Interaction between dietary content of protein and sodium chloride on milk urea concentration,urinary urea excretion,renal recycling of urea,and urea transfer to the gastrointestinal tract in dairy cows

Dietary protein and salt affect the concentration of milk urea nitrogen (MUN; mg of N/dL) and the relationship between MUN and excretion of urea nitrogen in urine (UUN; g of N/d) of dairy cattle. The aim of the present study was to examine the effects of dietary protein and sodium chloride (NaCl) intake separately, and their interaction, on MUN and UUN, on the relationship between UUN and MUN, on renal recycling of urea, and on urea transfer to the gastrointestinal tract. Twelve second-parity cows (body weight of 645 ± 37 kg, 146 ± 29 d in milk, and a milk production of 34.0 ± 3.28 kg/d), of which 8 were previously fitted with a rumen cannula, were fitted with catheters in the urine bladder and jugular vein. The experiment had a split-plot arrangement with dietary crude protein (CP) content as the main plot factor [116 and 154 g of CP/kg of dry matter (DM)] and dietary NaCl content as the subplot factor (3.1 and 13.5 g of Na/kg of DM). Cows were fed at 95% of the average ad libitum feed intake of cows receiving the low protein diets. Average MUN and UUN were, respectively, 3.90 mg of N/dL and 45 g of N/d higher for the high protein diets compared with the low protein diets. Compared with the low NaCl diets, MUN was, on average, 1.74 mg of N/dL lower for the high NaCl diets, whereas UUN was unaffected. We found no interaction between dietary content of protein and NaCl on performance characteristics or on MUN, UUN, urine production, and renal clearance characteristics. The creatinine clearance rate was not affected by dietary content of protein and NaCl. Urea transfer to the gastrointestinal tract, expressed as a fraction of plasma urea entry rate, was negatively related to dietary protein, whereas it was not affected by dietary NaCl content. We found no interaction between dietary protein and NaCl content on plasma urea entry rate and gastrointestinal urea entry rate or their ratio. The relationship between MUN and UUN was significantly affected by the class variable dietary NaCl content: UUN = −17.7 ± 7.24 + 10.09 ± 1.016 × MUN + 2.26 ± 0.729 × MUN (for high NaCl); R² = 0.85. Removal of the MUN × NaCl interaction term lowered the coefficient of determination from 0.85 to 0.77. In conclusion, dietary protein content is positively related to MUN and UUN, whereas dietary NaCl content is negatively correlated to MUN but NaCl content is not related to UUN. We found no interaction between dietary protein and NaCl content on performance, MUN, UUN, or renal urea recycling, nor on plasma urea entry rate and urea transfer to the gastrointestinal tract. For a proper interpretation of the relationship between MUN and UUN, the effect of dietary NaCl should be taken into account, but we found no evidence that the effect of dietary NaCl on MUN is dependent on dietary protein content.     

Analytic validation of an infrared milk urea assay and effects of sample acquisition factors on milk urea results

The objective of this study was to determine if milk samples, as they are routinely collected by Ontario Dairy Herd Improvement, would yield accurate milk urea results with an infrared assay. This investigation involved analytic validation of the infrared assay and assessment of the effect of DHI routine sample acquisition factors on milk urea results. Analytic validation of an automated milk urea assay was performed by assessing the relative accuracy and precision of milk urea results produced by the Fossomatic 4000 Milk Analyzer, an infrared method of analysis, compared with the Eurochem test, an accepted reference method. Results indicated that, when interpreted at the group level, milk urea results between the infrared method and the reference test were in good agreement. The two tests shared a similar and high level of precision. Milk urea concentrations obtained from composite (metered) milk samples, and not quarter stripping samples, were most representative of concurrent serum urea concentrations. The addition of bronopol preservative did not result in a numerically important change in milk urea concentrations. Storage of preserved metered milk samples for up to 4 d at either room temperature or by refrigeration, or for up to 3 d by freezing, did not result in changes in milk urea concentrations. We concluded that milk samples, as they are routinely collected and handled by DHI, are suitable for measurement of milk urea concentrations with the infrared method of analysis if data are interpreted at the group level.     

Moisture profile determination in urea prill. I

Using Karl Fischer titration, the moisture profile along the radius in urea prill was determined. Having verified that during dissolution in methanol the urea grains diminish in radius linearly with time, it was possible to calculate that the layer with the highest water content is at a depth of one‐third of the radius. The moisture profile is linear, with the central moisture content equal to four times the global moisture content of the grain. Copyright © 2007 Society of Chemical Industry     

Prediction of ammonia emission from dairy cattle manure based on milk urea nitrogen: relation of milk urea nitrogen to urine urea nitrogen excretion

The objectives of this study were to assess the relationship between urinary urea N (UUN) excretion (g/d) and milk urea N (MUN; mg/dL) and to test whether the relationship was affected by stage of lactation and the dietary crude protein (CP) content. Twelve lactating multiparous Holstein cows were randomly selected and blocked into 3 groups of 4 cows intended to represent early [123 ± 26 d in milk (DIM); mean ± standard deviation], mid (175 ± 3 DIM), and late (221 ± 12 DIM) lactation stages. Cows within each stage of lactation were randomly assigned to a treatment sequence within a split-plot Latin square balanced for carryover effects. Stage of lactation formed the main plots (squares) and dietary CP levels (15, 17, 19, and 21% of diet dry matter) formed the subplots. Graded amounts of urea were added to the basal total mixed ration to linearly increase dietary CP content while maintaining similar concentrations of all other nutrients among treatments. The experimental periods lasted 7 d, with d 1 to 6 used for adjustment to diets and d 7 used for total collection of urine as well as milk and blood sample collection. Dry matter intake and yields of milk, fat, protein, and lactose declined progressively with lactation stage and were unaffected by dietary CP content. Milk and plasma urea-N as well as UUN concentration and excretion increased in response to dietary CP content. Milk and urine urea-N concentration rose at increasing and decreasing rates, respectively, as a function of plasma urea-N. The renal urea-N clearance rate differed among lactation stages and dietary CP contents. The relationship between UUN excretion and MUN differed among lactation stages and diverged from linearity for cows in early and late lactation. However, these differences were restricted to very high MUN concentrations. Milk urea N may be a useful tool to predict the UUN excretion and ultimately NH₃ emission from dairy cattle manure.     

Effect of urea and by-products on the in-vitro fermentation of untreated and urea treated finger millet (Eleusine coracana) straw

The in-vitro fermentation characteristics of untreated and 50 g litre^?1 urea-treated finger millet (Eleusine coracana) straw with four supplements (urea, rice bran, cottonseed and groundnut cakes) at three different ratios of straw: supplement were investigated. Gas production was greater from treated than untreated straw; groundnut cake was the most rapidly fermented supplement followed by cottonseed cake and rice bran. Urea incubated alone inhibited gas production. Untreated and treated straws were incubated with 22, 30 and 37 g rumen degradable nitrogen from the supplements per kg organic matter digested. Significant (P < 0.05) positive interactive effects on gas production were observed with untreated straw at all three levels of groundnut cake supplementation after 12, 52 and 166 h incubation. Similar interactions were observed for cottonseed cake supplementation of untreated straw and groundnut cake supplementation of treated straw, although statistical significance was not achieved for all supplementation levels at the three times for which data were analysed. No consistent significant interactive effects in gas production were observed between cottonseed cake and treated straw. Rice bran inhibited gas production after 12 h but, subsequently, had little effect on either type of straw. Urea inhibited the gas production from both straws at all three ratios of supplementation. Urea also significantly reduced dry matter disappearance of treated straw at two of three levels of urea supplementation. Interactive effects on gas production were most pronounced in the early stages fermentation and appeared to be related to the high content of highly fermentable material particularly in groundnut cake but also in cottonseed cake.     

Chemical assay of urea for automated sensing in milk.

Results of a new chemical assay for urea involving enzymatic hydrolysis to ammonium and carbonate and subsequent measurement of CO2 partial pressure are presented. The assay is simple to implement in an automated version, and the hardware used is not prone to fouling and damage by raw milk. The assay sensitivity at 24 degrees C is about 0.367 kPa per milligram per deciliter of urea N. The assay has no dependence on milk fat in the sample, and effects of milk proteins and lactose are slight (less than 2% change in sensitivity per change in w/v percent). Observed sensitivities to urea in spiked milk samples were not significantly different from each other or from standards in distilled water or 0.1 M phosphate-buffered saline. The standard error of the assay is about 0.3 mg/dl of urea N (0.1 mM) in standard solution, and about 1 mg/dl of urea N (0.3 mM) in milk in a range of 0 to 30 mg/dl of urea N (0 to 11 mM). The assay holds promise for use in an on-line sensor to measure milk urea N in the milking parlor.     

Kinetics of urea hydrolysis and binding of ammonia to wheat straw during ammoniation by urea

Chaffed wheat straw treated with urea (5% wt/wt) alone or with rumen liquor, a source of urease (EC 3.5.1.5), was stored in polythene bags at 4, 22, and 37 degrees C up to 60 d. Moisture concentration was adjusted to 40%. Urea remaining in the straw and ammonia concentrations in the bags were measured on 2, 4, 8, 12, 16, 25, 40 and 60 d. Urea hydrolysis increased exponentially with time. Hydrolysis of urea was highest at 22 degrees C followed by 37 and 4 degrees C. Addition of rumen liquor substantially increased rate of urea hydrolysis at all temperatures studied, suggesting that treatment time can be reduced by addition of rumen liquor. Rates of ammonia binding at different temperatures were in the order 22 degrees C greater than 37 degrees C greater than 4 degrees C. No hydrolysis of urea was observed up to 7 d of storage at 22 and 37 degrees C when straw was autoclaved and the treatment was carried out under aseptic conditions.     

Effect of dietary nitrogen content and intravenous urea infusion on ruminal and portal-drained visceral extraction of arterial urea in lactating Holstein cows

Urea extraction across ruminal and portal-drained visceral (PDV) tissues were investigated using 9 rumen-cannulated and multi-catheterized lactating dairy cows adapted to low-N (12.9% crude protein) and high-N (17.1% crude protein) diets in a crossover design. The interaction between adaptation to dietary treatments and blood plasma concentrations of urea was studied by dividing samplings into a 2.5-h period without urea infusion followed by a 2.5-h period with primed continuous intravenous infusion of urea (0.493 ± 0.012 mmol/kg of BW per h). Cows were sampled at 66 ± 14 and 68 ± 12 d in milk and produced 42 ± 1 and 36 ± 1 kg of milk/d with the high-N and low-N diets, respectively. The arterial blood urea concentration before urea infusion was 1.37 and 4.09 ± 0.18 mmol/L with low-N and high-N, respectively. Dietary treatment did not affect the urea infusion-induced increase in arterial urea concentration (1.91 ± 0.13 mmol/L). Arterial urea extraction across the PDV and rumen increased from 2.7 to 5.4 ± 0.5% and from 7.1 to 23.8 ± 2.1% when cows were changed from high-N to low-N, respectively. Urea infusion did not decrease urea extractions, implying that urea transport rates were proportional to arterial urea concentrations. Urea extraction increased more across the rumen wall than across the total PDV for low-N compared with high-N, which implies that a larger proportion of total PDV uptake of arterial urea is directed toward the rumen with decreasing N intake. The ruminal vein - arterial (RA) concentration difference for ammonia increased instantly (first sampling 15 min after initiation of infusion) to the primed intravenous infusion when cows were adapted to the low-N diet. The RA difference for ammonia correlated poorly to the ventral ruminal concentration of ammonia (r = 0.55). Relating the RA difference for ammonia to a function of both ruminal ammonia concentration and the RA difference for urea markedly improved the fit (r = 0.85), indicating that a large fraction of ammonia released to the ruminal vein is absorbed from an epithelial ammonia pool not in equilibrium with the ventral ruminal ammonia pool. Changing cows from high-N to low-N affected the relative blood urea clearance by kidneys and PDV. The clearance by the kidneys decreased from 41 to 27 ± 2 L/h and the clearance by the PDV increased from 52 to 105 ± 12 L/h when the diet was changed from high-N to low-N. In conclusion, urea transport across gut epithelia in cattle is adapting to N status and driven by mass action. Data are commensurable with a model for urea transport across gut epithelia based on regulated expression or activity of facilitative urea transporters.     

Fatty acids of boal fish oil by urea fractionation and gas-liquid chromatography.

The fatty acid composition of body and liver fats of boal, Wallago attu (Schn.), a cat fish, belonging to the family Siluridae and commonly known as fresh-water shark has been determined by urea fractionation and gas–liquid chromatography (g.l.c.). The percentages of major component acids were found to be, 16:0, 10.5; 16:1 ω9, 7.6; 18:0, 7.2; 18:1 ω9, 17.4; 18:2ω9, 8.4; 18:3ω3, 6.1; 20:4ω3, 3.7 and 22:6ω3, 4.4. In addition, a number of minor component acids have been detected and estimated. The liver oil fatty acids have also been determined without fractionation and the percentages of major component acids found were 16:0, 23.5; 18:0, 12.7; 18:1ω9, 7.0; 20:4ω3, 13.7; 22:6ω3, 11.2. The oil has been studied for the first time for its fatty acid composition.     

Percutaneous absorption of urea

The effect of several variables on the in vitro permeation of urea through hairless mouse skin has been studied in order to determine the causes of an increasing permeability phenomenon found in studies with a range of hydrophilic compounds.
The permeation of urea increased for a period of approximately 100 h after which a steady state permeation pattern was observed for approximately 25 h. Urea did not effect its own permeation in concentrations between 0.01 M and 1.67 M, and the same pattern of increasing permeation was followed in the presence of ( N -morpholine)propanesulphonic acid and tris(hydroxyme)amino-methane buffers, as in the presence of normal saline. Urea did not affect the permeation of tritiated water. Methanol and water exhibited the same pattern of increasing permeation as urea.
The continuously increasing permeation rate of urea up to 100 h is believed to be due to penetration and extensive association of water with the components of the stratum corneum, altering the ultra-structure of the stratum corneum and leading to the formation of large and extensive hydrophilic diffusion channels which do not exist in fresh, untreated skin. These presumed channels open the stratum corneum to facile permeation of highly polar substances such as urea. The physical events leading up to the ultra structural changes within the tissue at the microscopic level remain obscure and are the subject of ongoing research.
L'absorption percutanée de l'urée     

Moisture profile determination in urea prill. II. Fertiliser caking implications

In a previous study, Karl Fischer (KF) titration was used to measure the mass of water in concentric layers of urea prill. The obtained data demonstrated that the grains of this fertiliser have a linear moisture profile. In the present paper, complementary to the previous one, a theoretical analysis of the behaviour of a spherical grain sample with a linear moisture profile during KF titration is presented. The obtained curve of titration fits the experimental data perfectly. The moisture content at the grain centre is four times greater than the average moisture content, and the layer with the highest water content is located at two‐thirds of the radius from the centre. Using this theoretical grain model and assuming that the intensity of caking is proportional to the area and moisture content of the flat contact surface between broken or deformed grains, it is possible to explain many observed experimental data on fertiliser caking. Copyright © 2007 Society of Chemical Industry     

Relationship between ruminal ammonia and nonprotein nitrogen utilization by ruminants. III. Influence of intraruminal urea infusion on ruminal ammonia concentration.

In three trials, we studied the effect of incremental amounts of intraruminally infused urea on mean ruminal ammonia concentration of steer fed at 2-h intervals. Basal rations contained these percentages of crude protein and total digestible nutrients (dry matter basis); Trial I, 11.1 and 81; Trial II, 6.0 and 54; Trial III, 6.5 and 58. Mean ruminal ammonia concentration reached 5 mg ammonia nitrogen/100 ml rumen fluid at crude protein equivalents of 12.0, 9.3, and 9.4% in I, II, and III. Once ruminal ammonia began to accumulate, there was a linear relationship between intake of urea and mean concentration of amino acids of plasma, serving as an indirect measure of amino acid absorption from the intestine, was not increased by increased intake of urea in III. Results of this experiment support the concept from in vitro data that microbial protein synthesis is unaffected by ruminal ammonia concentration in excess of 5 mg ammonia nitrogen/100 ml rumen fluid.     

Effect of sodium chloride intake on urine volume,urinary urea excretion,and milk urea concentration in lactating dairy cattle

Milk urea nitrogen (MUN; mg of N/dL) has been shown to be related to excretion of urinary urea N (UUN; g of N/d) and total excretion of urinary N (UN; g of N/d) in dairy cows. In the present experiment, it was hypothesized that MUN and the relationship between MUN and UUN or UN is affected by urine volume as a result of dietary sodium chloride intake. Twelve lactating Holstein-Friesian dairy cows (mean ± SD: milk production 28.1 ± 3.23 kg/d and 190 ± 41 d in milk), of which 4 were fitted with catheters in the urine bladder and jugular vein, were randomly assigned to 4 dietary levels of sodium chloride (3, 9, 14, and 19 g of Na/kg of DM) according to a triple 4 × 4 Latin square design. Cows were fed at 95% of ad libitum intake, excluding salt addition. Milk was analyzed for MUN and protein content; urine was analyzed for total N, urea, and creatinine content; feces were analyzed for total N and DM content; and blood plasma was analyzed for urea and creatinine content. Creatinine clearance rate (CCR; L/min) and renal urea reabsorption ratio were estimated based on plasma concentrations of urea and creatinine, and total excretion of urea and creatinine in urine. Intake of DM and N, milk production, and milk protein content were (mean ± SD), on average, 21.4 ± 1.24 kg/d, 522 ± 32.0 g/d, 25.4 ± 2.53 kg/d, and 3.64 ± 0.186%, respectively. A linear relationship was found between Na intake and urine production [urine (kg/d; mean ± SE) = 7.5 ± 4.33 + 0.136 ± 0.0143 × Na intake (g/d)] and between Na intake and MUN [MUN (mg/dL; mean ± SE) = 13.5 ± 0.35 − 0.0068 ± 0.00104 × Na intake (g/d)]. Despite the decrease in MUN with increased Na intake, UN excretion increased linearly with Na intake. Excretion of UUN was not affected by dietary Na content. A linear plateau relationship was observed between CCR and renal urea reabsorption. An increase in CCR coincided with an increase in calculated renal urea reabsorption until a CCR breakpoint value (mean ± SD) of 1.56 ± 0.063 L/min was reached. We conclude that Na intake is negatively related to MUN, whereas UUN is not affected. Variation in mineral intake levels that affect urine volume should, therefore, be taken into account when using MUN as an indicator of UUN in dairy cattle.     

Effects of citrus pulp in high urea rations for steers.

Effects of pelleted and conventional citrus pulp as a replacement for corn, with soybean meal added to keep protein comparable, were tested in rations with 5% urea and 33.33% sugarcane bagasse for fistulated steers. Thus, all rations were low in readily fermented carbohydrates other than those of corn or citrus pulp. Evaluation criteria were concentrations of urea in blood and of pH, ammonia, and volatile fatty acids of rumen fluid. Citrus pulp for diets 1, 2, 3, and 4 was 0, 19, 38, or 55%. Rumen fluid and blood were sampled 1 h before and 2, 4, 7, and 12 h after feed was placed directly into the rumen. No differences between pelleted and conventional pulp or among time trends were significant except that for both forms rumen ammonia was lower with the two highest percents of citrus pulp. Addition of citrus pulp at 0, 19, 38, or 55% of the ration reduced rumen pH (6.85, 6.65, 6.61, 6.51). Blood urea and rumen ammonia decreased in steers fed 19, 38, or 55% pulp; thus, the acetic to propionic ratio was higher. Butyric acid changed only in the time trend. Total volatile fatty acid concentrations were higher at 19, 38, and 55% than at 0% pulp. They were higher at 38 and 55 than at 19%.     

Effects of isoacids, urea, and sulfur on ruminal fermentation in sheep fed high fiber diets.

The effects of isoacids, urea N, and S on ruminal fermentation of sugarcane bagasse- or corn stover-based diets were studied in sheep. Acetate production was taken as a measure of the fermentation rate. For the sugarcane bagasse diet, neither urea nor S supplementation changed ruminal acetate production. When N and S were combined, acetate production was 44% higher (3.16 vs. 2.18 mol/d). Similar effects were noted for the corn stover diet. Increasing the level of isoacids from .1 to .2 g/kg BW per d in the diet did not change acetate production for either diet. However, N supplementation of the sugarcane bagasse diet containing the low level of isoacids resulted in a 49% greater acetate production (2.86 vs. 1.91 mol/d). Acetate production was 90% higher (3.74 vs. 1.97 mol/d) when the diet containing the high level of isoacids was supplemented with N. The corresponding increases for corn stover were 12% (2.64 to 2.95 mol/d) and 35% (2.88 to 3.87 mol/d). The results suggest that NH3 N provided by the basal diet was more limiting than isoacids. Once the N deficiency was corrected, isoacids became limiting. Ruminal digestion of high fiber diets low in N was improved by supplementation with urea, isoacids, and S.     

Effects of urea and starch on rumen fermentation, nutrient passage to the duodenum, and performance of cows.

Four midlactation, multiparous Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design to determine the effects of supplementing urea or starch or both to diets containing fish meal on passage of nutrients to the small intestine and performance of lactating cows. The treatments (in a 2 x 2 factorial arrangement) were 1) control and control plus 2) urea, 3) starch, or 4) starch and urea. Supplementing diets with urea did not affect DMI; ruminal, postruminal, or total tract digestibilities of DM, starch, ADF, or NDF; ruminal fluid VFA concentrations or molar percentages; or ruminal fluid or particulate dilution rates. Feeding additional starch depressed DMI but did not alter ruminal or postruminal digestion of OM or VFA concentrations and molar percentages in ruminal fluid. Ruminal fluid ammonia concentration was increased by feeding urea and decreased by feeding additional starch. Passage of nonammonia N, nonammonia nonmicrobial N, or microbial N to the small intestine and efficiency of microbial CP synthesis were not affected significantly by supplying either urea or additional starch. Feeding urea increased passage of methionine to the small intestine, whereas feeding additional starch increased passage of methionine and arginine. Passage of other amino acids to the small intestine was not altered significantly by feeding urea or additional starch. Production of milk and milk protein was increased, but yields of fat and SNF were not altered by feeding diets supplemented with urea. Production of milk and milk fat was not affected, but yields of CP and SNF were decreased when additional starch was fed to cows.