Non-protein Nitrogen Source Research Articles

Fattening goats with sugarcane sprouts, corn stubble, protein concentrate, molasses and urea

Daily weight gains (DWG), dry matter intake (DMI) and cost of fattening were studied using a diet of 29% sugarcane sprouts, 29% corn stubble, 29% concentrate with 18% crude protein (CP), 9.5% molasses, 2% urea, 1% salt and 0.5% mineral salts. The study was conducted during three consecutive years (1990–1992), using a total of 374 goats of 12–36 months of age. Results showed DWG of 102 g ± 9 g day −1for the group less than 30 kg BW (Group 1) and of 86 g ± 8 g day −1 for goats with more than 30 kg BW (Group 2). The ratio of feed conversion was 11:1 for the first group, and 12:1 for the second group. DMI was 1.055 kg day −1 and 1.270 kg day −1 for Groups 1 and 2, respectively. Goats with an initial BW of less than 30 kg were more profitable ( P < 0.01). For effect of breed, growth of Nubians was superior ( P < 0.05) to that of Alpines. The diet had a cost of $US0.11 kg −, so $US1.21 was needed to gain 1 kg for Group 1 and $US1.32 for Group 2. The diet evaluated by DWG and index of conversion was profitable, with the mixture of agricultural by-products produced in the tropics such as sugarcane sprouts combined with molasses-urea, and corn stubble, adding a true protein source (commercial concentrate) and urea as a non-protein nitrogen source. It was concluded that the overall diet was a good alternative nutritional management for fattening goats in the dry season.

The potential of isobutyraldehyde monourea (propanal, 2-methyl-monourea) as a nonprotein nitrogen source for ruminant animals

Experiments were earned out with sheep and in vitro to evaluate isobutyraldehyde monourea (IBMU; propanal-2-methyl-monourea) as a slow-release nitrogen source for ruminant animals. Examination of the compound for carbon, hydrogen, and nitrogen composition and infrared, NMR and mass spectral analyses indicated that IBMU was present in significant amounts. Ten sheep were randomly assigned to diets containing bromegrass hay and corn grain and the following nitrogen supplementation treatments: (1) control, (2) urea, (3) soybean meal, (4) canola meal and (5) IBMU, with the protein supplements providing approximately 25% of the nitrogen intake. Similar treatments were also prepared and evaluated in vitro, with the exception that wheat straw rather than bromegrass hay was used in the incubation. The digestibility of nitrogen in the ration containing IBMU was higher (P &lt; 0.05) than its digestibility in the other rations when measurements were conducted with sheep over three 14-d periods. No differences in dry matter (DM) or energy digestibility were detected between the different treatments. The digestible energy content of IBMU was estimated to be greater than 21 MJ kg−1. The digestibilities of DM in vitro after 2, 4, 8, 12, 24, 48 and 72 h of incubation were not influenced by the presence of IBMU. No influence of nitrogen supplementation on nitrogen balance was observed, probably because of the high protein content of the control ration (10.6%). IBMU exhibited the characteristics of an ideal slow-release nonprotein nitrogen supplement, since concentrations of rumen ammonia nitrogen did not vary from 0 to 8 h after feeding and ammonia concentrations were higher (P &lt; 0.05) both before feeding and 8 h after feeding when IBMU was fed than when any of the other supplements were fed. The concentration of isobutyric acid averaged 2.6-fold higher when IBMU was fed than when canola meal or soybean meal was fed, confirming that most of the compound was degraded in the rumen. Sheep fed IBMU had lower concentrations of acetic, propionic and butyric acid in the rumen than those fed natural protein supplements. It was unclear whether the decrease in VFA concentration was positive or negative in terms of nutritional value. It was concluded that IBMU exhibited some ideal characteristics for a nonprotein nitrogen supplement for ruminant animals because it was degraded at an optimum rate in the rumen and provided rumen microflora with isobutyric acid. Further experimentation is warranted to determine its usefulness when nitrogen-deficient diets are fed to ruminant animals. Key words: Nonprotein nitrogen, isobutyric acid, isobutyraldehyde, slow-release, isobutyraldehyde monourea, propanal-2-methyl-monourea

Influence of source of rumen-degraded nitrogen on ruminal and whole tract digestion, plasma hormone and metabolite concentrations as well as milk yield and composition in dairy cows

Fifteen multiparous and 10 primiparous cows in early lactation (parturition through 16 wk postpartum inclusive) were fed one of five totally mixed diets. Diets differed in the source of supplemental nitrogen with isonitrogenous substitution of canola meal (a rapidly rumen-degraded true protein source) by Barlein (a rapidly rumen degraded nonprotein nitrogen source). All diets were 40% whole crop oat silage and 60% concentrate on a dry matter basis. Rumen pH, ammonia N and lactate concentrations as well as in sacco rumen degradability of whole diet nitrogen were not influenced by treatment. These results appear to support the assumption that Barlein nitrogen was released in the rumen at a rate similar to that of canola meal protein. Feed intake and body weight change did not differ among treatments. However, milk yield declined linearly as substitution of canola meal with Barlein increased. Milk composition of fat, protein, and lactose were not influenced by treatment although milk urea concentrations increased as substitution of canola meal with Barlein increased. Data collected did not conclusively identify the mechanism for the reduced performance; however, it seems most likely it was the result of reduced rumen microbial growth and escape as substitution of canola meal with Barlein increased, leading to a deficiency in metabolizable protein supply. Key words: NPN, dairy cattle, protein

Evaluation of condensed molasses fermentation solubles as a nonprotein nitrogen source for ruminants.

Condensed molasses fermentation solubles (CMS), an effluent from the production of lysine, was evaluated as a nonprotein nitrogen supplement for ruminants by measuring the availability of its nitrogen to rumen microorganisms grown in batch cultures and by comparing CMS to urea as a source of supplemental nitrogen for growing cattle. In vitro dry matter digestion studies showed that, with 1 ml or less of rumen inoculum, microbial digestion was enhanced more (P less than .05) by the addition of CMS than by the addition of urea to 100 mg of cellulose. These stimulatory effects of CMS were absent when either the amount of inoculum (5.0 ml) or cellulose (250 mg) was increased and when wheat straw or alfalfa replaced cellulose as the substrate. Growth rate and feed intake for cattle fed a high-cob/cracked-corn diet containing 2.5 or 5.0% CMS were lower (P less than .05) than for cattle fed the control diet containing urea. Digestibility of dry matter, crude protein, neutral detergent fiber and acid detergent fiber were reduced (P less than .05) by the addition of CMS. Addition of CMS also decreased feed utilization, although the differences were not statistically significant. In conclusion, the nitrogen in CMS was available to rumen microorganisms growth in batch culture; however, CMS was not satisfactory as a substitute for all the urea in a diet for growing cattle containing over 45% of dietary N from the supplemental N source.

EVALUATION OF TWO GLUCOPYRANOSYLAMINES AS NONPROTEIN NITROGEN SOURCES FOR CATTLE: DIGESTIBILITY AND EFFECT ON GROWTH AND FEED CONVERSION

N-[carbamoyl]-β-D( + )-glucopyranosylamine (NCG) and N-[N′-hydroxymethyl-carbamoyl]-β-D ( + )-glucopyranosylamine (HNCG), manufactured from glucose and urea with molasses or barley as the source of glucose, were evaluated as slow release nonprotein nitrogen (NPN) supplements in two feeding trials with steers and a digestibility trial with wethers. In exp. 1, 50 steers (initial weight of 263 kg) were assigned to five treatments providing no source of supplemental N, urea, soybean meal, NCG, or HNCG in diets consisting of 1.8 kg/day of concentrate, 0.93-1.13 kg/day of liquid supplement and ad libitum chopped timothy hay (10.1% crude protein). Daily gain was reduced (P &lt; 0.05) by 22% and dry matter per unit of gain was increased (P &lt; 0.05) by 24% when HNCG was added to the control diet. No differences were observed between daily gain and feed conversion of steers on the other four treatments.In exp. 2, 16 steers were assigned to each of three treatments entailing individual feeding of diets containing no supplemental N, soybean meal, or NCG during a growth (67% straw in diet) and a finishing (15% straw in the diet) period. In the first period steers fed soybean meal grew faster (P &lt; 0.05) than those fed no supplemental N while those given NCG grew at an intermediate rate. In the finishing period steers fed NCG grew more rapidly (P &lt; 0.05) than those fed soybean meal, but not faster (P &gt; 0.05) than steers fed the control diet. Dietary treatment had no significant influence on overall performance or carcass characteristics in this experiment. The digestible energy contents of NCG and HNCG supplements were estimated to be 14.6 and 12.6 MJ/kg dry matter respectively (SEM = 0.9) in exp. 3. Nitrogen balance of wethers was increased (P &lt; 0.05) from − 4.9 to + 4.9 and 6.4 g N/day when NCG and HNCG, respectively, replaced 20% of a pelleted sun-cured alfalfa ration. It was concluded that NCG is a potential commercial slow-release NPN supplement for cattle whereas further research with HNCG would be necessary before it could be recommended as a slow-release NPN source for ruminants. Key words: Glucopyranosylamines, NPN, cattle, digestibility, growth efficiency

Ammonium polyphosphate as a source of phosphorus and nonprotein nitrogen for monogastrics.

Ammonium polyphosphate (APP) was substituted for 0, 50 and 100% of the P supplied by defluorinated rock phosphate (DRP) in corn-soybean meal diets for growing rats and growing-finishing (G-F) pigs. The diets were formulated to contain 10% protein, .75% Ca and .60% P. Two-thirds of the P in the control diet was supplied by DRP. Replacement of 50 or 100% of the DRP with APP increased the dietary N by 7.25 and 14.5%, respectively. To evaluate nonprotein N (NPN) utilization, we used ammonium chloride (NH4Cl) to provide a level of N equivalent to that supplied by APP when it replaced 100% of the P supplied by DRP. These four treatments were repeated with supplementation of limiting amino acids (L-lysine, L-tryptophan and DL-methionine. Daily feed intake, rate of gain and feed:gain (F:G) of rats and G-F pigs were not influenced (P greater than .05) by the substitution of APP for DRP as a P source in corn-soybean meal diets with or without supplemental amino acids. F:G was improved (P less than .05) by the addition of limiting amino acids to diets for pigs, and a similar trend occurred in rats. The addition of NH4Cl to the 10% protein diets as a source of NPN resulted in no observable benefit for growing rats or G-F pigs. Percentages of ham and loin, percentages of bone ash and P content of the bone ash in pigs were not influenced by the dietary treatments.

The Use of Nonprotein Nitrogen Compounds, Sugar Beet Molasses, and Their Combinations in Growing Chick and Laying Hen Rations

Two experiments were conducted to study the utilization of nonprotein nitrogen sources (urea and diammonium citrate), sugar beet molasses, and their combinations by laying hens and growing chicks. Basal diets containing 12 and 20% protein and all essential amino acids according to NRC recommendation (1977) were formulated for laying hens and growing chicks, respectively. Basal diets were supplemented with 3% protein equivalent from soybean meal, urea, or diammonium citrate (DAC) both with and without 10% molasses. In the laying hen experiment, molasses was used also at 15 and 20% in the diet containing 3% supplemental protein from soybean meal.Egg production was increased significantly when the basal diet was supplemented with soybean protein or urea; however, the response to soybean meal supplementation was significantly greater than to that of urea. Diammonium citrate significantly decreased egg production and it had an adverse effect on feed consumption, egg weight, and nitrogen retention. Molasses failed to increase utilization of urea for egg production, but it reduced the adverse effect of DAC on egg production.In the chick studies a growth response was obtained when the basal diet was supplemented with soybean meal, but no response was obtained from urea or DAC. Molasses did not improve the performance of chicks with or without protein supplementation.Molasses per se can be used effectively as an energy source as it had no adverse effects on performance of laying hens and growing chicks up to the maximum levels which were used in these experiments.

Response of High Producing Dairy Cows Fed Alfalfa Hay and Corn Silage to Supplemental Protein and Urea

Thirty-two high producing Holstein cows were assigned randomly to three rations of varying percents and sources of protein: 1) 14.4% crude protein from natural sources, 2) 17.5% crude protein from natural sources, and 3) 17.7% crude protein from both natural and nonprotein nitrogen (urea) sources. Urea nitrogen constituted 11.1% of the total nitrogen in ration 3. Dietary treatments were examined in two trials during the first 84 to 140 days of lactation.Mean daily intakes of dry matter and total digestible nutrients were higher for cows fed elevated protein: 20.1, 14.0; 21.7, 15.2; and 22.1, 15.2kg for rations 1,2, and 3. Means of 3.5% fat-corrected milk were 32.5, 34.8, and 34.3 kg/day. The principal effect of elevated protein was an increase in intakes of dry matter and energy which may have been contributory to the small increase in milk production. However, the trend for higher milk production was established during the first 28 days of lactation when energy intakes were equal. No adverse effects of urea supplementation on feed intake or milk production were apparent.

Melamine as a Dietary Nitrogen Source for Ruminants

SUMMARY Three trials were conducted to determine the usefulness of melamine as a dietary non- protein nitrogen (NPN) source for cattle. Ruminally fistulated steers were fed diets in which the supplemental protein was provided by either cottonseed meal, urea or melamine. Rumen fluid was sampled for ammonia concen- tration periodically for 7 hr after feeding on six occasions during the first 49 days. After 88 days the steers fed cottonseed meal and mela- mine were fasted for 48 hr then refed and ruminal ammonia concentrations monitored. In vitro rumen ammonia concentrations produced by inoculation of either a cottonseed meal, urea, melamine or control (no supplemental nitrogen) substrate with rumen fluid from the steers fed either cottonseed meal or melamine were monitored. Results of these ammonia concentration trials indicated that melamine was slowly hydrolized in a ruminal environment. A 3 “ 3 replicated Latin square digestion and nitrogen balance trial was conducted using the three diets previously fed to the fistulated steers. Results indicated that melamine had little effect on the digestibility of dietary components. Melamine nitrogen was apparently digested to an extent equal to cottonseed meal nitrogen but not (P<.01) as completely as urea nitrogen. Larger (P<.05) amounts of nitrogen fractions other than ammonia and urea appeared in the urine when melamine was fed than when cottonseed meal or urea was fed. Nitrogen balance was lower (P<.05) for melamine than cottonseed meal and tended to be lower than for urea. Under the conditions of these trials, mela- mine may not be hydrolized in the rumen at a rate sufficient to promote maximum ruminal protein synthesis and incompletely hydrolized fractions may be absorbed and voided in the urine. These observations would tend to indicate that melamine may not be an acceptable NPN source for ruminants. (Key Words: Melamine, Urea, Non-Protein Nitrogen, Nitrogen Balance, Ruminal Ammonia, Protein Supplements, Beef Cattle.) INTRODUCTION There has been considerable interest in improving the utilization on non-protein nitrogen in ruminant diets. Basically, two approaches have been taken; optimizing urea utilization (Satter and Roffler, 1975; Burroughs

A comparative study of non-protein nitrogen supplements for sheep

SummaryA basal diet, or the basal diet supplemented with equi-nitrogenous amounts of either ammonium lactate, ammonium acetate or urea was fed to four re-entrant cannulated sheep in a randomized block design.Collections of duodenal digesta were carried out automatically for a continuous period of 4 days following a 10-day equilibration period for each sheep on each diet.Supplementation with non-protein nitrogen increased the passage of total amino acids to the duodenum and increased the proportion attributed to microbial protein. It improved pre-duodenal digestibility of modified acid-detergent fibre and increased post-abomasal digestibility of non-ammonia nitrogen, dry matter and gross energy.Supplementation with non-protein nitrogen increased the energetic efficiency of microbial protein production in the rumen.Ammonium lactate and acetate were safe and effective sources of non-protein nitrogen for dietary supplementation.Supplementation with ammonium lactate led to a greater passage of microbial protein to the duodenum than did equi-nitrogenous supplements of urea or ammonium acetate.

RESPONSE TO NONPROTEIN NITROGEN AND SULFUR SOURCES BY THE EARLY-WEANED CALF

Sixty Holstein bull calves were used in two experiments to evaluate two nonprotein nitrogen sources and several sulfur sources in calf starter rations. Experiment 1 compared urea and biuret, with and without sulfur (S), methionine hydroxy analog (MHA), and S plus MHA; experiment 2 compared the effect of elemental sulfur and sodium sulfate added to a urea-supplemented starter on calf response to these feeds. Performance of calves on the biuret-supplemented starters was significantly reduced as compared with urea-supplemented starters. The addition of sulfur or MHA to the NPN-supplemented starters did not affect animal performance significantly. However, sulfur did tend to improve performance of the urea-fed calves and had the reverse effect when biuret was fed, while MHA tended to depress performance when urea was fed. In the second experiment, the addition of either sulfur or sodium sulfate to the urea-supplemented started did not significantly improve animal performance, even when 40% of the total protein in the diets was supplied by nonprotein nitrogen sources. The urea-supplemented starter rations were found to have N:S ratios before sulfur supplementation of 11.4:1 (experiment 1) and 9.4:1 (experiment 2), which are close to the ratios considered optimum for ruminants.

Processed Poultry Waste Compared With Uric Acid, Sodium Urate, Urea and Biuret As Nitrogen Supplements for Beef Cattle Fed Forage Diets

Poultry waste products processed to recover compounds for industrial and medicinal uses were compared with four non-protein nitrogen sources as nitrogen supplements for beef cattle fed forage diets. In a metabolism trial, steers fed 50% of their dietary nitrogen from uric acid, sodium urate or a processed poultry waste product (containing 28% uric acid) digested dry matter, fiber and nitrogen equally well. Steers fed the diet containing poultry waste had greater urinary nitrogen losses and retained less nitrogen (P<05) than those fed the diet containing sodium urate. Ruminal fluid pH of fistulated steers from pre-feeding through 7 hr post-feeding was not different (P>.10) among treatments, but ammonia concentration averaged the highest (P<.05) for steers fed the poultry waste. During a 90-day growth trial, steers fed 40% of their dietary nitrogen from two processed poultry waste products gained weight more (P<.05) rapidly and efficiently than steers fed similar dietary percentages of nitrogen from either urea or biuret. The results from a second metabolism trial confirmed this trend, but nitrogen retention was not different (P>.05) due to nitrogen source. Neither the concentration of plasma free amino acids nor the concentration of ruminal fluid volatile fatty acids differed (P>.05) among treatments. Results in an adaptation study indicate that ruminal microbes could not readily degrade biuret after 4 days of adaptation to the diet; but after 28 days, ruminal ammonia concentrations averaged 30% higher with steers fed biuret than with those fed urea. Results of these trials indicate that poultry waste that has been processed to recover compounds for industrial and medicinal uses is similar to uric acid and sodium urate but superior to urea or biuret when used as nitrogen supplements for beef cattle fed forage diets.

NITROGEN ADDITIVES TO CORN SILAGE FED TO GROWING CALVES

Three separate experiments were conducted to investigate performance of light-weight calves fed corn silage supplemented with different non-protein nitrogen (NPN) sources added at ensiling time. In one experiment NPN was also added at feeding time. For calves up to approximately 290 kg body weight all supplements containing only NPN reduced weight gains by approximately 0.10–0.15 kg/day compared to soybean meal or low-urea supplements. Corn silage treated with NPN silage additives resulted in reduced dry matter intake compared to soybean meal supplementation. Thus, the effect on feed efficiency was not as great as on weight gains. Treated silages tended to be higher in pH and lactic acid but lower in acetic acid content. A large portion of the NPN added at ensiling time was analyzed as ammonia in the silages. Also, true protein content of the treated silages tended to be higher than that of the controls.

Evaluation of Beef Cattle Range Supplements Containing Urea and Biuret2

Two winter trials were conducted with 304 lactating range cows on dry grass to evaluate non-protein-nitrogen (NPN) in 30% protein supplements containing biuret (pure and feed grade), urea and extruded grain-urea. The NPN sources contributed one-half of the supplemental nitrogen with natural 15 and 30% protein supplements serving as negative and positive controls. Winter weight loss of cows was greater (P≈.02) on the negative than on the positive control in both trials. The apparent utilization of all NPN sources was low and the utilization of urea and extruded grain-urea was less than pure or feed grade biuret. Rumen biuretolytic activity was apparent within 6 days and reached and maintained a high level of activity 20 days after the initiation of feeding biuret, even with intermittent supplementation. Apparent value of NPN supplements was slightly improved with 40% dehydrated alfalfa but not with methio-nine-hydroxy-analogue (MHA). Palatability of supplements was lowered by urea and especially by MHA and extruded grain-urea. In a third trial with yearling heifers fed prairie hay, gains were similar on natural protein and supplements containing urea or extruded grain-urea to provide one-half of the nitrogen. When the heifers were fed the same supplements but low quality winter harvested range grass, NPN utilization appeared to be low.

An evaluation of ammonium sulphate as a potential NPN source for ruminants

Experiments were undertaken to examine the comparative toxicity to sheep of ammonium sulphate and urea given as single doses and the value of ammonium sulphate fed alone or in combination with urea as a supplement to low nitrogen roughages. Ammonium sulphate dosing produced significantly lower mean blood ammonia levels than urea dosing. Fifteen grams of nitrogen as ammonium sulphate were tolerated as a single dose but the equivalent level of urea was toxic. lnappetance and ruminal stasis was noted when sheep fed a low nitrogen roughage (0.5 per cent nitrogen) received ammonium sulphate supplement as the sole non-protein nitrogen source. Ruminal stasis and inappetance may have been due to sulphide toxicity. Ammonium sulphate when used at lower levels in varying combinations with urea was well utilized as a nitrogen and sulphur source even when supplying 50 per cent of the supplemented nitrogen.

Biuret and urea in maintenance and production diets of cattle

SUMMARYA series of five field trials with cattle was carried out to study the comparative efficiency of utilization of urea and biuret in various maintenance and production nutritional situations. It was shown that in maintenance diets with energy intake above 8 Meal/head/day and where half of the nitrogen requirements of the animals was contributed by one of the two non-protein nitrogen (NPN) sources, biuret was utilized 30% more efficiently than urea. No difference in the degree of utilization of urea or biuret was apparent when the energy was reduced to 6·7 Meal/head/day. On the other hand, a high intake of nitrogen in production rations had a masking effect on the nitrogen contribution of the NPN sources and no significant differences in bodyweight gain were recorded.

Complete Rations for Dairy Cattle. IV. Comparison of Supplemental Nitrogen Sources by Metabolizable Protein Concept

Four types of 3×3 Latin squares differing in nonprotein nitrogen source and protein percent were used with 4-wk periods and 36 Holstein cows grouped in trios. Basal rations (9.0 to 10.6% crude protein) high in citrus pulp and pelleted cane bagasse, were equalized in estimated metabolizable protein, ignoring urea fermentation potential, by adding raw urea, extruded corn-urea, or soybean meal at three percents. Corresponding rations of higher protein (12.1 to 13.4%) contained a soybean meal increment partially replacing corn. Mean daily feed intake was lower for basal than soy-increment rations (18.0 versus 19.3kg) as were milk and solids-corrected milk yields (16.0 to 18.3kg and 12.8 to 14.8kg). All-soy controls were superior in milk production by 1.35 and .92kg. Liveweight changes and milk composition were little affected by treatments. Milk fat and protein percents averaged 2.71 and 2.92 overall. Molar porportions of rumen acetate in Period 3 were relatively low, but not acetate/propionate ratios. Increased rumen ammonia concentrations resulted from higher protein, higher nonprotein nitrogen, and urea exceeded extruded corn-urea exceeded soybean meal.

Evaluation of Ammonium Lignin Sulfonate as a Non-Protein Nitrogen Source for Sheep2

Evaluation of Ammonium Lignin Sulfonate as a Non-Protein Nitrogen Source for Sheep2

Urinary Nitrogen Excretion of the Cockerels Fed Non-protein Nitrogen Diets

Under specific conditions, it has been shown that some monogastric animals are able to utilize the nitrogen from non-protein nitrogen (NPN) sources to a limited extent.FEATHERSTON et al.1) were able to show that chicks fed a diet containing all the essential amino acids and supplemented with several sources of nitrogen retained more nitrogen and higher plasma levels of non-essential amino acids. In their study, urea and diammonium citrate (DAC) were effective sources of nitrogen, thus indicating that nitrogen from non-protein sources could be utilized by the chick. YOUNG et al.2) reported that laying hens fed a low protein diet were able to utilize NPN to partially satisfy the total nitrogen requirement. Diammonium citrate and glutamic acid were proved to be effective in a diet adequately balanced.The present experiments reported herein were designed to determine the relative effectiveness of NPN, such as L-glutamic acid, dibasic ammonium phosphate (DAP), DAC and urea in the cockerels by judging from the nitrogen balance index and urinary nitrogenous constituents.

Influence of Dietary Nitrogen Source, Concentrate Level and Biuret Level in Sheep on the Adaptation of Rumen Microorganisms to Biuret as a Nonprotein Nitrogen Source

Influence of Dietary Nitrogen Source, Concentrate Level and Biuret Level in Sheep on the Adaptation of Rumen Microorganisms to Biuret as a Nonprotein Nitrogen Source