xt7kkw57ft9f https://exploreuk.uky.edu/dips/xt7kkw57ft9f/data/mets.xml   Kentucky Agricultural Experiment Station.  journals kaes_circulars_004_530 English Lexington : The Service, 1913-1958. Contact the Special Collections Research Center for information regarding rights and use of this collection. Kentucky Agricultural Experiment Station Circular (Kentucky Agricultural Experiment Station) n. 530 text Circular (Kentucky Agricultural Experiment Station) n. 530  2014 true xt7kkw57ft9f section xt7kkw57ft9f Why I t Varies
By T. R. FREEMAN
SUMMARY Q The Breed is the most important factor influencing
the fat test of milk. Ranking from highest to lowest in the richness
of their milk are the jerseys, Guernseys, Brown Swiss, Ayrshires, and
A Holsteins. Even within a given breed there is much individual varia-
. tion among animals in the fat content of their milk. This variation is
probably the next most important factor in explaining differences in
fat tests of milk. Although it is recognized that the health of the cow
may influence the fat test of her milk, it is not possible to predict just
what that influence may be. A diseased cow may be producing milk
which is high, low, or normal in fat content. Generally speaking, as
the age of the animal increases the fat test of her milk decreases slightly.
This drop in fat test amounts to only about 0.5 percent, on the average,
. during the productive life of a dairy cow. A seasonal trend in the rich-
’ ness of herd milk has been observed: usually the fat test is highest in
winter and lowest in summer. As the stage of lactation of a cow ad-
vances the fat content changes. For about the first 2 months the fat
drops slightly, remains fairly constant for 2 or 3 months, and then
increases gradually to the end of the lactation period. Conditions
- related to the milking operation may affect the fat test of the milk.
The first portion of milk drawn is much lower in fat than the strip-
pings. If the intervals between milkings are not the same, the milk
_ drawn after the shorter interval will test higher in fat. There is also
some variation in the fat content of milk from the different quarters
of the same udder. The kind of feed which the cow receives will nor-
mally have little or no effect on the fat test of her milk. Seemingly,
however, feeding a ration deficient in roughage may reduce the fat
_ test of the milk.
CIRCULAR 530
UNIVERSITY OF KENTUCKY
College of Agriculture and Home Economics
Extension Service
FRANK J. WELCH, Dean and Director

 
 The Fot Content of Milk: Why It Vornes
By T. R. Freeman
Probably no other single topic of discussion in the entire dairy
V industry is characterized by so much misunderstanding, mutual sus-
picion, accusation, counter—accusation, bickering and other enervating
forms of verbal activity as that dealing with the fat content of normal
cow’s milk. Some adjustment in the degree to which butterfat domi-
nates our dairy economy appears to be taking place. The outcome of
this apparent shift is, of course, problematical. Come what will, but-
terfat no doubt always will be considered an important constituent
of milk. It is not the purpose of this publication to pursue a discussion
of the relative importance of fat among the several constituents of
milk, but rather to point out the many conditions which are known
or believed to have an effect on the amount of fat present in normal
milk.
· The following factors will be considered: the breed, the individual
‘ cow, health of the cow, age of the animal, season of the year, stage of
S lactation, the milking operation, feeding conditions, and other man-
agement factors. Some of these factors will be of interest only when
comparing one herd with another, or one locality with another. Many
of the conditions to be considered, however, will help the dairyman
understand why his herd varies from one time to another, and why
there may be considerable variation among the individual animals in
his herd.
THE BREED
It is almost universally recognized that the breed of dairy cow
involved is the most important single factor determining the fat con-
tent of normal milk. Investigators interested in this problem have
made hundreds of thousands of fat tests on milk produced by the
V various dairy breeds all over the world. The average values which
they report do not always agree precisely, because each investigator
has obtained samples of milk produced under slightly different cir-
_ cumstances. However, the results of these studies can be used as
' valuable, practical guides in setting up "norms" or standards for com-
parative purposes.
In the United States are five recognized breeds of dairy cattle. The
following values can be considered reliable for purposes of comparison,
. as they are what would ordinarily be referred to as the "average fat
test" for each breed:
Pmzcrzwr FAT IN Mm:
jersey 5.30
Guernsey 5.03
Brown Swiss 4.00
Ayrshire 3.95
Holstein 3.48
8

 4
The least amount of information is available on the composition
of Brown Swiss milk. Consequently the value given for the fat content
of milk of this breed may need slight revision in the future as more
data are made available.
INDIVIDUAL VARIATIONS
It has just been noted that each breed produces milk which, on
the average, contains an amount of fat characteristic of that particular "
breed. For instance, jersey milk is said to have an average fat content
of about 5.3 percent. This "average" was determined after the testing
of many thousands of samples of milk obtained from hundreds and
hundreds of individual animals of that breed. "
lf one were to examine all the individual fat tests used in calcu-
lating the average value for jersey milk, he would find that they vary
from considerably less than 5.3 percent to considerably more. A simi-
lar observation could be made concerning each of the other breeds.
These individual variations are the result of each animal having a
slightly different inheritance than that of every other animal. These _
small differences in inherited ability to produce milk of a certain fat .
content are sometimes difficult to demonstrate because so many other
things may also cause individual samples of milk to deviate consider-
ably from the "average" or "standard" fat content.
Several years ago workers at the Illinois Agricultural Experiment
Station published figures to illustrate this matter of individual varia-
tions. They found, for example, that samples of milk from individual
jersey cows varied from a low of 3.28 percent to a high of 9.37 percent. »
The values which they published for other breeds showed variations A
of similar magnitude. So if one were to determine the average fat
test for each animal in a jersey herd (or other breed), based on an
entire lactation period, a considerable spread among the averages
would be observed.
HEALTH OF THE COW _
Obviously, health is ordinarily significant only when dealing with
individual animals. It is not likely that more than one or two cows
in a herd would be producing abnormal milk because of sickness. A
Except in a very small herd such a condition would have little effect
on the composite test from the mixed herd milk.
After searching the scientific literature for information on this
point, one is disappointed to learn that a relatively small amount of
work has been done. Some of the earliest experiments were not well _
controlled, and the early methods of testing for fat were perhaps not
so reliable as those now used. In brief, there is only a very limited
amount of dependable information available to help us understand
the relationship between the state of health of the cow and the fat
test of the milk she produces. Further beclouding the issue, this in-
formation does not show a consistent, clear-cut cause-and-effect rela-

 5
tionship. This is true whether one considers sickness in general or
some specific malady. Sickness usually causes a decrease in milk How,
but may or may not affect the fat test. It has been said that the milk
produced by inflamed udders tends to approach the composition of
blood. However, the effect on the fat content of the milk is not con-
sistent. In some cases the fat test may be greatly reduced, while in
‘ others there may be no material change. One investigator reported
that the fat content is, generally speaking, more likely to be increased
than decreased as a result of the effect of disease. From a practical
viewpoint this inconsistency means that one cannot predict any defi-
nite relationship between disease in the cow and the fat content of
her milk—the latter may be high, low, or normal.
AGE OF THE ANIMAL
Most investigators who have studied this factor have observed a
general tendency for the milk to decrease in fat content with successive
. lactations. The drop in fat test is not very great, however, being of
‘ the magnitude of only about 0.3 to 0.7 percent during the productive
life of the animal. This observation is based upon results published
by American and European workers. However, the effect of age of
the animal is ordinarily of no significance in explaining variations in
the fat t€st of herd milk or of individual cow samples over short
periods of time.
SEASON OF THE YEAR
` A great volume of material has been published by many workers
interested in the relationship between season and the fat content of
the milk. Most of the information indicates a definite seasonal trend
in the average fat test of cow’s milk. The investigators disagree as to
the exact time of year when the fat test is highest or when it drops
V to its minimum. All agree, however, that the test is highest in the
winter and lowest in the summer.
At least three different explanations have been suggested to ac-
. count for this seasonal variation, including (1) changes in feeding
conditions, (2) changes in average period of lactation of the herds,
and (3) the seasonal changes in atmospheric temperature. Those who
propose the first explanation believe that putting cows on lush spring
pasture stimulates an upsurge in milk flow-the spring "flush"—which
is accompanied by a lowered fat test in the milk. Others maintain
A the second explanation is more logical and believe that the changes
in the milk are the result of a gradual change in the average stage
of lactation. Most dairymen, they say, breed their cows to freshen in
the spring. This makes the peak volume of production (and corre-
sponding low-fat test) come during the summer months. By winter
the cows have reached the latter part of their lactation period, and
the fat test is increasing.

 6
The third group believes that the cow responds physiologically to l
changes in atmospheric temperature, secreting more fat in cold weath-
er and less in warm weather. As a matter of fact, experiments have
been performed with cows maintained in temperature—controlled stalls,
with results that seem to support this theory.
Of course it doesn’t mean that, just because there are three theories,
only one of them is entirely correct. In fact, it seems reasonable to
believe that all three theories may be partly right—that each of the V
conditions discussed above may be involved in a true explanation of
seasonal changes in the fat content of milk. From a practical view- A
point two things must be recognized: (l) there usually is a gradual
change in the fat content of milk as the seasons progress; and (2) this ~
seasonal change is probably less than most persons might suppose.
It is doubtful if the highest average fat test of a commercial herd in
winter is more than about 0.5 percent above the lowest test in the
summer.
STAGE OF LACTATION
The effect of stage of lactation on the fat content of the milk _
probably would seem to most persons to be one of the simplest of the .
factors to determine experimentally. One would need only to make
a fat test on milk samples taken at regular intervals from the time the
cow freshens until she is dried off. However, it is not quite so simple
as it seems at first glance. The average normal lactation period is 9
to l2 months in length, traversing in many cases an entire cycle of
seasons.
Obviously then the experimenter has a difficult problem to resolve ·
if he is to arrive at the truth. The problem is of this type: if a cow _
calves in March, the decreases and increases in the fat test of her milk
will parallel both the seasonal progression and the advancing stage
of lactation. How much, if any, of the change in fat content of the
milk should be attributed to physiological changes in the cow as she A
advances in lactation? To arrive at an answer to this question many
research workers have obtained milk samples from individual cows .
throughout hundreds of lactation periods. These studies represent all
dairy breeds and include a fairly uniform distribution of lactations
beginning in each month of the year. A careful survey shows a rather A
consistent trend. The fat content of the milk decreases during the
first 2 to 3 months, remains fairly constant for a month or so, and
then slowly increases to the end of the lactation period.
On the average, the maximum variation in the fat test of the milk
during a single lactation (excluding the colostrum) is probably 0.5 .
percent or less. This applies, of course, to individual cows. The varia-
tion in the fat test of herd milk resulting from this factor will be even
less, the range depending upon the number of animals in the herd
and the extent to which the breeding schedule is spread over the en-
tire year.

 · 7
THE MILKING OPERATION
The first portion of the milk drawn from the udder will contain
a smaller percentage of butterfat than will the strippings. In a study
of this phenomenon in four breeds of dairy cows, one experiment
station found that if the initial 8 or 9 percent of the milking were
withheld the remainder of the milk would test about 0.2 percent
» higher in fat. Many years previously workers at another station had
l studied this same problem. They divided the milking into nine suc-
cessive portions and tested each portion to find the fat content. In a
single milking the fat test varied from as low as 1.4 percent in the
first portion to as high as 11.0 percent in the last portion. This shows
why it is so essential to mix thoroughly a complete milking from a
cow if one wishes to determine the true fat test of her milk.
In respect to the milking operation it should be mentioned that
the interval between milkings may have some influence on the fat
test. If the milkings come at approximately equal (12-hour) intervals
· there will probably be little variation in fat test from one milking to
· the next. However, if the two intervals are not uniform the fat test
° usually is higher from the milking following the short interval. If in
the summer the dairyman milks early in the morning and late in the
evening, one would expect the morning milk to be the richest in fat.
Because of those conditions it is very important to mix thoroughly
the samples obtained from two successive milkings in order to de-
termine the true average fat test of the milk.
There will also be some variation in the fat test of milk from the
different quarters of the same udder. This behavior follows no uni-
‘ form pattern, even in the same uclder. While the greatest difference
between quarters of the same udder is not large, probably averaging
about 0.2 percent fat, it nevertheless lends emphasis to the importance
, of obtaining a complete milking from a cow that is being tested for
ability to produce fat.
· FEEDING CONDITIONS
The possible effect of feed on the composition of milk, particularly
· its fat content, has long been a subject of great interest to dairyman,
teacher, and scientist. To say that it has been a controversial subject
is certainly an understatement. In the early history of scientihc agri-
culture an attempt was made to associate high-fat dairy rations with
the production of milk rich in fat. Experiments have repeatedly
_ proven, however, that the fat test of the milk cannot be increased
significantly by adding fat—rich feeds to the ration. If the cow is re-
ceiving a reasonably well-balanced ration, a low fat test in the milk
cannot be ascribed to the feed she is receiving.
It does appear, however, that an adequate amount of good quality
roughage in the ration of the dairy cow is necessary if she is to produce
milk of normal composition. One of the earliest observations of this

 8
relationship was made at the New York Agricultural Experiment
Station over 50 years ago, in connection with cheese making experi- ‘
ments. This phase of their studies received very little recognition,
and it has only been during recent years that dairy investigators have
"discovered" this relationship. It now appears to be a fairly well
established fact, however, that cows inadequately supplied with rough-
age are likely to produce milk containing an abnormally low concen-
tration of both fat and solids-not-fat. This observation is substantiated
by reports from at least three experiment stations in the United States,
as well as from investigations in England and Australia. `
If silage or good quality hay is not available during periods when
pastures are nonproductive, the quality of the milk may suffer until
roughage is again provided. This situation could conceivably occur
at any season of the year, depending upon geographical location and
weather conditions. In some instances the effect has been so pro-
nounced as to cast suspicion on the honesty of the dairyman producing
such milk.
All factors which may affect this phenomenon have not yet been
exhaustively studied. Nevertheless, when a milk sample is observed
to be low in fat, and the usual explanations do not seem to suffice, _
an inquiry into the roughage feeding program might provide the .
answer to the problem.
OTHER MANAGEMENT FACTORS
Some writers have stated that management is one of the most im-
portant of all factors affecting the fat content of milk. The dairy cow
is a creature of habit. lf her habitual daily routine is suddenly changed _
she may respond with a change in the amount and composition of the
milk she produces. ·
For instance, changing a herd from hand milking to machine
milking (or vice versa) may cause at least a temporary change in the
fat test of the milk. A change in milkers, sudden fright, mistreatment, _
etc. are all likely to affect the milk to a greater or lesser degree. In
general, any change in management practices which brings about less
desirable conditions usually results in the production of milk with I
lower fat content.
Lexington, Kentucky
April 1955
 
Cooperative Extension Work in Agriculture and Home Economics: College of Agriculture
and Home Economics. University of Kentucky, and the United States Department of Agri-
culture, cooperating. Frank J. Welch, Director. Issued in furtherance of the Acts of
May B and June 30, 1914.
10M-4-ss