urea as a non-protein nitrogen sources for ruminants · pdf filealltech young scientist...

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Dinesh Panday

Review Article

UREA AS A NON-PROTEIN NITROGEN SOURCES FOR RUMINANTS

Dinesh Panday

B. Sc. Ag. 2nd

year

Email: [email protected]

Institute of Agriculture and Animal Science (IAAS), Rampur, Chitwan, Nepal

ABSTRACT

Urea is used as most common non-protein nitrogen feed source for ruminants, which contains 46.7 percent of nitrogen. It is fed as a replacement for a part of the protein in a ration. The ability of microorganisms present in the rumen of ruminants, use of feeding urea reduces the need for imported protein supplements with no deleterious effects on the animal. Treating with urea is based upon its transformation into ammonia. The amount of urea included in concentrate mixtures for cattle or sheep should not exceed 3 percent and usually the addition of 1 to 1.5 percent will prove adequate. Favorable results have been recorded with ensiling urea to green maize at the rate of 0.5 percent of the weight of the fresh forage. Urea feeding has several advantageous effects on body weight, growth rate, and higher milk yields, even under adverse conditions. Source of readily available carbohydrates, frequency and level of feeding urea, proper mixing, solubility of proteins, adequate supply of minerals, etc. are the factors affecting urea utilization in ruminants. Excess level of urea feeding may develop a problem of Urea toxicity (poisoning), due to poor mixing of feed or to errors in calculating the amount of urea to add to the ration. Methods are needed to reduce the fast rate of urea breakdown in the rumen to ensure slow absorption. Research on slow-release pellets or on new compounds that would allow urea to be released in about five hours would safeguard its use.

INTRODUCTION

Ruminants are capable of utilizing different protein sources due to their stomach physiology. Feeding management for ruminant has been one of the major concerns in livestock. Feeding grass, fodder and concentrates of low nutritive value doesn’t always meet the nutritional needs of ruminants, hence they should be replaced with suitable alternatives in feed one of such alternative is the use of non-protein nitrogen (NPN) compounds.

Protein rich leguminous forages are not widely grown in many areas grazed by ruminants, and vegetable protein supplements are usually expensive or unavailable. The manufacture of urea and ammonia to be used as fertilizer has been greatly expanded in many countries, but these could not be used more widely in feeds for ruminants.

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Urea is a simple compound that contains 46.7 percent of nitrogen compared to 16 percent for most proteins. When plant protein feeds, such as soybean meal, are high priced, it is economical to use urea as a protein supplement in ruminant rations. Using the protein equivalent of 281 percent, 13.5 pounds of urea and 86.5 pounds of corn or similar grain are equal in protein and energy value to 100 pounds of 44 % protein soybean meal or similar protein supplement for ruminant animals. The cost of the urea-corn mixture normally would be less than the cost of soybean meal, and the use of urea obviously as an economical replacement for a part of protein in a ration (Stanton and Whittier, 1998).

The ability of the micro-organisms in the rumen of cattle and sheep to utilize these NPN sources to form true protein that can be converted to meat and milk by the animals represents an important contribution to human's food supply. Animals with simple stomachs (pigs and chickens) cannot make use of large concentrations of NPN compounds because of a lack of enzymes and bacteria to break down the NPN to ammonia and synthesize it into protein. But while feeding urea to ruminants, urea toxicity (poisoning) may be a problem if urea is fed at high levels or mixed improperly.

Thus, the aim of this review is to elaborate strength and scope as well as to bring together

selected examples of research in which urea has been used successfully to replace the short

supplies of vegetable protein feeds as well as to direct attention to limitations in the use of urea

and other NPN sources.

BODY OF REVIEW

Non-protein nitrogen (or NPN) is a term used in animal nutrition to refer collectively to components such as urea (NH2)2CO; protein equivalent 281, biuret NH2CONHCONH2H2O; protein equivalent 219, and ammonium carbamate NH2CO2NH4 ; protein equivalent 225 which are not proteins but can be converted into proteins by microbia in the ruminant stomach (Wikipedia, 2010). Many other products have been used experimentally and commercially, but most of them do not compare favorably to urea, because of greater toxicity, higher cost or lower palatability. Thus, urea is most common NPN source for ruminants.

1.1 Mechanism of urea utilization

When urea with feed sources enters the rumen, it is rapidly dissolved and hydrolyzed into ammonia by bacterial urease. The ammonia can then be utilized by the bacteria for synthesis of amino acids required for their growth. Amino groups are also split from amino acids and from intact proteins and used by bacteria in the same manner. Protein synthesis within the rumen by micro-organisms is very closely associated with the activity of those organisms in breaking down cellulose and other carbohydrate materials and in the formation of organic acids as by-products of this fermentation process. The solubility of natural proteins varies greatly and thus the rate at which they are hydrolyzed and utilized by bacteria differs appreciably. However,


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fairly high proportion of the more soluble proteins such as casein is utilized by bacteria in the same way as the ammonia from urea. When ammonia is produced too rapidly in the rumen or if the concentration becomes too high, appreciable amounts are absorbed directly into the bloodstream, reconverted to urea in the liver, excreted through the kidneys in the urine, and thus lost from the animal. There is, however, always a small amount of urea in the bloodstream and other body fluids. This urea finds its way into the saliva and re-enters the rumen. Urea has been shown to pass into the rumen directly through the rumen wall from the circulating blood.

True Protein NPN compounds in Food

Peptides

Amino acids Ammonia Absorbed

Microbial Protein through saliva converted Urea in Liver

Digested in Lower gut Excreted in Urine

` Fig: Digestion and absorption of nitrogenous compounds in ruminants

1.2 Advantages of the use of urea

a) Drought feeding for survival

This is perhaps one of the most important applications of urea in the true pastoral areas, which are usually subject to periodic severe droughts. Morris (1958a, 1958b, 1958c) and Briggs et al. (1960) stated that supplements of wheat and urea improved the survival rate and increased the roughage intake. Ryley (1961) found that urea greatly increased intake of silage, increased birth weight of calves, reduced calf mortality, improved calf growth rate, and increased milk production. Beames (1963) has reported the conditions that the addition of urea to the ration enabled the animals to survive during drought.

b) Maintenance of breeding cows and ewes

Ryley (1961) found that with the small addition of sorghum, urea reduced body weight loss, improved birth weight of calves, reduced neonatal mortality, and led to higher milk yields and calf growth rate. It appears to be great scope here for supplementing the low quality forage available during the dry season where beef cows are exposed to nutritional stress during pregnancy or lactation, which may seriously impair their lifetime productivity.


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c) Feeding growing and fattening lambs

In early studies by Harris and Mitchell (1941) and Johnson et al. (1942, 1944), showed that lambs could gain in body weight and store body nitrogen on rations containing 40 to 65 percent of the nitrogen in the form of urea, the rates of gain were less than desired for efficient lamb fattening operations. Balance studies in Illinois (Hamilton et al., 1948) showed that the nitrogen of urea was as well utilized as equal nitrogen from dried skim milk, gluten feed or casein. Lambs stored slightly more nitrogen on a urea supplement than on soybean meal (Tillman and Swift, 1953) and both were superior to ammoniated molasses products.

d) Feeding weaner cattle for growth

Beef heifer calves grazing dry grass during the winter made approximately equal growth on a pelleted supplement, in which 25 percent of the nitrogen was supplied by urea, as on a diet supplying a similar amount of total nitrogen from cottonseed meal (Briggs et al., 1948). McClymont (1948) reported that urea gave increased growth rate of similar magnitude to that given by protein. Hence, urea is likely to find useful application only when grains are much cheaper than protein feeds or when protein feeds are not available.

e) Supplementing rations for dairy cattle

The favorable responses obtained by Bartlett and Cotton (1938), Hart et al. (1939) and Work and Henke (1939) stimulated research on the use of urea as a substitute for protein in rations for cattle and sheep in the United States. Most research results and experiences in feeding dairy cattle have been favorable enough to allow mixed feeds containing urea at a level up to one third of the nitrogen to be fully accepted and widely used as long as there remains an advantage in feed prices.

f) Growing and lactating dairy cattle

Loosli and McCay (1943) demonstrated that two-month-old dairy calves were able to use urea in dry starter rations. Brown et al. (1956) fed dairy calves, starting at two days of age. Performance of the calves fed the urea-mixture was similar to those receiving linseed meals. Stobo et al. (1967) reported that Ayrshire and Shorthorn calves, weaned at five weeks on to concentrates, hay and water, gained significantly faster on a concentrate containing 20 percent protein from vegetable sources than those given concentrates containing either 12 percent protein or 18 percent protein of which 33 percent was in the form of urea. The primary advantage of using urea in practical rations has usually been its lower cost and abundant supply when vegetable protein feeds may be scarce.

Nehring (1939) reported that urea was able to replace protein at low levels of milk yield, but higher yields were not satisfactorily maintained. Urea and ammoniated pineapple bran were as effective in supporting milk production as soybean meal and the feed cost was low (Otagaki et al., 1956). Urea can replace part of the protein source in rations for lactating dairy cows.


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g) Addition of urea to silage and hay

Coppock and Stone (1965) have reviewed the extensive literature dealing with the use of maize silage

for dairy cattle. Only recently has there been appreciable interest among dairymen in the addition of

urea to increase the crude protein value of the maize silage. It is probable that urea is of no value as a

supplement to good quality hay that contains over 10 percent crude protein. In consequence, addition

to low quality hay will be employed only for maintenance or survival rations. Favorable results have

been recorded with dairy and beef cattle when urea has been added at the time of ensiling to green

maize at the rate of 0.5 percent of the weight of the fresh forage.

h) High-urea supplements

Adding more urea to the premix did not improve performance, but reducing the urea and lowering the crude protein intake depressed the rate of gain. When the same amount of crude protein was supplied by soybean meal cattle gained faster and required less feed per unit of gain, but the feed costs were higher; thus the high-urea supplements are being used in feedlot fattening of cattle.

1.3 Factors affecting urea utilization

Stanton and Whittier (1998) mentioned following factors that affecting the urea utilization in ruminants;

a) Source of readily available carbohydrates. The single most important factor influencing the amount of urea a ruminant animal can use is the digestible energy or total digestible nutrients (TDN) content of the ration. Rations high in digestible energy (high grain) result in good urea utilization; those that are low in digestible energy (high forage) result in a lowered utilization of urea.

b) Frequency of feeding urea. Feed urea containing supplements at least daily. A constant or continuous intake of urea will improve its utilization over abrupt or periodic intake.

c) Level of urea fed. Low levels of urea are utilized more efficiently and with less problems than high levels.

d) Thorough mixing of urea-containing supplements into the daily feed. If urea-containing supplements are mixed with the entire daily ration, the intake of urea at any one time likely will not be great, and the ability of the microbes to synthesize protein likely will not be exceeded.

e) Adequate supply of phosphorus, sulfur and trace minerals. Substitution of urea for natural protein sharply changes the quality and quantity of minerals available for ruminal bacteria and ruminants. Although needed only in small quantities, these elements are necessary building blocks for microbial protein synthesis. Feeding dehydrated alfalfa meal, which is high in trace


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minerals and sulfur, aids urea utilization. These often are found in many urea-containing supplements.

f) Solubility of proteins. Natural proteins such as soybean meal and cottonseed meal have different solubility or rates of hydrolysis in the rumen. The more soluble the protein, the more rapidly it is hydrolyzed to ammonia in the rumen. For this reason, some natural proteins may be more competitive with urea.

1.4 Practice of urea treatment

Treating with urea is based upon its transformation into ammonia. For successful treatment, most of the urea must first be hydrolyzed into ammonia and then this must diffuse correctly so fixing itself to the forage and modifying it chemically. One must therefore ensure favorable conditions for both good ureolysis and good ammonia treatment, in the knowledge that these two processes take place simultaneously within the forage matter.

In the presence of water and the enzyme known as urease, and if the ambient temperature is sufficiently warm, the urea hydrolyses into gaseous ammonia and carbonic gas through reaction with the enzyme which may be described in a simplified manner as follows:

heat

CO (NH2)2 + H2O ----------------> 2 NH3 + CO2

urease

urea water Ammonia carbonic gas

Once hydrolysis is completed one molecule of urea(i.e. 60 g) generates two molecules of

Ammonia (i.e. 34 g). 5 kg of Urea thus allows production of 2.83 kg of Ammonia.

The ammonia thus generated, provokes the (alkaline) reaction which gradually spreads and treats the mass of forage. Net effects on the forage are increase on its digestibility (by 8 to 12 points), on its nitrogen content, to the intake (by 25 to 50 %), and thus to the nutritive value.

Nguyen Xuan Trach (2004) observed that the positive effect of rice straw treatment for growing beef cattle and found that cattle fed on urea-treated straw ate more and grew faster than those raised as usual. Dawadi (2009) showed that considering weight gain, urea treatment rice straw with 1.5 kg berseem plus molasses had comparatively better, but results in terms of net profit per unit meat production, untreated rice straw and berseem was better. Therefore the result provided the option: farmers can earn per unit higher profit even if untreated rice straw


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could be supplied with good legume such as berseem; whereas in terms of body weight gain, rice can be supplied by treating with urea along with molasses supplemented and legume.

1.5 Recommendations for Urea Feeding

According to Stanton and Whittier (1998) recommendations for urea feeding are given as follows;

a) Feedlot Rations

Feed no more than:

Up to 15 to 25 percent of total crude protein (CP) in cattle and sheep fattening rations. 0.1 - 0.25 pound urea and 0.28 - 0.70 pound CP per head per day to cattle. Up to 0.5 to 1.0 percent urea in total air dry beef ration. Current recommendation is 0.7

percent urea.

Dry Cows

Feed no more than:

0.05 pound actual urea per cow per day. 0.14 pound protein equivalent from urea per cow per day.

It is best not to feed urea in high protein supplements (40 percent CP) to cows on winter range.

b) Lactating Cows

Feed no more than:

0.05 to 0.10 pound actual urea. 0.14 to 0.28 pound protein equivalent from urea.

c) Calves

Do not feed urea to 300- to 450-pound calves.


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Table 1. Maximum amounts of urea that should be fed to yearlings and calves.

Concentrate content of the ration (%) Pounds of urea per day

Yearlings Calves

81-100 0.25 0.20

61-80 0.20 0.17

40-60 0.15 0.14

Less than 40 0.12 0.10

Yearlings: 650 pounds and heavier ; Calves: 450-650 pounds

To convert to metrics use the following conversion: 1 pound = 0.45 kilogram.

RESULTS AND DISSCUSSION

Suggested method of feeding urea

a) Urea in concentrate mixtures

Concentrate mixtures containing 12 to 20 percent crude protein, designed for direct feeding to dairy cattle, usually contain 1.0 to 2.0 percent urea to replace an equal amount of nitrogen from oilseed meals or protein-rich by-product feeds. These mixtures usually contain large amounts of cereal grains or by-products rich in starch. When as much as 3 percent urea has been incorporated into meal mixtures of cereal grains, palatability has sometimes been lower than desirable for high-producing cows, even when 7 percent cane molasses was included. When such mixtures were pelleted, dairy cattle accepted these feeds, with urea or other NPN compounds, as well as they consumed mixtures derived from vegetable protein sources only (Reaves at al., 1966). It is important to maintain a high digestible energy content in meal mixtures containing urea in order to ensure a performance similar to that from rations containing only vegetable proteins.

b) Urea in high-protein supplements

It is often convenient and less expensive to use a higher protein feed because smaller quantities will then satisfy the requirements of cattle or sheep. Beeson (1965), Burroughs (1965) and Conrad and Hibbs (1966) have reported good results with a number of high-protein supplements containing urea. Care must be exercised to limit the amounts of high-protein supplements containing urea which are fed to animals so that they do not cause toxicity.


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Mixtures containing as much as 80 percent or more crude protein but with a high urea content should be fed at a level not exceeding 0.3 to 0.5 kilogram daily to cattle weighing 350 kilograms or more and they should be fed along with other concentrates. Small animals should receive correspondingly less of these supplements.

Toxicity of urea

Urea toxicity (poisoning) may be a problem if urea is fed at high levels. Most cases of urea poisoning are

due to poor mixing of feed or to errors in calculating the amount of urea to add to the ration. Urea

toxicity is characterized by uneasiness, tremors, excessive salivation, rapid breathing, incoordination,

bloat and tetany. These symptoms usually occur in about the order listed. Tetany is the last symptom

before death occurs. Laboratory findings of urea toxicity include a sharp rise in blood ammonia levels

and a rise in rumen pH about 8, and the normal function of the rumen will cease.

As an emergency measure, 1 gallon of vinegar may be administered to cattle as a drench. Acetic acid furnished by the vinegar lowers rumen pH and neutralizes ammonia, thus preventing further absorption of ammonia into the bloodstream. Animals that have not been fed previously, and especially underfed animals receiving only poor quality hay or pasturage, may be unusually sensitive to urea toxicity and they must gradually be adapted to urea feeding.

SUMMARY AND CONCLUSION

Feed-grade urea contains 42 to 45 percent nitrogen (262 to 281 percent crude protein equivalent). Fertilizer-grade urea usually contains 46 percent nitrogen (290 percent crude protein) because smaller amounts of conditioners have been added to prevent lumping. One kilogram of urea plus 6 kilograms of maize or other grain furnishes the same amount of nitrogen as 7 kilograms of soybean meal or an equivalent high-protein feed, but it-may be lower in energy content since urea adds no useful energy.

The amount of urea included in concentrate mixtures for cattle or sheep should not exceed 3 percent and usually the addition of 1 to 1.5 percent will prove adequate. In the total ration, the amount of urea should not exceed 1 percent. In Canada feed manufacturers are not permitted to use urea in greater amounts that will supply one third of the total nitrogen of the grain mixture for ruminant animals. This in effect limits the use of urea to supplying less than one sixth of the nitrogen in the total ration. It is generally considered that this maximum amount can be effectively used for beef cattle.

Success from the use of urea has not been as great in Canada as in the United States. This may be due to the use of barley, oats, and wheat as the main high-energy feeds, whereas maize is the main grain in the United States.


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Nearly all the literature in Australia and South Africa has been concerned with the use of urea to improve the nutritive value of low quality roughages with the general objective of converting sub maintenance to a maintenance ration. In spite of the great number of experimental observations recorded, this review is forced to the conclusion that no evidence is yet available to support the contention that urea can be employed profitably with low-quality roughages in genuine pastoral conditions. This is regrettable because large quantities of urea preparations are at present being used. It would be wrong to assume from the magnitude of this commercial enterprise that the results are favorable in practice. Of course, the point must be made that lack of evidence cannot be taken to disprove the proposition that urea feeding is beneficial.

Further research requirements

Besides being less palatable than the more commonly used protein supplements, urea may often be broken down to ammonia in the rumen at a rate faster than the rumen microflora can utilize, for the formation of proteins, amino acids, or other nitrogenous compounds. The result is that the excess of ammonia is absorbed through the rumen wall directly into the bloodstream and much of it may then be excreted in the urine if the intake is higher than the amount required. Methods are needed to reduce the rate of urea breakdown in the rumen. Coating the urea particles with waxes and similar substances has been tried but has been found ineffective. However, it should be possible to incorporate urea into some other material that breaks down slowly to release the urea at a sufficiently slow rate, in the same way that cobalt is slowly released from “cobalt bullets.” Research on slow-release pellets or on new compounds that would allow urea to be released in about five hours would seem warranted.


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ACKNOWLEDGEMENTS

The author wishes to express his sincere gratitude to Prof. Dr. M. Sapkota and Prof. Dr. J.L.

Yadav for their helps and supports to accomplish this work. Lastly, the author thanks Assoc.

Prof. Dr. Subir Singh for his intellectual and technical backup during the preparation of this

paper.

Note:

This review paper was selected in 2010 Alltech Young

Scientist Competition as First Position Local winner from

Nepal and the author (Dinesh Panday) was awarded with

Certificate and Medal from Alltech Young Scientist Program.

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