

Nucleic acid synthesis from blood urea 15N in the sheep

In experiments on 4 sheep fed on a low protein diet [6.2 g N/day] and given a single i.v. dose of 15N-labelled urea [15 mg 15N/kg body mass], the authors found that, from 0.5 to 6 h, mean 15N incorporation rose progressively in the total rumen fluid nitrogen from 0.23 to 0.44 at. % 15N and in the rumen bacterial nitrogen from 0.11 to 0.51 at. % 15N. Up to 3 h, total nitrogen enrichment was greater (0.5 at. % 15N) than enrichment of bacterial nitrogen (0.28 at. % 15N), but from 3 to 6 h there was little difference between them. The mean 15N values in the nucleic acids isolated from rumen fluid bacteria in samples collected 3 and 6 hours after injecting labelled urea into the blood were 0.15 and 0.19 at. % 15N respectively, in nucleic acids isolated from the liver 0.042 and 0.04 at. % 15N, in the total rumen bacterial nitrogen 0.28 and 0.51 at. % 15N and in the total liver nitrogen 0.11 and 0.11 at. % 15N. It is concluded from the results that blood urea nitrogen is utilized for synthesis of the total nitrogenous substances of the sheep's rumen bacteria and liver far more intensively than for synthesis of the nucleic acids isolated from them. At the same time, it is utilized more intensively for nucleic acid synthesis in the rumen bacteria than in the liver.     

Transformation of15N-labelled urea and its modified forms in tropical wetland rice culture

Summary The fate of 100 kg N ha^–1 applied as¹⁵N-urea and its modified forms was followed in 4 successive field-grown wetland rice crops in a vertisol. The first wet season crop recovered about 27 to 36.6% of the applied N depending upon the N source. In subsequent seasons the average uptake was very small and it gradually decreased from 1.4 to 0.5 kg N ha^–1 although about 18 to 20, 12 to 17 and 14 to 18 kg ha^–1 residual fertilizer N was available in the root zone after harvest of first, second and third crops, respectively. The average uptake of the residual fertilizer N was only 7.6% in the second crop and it decreased to 4.5% in the third and to 3.2% in the fourth crop although all these crops were adequately fertilized with unlabelled urea. The basal application of neem coated urea was more effective in controlling the leaching loss of labelled NH₄+NO₃–N than split application of uncoated urea. In the first 3 seasons in which¹⁵N was detectable, the loss of fertilizer N through leaching as NH₄+NO₃–N amounted to 0.5 kg ha^–1 from neem-coated urea, 1.5 kg from split urea and 4.1 kg from coal tar-coated urea. At the end of 4 crops, most of the labelled fertilizer N (about 69% on average) was located in the upper 0–20 cm soil layer showing very little movement beyond this depth. In the profile sampled upto 60 cm depth, totally about 13.8 kg labelled fertilizer N ha^–1 from neem-coated urea, 12.7 kg from coal-tar coated urea, and 11.8 kg from split urea were recovered. The average recovery of labelled urea-N in crops and soil during the entire experimental period ranged between 42 and 51%. After correcting for leaching losses, the remaining 47 to 56% appeared to have been lost through ammonia volatilization and denitrification.