r- 3 6 n
Dairy Science Mimeo Report DY 68-1
August 1, 1967
SIF.A.S. Univ. of Florida
II \ I
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NON PROTEIN NITROGEN SOURCES AS PROTEIN REPLACERS
R. B. Becker
Department of Dairy Science
University of Florida, Gainesville
NON-PROTEIN NITROGEN SOURCES AS PROTEIN REPLACERS
R. B. Becker
Utilization of non-protein nitrogen compounds has been the subject
of many investigations (3, 11, 53, 66). These non-proteins will become
more important as demands increase without increasing sources of natural
protein supplies. It was learned long ago that monogastric animals re-
quire true proteins in their diet, whereas ruminants utilize both protein
and non-protein nitrogen. Use of the non-protein nitrogen is only indir-
ect, after those compounds have been synthesized into proteins by the
symbiotic microorganisms in the fore-parts of the ruminant stomach. The
ruminants then digest the microorganisms (75) to obtain proteins which
have been built up in their protoplasm.
Since library facilities are incomplete in any institution, reviews
(3) by other workers have been sources of some publications. Several
early investigations concerning nutrient requirements of animals were
conducted in Germany. Proteins were estimated as crude proteins, based
on the principle that, on the average, true proteins contain about 16%
nitrogen. Hence the practice of multiplying total nitrogen in a feed by
the factor 6.25 (100 + 16) to calculate crude protein.
There was a large sugarbeet industry in Germany. Much of the nit-
rogen in the pulp residue of sugarbeets is not true protein. Many such
compounds are soluble in water. Coagulation by boiling, use of copper
hydrate as a precipitant, or saturation of solutions with ammonium sul-
fate to salt out the proteins by competitive solubilities, separated
true proteins from non-protein nitrogenous compounds. Since sugarbeets
are relatively high in such nitrogen compounds, it was logical that nut-
ritional utilization of non-protein nitrogen was investigated in Germany.
Advances were made step by step, in understanding their nutritional val-
ues, and that classes of animals differed in ability to utilize such
Weiske and associates (84) may have been the first (in 1879) to
suggest the possibility of non-protein nitrogenous compounds as protein
substitutes in feeding ruminants. Twelve years later, Hagemann (29) be-
lieved that in ruminants, bacterial proteins were digested in the ali-
mentary tract beyond the rumen. He stated "asparagin has a definite
significance for animal nutrition which exerts a protein-sparing, and
thus caused a gain in protein"which he learned from a 15-day balance
trial with wethers. Four years later, Munk (58) conducted a balance
trial with a dog fed a low-protein diet to which he added asparagin, and
decided that asparagin was not adapted for carnivora.
Zuntz. (93) deduced from previous short trials by Hagemann (29) with
a carbohydrate-rich diet that efficiency of asparagin utilization depend-
ed on the character of the digestive system, especially the fermentation
processes in the digestive tract of ruminants. Non-ruminants require
true proteins and their fractions, down to amino acids, as sources of
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nitrogen in nutrition. Ruminants render a great service by utilizing
the nitrogen of non-protein compounds through cooperation of symbiotic
microorganisms, which their metabolisms convert into proteins of quality
adequate to serve their hosts, and non-ruminants in turn.
Kellner (39) confirmed in 1900 that nitrogen of ammonium acetate
and asparagin could be used to increase body tissues in ruminants. He
believed such action also increased digestibility of nitrogen-free ex-
tract and crude fiber in feeds. Voltz (77) may have been the first to
study urea utilization, by a lamb that also received rye straw, starch
and mineral matter. It gained 40% in weight in eight months.
Morgan (3, 56, 57) concluded that 3 ewes and 2 milk goats obtained
15 to 45% of their nitrogen from non-protein nitrogenous compounds in the
feed which consisted of sugarbeet pulp, straw, low-protein hay, starch,
sugar, wheat gluten, oil, and malt sprout extract. One year later, these
workers reported that non-protein nitrogen, as ammonium salts or aspara-
gin, replaced 63% of the digestible true protein needed by their animals
for milk production. Balance trials showed 37 to 45% of the nitrogen
requirements were derived from these non-proteins. Two years later,
Kellner and associates (40) compared ammonium acetate and asparagin in
nitrogen-balance studies with lambs receiving straw, starch, sugar and
minerals. They concluded that digestive bacteria converted the ammonia
and asparagin to protein which maintained body weight of their lambs.
Armsby (3) reviewed most of these German reports.
During World War I, Germany was unable to import foreign oilmeals
for feeding, and used synthetic nitrogen compounds to supplement pro-
teins for cattle and sheep. E. B. Hart of Visconsin learned of this use.
After the war, Bartlett and Cotton (8) fed heifers on a low-protein
intake of meadow hay, oat straw, angels and limited concentrates. They
obtained 0.24 lb. gains per day when 0.127 lb. of urea was added to the
feed daily. Ziemer (92) fed milk goats ammonium carbonate and starch
with silage and sliced sugarbeets. He concluded that replacement of
more than 50% of the nitrogen with ammonium carbonate was not possible.
In nitrogen balance trials with calves, Fingerling, et al., (24) showed
in 1937 that urea and other non-protein nitrogenous compounds could sup-
ply part of the protein needed for growing calves. Rickter and Herbst
(67) found that cows decreased in milk yield when urea and glycocoll re-
placed one-half of the protein in their rations. Smith and Baker (70)
placed urea in rumen liquor with glucose and sucrose, where microorgan-
isms synthesized it into protein. Rats synthesized some non-essential
amino acids (68) when urea and ammonium salts were supplied with only
the essential amono acids.
then urea plus starch replaced bloodmeal as 25% of the nitrogen in-
take of 7 Ayrshire cows in Scotland (61), milk yields held up well. Com-
position of their milk was not changed measurably.
The DuPont Company began to convert atmospheric nitrogen and coke
into ammonia compounds and urea for industrial uses. Ward H. Sachs of
their Ammonia Department stimulated research in this country, using
these products in industry, fertilizers and feeds. Several experiment
stations soon undertook tests with urea as a feed supplement. E.B.Hart
and associates began feeding trials with calves, heifers and milking
cows (69, 81, 82). Six reports appeared in 1939 to 1944.
Three groups of 4-month old Holstein calves were placed on feed
in 1936 (55) comparing casein, ammonium bicarbonate and urea, with a
basal ration of ground timothy hay, starch and yellow corn. Urea was
included at 1.4, 2.8 and 4.3%; and ammonium bicarbonate and casein at
11% of the rations. Corn molasses improved palatability of the feed.
Urea was utilized to build protein, but some damage to the kidney tis-
sue resulted at the highest urea intake. Starch (3 to 5%) was more
effective than molasses in aiding urea utilization.
Urea added to rumen contents in vitro (81) soon showed loss of
ammonia, and an increase in non-filterable nitrogen compounds presum-
ably proteins from activity of the rumen microorganisms. A rumen-fis-
tulated Holstein heifer receiving a basal ration of corn silage, timothy
hay and equal parts of ground yellow corn and oats, was given urea suc-
cessively at 0, 6, 12 and 18% crude protein levels in the grain in com-
parison with linseed oilmeal at equal nitrogen levels. The maximum urea
was 4.5% of the grain ration. Protein increased in the rumen contents
as ammonia decreased, though the rate of conversion reduced with time
at the higher intakes of urea. When starch was added (54), urea at the
maximum level was utilized within six hours. Linseed oilmeal was added
to the basal ration for the second group; 3% urea in the concentrates,
and urea plus corn molasses for the third and fourth groups of animals.
Differences in milk production between the linseed and urea groups did
not differ significantly (69), nor was the flavor of milk affected.
Archibald (2) conducted a double-reversal feeding trial in Massa-
chusetts, with urea at 2, 2.5 and 3% of the mixed concentrates. Corn
starch was added to balance the energy. Milk yedlds did not differ sign-
ificantly, nor was milk flavor affected. The Hawaii station (31) fed
four steers, and found 74% apparent digestibility of urea, as compared
with 78% for the protein nitrogen of soybean oilmeal. Cows yielded
more milk on the control ration (86) than with urea at 0.24 or 0.48 lb.
levels. Can molasses, fed at one-fourth of the concentrates, did not
change synthesis of protein from the urea in the rations.
Illinois workers (30, 36) fed eight sheep in metabolism crates.
With urea at 3.15% of the dry matter intake, investigators calculated
biological value of the urea nitrogen at 62%, in comparison with 79%
for casein nitrogen. Lambs appeared to need some true protein to en-
hance use of urea nitrogen in metabolism. Rumen bacteria and protozoa
were separated, and cultured rumen bacteria were dried. The dried mic-
roorganisms were fed to rats. Johnson, et al., (37) computed the value
of their proteins as :
From dried rumen bacteria From rumen protozoa
Digestibility of protein 55% 86%
Loosli and McKay (49) found no advantage from feeding riboflavin
to calves that were on positive nitrogen balance with urea as part of
UREA IN SILAGES
Urea was added at 0.5% level to sweet sorghum at ensiling, for
steers at the Mississippi Station (18) in 1942-1943. One percent of
urea was added to corn at ensiling at Clemson College (88). Woodward
and Shepherd (90) began a trial with 0.5% of urea in corn silage at
Beltsville, and a trial was initiated at the Florida Station (19) incor-
porating 0.5, 1.5, and 2.5% of urea into sorghum silage, for palatabil-
ity and chemical tests. All of these silages were satisfactory, except
that cows refused to eat that with 2.5% urea until ammonia volatilized
from it. Knowledge of urea's value in ruminant nutrition and feeding
had advanced roughly to this extent when the United States declared
war on Germany during World War II.
SCARCITY OF FEED PROTEINS
When World War II broke out, ships were diverted largely to war
transportation. Lykes Brothers had purchased the Dollar Line vessels,
and moved them from the Pacific to Atlantic ship-lanes. No flax was
brought from Argentine; no copra from Pacific islands, nor soybeans
from Korea. Protein supplies were short in America. The government
released some synthetic nitrogen for fertilizers in lieu of nitrate from
The USDA called a regional Protein Conservation Conference in At-
lanta on April 12-13, 1943. Key state representatives were assembled,
to be informed of the situation, and directed to plan on conserving
all protein feed supplements. Swine, poultry, and dairy representatives
then separated to discuss ways of conserving protein supplies. The
dairy group decided that if there was less protein, correspondingly
less milk would be produced. They questioned among themselves a poss-
ibility of limited urea supplementation.
On re-assembling, each group reported the plans they would propose
for using protein feeds in their states. The chairman was not pleased,
when a spokesman appointed by the dairy group reported that if there
was less protein feed, less milk would be produced. His sole response
was: "Well, see what you can do about it!" The dairy group got togeth-
er again Frank Fitch of Georgia, L. A. Higgins of Mississippi, U. P.
LaMaster of South Carolina, C. E. Wylie of Tennessee, R. B. Becker of
Florida, and others. Pitch moved that Becker be asked to see what
could be done to possibly obtain an allotment of urea to supplement
protein in mixed dairy feeds. The group were acquainted with urea
feeding trials at Michigan, Mississippi, New York, Wisconsin, and pro-
jected plans with silage in Florida. Urea for those trials had been
obtained through Ward H. Sachs of the Ammonia Department, E. I. DuPont
de Nemours and Company.
Dr. E. B. Hart (32) replied to my letter:
We would recommend urea feeding and have done so. Under the
present stress of protein shortage, the Animal Nutrition Committee of
the National Research Council has recommended to the government that
150,000 tons of urea be made available for cow and sheep feeding to
offset the scarcity and to release protein concentrates for poultry
and pigs. However nothing has happened yet in Washington. There is
very little urea available at present, Du Pont putting all the nitro-
gen into nitric acid, and they are the only manufacturers in this coun-
try. As you say, there is some available for fertilizer and that might
be released,now that the planting season is pretty well over,for feed-
ing purposes, but what is going to happen I do not know."
Letters were sent next to F. B. Morrison of Cornell, C. F. Huffman
of Michigan, Gus Bohstedt and Paul Phillips of Wisconsin, asking that
they meet with me one day in advance of American Dairy Science Associa-
tion at the University of Missouri in June, 1943. At our committee
discussion, Phillips said not enough investigation had been done to
base such feeding. Bohstedt replied that more was known than when
urea was fed to cattle and sheep in Germany during World War I. Phillips
agreed to this.
This unofficial committee on the feed situation then drafted a Re-
solution to the effect that:
In view of the shortage of high protein concentrates, the Amer-
ican Dairy Science Association recommends that urea be released by the
War Production Board as a source of feed nitrogen for dairy cattle,
providing nitrogen from other sources is adequate for fertilizer needs.
It recommends also that high protein ingredients be made available to
farmers to mix with farm-grown grains and that they be fed in accordance
with the Government and Feed Industry Council protein conservation pro-
The Resolution was adopted by the Production Section, and then by
the business session of the American Dairy Science Association. Secre-
tary R. B. Stoltz forwarded copies to the USDA Secretary of Agriculture
and to the War Production Board. Information on action of ADSA was
sent, as previously agreed, to Ward H. Sachs on July 20, 1943. When
the Resolution came before the War Production Board later, Mr. Sachs
(Nitrogen representative on the Board) asked to see whose names were
appended to it. He recognized those for whom he had obtained urea for
feeding experiments, and said "I raise no objection to it." 20,000
tons were allocated for dairy use, instead of the 150,000 tons suggest-
ed by the Animal Nutrition Committee of the National Research Council.
The first shipment went to Cooperative Mills of Baltimore, Dr. C. D.
Caskey taking charge of it. The first commercial trial was successful,
and urea has been available continuously since that time.
Instead of a single domestic processor, now there are at least
25 others in the United States. Considerable tonnage is imported as
well. Urea is used industrially, in fertilizers, and more than 200,000
tons yearly go into feeds for ruminants.
Hastings (34) wrote of that period:
"In November, 1943, a small amount of crystal urea was made avail-
able under allocation to feed manufacturers. Previous to that time
most of the urea not used for the war industries was.allocated to the
fertilizer trade. For several years the experiment stations in the
large dairy states have been getting urea for research use; and in
1941 the Association of Peed Control Officials, foreseeing its feeding
use, adopted a resolution accepting urea as an ingredient in propriet-
ary cattle feeds. The protein shortage which developed in 1943 made
it advisable to use urea before all the questions had been answered."
He arranged for a trial in a college herd, with urea increased
from 35 to 60 lb. per ton in concentrates over a four-months period.
Milk fat and protein were not changed significantly. When urea was
added to samples of silage, urease activity was observed on standing,
but not when concentrates were being fed on silage in the manger.
Nutritional investigations with urea increased greatly in Europe
and the United States after World War II. Although substantial, Jap-
anese and Russian investigations were not reviewed.
Joel Axelsson (5) pointed out in 1942, that certain yeasts and
rumen bacteria converted the nitrogen of urea into protein, from rat-
ions rich in digestible carbohydrate concentrates. Poisoning could
occur when urea was fed improperly. He advised dissolving urea in hot
molasses, and mixing it with beet pulp or potato flakes.
At Hannah Dairy Institute, Smith and associates (63) found that
addition of starch facilitated bacterial conversion of urea, ammonium
bicarbonate and ammonium sulfate to protein on incubating the cul-
tures for 3 hours. Glucose or maltose also contributed to such con-
version in the laboratory.
In 1949, Davidson and associates (45) synthesized urea contain-
ing the isotope nitrogen-15. They fed this tagged urea to sheep (79),
and found it in the body tissue four days later. McDonald (51) found
that some rumen bacteria have high urease activity. Ammonia was the
main non-protein nitrogen in the rumen fluid. Urea in sheep's saliva
was a source from which symbiotic bacteria obtained nitrogen for their
development. Forty percent of zein in a sheep's diet (52) was con-
verted into microbial protein in the rumen.
Campling, et al., (15) found that feed residues remained in the
digestive tract less average hours (104 to 83 hrs.) when 150 grams of
urea were infused into the reticulo-rumen of their dry cows, and con-
sequently they ate more:oat straw. Digestibility of crude fiber and
N-F E also increased 11% and 9% unites respectively.
Gartner, et al., (26) measured absorption of ammonia through the
rumen wall of 3 goats given urea containing carbon-14; when there was
more urea consumed, more ammonia passed into the venous blood. Vatson,
et al., (80) fed urea with nitrogen-15 to sheep four days before
slaughter. The tagged nitrogen was present in tissue protein and
non-protein factions of blood, kidneys and liver.
INVESTIGATIONS IN THE UNITED STATES
Following S. I. Bechdel's discovery (9) that water soluble vita-
mins are synthesized by bacteria in the cow's stomach, other workers
have confirmed this for the separate vitamins in the group. Later
controlled feeding trials with non-protein nitrogen compounds frequent-
ly depend on this knowledge.
Jones and Haag (38) at the Oregon station, offered a mixed con-
centrate containing 7% of urea to heifers. The feed was unpalatable,
so the proportion of urea was reduced to 3%. The hay and concentrate
without urea, contained only 6.2% of crude protein. They added 1% of
sodium sulfate to the urea-concentrates. Eight of 11 pairs of heifers
gained slightly more weight with the sulfur addition. The differences
were not significant. Loosli, et al., (50) fed 3 lambs and 2 goats
with a purified diet containing urea as the nitrogen source. Rumen
samples, obtained by stomach tube, contained arginine, histidine, iso-
leucine, leucine, lysine, methionine, phenylalanine, threonine, trypto-
phan and valine in reasonable amounts. Four years later, Michigan
workers (23) offered 7 rumen-fistulated calves a purified diet in which
urea was the only source of dietary nitrogen. Microorganisms in surh
animals (43) were able to convert urea into the necessary amino acids.
UREA FOR DAIRY HEIFERS
Digestibility of urea was reduced markedly at Cornell (12) when
a high molasses intake was given in lieu of corn to heifers. Those
receiving soybean oilmeal gained more w.-ight than those with supplemen-
tary urea. When good quality alfalfa replaced timothy hay in the ra-
tions, excellent growth resulted. Parkham, et al., (62) in Louisiana
compared urea with ammoniated molasses (32% crude protein equivalent)
as substitutes for cottonseed meal. The protein substitutes contrib-
uted 30% of protein equivalent in the concentrates and 18% in the total
ration of grass hay, corn-and-soybean silage, ground corn and oats.
The heifers gained .92 lb. daily when their feed was supplemented with
urea, 1.04 lb. on the ammoniated molasses ration, and 1.23 lb. on the
control ration with cottonseed meal.
Colovos (16) added urea at 0,10,20, and 40 lb. per ton to mixed
concentrates having 5 or 10% of crude fiber for twin heifers. Eighty
digestion trials were determined by the chromogen ratio technique.
Digestibility of the dry matter was not affected adversely by urea in-
take, the highest level being 3% urea. He emphasized that the hay fed
was early-cut and of good quality. Presence of urea (72) did not dim-
inish the excretion rates of three water soluble vitamins observed
with their cows.
Lassiter, et al., (44) in Michigan, fed Holstein heifers on ground
corn cobs and concentrates with urea at 3, 5, and 7% of the grain. Aver-
age daily gains decreased significantly as urea was increased, being
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1.14, 0.85, and 0.64 lb. per day for 150 days. They suspected that
low sulfur possibly may have been involved with the rations.
LATER TRIALS WITH MILKING COWS
Virtanen (76) reported feeding milking cows in Finland through
three lactations on purified diets, with urea and ammonium salts as
almost the sole nitrogen sources. A maximum of 650 grams per day was
eaten at the peak by one cow. The ingredients were pelleted. Cows
ate slowly at several intervals, after being accustomed gradually to
the purified diet, and consequently exhibited no toxic effects. Energy
came from 57% starch, 20.9% sucrose. Cellulose powder was 9.5% of the
ration, little of which apparently was digested.
Milking cows in Virginia (74) received hay (18% crude protein),
corn silage, and concentrates with 2 to 3% of urea, or with cotton-
seed meal in the mix. DL-methionine was added, but without benefi-
cial results from this sulfur-containing amino acid. Ward (78) ob-
served no benefit at the Michigan Station, from adding sodium sulfate
to rations consisting of timothy hay, ground yellow corn, cane molas-
ses and 2% of urea in the concentrates, as compared with 15% of soy-
bean oalmeal. Molasses contains some sulfur.
Conrad and Hibbs (17) reported recently on pelleting two parts
of dehydrated alfalfa with one part of urea, 2% of monosodium phos-
phate and 0.4% of sodium metabisulfite. When 9% of these pellets were
added to cornmeal, the mixture contained 18 to 19% of crude protein
and just below the 3% legal limit of urea. Heavy milking Holsteins,
receiving 1 lb. of urea and 2 lbs. of dehydrated alfalfa with other
feed, produced equally well as those having soybean oilmeal instead.
These workers believed that pelleted urea was released slowly in the
rumen, and hence no harm had occurred from the high daily intake of
FEEDING TRIALS WITH STEERS
Urea has been investigated in many feeding trials with steers.
Some reports were selected as representative. Part of the extensive
trials with urea at Oklahoma (10) were with steers, using prairie hay,
starchy grains and urea. No apparent changes in digestibility of
nutrients resulted from urea additions. More urea nitrogen was re-
tained with corn in the ration than with cane molasses.
Baker (6) reported 3 trials at Nebraska stations where .046 and
.133 lb. of urea were offered per animal daily in pellet form with
corn and soybean oilmeal. Alfalfa, prairie hay or corn silage were
the forages supplemented. Gains of calves and yearlings were satis-
factory at all levels offered.
In vitro studies (14) at the Wooster, Ohio station indicated that
utilization of urea was stimulated by the ash of alfalfa, molasses,
iron, and phosphorus in addition to the mineral nutrients of artifi-
cial saliva, which are sodium, potassium, calcium, magnesium, chlorine
and sulfur. Kirk, et al., (41, 42) replaced 40% of the nitrogen of
cottonseed meal with urea for fattening steers. They gained slowly for
the first 60 to 90 days, then more rapidly. Responses did not differ
significantly between them and the control group having cottonseed meal
in the basal ration, with grass hay, silage, or pasture and citrus pulp.
There was a disadvantage, however, from .ows wintering on native pasture
plus 1 lb. citrus meal and citrus molasses containing 3% of urea. Urea
provided part of the nitrogen successfully at Cornell (21) with a basal
ration of hay, cornmeal and molasses supplemented with either ammoniat-
ed citrus pulp, furfural residue, or urea. Nitrogen balances favored
the addition of urea over 3 other ammoniated products.
UREA SUPPLEMENT WITH LAMBS
Lambs have been used extensively with urea supplement at the Kentucky,
Illinois, New York (48, 87), Oklahoma (89) and Oregon stations. Thomas,
et al. (73) noted that inorganic sulfate contributed to urea utilization.
Without it, wool grew at the expense of body weight. Lambs without sul-
fur ate wool off each other in Kentucky (7.) for positive sulfur balances.
Starks found that sheep could use elemental sulfur when it was added to
a low-sulfur ration.
Lofgreen, et al., (47) observed no significant difference in nitro-
gen utilization between lambs with or without sodium sulfate addition to
rations containing urea. Only a trace of inorganic sulfate remained in
the rumen contents at 3 and 5 hours after feeding. Green (27, 28) stat-
ed that non-lethal large doses of urea stopped ruminal motility in a
sheep, accompanied by a rise in rumen pH. Lack of palatability, in his
judgement, may indicate a ration low in cobalt, phosphorus, or some oth-
er limiting nutrient.
TOXICITY FROM EXCESS UREA
Urea fed at 4.3% level in the concentrates damaged kidney tissues of
a growing heifer, but others were unharmed on 1.4 or 2.8% levels in con-
centrates. Hart, et al., (33) recommended that urea not be fed in ex-
cess of 3% in the concentrates. Hawaiin workers (91) did not observe
liver or kidney damage when uramon ("262") was fed to steers at .88 or
2.29% of their dry matter intakes. A mill accident in New York (1) caused
deaths of 15 to 20 cows in 1944-1945. Deaths occurred from carelessness
of a feedmill workman in Ocala. A family cow died from eating fine
sweepings from the floor of a feedmill near Apopka, Florida. Osewald
(60) reported death of a calf in spasms that ate some fertilizer with
42% nitrogen, nearly pure urea.
Cattle drenched with 116 grams of urea in water at the Oklahoma sta-
tion (22, 25, 64) developed tetany, ataxia, retarded respiratory rate,
and salivation in about 10 to 20 minutes. About 16 to 18 milligram per-
cent of urea and ammonia were in the blood when ataxia was noted. Tetany
became more pronounced as the ammonia nitrogen content of the blood in-
creased. The animals were down and bloating in 30 to 45 minutes. Symp-
toms of alkalosis followed by death occurred at a blood level of 4 milli-
gram percent. No ill effects occurred when up to 400 grams of urea per
day were eaten slowly in mixed concentrates. Two steers died in 2 to 3
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hours, while 5 recovered.
At the Florida station (20), 12 yearling cattle received urea in
a gelatin capsule, mixed in concentrates, or as a drench. Six receiv-
ing 14.1 to 22 grams per 100 lbs. live weight, died in 1 hour 30 min-
utes; sooner on the higher intakes. One Jersey showed slight ataxia
from 15.8 grams per 100 lb. live weight. One recovered from a drench
of 15.6 grams per 100 lb. live weight. Two consuming 8 grams per 100
lb., showed no apparent ill effects. Two cattle receiving 15, or 22.5
grams of urea per 100 lb. recovered on being drenched with 3500 ml. of
5% acetic acid. Two Jersey heifers consuming 8 grams of urea in con-
centrates per 100 lb. live weight, showed no apparent ill effects.
The risk is greater with hungry animals on feeds low in carotene
content, or on direct administration of small amounts of pure urea (66)
in a short time. Weinstein and McDonald (83) found that urea and some
related compounds would retard growth, or even kill certain bacteria
when the compounds were present in too great concentrations. Urea was
less harmful than urethane and other carbamates investigated. Lewis
(46) used 8 sheep with rumen fistulas. He reasoned that excessive am-
monia levels in the blood was one cause of deaths, but the population
of the rumen organisms adjusted within 7 days to synthesize fairly
large amounts of ammonia into other nitrogen compounds. L-arginine
did not alleviate the ammonia toxicity noticeably.
Urea at 2 to 3% levels in concentrate feeds lowered palatability.
Bowstead and Fredeen (13) found under their feeding conditions at a
Canadian station, that .05 grams of cobalt chloride was more effective
than beet molasses in improving palatability of the mixed concentrate-
urea feed. They thought this problem was related to alterations in
the rumen flora. Balch (7) at the National Institute for Research in
Dairying, observed no response from adding ethyl alcohol to the urea
and concentrates given to Friesian cows. Balch and Campling (7) deter-
mined that milking cows utilize urea nitrogen to prevent withdrawal of
nitrogen from the body for milk production.
Raleigh and Wallace (65) gave urea to calves at 4 different levels.
With 2.52% of urea in the feed, two calves went off-feed, developed
convulsions, and died in the 5th and 6th weeks with symptoms of ammon-
ia toxicity. The basal ration consisted of pelleted prairie hay and
cottonseed meal. No starchy feed was offered.
Oltjen, et al.,(59) of Oklahoma, drenched sheep with 20 grams of
urea per 100 lb. live weight. One died within 15 minutes. Others
went down in coma, but recovered in 45 minutes. Di-ammonia phosphate
was less toxic, but an amount equivalent to 40 grams of urea caused
death in 40 minutes. Di-ammonia phosphate lost about 50% of its nit-
rogen as ammonia with the moisture, heat and pressure of pelleting.
VOLUME OF UREA PRODUCTION
Hodges (35) estimated domestic production of urea at 1,445,400 tons
in 1966, while 271,000 tons were imported and 37,432 tons exported in
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1964. He estimated that about 300,000 tons were consumed by cattle and
sheep in 1963, equivalent to about one-fifth of all oilmeal and grain
protein tonnages. Importance of non-protein nitrogen in total feed sup-
plies will increase gradually. It has been computed that 14 lb. of urea
and 100 lb. of corn grain are equivalent to crude protein and energy val-
ue of 100 lb. soybean oilmeal.
Key references have been added to the non-protein nitrogen review.
Voltz (100) fed urea first to a wether and three lambsin a 155-day
N-balance trial on low-protein basal feed. Some urea was utilized in
wool production. In 1922, they (101) reported on 40 N-balance trials
using up to five cows, with a basal low-protein diet that included potato
starch residue and sugarbeets. Digestible crude protein was provided for
body maintenance, while urea was converted by bacteria into the protein
for 9.53 to 16.73 kg. of milk or 1188.7 to 1834 grams of milk solids
daily. Urea was utilized more efficiently when fed with potato than with
sugarbeet material. He recommended that not over 150 grams of urea be
given daily per cow.
Honcamp and Schneller (97) fed two wethers meadow hay, oat straw,
potato starch, raw sugar and cornmeal in the basal ration, supplemented
with urea. Highly digestible carbohydrate aided in efficient building
of urea into protein by bacteria for the animals.
Morgen (99) compared soybean cake with urea in feeding five sheep
and eight goats on a basal ration of hay, straw, chaff, potato flakes
and corn. No benefit was observed from adding urea to a protein-adequate
Ehrenberg, et al., (94, 95, 96) conducted balance trials with Rrie-
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bicarbonate nitrogen for milk synthesis appeared highly probable.
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many investigators. He concluded that rumen bacteria utilize preferent-
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