Y I FLORIDA AGRICULTURAL EXPERIMENT STATION
Dairy Science Mimeo Report 62-1
January 10, 1962
The Effect of Methionine Hydroxy Analog As an Additive
To a High-Urea Dietary for Dairy Steers
J. M. Wing1I
Urea as such is of no value directly as protein for livestock. Yet it
is used widely to replace a part of the protein in feeds for ruminants. When
urea and carbohydrates are supplied simultaneously, bacteria in the rumen
convert them into bacterial protein which subsequently is used by protozoa
and then by the cow. Of course some bacteria are digested and absorbed by
the cow before they can be used by protozoa. This bacterial protein seems
to be of rather high quality though it may not be as nutritious as protozoan
protein. Since microbial action is essential to the utilization of urea,
this material has no practical function in the feeding of single stomach
Urea is 46% nitrogen. Protein usually contains about 16% of nitrogen.
To convert nitrogen to a crude protein equivalent it is customary to multiply
by a factor of 100 = 6.25. Hence nitrogen x 6.25 = protein. A pound of
urea contains .46 pounds of nitrogen. Thus it is said to be equivalent to
.46 x 6.25 = 2.9 pounds of crude protein. Pure urea is extremely difficult
to store and mix and hence generally it is combined with an inert carrier
which makes it equivalent on a nitrogen basis to 2.62 pounds of protein per
It should be remembered, however, that in 2.62 pounds of protein, there
is only .46 pound of nitrogen and this is the only part of the protein which
can be supplied from urea. Hence, 2.62 .46 = 2.16 pounds, which must be
supplied to the rumen bacteria from another source. This usually is a
carbohydrate which is high in starch. Soluble carbohydrates in the form of
sugars or molasses can be used but are less effective than such high quality
ingredients as corn, grain sorghum, or hominy feeds.
When urea is fed at levels which are too high for microbial processing,
it is extremely toxic. Thus until further information is available, it seems
essential to limit the use of urea to an amount essential to supply approxi-
mately one-third of the protein needs. When the process of protein synthesis
is understood fully so that it can be stimulated, it seems likely that twice
to three times as much use can be made of urea or other non-protein nitrogen-
Florida Agricultural Experiment Station Bulletin 611 sho
of urea as high as 1% of the total ration were safe. The to daily dose,i
conditioning of the animal, and complete dispersal of the urk feed wer c
essential for use of levels in excess of 14 to 20 grams per g. dy
weight daily. Such high levels were poorly utilized and hav t been
1* Associate Dairy Husbandman 7 ..
It seems possible that a high level of urea could be utilized well if it
were supplemented with some essential protein components (amino acids) which
are characteristic of high quality animal protein. One of these amino acids
is the sulphur-containing protein component, methionine. Methionine is known
to be an essential amino acid and the addition of elemental sulphur has been
shown to raise the potential level for urea feeding. Perhaps the supplemental
sulphur was used for bacterial synthesis of sulphur-containing amino acids.
It is known also that at very high levels methionine is toxic but the upper
level for methionine feeding has not been established with cattle. The
hydroxy analog of methionine appears to be equally effective and virtually
non-toxic even at very high levels.
The purpose of the present work was to determine the effects of a very
high level of methionine hydroxy analog in a high-urea diet for dairy steers.
The basal feed was composed of citrus pulp 600 parts, ground oats 400 parts,
urea 30 parts, salt 10 parts, bonemeal 10 parts, and calcium carbonate 10 parts.
This feed contained approximately 16% of crude protein, almost half of which
was in the form of urea. The mixture for the experimental group was the same
except that 10 parts of methionine hydroxy analog were included, This seemed
to affect the palatability of the feed adversely and was reduced to 5 parts
during the last month. Other than its effect on palatability, no detrimental
effects of the 10 part level were observed.
Hay and permanent pasture grasses were available to all animals. The
concentrates were fed on a group basis; 5 pounds per head daily at the
beginning with a gradual increase to 8 pounds by the end of the experiment.
The results shown in Table 1 do not indicate any benefit from the use of
methionine hydroxy analog. It appears that the rather high level of urea
was utilized reasonably well by both groups. Of course, the concentrates
were fed in somewhat limited amounts and thus while the level was higher than
the recommended one, the total intake of urea was not excessive according to
the data from Bulletin 611. While it appears from the present data that
urea may be used safely to supply half the crude protein for growing animals,
such high levels may not be satisfactory for milking cows since they consume
such large amounts of concentrate feeds and thus would be more likely to
obtain a toxic amount.
The two most practical questions are how much starchy carbohydrates to
incorporate with a given amount of urea, and whether the use of urea at all
is economical. Both questions can be answered easily by determining how
much of an ordinary protein supplement can be replaced by a pound of urea
with appropriate carbohydrates. For purposes of illustration, consider a
41% protein oil meal. Thus, 2.2 = 6.4 bs. of 43% protein feed to supply
2.62 pounds of protein (the equivalent of 1 pound of urea). For each pound
of urea used, add at least 6.4 1.0 = 5.4 Ibs. of a carbohydrate, if the
urea-carbohydrate mixture is to be the equivalent of a 41% protein supplement.
The answer to the question of economy follows easily. If 5,4 pounds of a
carbohydrate feed and 1 pound of urea cost less than 6.4 pounds of a 41%
protein supplement, urea may be used, but not if the reverse is true.
Effects of supplemental hydroxy methionine to a high-urea diet for steers
Days on experiment
Steer No. 0 30 60 90 120
. Body weights
Average 500 540 582 608 650
500 540 582