G2O-Lancaster Farming, Friday, January 10, 1997
JAMES D. FERGUSON
Associate Professor
New Bolton Center
Concentrations of urea in milk
arc variable from herd to herd and
from cow to cow in the same herd.
Across all cows in Pennsylvan
ia we could expect to find a wide
variation m MUN (milk urea ni
trogen) concentrations. This is the
case for samples run in the Pa.
DHIA testing laboratory.
Since Sept. 25, 1995, through
Sept 30,1996, a total of 566,764
samples have been analyzed for
urea concentration by the Pa.
DHIA laboratory. Across all
cows, mean urea nitrogen was
14.3 mg/dl with a range of .5 to
39.5 mg/dl and a standard devia
tion of 4.2.
There was no different in mean
MUN by lacatation number.
To look at production effects,
MUN was examined by dividing
herds into quartiles of milk pro
duction (RHA) within breed.
What Should Values Be?
The variation in milk urea con
centrations between herds and
between cows indicates wide var
iations in protein, energy and
water intake.
Rations should be appropriately
balanced for rumen digestion and
absorption of needed nutrients for
maintenance of both body tissue
and production of milk. When
rations are well formulated, they
contain acceptable rations of
rumen degradable and undegrad
able protein, rumen fermentable
carbohydrate, and post-ruminal
absorption of energy metabolites.
Given typical ranges of dry
matter intake and production for a
herd consuming a diet that is
blended for a certain level of milk
production, the mean MUN
should be within a predictable
range. If the MUN was outside
this range, it would suggest prob
lems with a feeding program.
It could not be used to identify a
specific problem.
However, looking at urea con
centration in milk may provide an
opportunity to address problems
with the feeding program on a
farm.
Important questions are: What
should milk urea concentrations
be? What should the herd average
be? What should cows average at
different production levels?
Just as somatic cell counts are
only interpretable within the
framework of a goal, milk urea
concentrations are only interpret-
New Bolton Researcher
Explains Use Of MUN
able in relation to goals acceptable
by the dairy producer and his/her
advisors.
Deviation from an acceptable
range suggests that there ate fac
tors within the feeding program
that need to be examined.
If mean MUN is outside an
acceptable range, changing MUN
concentrations may not be made
without some functional change in
the forage program on the farm.
Urea values should not be inter
preted alone.
That is, they should not be
interpreted without also examin
ing the entire feeding program on
TABLE A
Breed
Ayrshire
Brown Swiss
Guernsey
Holstein
Jersey
Mixed Breed
Red and White
TABLE B
Breed
Ayrshire
Brown Swiss
Guernsey
Holstein
Jersey
Mixed Breed
TABLE C
uartile-
1209 13.5
2469 16.7
3784 14.2
534760 14.3
17987 16.7
4479 15.0
1942 15.4
Num. Herds MUN, mg/dl Mean sd
22
65
54
6543
260
366
RHA, lbs MUN, mg/dl Mean sd
15829 14.0*
18704 14.6 b
20391 14.6 b
23280 14,7 b
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the farm, including ration formu
lation, ration delivery, mixing of
feeds, feed intake, and water
intake.
Qiven these provisions, what
should urea values be?
MUN values in cows fed at
optimal dry matter intake typically
fall in the range of 10 to 14 mg/dl.
The range of MUN concentration
for individual cows consuming the
same diet is +6 or -6 from the
mean of the group. That is, if a
group of cows averaged 12 MUN
mg/dl, 95% of the group would
fall between the values of 6 to 18
mg/dl MUN.
;/dl sd
Urea N, mi
3.1
3.0
3.1
3.1
•J;#:
DMA
How many cows should I
sample?
Given the variation of milk
urea, at least eight cows should be
tested within a group to have inter
pretable results. Testing fewer
than eight cows will not result in a
meaningful average value of milk
urea and cannot be interpreted. In
addition, the cows to be tested
should be cows that have free
access to feed and are healthy.
If mean values of milk urea
should be 10 to 14 mg/dl, why is
my herd at 16 mg/dl and should
I be concerned about it?
The fact that a mean milk urea
nitrogen concentration of 16 mg/
dl is found means there is some
inefficiency in protein feeding.
High MUN suggests that mere
protein is being fed than is neces
sary for production for that group,
or that feed intake is not as uni
form as desired for the group.
If diets contain high amounts of
rumen degradable protein, such as
high alfalfa diets, MUN may be
“high.”
Alfalfa haylage or hay provides
a high concentration of rumen
degradable nitrogen which may
not be captured as microbial pro
tein given constraints on the
rumen fermentable carbohydrate
included in the ration. In this situ
ation. MUN may be higher than
ideal.
If the milk urea levels are 16
mg/dl, should'l try to reduce
them?
The higher levels of MUN con-
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centration suggcts that there are
opportunities to improve the pro
tein feeding system. You need to
determine what factors may be
contributing to the elevated milk
urea and examine management
options which may balance the
nitrogen supply in the rations.
These may also be opportunities
to reduce ration costs and improve
efficiency of feed delivery.
Experiences With MUN
At our dairy at the University of
Pennsylvania we have examined
blood urea, milk urea through the
DHIA test, and milk urea from
a.m. samples and p.m. samples
using our clinical laboratory, from
295 samples.
The table contains the mean
values for blood, milk urea a.m.,
milk urea p.m. and DHIA milk
urea for 295 samples from 37
cows samples repetitively from
December through August Cows
are fed a total mixed ration at 11
a.m.
One group is feda high produc
tion ration balanced for 90 lbs. of
milk and a low production group
ration is balanced for 55 lbs. of
milk. Milking occurs twice a day
at 5 a.m. to 7 a.m. and 4 p.m. to 6
p.m. Blood samples were col
lected around 2 p.m. The average
fat test was 3.6% and protein
3.3%.
The DHIA MUN concentration
represents a composite sample
taken from morning and evening
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