Front Cover

Title: Urea in dairy rations
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00049923/00001
 Material Information
Title: Urea in dairy rations
Physical Description: Book
Language: English
Creator: Harris, Barney
Affiliation: University of Florida -- Institute of Food and Agricultural Sciences -- Florida Agricultural Extension Service
Publisher: Florida Agricultural Extension Service, IFAS, University of Florida
Publication Date: 1967
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Bibliographic ID: UF00049923
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Front Cover
        Front Cover
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
Full Text


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source

site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida




Urea In Dairy Rations

Barney Harris, Jr.
Assistant Extension Dairyman

Utilization of urea in dairy ra-
tions to replace some of the high
protein feeds is increasing and will
continue to increase as we learn
how to use it more effectively in
dairy rations. Fortunately, we al-
ready have available much research
information as well as practical
feeding results which serve as a
guide for incorporating urea into
rations. Even so, some dairymen
are still reluctant to freely accept
its use in dairy rations.
Urea, as such, has no food value
but when added to a high energy
ration, serves as an excellent
source of nitrogen for conversion
into protein by bacteria. Urea is
a simple non-protein organic com-
pound which contains 42% nitro-
gen and has a protein equivalent
of 262% protein. It is a white,
crystalline powder which is
soluble in water. Each 1% of the
synthetic compound in a ration
contributes nitrogen equivalent
to 2.62% of crude protein. Re-
cently, a micro-prilled 45% nitro-
gen product equivalent to 281%
crude protein has been made avail-
able for feed purposes. Each 1%
of this urea compound contributes
2.81% equivalent crude protein.
When urea-containing rations
are fed to ruminant animals, the

urea is rapidly broken down or
hydrolized to ammonia and car-
bon dioxide by the enzyme urease
which is secreted by microorgan-
isms in the rumen. Ammonia is
also released into the rumen
from protein feeds such as the oil
meals when attacked by rumen
microorganisms. The ammonia
formed in the rumen from urea
and other feeds is utilized effici-
ently by rumen microorganisms
for the synthesis of their own
microbial protein. As the micro-
organisms move with the feed
material through the digestive
tract of the cow, the acidity of
the abomasum or true stomach dis-
integrates the protozoa and de-
stroys most of the bacteria. The
nutrients and cell walls of the dis-
integrated protozoa and bacteria
are further broken down by
enzymes of the abomasum and
small intestine for utilization by
the host animal.
Ammonia not utilized in the
synthesis of microbial protein is
absorbed through the rumen wall
and added to the ammonia pool
of the body or it is converted to
urea in the liver. The urea formed
in the liver may be excreted in the
urine, possibly utilized as a nitro-
gen source by body tissues, or re-
cycled into the rumen via the

saliva. Thus, we can see that a
small amount of urea is available
in the rumen at all times to be

converted into bacterial protein.
This is true whether or not urea
is added to the ration.

How Does Urea Compare With Other Protein Supplements?

It requires about 13 lbs. of urea
(281%) and 100 Ibs. of corn meal,
or comparable grain to be equal
to 100 lbs. of soybean meal (44%)
in terms of energy and equivalent
crude protein. Therefore, any
time the urea-grain combination
can be purchased for less money
than the oil meals, it would be well

to consider adding some urea to
the ration. Citrus pulp and mo-
lasses may also serve as good
sources of energy. Since the oil
meals are generally good sources of
phosphorus, care must be taken to
assure that the urea-ration remains
adequate in phosphorus.

How Should Cows be Adapted to Urea Rations?

The rumen contains many kinds
of bacteria and protozoa. Some
of these microorganisms utilize
roughages while others utilize con-
centrates. Also, only certain kinds
of bacteria can utilize urea, along
with energy feeds, to build pro-
tein. For this reason, the urea
level in the ration should be in-
creased gradually so the micro-
organisms that utilize the urea will
have ample time to multiply and
increase in numbers. Generally, 10
to 14 days are required to develop

a population of rumen organisms
adapted to utilizing the ordinary
allowance of urea for protein
Most dairymen have not en-
countered any drop in feed intake
or milk production when 1% urea
(20 lbs. per ton) was added to the
ration. This has been especially
true where the ration contained
from 5 to 10% molasses. However,
molasses is not essential for good
utilization of urea if adequate high
energy feeds are available.

How Much Urea Can be Added to the Ration?

Numerous feeding trials compar-
ing urea-containing rations with
those containing natural proteins
have led researchers to develop a
number of rules concerning the
addition of urea to rations. Up to
1/2 pound per cow per day may be
fed satisfactorily. Another rule is
that the equivalent crude protein

from urea and other non-protein
nitrogen sources should not exceed
more than one-third of the total
crude protein in the ration. Thus,
dairymen feeding a complete feed
with little or no forage (silage,
pasture, hay, etc.) could safely
feed 1% urea or 20 lbs. per ton of
feed. Dairymen using an adequate

forage program (10-14 lbs. hay or
its equivalent as silage or pasture)
can add up to 2% urea or 40 lbs.
per ton of feed. Nutritionists sug-
gest that as much as 3% urea can
'be added to the concentrate when
cattle are provided with an excel-
lent forage program. When adding
urea to the ration on a percentage
basis, one should calculate daily in-
take of urea to see that it does not
exceed the above rules.
Feeding trials from various re-
search stations have shown that

Does Urea Affect Palatability?

It has been quite well establish-
ed by researchers that urea-con-
taining feeds are slightly less
palatable than feeds containing
natural proteins. However, this is
not usually a real problem with
most herds when urea is added at
the recommended level. Generally,

urea is not used efficiently when
the added amount of urea to the
ration exceeds the recommended
level. Also, the addition of extra
crude protein in the form of urea
to rations already supplying the
protein requirements of the cow
serves no useful purpose. Thus, for
efficient utilization of urea, follow
the levels recommended. Also,
balance the urea-containing ration
according to the requirements for
protein using the average produc-
tion of the herd.

this problem appears when cattle
are first changed to feeds contain-
ing urea but it will clear up in a
short time. The palatability prob-
lem is seldom noticed when cattle
receive rations containing 6 to 9
percent molasses.

Can Urea be Added to Rations for Growing Heifers?

The rumen of a newborn calf
is non-functional at birth and the
calf is called a simple stomach ani-
mal. However, in a short time, the
calf starts eating some grain and
by the time the calf reaches two
weeks of age, the rumen has begun
to develop; by one month of age,
the rumen should be functioning.
The calf is now called a ruminant
and should be eating from 1 to 2
lbs. of grain per day. The rumen
of the calf will not develop, how-

ever, if the calf is restricted to a
milk diet.
All ruminant animals can utilize
urea as a source of protein. This
is true for young calves and heifers
as well as mature animals. The
levels of feeding as recommended
for mature cows will also apply to
young calves and heifers. It is
generally recommended, however,
that urea-containing rations not be
fed to dairy calves under two
months of age.

Can Urea be Fed in Rations Containing Ground Raw Soybeans?

Urea should not be added to ra-
tions containing ground raw soy-
beans. The reason is that raw
soybeans contain a fairly high
level of the enzyme urease. This
enzyme splits the urea into am-
monia and carbon dioxide, and the

ammonia will be lost from the feed.
If the feed is in an enclosed area,
the odor of ammonia may be very
strong. This loss of ammonia rep-
resents the loss of potential pro-
tein when ground raw soybeans are
mixed with rations containing urea.

Can Urea Cause Toxicity in Dairy Animals?

Urea, as many other feed in-
gredients, can cause toxicity in
dairy animals if fed in excess. High
quantities of urea suddenly intro-
duced into the rumen cause a rise
in the urea and ammonia concen-
trations of the systemic blood. Ap-
parently, all cases of urea poisoning
have resulted from the misuse of

the product.
Wet or damp urea that has be-
come lumpy or hard should be
finely ground before being added
to the dairy ration. Such urea has
often been found to remain in
lumps after passing through the

How Can I Tell How Much Urea is Added to the Commercial
Feed That I am Using?

Every commercial feed tag con-
tains a list of the feed ingredients
and a guaranteed analysis. From
the information given on the

guaranteed analysis, you may cal-
culate approximately the amount
of urea in the feed. As an example,
consider the-following information:


Crude Protein, not less than 11.00
(This includes a
maximum of 4.00
equivalent crude protein
from non-protein
Crude Fat, not less than 2.50
Crude Fiber, not more than 15.00
Mineral Added, not
more than ........... 3.00

In order to calculate the amount
of urea in the above feed, divide
4.00 by 2.81 (Most urea contains
281% equivalent crude protein).
Use 2.62 if the label on the urea
specifies 262% equivalent crude
4.0 -- 2.81= 1.42% urea
1.42% x 2000 = 28.4 lbs.
of urea per ton of feed

How Do I Calculate the Total Protein From Urea?

In order to calculate the total
protein equivalent from urea, in-
formation must be obtained on the

amount of urea present in the total
ration. As an example consider
the following information:


Corn meal
Citrus pulp
Soybean meal
Urea (281%)
Trace Mineral Salt
Def. Phosphate

The following calculations show
how the equivalent crude protein
from urea may be determined
from the information shown in the
above grain ration.
Protein equivalent furnished
by 30 lbs. of urea equals
2.81 x 30 = 84.3 lbs.
Protein equivalent furnished
by urea in ration equals
84.3 289.7 = 29 percent.
As stated previously, nutrition-

ists have suggested that the
equivalent crude protein from urea
and other non-protein sources
should not exceed more than one-
third of the total crude protein. As
you will note, the above feed ration
contains only 29% equivalent crude
protein from urea. Addition of
other feeds such as forages would
slightly decrease the percent of
the total protein in the ration sup-
plied by urea.

Does Urea Have Any Effect on Reproduction or Sterility?

To date, no research has indi-
cated that rations containing urea
have any effect on reproduction or

sterility. Many of these experi-
ments have been conducted over
long periods of time.

Does Urea Exert Any Adverse Effect on Vitamin A Nutrition?
Results from experiments con- suggest that feeding urea has lit-
ducted in Oklahoma and Illinois tle, if any effect on Vitamin A nu-









trition of ruminants. The addition
of 4 million USP (United States
Pharmacopecia) units of vitamin A

palmitate per ton, however, would
safeguard against any possible
borderline deficiency of vitamin A.

Are There Any Advantages in Adding Urea to Silage?

In recent months, the addition of
urea to corn and sorghum silage
has increased in popularity. Feed-
ing such silage minimizes the
palatability problem associated
with the addition of high levels of
urea to concentrates. Also, the con-
sumption of urea-containing feeds
is spread over a longer period dur-
ing the day.
Michigan workers have reported
that several dairymen have accept-
ed the practice of adding urea to
silage at the time of ensiling. The
urea was added by spreading it on
top of the silage in a self unloading
wagon at the rate of 10 lbs per ton
of silage. It was reported that the
urea-treated corn silage on a fresh

basis contained 35 percent dry
matter and 4.53 percent crude pro-
Workers at Iowa State Universi-
ty have recently reported a com-
parison of urea-treated corn silage
and untreated corn silage. The
urea was added at the rate of 10
lbs. per ton at the time of ensiling.
Crude protein content of the un-
treated silage was 2.5 percent and
that of the urea-treated silage was
3.7 percent. Ninety percent of
the added urea nitrogen was re-
covered in the treated silage. Milk
yields, feed intakes and body
weight gains during the 80-day
feeding period are shown in Table I.

Av. Daily Feed Intake, Lbs. Daily Av. Daily
Corn Milk Wt. Gain
Group Hay Silage Concentrates Lbs. Lbs.
Control 5.0 50.6 25.4 (17.4% C.P.) 57.6 0.68
Urea-Silage 5.0 49.9 25.3 (11.9% C.P.) 55.4 0.72
Urea-Silage +
Urea-Concentrate 5.0 51.8 24.7 (12.7% C.P.) 55.4 0.71

The difference in milk yield and
composition was not significant.
Feed intakes were about the same
for all groups. The authors con-
cluded that feeding urea in the
manner done in this experiment

will have little or no depressing
effect upon milk production.
Theoretically, the addition of 10
lbs of urea (281%) to a ton of
silage will increase the crude pro-
tein content by about 1.4 per cent.

Generally, however, one may ex-
pect some nitrogen loss and this
may vary from 8 to 20 percent
or more, depending upon the na-
ture of storage.
The question may arise as to the
value of adding urea to grass or a
combination of grass and legume
silage to increase the protein con-
tent. Generally, grass silage and
especially legume silage will con-
tain considerably more protein and

less energy than corn or sorghum
silage. For this reason, it is doubt-
ful if any advantage could be ob-
tained by the addition of urea to
grass or a combination of grass or
legume silage. This is especially
true where dairymen feed only 30
to 40 lbs. of silage per cow per
day. Also, the additional protein
required could be easily obtained
from the grain ration.


Without doubt, urea is the most
important non-protein nitrogen
source for feeding ruminant ani-
mals. Its value in dairy rations has
been extensively investigated by
many workers. When properly fed
to ruminants, this nitrogen source
is of real protein value.
Urea must be used with care.
A safe rule is that the total pro-
tein equivalent from urea and oth-
er non-protein nitrogen sources
should not exceed one-third of the
total crude protein in the overall
ration. Also, it is important that
the urea be thoroughly mixed with

the ration.
Even though urea is an excel-
lent source of nitrogen, it sup-
plies no energy, no minerals and
no vitamins. For this reason, care
must be taken to assure that ra-
tions containing urea remain well-
balanced in all nutrients.
The justification for using a synthetic
non-protein nitrogen source (urea) in a
dairy ration is economics. Generally, it
requires about 13 lbs. of urea and 100 lbs.
of corn or comparable feedstuff to replace
100 lbs. of soybean meal. In most cases,
an economic gain can be obtained by
using a urea-grain combination to supply
a part of the needed protein.

April 1967

(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
and United States Department of Agriculture, Cooperating
M. O. Watkins, Director

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