• TABLE OF CONTENTS
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 Title Page
 Table of Contents
 Milk fat content
 Solids-not-fat content
 General discussion
 Conclusions
 Acknowledgement
 Literature cited






Group Title: Bulletin - University of Florida. Agricultural Experiment Stations ; No. 692
Title: Subnormal milk
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Permanent Link: http://ufdc.ufl.edu/UF00027207/00001
 Material Information
Title: Subnormal milk cause and correction
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 36 p. : charts ; 23 cm.
Language: English
Creator: Becker, R. B ( Raymond Brown ), 1892-1989
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1965
 Subjects
Subject: Milk -- Composition   ( lcsh )
Milk -- Quality   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 32-36.
Statement of Responsibility: R.B. Becker ... et al..
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
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Table of Contents
    Title Page
        Page 1
    Table of Contents
        Page 2
    Milk fat content
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Solids-not-fat content
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
    General discussion
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
    Conclusions
        Page 31
    Acknowledgement
        Page 32
    Literature cited
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
Full Text
Bulletin 692


July 1965





Subnormal Milk--

Cause and Correction




R. B. Becker
P. T. Dix Arnold
C. J. Wilcox
W. A. Krienke
L. E. Mull
E. L. Fouts










Agricultural Experiment Stations
University of Florida, Gainesville
J. R. Beckenbach, Director









CONTENTS


Page
I. Milk Fat Content ------------------ 3
The Problem .----------------- 3
Field Surveys .........------------------ 3
Review of Literature .. ....----------------- 5
Experimental Methods ------------... 9
Results -----.-- - ---------- 10
Discussion ----------------- -..------- 11
Summary ------------ -...... ....--------- 13

II. Solids-Not-Fat Content ......------------------- 14
The Problem ........--------------------- 14
Field Surveys ---------.------ ---- --- 14
Review of Literature ........----------------- 15
Experimental Methods ------- 16
Results ........------------------------ 17
Discussion ..--------------------- 18
Summary ..---------------------------------- 18


III. General Discussion .......------------------ 19


IV. Conclusions .--------- ---------------- 31
Acknowledgements ....-------------------- 32
Literature Cited ...............-------------------- 32







SUBNORMAL MILK -

CAUSE AND CORRECTION

R. B. Becker, P. T. Dix Arnold, C. J. Wilcox, W. A. Krienke,
L. E. Mull, and E. L. Fouts'

I. MILK FAT CONTENT

The Problem
The problem of subnormal milk fat content is one of both
practical and scientific interest. In Florida, the problem was
first recognized in 1944 when dairymen were suspected of water-
ing milk after milk plant operators received bulk milk deliveries
from Jersey and Guernsey herds which tested as low as 2.8 per-
cent fat.
Investigation by one of the staff of the Florida Agricultural
Experiment Station showed that the dairymen were not water-
ing the milk and that the cows were truly producing milk of
abnormally low milk fat content. Research available at the time
(29, 39, 40, 41)2 suggested that nutritional factors associated
with low-level forage feeding could be involved.
The objectives of the present report were to study the cause
and prevention of this subnormal milk. Four preliminary re-
ports have been presented (10, 11, 12, 27).

Field Surveys
A number of observations were made in several Florida dairy
herds with the cooperation of dairymen, county agents, milk
inspectors, and feed salesmen. In 1944, a herd of registered
Jerseys reported producing low-fat milk was investigated. The
SBecker: Dairy Husbandman, Emeritus.
Arnold: Associate Dairy Husbandman, Emeritus.
Wilcox: Assistant Geneticist.
Krienke: Associate Dairy Technologist.
Mull: Dairy Microbiologist.
Fouts: Dairy Technologist and Head, Dairy Science Department,
Florida Agricultural Experiment Station.
Drs. S. P. Marshall and J. M. Wing aided in selecting experimental
cows and provided feeds used during the controlled feeding trials. Drs.
G. K. Davis and J. T. McCall supervised proximate analyses of feed in-
gredients.
SItalic figures in parentheses refer to "Literature Cited" in the back of
this bulletin.









Table I.-Relation of milk fat percentages to feeding practices in selected herds during 1943-1945.


Number of Average of Fat Lowest Number
Year Herd Tests Tests Fat Test below 4% Forages Fed


4.22%
4.43
4.28
3.91
3.47


3.9%
4.0
3.9
3.5


Drouth period: winter, spring, early summer.
A 12 3.66
B 11 4.08
C 29 3.93
D 14 3.47
E 24 3.57


Autumn, after rains


stimulated growth of grass.
4.36 3.5
4.47 4.1
4.35 4.1
3.90 3.8
4.43 4.1


1943


1944


1945


adequate pasture
adequate pasture
pasture, silage
too many cows per acre
some pasture



no pasture
long hay
silage
too many cows per acre
no pasture


adequate pasture
pasture, hay
pasture, silage
some pasture, too many cows
pasture, long hay

adequate pasture
pasture, long hay
pasture, silage
some pasture, too many cows
pasture, long hay






Subnormil Milk Cauese and Correction


45 cows were fed and milked separately, and a composite milk
sample was analyzed. Milk fat was far below the breed average.
The cows were not receiving appreciable amounts of leafy for-
age. When the herd subsequently was fed baled timothy hay,
milk fat returned to acceptable levels.
In five additional dairy herds, inspectors' analyses of 294
samples of bulk (herd) milk were obtained during 1943-1945.
Of these, 113 (38 percent) tested below 4.0 percent fat. Many
of these occurred during the drouth period of 1944 when little
or no forage was available locally. At that time the cows were
receiving adequate amounts of total digestible nutrients (TDN)
from rations consisting mostly of purchased concentrates. When
leafy forage became available to these cows, milk fat content
tended to increase, as may be seen in Table 1.
Severe rainstorms inundated much pasture land in 1947.
Three-fourths of the grazing land was under water and provided
no grazing for one herd. For the first time in this herd, abnormal-
ly low-fat milk was reported. A killing frost destroyed all green
grass on another farm in November 1950. In the absence of
leafy forage, fat content of the milk gradually decreased from
an average of 4.6 percent to a low 6 weeks later of 3.6 percent.
Two weeks after hay was made available, milk fat content had
increased to an average of 4.4 percent.
In the winter of 1955-1956 twelve severe frosts occurred in
one area. White clover and other tender pasture forages were
killed or retarded greatly. A herd of predominately Jersey and
Guernsey cows experienced low milk fat levels. Little forage was
available, and the cows were fed mixed and bulky concentrates.
When forage became available again, milk fat content gradually
returned to previous level.


Review of Literature
Powell (39) believed as early as 1926 that the physical char-
acteristics and/or the amount of forages in the rations would
affect milk fat percentages, although such a possibility was not
being considered by other investigators at the time. Powell con-
cluded from results of research with 31 grade Holstein cows fed
during 79 complete lactations, that low-fat milk could be caused
by withholding forage, and that the physical condition of the
forages, and not the fiber content, was important. Higher fat
content resulted when chopped forages (1A-inch to 1-inch lengths)






Florida Agricultural Experiment Stations


were fed than when these forages were finely ground. Cows
fed a forage-deficient ration for as long as three lactations pro-
duced milk of normal composition after they were returned to
a normal ration.
Suspecting a relationship between rumen function and milk
fat percentages, Powell (39, 40, 41) reduced the fat percentage
in milk of 22 Holsteins by allowing them only 6 pounds of long
alfalfa hay each per day. Then the usual concentrates of three
of these cows were wetted and fermented with rumen fluids ob-
tained from cattle at the slaughterhouse. The cows responded
with an average increase in milk fat of about 1 percent. Powell's
were the first controlled trials to show the influence of physical
condition and amounts of forage on fat content of milk. He be-
lieved that solids-not-fat (SNF) of the milk was influenced
similarly, but data were too limited to be conclusive.
In 1939, Marshall (29) concluded from controlled exper-
iments that feeding a full forage ration (22 pounds of alfalfa
hay) in the ground condition and/or limiting the forage intake
caused a reduction in the milk fat test, but did not appreciably
affect the SNF content of the milk. Twelve cows received ground
hay for part of the lactation period with lesser effect on fat tests
than Powell had observed in entire lactations. One of the six
cows on limited hay intake for the short period decreased in milk
fat percentage substantially.
Holstein cows fed concentrates and only 5 pounds of hay
daily by Loosli, et al. (28) decreased in both milk yield and fat
percentage, as compared with cows receiving concentrates, 30
pounds of corn silage, and 12 pounds of hay.
Four feeding trials were supervised by Allen between 1949
and 1954 using Powell's method (39, 40, 41) of restricting the
offering of hay to decrease the percentage of fat in the milk.
Stoddard (49) noted a marked reduction in milk fat without
change in other milk solids. The fat percentage returned toward
normal when sodium acetate was given by stomach tube, but it did
not when sodium propionate was given. Tyznik (50) observed
that the rumen organic acids taken from cows fed normally were
usually around 65 percent acetic, 20 percent propionic, and 15
percent butyric acid. On the low-forage rations, acetic acid pro-
duction decreased in the rumen and propionic acid increased
proportionately. Four low-forage cows fed 0.25 to 1.0 pound of
sodium acetate produced milk with increased fat percentage.






Subnormal Milk Cause and Correction


The fat percentage dropped immediately when the acetate was
withheld. According to Van Soest (53, 54), feeding sodium pro-
pionate or carbonate had little effect on the milk fat in a later
recovery trial. The feeding of sodium acetate tended to increase
milk fat percentage, and propionate tended to lower it further.
In other trials ground alfalfa hay was fed for 2 to 11 months
with decreases of 0.5 to 1.75 percent in milk fat percentages.
Sodium acetate was added to the concentrates on 12 occasions,
and increased the fat percentages a significant number of times.
In 1952, Balch, et al. (6) fed concentrates and three levels of
hay to three lots of Dairy Shorthorn cows for 4 to 7 weeks. The
daily hay offering and average milk fat respectively for the lots
were: 18 pounds, 3.8 percent; 6 pounds, 3.3 percent; and 2
pounds, 3.2 percent. SNF was not affected appreciably. Short-
horns and British Friesians were fed 12, 8, and 4 pounds of long
hay, and 8 pounds of ground hay as the forage in a later trial
(7). A greater decrease in the milk fat percentage from cows
on ground hay confirmed the results of Powell (41).
Shaw, et al. (46) fed various concentrate mixtures with three
levels of hay to dairy cows. No significant changes were observed
in SNF contents of the milk from cows supplied with 100 percent
of total digestible nutrient (TDN) requirements. The milk fat
percentages were lower with cows on the cooked high-starch
feeds. Some variations observed may have been attributable to
the responsiveness of the individual cows.
The milk of Ayrshire cows grazing on young tender win-
ter oats (6 to 12 inches tall) in Australia (32) decreased in
fat content from 4.0 to 4.5 percent to 2.6 to 2.8 percent. A control
group on similar pasture, plus 20 pounds of chaffed saccaline (a
variety of sorghum), maintained normal fat percentages. Fat
percentages of milk from the experimental cows returned grad-
ually to normal after 9 days when receiving adequate amounts
of long forage. McClymont (31) cited six herds with subnormal
fat tests under winter feeding on young oats, young tender al-
falfa, or wet brewers' grains. The milk from these herds returned
to normal fat content when some oat hay or older pasture was
supplied.
Reduced flow of saliva due to character of the feed has been
indicated as a reason for depressed milk fat percentages. Michi-
gan workers (47) calculated that the average sodium content of
bovine saliva in their studies was 234 milligrams per 100 milli-






Florida Agricultural Experiment Stations


liters. This is a major source of sodium necessary for the ab-
sorption of the volatile fatty acids during stomach digestion.
Bailey (3) used three fistulated Shorthorn cows and sampled
swallowed food at the cardia as it entered the rumen. Five times
as much saliva was present per gram of hay or dried grass as
with pelleted concentrates. Hay and dried grass were eaten at a
slower rate than pelleted concentrates, fresh grass, or silage.
More saliva accompanied the dry forages into the stomach. He
calculated that three dry cows secreted 74 to 96 liters of saliva
when eating hay, and 90 to 110 liters with grass. Variations in
flow of saliva with particular rations may have been involved in
responses to sodium or potassium acetate (43, 48, 53) and to
sodium bicarbonate (19, 30, 33) or adverse responses to pro-
propionate additions (43, 45, 53).
Bancroft, et al. (8) observed the absorption of organic acids
directly by sampling from stomach veins of a sheep under anes-
thesia. The organic acids from microbial digestion, especially
acetic, were absorbed mostly from the rumen and reticulum, less
from the omasum, and little from the abomasum. Danielli, et al.
(17) noted that the organic acids, acetic, propionic, and butyric,
were absorbed largely as their sodium salts from the rumen,
reticulum, and omasum. Very little of these acids reached the
abomasum. They are primarily end-products of carbohydrate
and protein fermentation in the ruminant stomach.
Popjak, et al. (38) injected 5 microcuries of radioactive sodi-
um acetate, containing carbon"1, into the jugular vein of a lac-
tating goat. The animal was milked hourly at the start and later
at progressively longer intervals. The milk fat was separated
and assayed for radioactivity. Incorporation of radioactivity
from acetate into the milk fat reached a maximum within 3 to
4 hours. This demonstrated the rapid synthesis of milk fat from
acetate.
A thin Jersey cow at the New York (Geneva) (25) station
was fed for 95 days on feeds that had been largely solvent ex-
tracted. She produced 62.9 pounds of fat and gained 47 pounds
in body weight. The ether extract (crude fat) in her feed
amounted to 11.6 pounds (5.7 pounds of digestible fat). More
milk fat was produced than could have come from proteins.
Jordan and Jenter (25) concluded that much of the milk fat was
derived from carbohydrates in the feed.
Emory and Brown (19) fed two groups of Holstein cows 24






Subnormal Milk Cause and Correction


pounds of grain and 2 pounds of alfalfa hay each in three periods
of 21 days each. Adding 1 pound of sodium or potassium bicar-
bonate prevented the decrease in milk fat that usually results
from such restricted hay feeding. These periods possibly were
too short to evaluate such treatments fully.

Experimental Methods

Five controlled feeding trials concerning subnormal milk fat
were completed at the Dairy Research Unit. These were pat-
terned in part upon feeding practices observed in the field sur-
veys. Guernsey and Jersey cows were selected that had calved at
least 4 weeks previously in the second or later lactations. They
were milked and fed individually in the dairy barn. They were
kept in a drylot at other times with access to drinking water and
mineral matter in a three-compartment box.
Each trial consisted of a standardization or pre-period of at
least 1 week followed by a comparison period of 7 to 10 weeks.
During the course of the experiment, 46 cows received no leafy
forage, being fed mixed and bulky concentrates. The bulky con-
centrates consisted of 200 pounds of dried beet pulp, 200 pounds
of dried citrus pulp, and 100 pounds of dried brewers' grains,
and were offered according to body weight. The mixed concen-
trates in the several trials contained ground corn, ground or
crimped oats, wheat bran, dried citrus pulp, and an oilmeal (cot-
tonseed, peanut, or soybean, depending on price). The mixed
concentrates contained about 17 percent total crude protein.
These animals are henceforth referred to as the treated group.
Ten additional cows served as controls. They were fed leafy
forages (corn silage, hay, and/or pasture) and mixed concen-
trates according to usual management recommendations.
Rations were calculated to meet the recommended level of
the Morrison standard (35) at monthly or shorter intervals. Re-
quirements of each cow were based on the average of three con-
secutive daily body weights, milk yields, and averages of daily
milk fat tests.
Each milking was sampled individually and refrigerated at
least 6 hours before being tested for milk fat (34). After being
refrigerated at 40F, the sample bottles were set in a water bath
(60F) at a depth to surround the cream layer. The cream was
mixed in with a small nylon brush. Evening and morning sam-






Florida Agricultural Experiment Stations


ples were combined and mixed by pouring gently four times.
This procedure of sample preparation was necessary for Que-
venne lactometer testing which was done at the time of sampling
for Babcock fat testing. Milk samples were pipetted into Bab-
cock test bottles and held in refrigeration. Milk tests were made
twice weekly.
The treated cows were divided into several groups for the
recovery at the end of the comparison period. Mixed and bulky
concentrates were offered as before, but a limited amount of for-
age was given to the selected individuals. Such feeds varied ac-
cording to the trial, examples being 15, 20, 30, or 45 pounds of
corn silage per 1000 pounds body weight; 4 pounds of pasture
clipping hay (mixed white clover and grass) ; 6 or 12 pounds of
Pangola hay; 1 pound of alphacel (an alpha cellulose); or 2
pounds of screened slash pine shavings. Use of the latter prod-
ucts was based on an observation that the cows had chewed slash
pine posts in the drylot. Results with the latter two products
were not conclusive, being based on only two cows per group.


Results

Trial 1, conducted in 1952-53, included two control and eight
treated cows. Results were quite consistent from year to year,
with no evidence of treatment by year interactions. Details of
Trial 1 are given as a representative of the five trials. A 9-day
standardization period was followed by a 62-day comparison
period. Fat percentages dropped 1.8 to 3.1 percent in milk of
three treated cows, and to a lesser extent with the others. At the
end of the comparison period, two pairs of cows received either 5
pounds of white clover and dallis grass hay, or an increase of
from 8 up to 16 pounds of bulky concentrates. Four remaining
cows, that decreased an average of 0.95 percent milk fat during
the comparison period, served as additional controls. Their re-
sponse in the recovery period averaged only 0.43 percent increase
in comparison with 1.40 percent by those on the recovery rations.
As shown in Table 2, the average decline in fat content was
0.97 percent, as estimated for 56 cows by covariance analysis
of the data. There were no apparent differences in the response
to the various forages offered after the comparison period. Fat
percentages of the milk from the treated cows had increased by
0.75 percent after an average recovery period of 4 weeks, and






Subnormal Milk Cause and Correction


Table 2.-Effect of lack of leafy forage on performance.
Period Group
Control Treated
Number of cows 10 46
Standardization
Milk fat (%) 5.85 5.61
Milk yield (lb) 26.2 26.8
Body weight (lb) 953 936
Comparison
Milk fat ('%) 5.81 4.72
Milk yield (lb) 21.1 18.0
Body weight (lb) 963 874
Treatment effect
Milk fat (%)) --0.97**
Milk yield (lb) -3.6 **
Body weight (Ib) -73. **
? Estimates obtained by covariance analysis.
** P < 0.01.

did not then differ significantly from the control group. Fat
percentage did not change appreciably when the cows were re-
turned to the herd.
There were marked differences among the groups in milk
yield and body weight changes. Differences of 3.6 pounds of milk
daily and 73 pounds in live weight were highly significant
(P < 0.01). Milk of cows became pale in color while under
treatment, possibly because of decreased carotene content. Re-
coveries of color were observed soon after leafy forage was re-
turned to the rations.

Discussion

Synthesis of milk fat begins by digestion of cellulose and
other nutrients by bacteria and protozoa in the cow's rumen.
Several short chain fatty acids are synthesized; the proportions
of acetic and propionic acids depend in part on the amount of
long leafy forage consumed. This process requires time in the
rumen, as well as a sufficient amount of forage. When the forage
was limited in amount, due to drouth, flooded pasture lands, or
too frequent killing frosts, insufficient leafy forage was available
for use by the microorganisms in the rumen. Milk from cows
under these feeding conditions decreased in fat content. Com-
parison periods in the controlled feeding trials possibly were too
short to cause the extremes of low milk fat content noted by






Florida Agricultural Experiment Stations


Powell (41) and in the field (11).
Once the condition of subnormal milk fat percentage had
been attained, recovery of the fat percentage was observed to be
gradual, sometimes as long as 2 weeks, after leafy forage was
restored to the rations. High quality dairy-cut hays, silage, or
increased amounts of fresh forage corrected the condition. How-
ever, pastures should not be too young and tender to accomplish
this, as observed in Australia (32 )and in Florida (10, 11). On
the other hand, old dead grass or too mature hays were less valu-
able than good quality leafy forages.
Carotene determinations were not made. However, carotene
reserves in the body possibly became depleted, since milk fat
soon became pale in color after the cows were deprived of leafy
forages. With their restoration this color returned gradually.
These changes probably were coincidental rather than a cause
of subnormal milk fat percentages.
Finely ground or pelleted forages pass through the rumen
too rapidly for rumen microorganisms to synthesize sufficient
amounts of acetic acid. When long hays were restricted to 6
pounds or less for a 1000-pound cow, milk fat percent was low-
ered. This may have been due to less saliva produced per pound
of dry matter in the ration eaten (3). Saliva supplies sodium to
aid in absorption of acetic acid (8, 33 42) Some workers sup-
plemented the low saliva production by providing sodium or
potassium bicarbonate in the concentrates The ultimate effects
of continued bicarbonate feeding upon rumen fermentation and
milk fat production have not been determined.
Powell and others (6, 7, 28, 39, 40, 41) produced subnormal
fat percentages in Holstein milk when the cows consumed 6
pounds or less of long hay per day. Hence, it is suggested that
high quality hay or an equivalent amount of dry matter as silage
or other high quality leafy forage be provided in the rations of
cows at the rate of 8 or more pounds per 1000 pounds live
weight. Dairy-cut hays (1 to 2 inch lengths) have been suffi-
ciently coarse to perform the functions in rumen digestion.
Cottonseed hulls have not been used experimentally, but they
are not coarser than dried citrus pulp, dried beet pulp, and dried
brewers' grains, which were the bulky concentrates used in these
trials. Good quality hays, silage, and pastures at a reasonable
stage of growth have proved effective in correcting and prevent-
ing subnormal milk fat percentages.






Szbnormal Milk Cause and Correction


It is now known that cows make a considerable proportion of
milk fat from carbohydrates as well as from crude fats in the
feed. Rumen fermentation results in many end-products includ-
ing acetic, propionic, and butyric acids. Saliva is secreted in
amounts somewhat in accordance with the character of the feeds,
and provides sodium for combination with the organic acids.
Sodium acetate in particular is synthesized into part of the milk
fat in the udder (38). Sodium propionate, produced in larger
amounts during digestion of concentrates, did not correct sub-
normal milk fat percentages. When sodium acetate was placed
in the rumen of cows producing subnormal milk fat, the fat con-
tent increased in their milk.
With the four cows fed alphacel or wood shavings, it was not
possible to demonstrate that a cellulose compound per se was the
nutrient used in rumen fermentation for synthesis of short chain
fatty acids. Low palatability of the rations when such products
were added, and irregularity of responses by the cows, made
these trials inconclusive.
Cows need adequate amounts of long leafy forage as hay,
silage, or fresh green forage of reasonable growth stages. Both
in the field and in controlled feeding trials, greater recoveries in
milk fat percentages appeared to result when offerings of silage
or hay were liberal in the recovery period. These feeds enable
sufficient organic acids to be made during microbial fermenta-
tion in the rumen. Good quality forages favor this action.
Research at other stations indicated that rations which result
in low fat content need not necessarily cause decreases in milk
yields and body weights. Some rations have even resulted in in-
creased yield and decreased fat percentages. The rations offered
in the present investigation were patterned after those used by
dairymen in Florida who experienced low-fat problems.

Summary
Observations in Florida as early as 1944 suggested that lack
of leafy forages in the rations of dairy cows could be a con-
tributing cause of abnormally low milk fat percentages. Research
with 56 Jersey and Guernsey cows indicated that decreases aver-
aging 0.97 percent milk fat (P< 0.01) resulted from such
rations by 7 to 9 weeks. These fat percentages returned to
normal in 2 to 4 weeks when cows were receiving adequate leafy
forages.






Florida Agricultural Experiment Stations


II. SOLIDS-NOT-FAT CONTENT

The Problem
During investigations of subnormal fat percentage in milk,
a second problem was reported by producers, processors, and
milk inspectors. Milk that met the fat standard sometimes fell
below 8.5 percent of solids-not-fat (SNF). The condition occur-
red in a number of herds that formerly depended on pasture
and/or silage during the winter period.

Field Surveys
Visits were made in cooperation with the Agricultural Ex-
tension Service to dairies where milk had been reported with
less than 8.5 percent SNF. Two possible contributing factors
became apparent. Supplies of high quality forages were ex-
hausted early, and less winter grazing was available than in
previous years. These high quality forages had been substituted
by low energy feeds such as cottonseed hulls, ground corn cobs,
oat mill feed, and/or over-mature grass hays. Cows in some
dairies were fed in large groups without regard to level of milk
production. Such herds often had cows in thin condition and
with rough hair coats, indicative of underfeeding.
Inspectors' analyses of consecutive milk samples from the
same herds were summarized with relation to the predominant
breed. The SNF analyses falling below the 8.5 percent standard
were tabulated. Although breed is a factor in this characteristic,
low-testing individuals occur in all major breeds of dairy cattle.
Milk with a naturally low SNF percentage has a slight margin
from the 8.5 percent standard. Analyses of 1,273 milk samples
of Florida herd milk are presented in Table 3.

Table 3.-Inspectors' samples of mixed milk from Florida herds, grouped accord-
ing to the predominant breed represented.

Predominant Inspection Average Average Samples below
Breed in Herd Samples Milk Fat Solids-not-fat 8.5%, SNF
number percent percent number
Ayrshire 18 4.04 8.96 0
Guernsey 377 4.64 9.05 2
Holstein 384 3.78 8.61 126
Jersey 143 4.81 9.15 8
Mixed breeds 351 4.29 8.82 11






Subnormal Milk Cause and Correction


Review of Literature
William Aiton (1) described the effects of insufficient feed
upon cows and milk in 1811:
Such meagre feeding for as long a period of time (win-
ter in Scotland) reduced the cow to a skeleton It is
not till they have been several weeks at the grass that they
give either much milk, or of a rich quality.
Before 1900, Van Slyke (51, 52) had analyses of milk sam-
ples from 48 cheese factories and from 50 herds in the Mohawk
Valley in New York during a July and August drouth. Casein
content of cheese per 100 pounds of milk decreased, while the
milk fat percentage appeared normal. The decrease was not ob-
served with the New York (Geneva) station dairy herd that
received supplemental forage during the drouth. He commented
that the drouth and probably insufficient nutrition due to pas-
tures drying up caused an abnormal fat-to-casein ratio during
that period.
Babcock (2) analyzed milk delivered to the University of
Wisconsin creamery during a drouth period in the summer of
1895. Milk from six herds which were fed some grain averaged
8.82 percent SNF and 4.22 percent milk fat as compared with
8.19 percent SNF and 4.02 percent fat from other herds. Mixed
milk from other herds during April, May, and October averaged
9.0 percent SNF. Eckles and Palmer (18) observed that the case-
in content of milk was decreased by a reduced level of nutrition,
but lactose was not affected. White and Judkins (57) pointed out
that cows with the same average milk fat percentages may vary
in average SNF percentages during lactation. Breirem (13) of
Norway reported in 1954 that a deficiency of protein intake over
three to four months did not affect the fat content, but the
percent protein in the milk tended to decrease. Kay (26) found
that by decreasing energy intake of cows by 25 percent, or by
holding energy intakes adequate while decreasing the protein
by 40 percent, the milk from stall-fed cows dropped from 8.7 to
8.3 percent SNF in a few weeks due to energy shortage, or down
to 8.5 percent from protein feed shortage. Waite, et al. (55, 56),
Rook and Balch (43), and Rook, et al. (44) found that the fre-
quently observed increase in SNF of milk when cows were
changed from stable to pastures in spring did not occur when
they had received adequate nutrient intakes during the previous
winter.






Florida Agricultural Experiment Stations


Extensive investigations conducted at the National Institute
for Research in Dairying (5, 9, 14, 15, 26), and in New Zealand
(16, 20, 36) in 1948 to 1957, showed that a deficiency in total
energy intakes of cows resulted in significant decreases in SNF
contents of their milk. Variations in percentage of SNF in milk
were influenced by age of cow, season of the year (winter versus
summer feeding), stages of lactation and gestation, breed, and
other factors. It was theorized, but later disproved, that hor-
mones present in spring pastures caused an increase in SNF.
The increase of SNF in the spring was found to be caused by
shortage of productive energy during the winter stall-feeding
period. The milk returned to normal composition when pastur-
age provided adequate TDN to meet needs of the cows. Depres-
sion of SNF occurred independently of the milk fat percentage
under these conditions.
Holmes, et al. (22) fed Ayrshire cows concentrates at three
starch equivalent levels of 59, 67, and 75 percent respectively.
Milk obtained from feeding the medium level concentrates was
higher in SNF, due almost entirely to a higher protein content
in the milk. A higher starch-equivalent intake did not result in
further increase in SNF. They concluded that the Woodman
feeding standard in England was too low, and that the total
ration should be at 110 to 117 percent of that standard.
Wilcox, et al. (58) found variations in SNF content with
year and season, stage of lactation, advancing gestation, and
breed. Advancing gestation exerted a greater tendency to in-
crease SNF than did other factors analyzed by Gorrie and Harvey
(21), the effect being noticeable at 100 days after conception.
Bailey (4) indicated that this stimulation began two months
after conception. Politiek (37) stated that contents of SNF,
protein, and lactose had heritabilities of 0.5 to 0.7.

Experimental Methods
Methods of management used in feeding trials relating to
effect of energy intakes on composition of milk were similar to
those used with the subnormal milk fat trials. In contrast to the
subnormal milk fat trials, corn silage was fed at the rate of 30
or 40 pounds per 1000 pounds live weight, as the bulky part of
the feed. Mixed concentrates with about 17 percent total crude
protein were offered for the total ration to provide 75, 85, or
100 percent of the estimated TDN requirements (35). When






Subnormal Milk Cause and Correction


necessary to meet full digestible crude protein needs, cottonseed
meal (41 percent crude protein) was included in the ration. The
standardization pre-periods were 7 to 10 days, and comparison
or experimental periods were 7 to 10 weeks.
Five trials were conducted in successive winter periods, the
first trial being in 1957-58. During the fourth and fifth trials,
milk sampling was reduced to 3 consecutive days each week,
rather than daily. Quevenne lactometer readings (34) were
taken along with the Babcock test for milk fat. Standard tests
were used for apparent acidity, protein formoll titration), and
chloride (Mohr titration). Curd tension values were measured
with a curd tension meter. Separate batches of cottage cheese
were made of milk from individual cows.

Results

The effects of low-energy feeding were reflected quickly by
performance of the cows in all five of the feeding trials dealing
with SNF. Since there was no evidence of year (trial) by treat-
ment interactions, the data have been combined into Table 4.

Table 4.-Effects of reduced TDN feeding on performance and body weight.

TDN Feeding Level
Variable 100% 85% 75%
Number of cows 21 23 21
SNF (%) 9.57' 9.44 9.24
Protein (%) 3.89 3.57 3.49
Milk fat (%) 5.70 5.70 5.49
Chloride (%) 0.145 0.150 0.152
Acidity (%rc) 0.153 0.156 0.150
Milk yield (lb) 24.5 14.8 15.0
Body weight (Ib) 984 877 850
SValues are covariance adjusted treatment means and represent performance during the
last 2 weeks of the comparison period. Values underscored do not differ at P < 0.05.

Means presented here have been adjusted by covariance
techniques for differences among the groups during the stand-
ardization periods. The means shown in the table represent
performance during the last 2 weeks of the comparison periods.
Advancing gestation tended to retard the decline in SNF, as
others (4, 21, 58) also have observed.






Florida Agricultural Experiment Stations


Treatment effects were statistically significant for SNF
percent, protein percent, milk yield, and body weight changes.
Differences among treatment means were not detected for per-
centages of milk fat, chloride, or acidity. Of the significant
effects, differences between the 75 and 85 percent TDN levels
were detected for SNF percent and body weight.
During these trials, utilization of "subnormal milk" was
studied in the manufacture of cottage cheese. The initial com-
parisons with milk from four cows (27) resulted in data that
markedly indicated some change in character of milk protein
(casein). Curd tension values were low, and the cottage cheese
coagula were weak. These conditions resulted in inferior finished
cottage cheese curd. In four subsequent trials these changes did
not always occur, at least not to the same degree as in the initial
trial. Therefore no definite conclusions can be drawn from the
cottage cheese study.

Discussion
It is apparent that the decline in SNF can be attributed pri-
marily to decline of the protein fraction. In fact, protein de-
creased more than other fractions of the SNF. Research at other
stations (2, 18, 20, 22, 44, 52) also has indicated that the major
effect of low-energy feeding was upon the protein fraction
rather than upon lactose or minerals. Burt (14) suggested that
when the cow was underfed the demand for energy was met by
protein breakdown and nitrogen excretion with a resultant
shortage of precursors for milk protein synthesis.
Although no measurement of lactose was made in the present
study, changes in chloride, a highly correlated variable, were
slight and not significant.
Contents of milk fat and acidity likewise were affected little
by the rather severe treatments imposed. Declines in milk yields
were extreme and in agreement with numerous other investiga-
tions. Changes in body weight reflected actual loss as well as
difference in body fill.

Summary
Performance was measured on 65 cows assigned to one of
three treatment groups: (a) fed to meet 100 percent of Morrison
standards, (b) fed at a TDN level of 85 percent of the standard,
or (c) fed at a 75 percent level. Percent of SNF, milk protein,






Subnormal Milk Cause and Correction


average daily milk yields, and body weights of the low TDN
groups were significantly lower than for the control group (a).
Adjusted treatment means for these variables were (a) 9.57
percent, 3.89 percent, 24.5 pounds, and 984 pounds; (b) 9.44,
3.57, 14.8, 877, and (c) 9.24, 3.49, 15.0, 850, respectively. No
differences due to treatments could be detected for milk fat per-
centage, chloride, or apparent acidity. Feeding of TDN at levels
recommended for profitable milk production should prevent de-
clines in SNF and protein contents.


III. GENERAL DISCUSSION

Effects of three feeding practices on composition of milk are
shown typically in Figures 1 through 5. They are placed con-
secutively for visual comparisons. Each figure represents actual
daily results from individual cows fed differently but managed
similarly during the winter of 1957-1958. The upper graph in
each figure presents body weights and daily milk yields in
pounds. Two middle graphs show daily milk fat and SNF in
percentages. The lower bar graph presents day-to-day ratios of
milk fat to SNF in comparison with Jacobson's averages (24).
Jacobson computed averages from over 100,000 weekly samples
of mixed herd milk in the New England states. His samples
ranged between 2.8 and 6.0 percent fat, and varied widely in
SNF, which are largely independent at times. Deviations up-
ward of the daily ratios from Jacobson's averages are repre-
sented by black bars (for less fat), and inversely by low bars (for
less SNF). Jacobson's averages were selected for comparisons
since they were based on more samples than were others (23).
This relationship changed drastically on certain days, possibly
from an unintentional error in sampling, analysis, or recording
the readings. Such occurrences were few and did not disrupt the
general trends arising from controlled factors of the study. All
cows were subject to the same weather conditions under identical
handling.

Control Cows
Figures 1 and 2 represent the records for control cows L-214
and 623. They had adequate feed intakes and a liberal supply
of forages (hay, corn silage, and/or pasture in season) with the
general milking herd. L-214 was a Guernsey with above average











COW L-214 CONTROL

CONTROL FEEDING
Pre ADEQUATE TD.N AND AMPLE ROUGHAGE -J
vi Period
mI
-J +80 _
z 24
O -------.- -
o
16 0

o Daily Milk Production .
S--- Change in Body Weight -80 U


200
Nov.I Dec.I Jan.I Feb.I Mar. I Mar. 28

Pre
9.5 Period Daily Values
10 Day Running Average
--- Pre-Period Base --


n9.0

8.5


Jan.I Feb.I


Mar. Mar. 28











MILK FAT ',


- Daily Values
- 10 Day Running Average
---Pre Period Base


5.0 .



4.0
Nov I Dec. I Jan.I Feb. I Mar I Mar. 28





Pre
Period
+0.8 -)





-0B
DEVIATIONS FROM JACOBSON'S AVERAGE VALUES _
RATIO SN F TO F,


Figure 1.-Guernsey Cow L-214-Control. She decreased gradually in milk production with advancing lactation, and increased
slightly in body weight while receiving adequate TDN and liberal forage with the dairy herd. The SNF percentage decreased slightly
when spring pasture replaced hay and corn silage. Her milk was below breed average in SNF, and sometimes was below legal
standard of 8.5 percent, but above the breed average in milk fat percentage. Consequently, the ratio of SNF: milk fat sometimes
was below Jacobson's averages (24).










COW 623 CONTROL
CONTROL FEEDING
ADEQUATE T.D N. AND AMPLE ROUGHAGE



-


- Daily Milk Production
-- Change in Body Weight


o-32

o
0
F24
0
0 --
E16


N .8
Nov.I


Decl Jan.I Feb.I Marl


Pre
Period


-,\\


A.


(d


I-

+80O: 0

oz


Ad
(D

c a


Mo:28 Z











!4


~V V ~JJ~/*~I~AM/I`A







- Daily Values
- 10 Day Running Average
,---Pre-Period Base


4.01 1
4.01_____ __--_____________________________-_-________________________-----------_
Nov. Dec.1 Jan.1 Feb.1 Mar. I Mar.28



C1










D Extrapolated beyond the range of Jocobson's Values
DEVIATIONS FROM JACOBSON'S AVERAGE VALUES
RATIO S N.F TO F.
Figure 2.-Jersey cow 623-Control. Her milk production decreased gradually with advancing lactation, while body weight in-
creased slightly on an adequate intake which included forages. Her milk was high in fat and SNF percentages, the latter decreasing
when young tender grazing became available in February and early March. The SNF percentage was sufficiently high that the
SNF: milk fat ratio was mainly above Jacobson's averages (24).










COW 729 EXPERIMENTAL


EXPERIMENTAL FEEDING
ADEQUATE T D.N., NO ROUGHAGE








Daily Milk Production
-- Change in Body Weight


I i


Mar I Mar.15


Pre
Period


Recovery Period





c-- : --------


OL
No


V. I


0j
m
-J
I-
+80 o


OD
0


-80
LJ
0
(D
Z
I
0


Feb. I





















Nov. I Dec. I Jan. I Feb. I Mar. I Mar. 15





+0.8




-0.8
I As




0

DEVIATIONS FROM JACOBSON'S AVERAGE VALUES O Extrapolated beyond the range
RATIO S N F TO F. of Jacobson's Values
Figure 3.-Jersey cow 729. This cow received bulky concentrates in lieu of leafy forages during the treated or experimental
period. Body weight decreased with less fill, and remained fairly constant. Milk yield decreased gradually with advancing lacta-
tion. The SNF percentage tended to increase slightly, while milk fat percentage decreased fully 1.0 percent. When leafy forage
(pangola hay) was returned to her ration on February 1, the milk fat percentage increased steadily in two weeks to about 5.0
percent. The changes in ratio of SNF: milk fat were reflected markedly with relation to Jacobson's averages (24). 0n










COW 647 EXPERIMENTAL


EXPERIMENTAL FEEDING
LOW ENERGY INTAKE 75%9 NORMAL


Recovery Period


- Daily Milk Production
-- Change in Body Weight


3.
+80


0 "








r. 28 .






0
Ce+
-Io t
H"*
m'1
CO2


Mar I Mar28






Daily Values
10 Day Running Average
--Pre-Period Base
Pre Recovery Period
7.0 Period


6.0 .


5.0

MILK FAT '
4.0
Nov.I Dec.l Jan.I Feb. I Mar. I Mar28







+ 0.8





-o.8 ry *
SExtrapolated beyond the range of
DEVIATIONS FROM JACOBSON'S AVERAGE VALUES Jacobson's Values.
RATIO S.N F TO F
Figure 4.-Jersey cow 647. She received adequate protein, but only 75 percent of her estimated TDN requirements (35). Body
weight and milk yield decreased rapidly, while the milk fat percentage increased. When adequate energy was restored to her ration
after 80 days, there was a tendency for the SNF: milk fat ratio to return to the normal of Jacobson's averages (24).










COW 593 EXPERIMENTAL


EXPERIMENTAL FEEDING
LOW ENERGY INTAKE 75; NORMAL


- Daily Milk Production
--- Change in Body Weight


'v- v\V\


Pre
Period


Recovery Period


C)

I
_1

+80St





-80
CD
2
-160'1
u


Mar28


Mar28


\, An


~-----------Cw





- Daily Values
- 10 Day Running
- Pre-Period Base


Jan I


Recovery Period


Mar 28 -


I I DEVIATIONS FROM JACOBSON'S AVERAGE VALUES Extrapolated beyond the range of Jocobson's Volues.
RATIO S.N F. TO F
Figure 5.-Jersey cow 593. She was fed similarly to 647, except for 28-day longer period of underfeeding. This resulted in a
continued low SNF percentage in her milk, while that with 647 tended to recover sooner when returned to full TDN needs. This
downward trend in the milk yield of 593 was checked, and slight recovery in SNF percentage had begun to occur before the end of
the trial. The changes in the SNF: milk fat ratio were evident by comparison with Jacobson's averages (24).






Florida Agricultural Experiment Stations


milk fat percentage, but below the breed average in SNF content
of her milk. Jersey cow 623 was above average of the Jersey
breed in both fat and SNF percentages. Both cows underwent
the expected changes in body weight and decline in daily milk
yield with advancing lactation. Their graphs serve as controls
for visual comparison with the following ones.

Non-Forage or Subnormal Fat
Jersey cow 729 (Figure 3) received bulky concentrates dur-
ing the middle or experimental period in lieu of leafy forages.
The bulky concentrates consisted of dried beet pulp, dried citrus
pulp, and dried brewers' grains. Her ration contained 12 pounds
of pangola hay per 1000 pounds live weight during the recovery
period. Gradual lowering of the fat percentages in her milk
during the experimental period without forage was typical of
this feeding practice. Recovery of the fat percentage was gradual
after restoration of forage to her ration. Use of "10-day running
averages" in representing daily analyses reduced the effects of
daily variations, and generalized the response upon restoration
hay to her ration. The ratio of milk fat to SNF percentages
showed up markedly on recovery of the fat percentage in her
milk.

Underfeeding of TDN
Four Jersey cows received 75 percent of the estimated TDN
needs during the first trial with relation to underfeeding of
TDN and its effect on composition of milk. While cow 647
(Figure 4) was underfed for 80 days, the SNF percentage drop-
ped from about 9.5 to under 9.2 percent, and the milk fat tended
to increase slightly. The ratio of milk fat to SNF approached
normal when full TDN needs were supplied in her ration. Milk
samples were not analysed for protein during the first trial.
Underfeeding continued an additional 28 days with cow 593
(Figure 5). The SNF in her milk also began to increase gradu-
ally after her feed intake was restored to meet full TDN needs.
The status of milk composition was more clearly evident when
the ratios of milk fat to SNF were compared with Jacobson's
averages (24).
An extensive review of the literature, field surveys in Florida,
and data from 10 controlled feeding trials at the Florida Agri-
cultural Experiment Station have resulted in knowledge of






Subnormal Milk Cause and Correction


separate feeding practices that affect the composition of milk.
Milk fat percentages were lowered by continual underfeeding of
forages. Protein analyses of milk samples during four consecutive
trials showed a slightly greater decrease in the protein fraction
than in SNF.
Results from two of the cows used as controls indicated
that considerable individuality existed among cows, in that
those with high milk fat percentages were not necessarily also
high in SNF. Although depression of fat and SNF in milk
simultaneously was seen in the field, no attempt was made to do
so in the controlled feeding trials. It did occur in herds on low-
forage intakes, and with some cows underfed at the same time.
Such cows were in thin condition. Other factors, including ad-
vancing gestation (37, 58), also tended to affect the SNF con-
tent of milk.

IV. CONCLUSIONS
Composition of milk is affected by a number of factors. Re-
search and review suggest the following conclusions.
1. Amount and physical condition of leafy forages can affect
the percentage of fat in milk. Character of the feeds affects the
volume of saliva secreted per pound of dry matter in the feeds,
and hence the amount of sodium needed for absorption.
2. Reducing the amount of leafy forages or replacing them
with bulky concentrates resulted in significantly subnormal
percentages of fat in the milk of dairy cows.
3. An increase in amount of chopped or long leafy forages
enabled a gradual increase in the percentage of fat in milk
toward a normal level.
4. Depression of percentage of milk fat may be independent
of any significant change in the SNF content of milk.
5. Undernourishment of the cow reduced the casein content
of cow's milk, as well as caused a loss of body weight and lower
milk yields.
6. Results of the controlled feeding trials showed that pro-
tein in the milk was depressed more than the SNF by underfeed-
ing of TDN.
7. Restoration of an adequate TDN to the feed intakes was
followed gradually by a return in SNF and protein toward
normal.






Florida Agricultural Experiment Stations


8. Milk fat and SNF are somewhat independent variables
in milk of individual cows. These are influenced greatly by
heredity.
9. A larger proportion of milk samples from predominately
Holstein herds was below the 8.5 percent SNF standard than
was the milk of others analyzed in the field survey.
10. Advancing gestation tended to retard decline in the
SNF content of milk.
11. Chloride, apparent acidity, and milk fat were affected
little by changing TDN intakes of the experimental cows.
12. Protein (casein) and curd tension values were low and
cottage cheese coagula weak in "subnormal milk" from four
cows in the first trial. Variations in the four subsequent trials
and less marked values indicate that final conclusions cannot
be drawn on this point.


ACKNOWLEDGEMENTS
Sincere acknowledgements are due to C. B. Matthews, F.
Koger, and others for full cooperation and use of milk inspection
records of selected herds in the area over a 3-year period. Feed
dealers supplied formulas of bulky concentrates being used
locally. Cooperation of H. Brown of Duval County and C. E.
Phillips of Hillsborough County provided observations under
different conditions. R. Peeples collected records and facilitated
observations in a Pinellas County dairy. All of these sources
provided essential segments of the field surveys on subnormal
milk fat tests under prevailing conditions. S. Noles gave access
to analyses of inspectors' milk samples in a broad field survey.
G. W. Snedecor of Iowa State University and H. A. Meyer of
the Statistical Laboratory approved the experimental design
of the controlled feeding trials for this exploratory type of in-
vestigation. J. Donker of the University of Minnesota was con-
sulted about plans concerning the SNF trials.


LITERATURE CITED
1. Aiton, W. General review of the agriculture of the County of Ayr. 1811.
2. Babcock, S. M. The relation between milk solids and the yield of
cheese. Wisc. Agr. Exp. Sta. 12th Ann. Rpt. 100-119. 1896.
3. Bailey, C. B. The rate of secretion of mixed saliva in the cow. Proc.
Nutr. Soc. (London) 18:xiii. 1959.






Florida Agricultural Experiment Stations


8. Milk fat and SNF are somewhat independent variables
in milk of individual cows. These are influenced greatly by
heredity.
9. A larger proportion of milk samples from predominately
Holstein herds was below the 8.5 percent SNF standard than
was the milk of others analyzed in the field survey.
10. Advancing gestation tended to retard decline in the
SNF content of milk.
11. Chloride, apparent acidity, and milk fat were affected
little by changing TDN intakes of the experimental cows.
12. Protein (casein) and curd tension values were low and
cottage cheese coagula weak in "subnormal milk" from four
cows in the first trial. Variations in the four subsequent trials
and less marked values indicate that final conclusions cannot
be drawn on this point.


ACKNOWLEDGEMENTS
Sincere acknowledgements are due to C. B. Matthews, F.
Koger, and others for full cooperation and use of milk inspection
records of selected herds in the area over a 3-year period. Feed
dealers supplied formulas of bulky concentrates being used
locally. Cooperation of H. Brown of Duval County and C. E.
Phillips of Hillsborough County provided observations under
different conditions. R. Peeples collected records and facilitated
observations in a Pinellas County dairy. All of these sources
provided essential segments of the field surveys on subnormal
milk fat tests under prevailing conditions. S. Noles gave access
to analyses of inspectors' milk samples in a broad field survey.
G. W. Snedecor of Iowa State University and H. A. Meyer of
the Statistical Laboratory approved the experimental design
of the controlled feeding trials for this exploratory type of in-
vestigation. J. Donker of the University of Minnesota was con-
sulted about plans concerning the SNF trials.


LITERATURE CITED
1. Aiton, W. General review of the agriculture of the County of Ayr. 1811.
2. Babcock, S. M. The relation between milk solids and the yield of
cheese. Wisc. Agr. Exp. Sta. 12th Ann. Rpt. 100-119. 1896.
3. Bailey, C. B. The rate of secretion of mixed saliva in the cow. Proc.
Nutr. Soc. (London) 18:xiii. 1959.







Subnormal Milk Cause and Correction


4. Bailey, G. L. Studies on the variations in the solids-not-fat of milk.
II. Variations due to stage of lactation. J. Dairy Research 19:102-
108. 1952.

5. Bailey, G. L. Studies on the variations in the solids-not-fat of milk.
V. Variations due to winter feeding. J. Dairy Research 19:169-178.
1952.

6. Balch, C. C., D. A. Balch, S. Bartlett, C. P. Cox, and S. J. Rowland.
Studies on the secretion of milk of low fat content on diets low in
hay and high in concentrates. I. The effect of variations in the
amount of hay. J. Dairy Research 19:39-50. 1952.

7. Balch, C. C., D. A. Balch, S. Bartlett, Z. A. Hosking, V. W. Johnson,
S. J. Rowland, and J. Turner. Studies on the secretion of milk of
low fat content by cows on diets low in hay and high in concentrates.
III. The effect of variations in the amount and physical state of the
hay and a comparison of the Shorthorn and Friesian breeds. J. Dairy
Research 21:172-177. 1951.

8. Bancroft, J., R. A. McAnally, and A. T. Phillipson. Absorption of vola-
tile acids from the alimentary tract of the sheep and other animals.
J. Exp. Biol. 20:120-129. 1944.

9. Bartlett, S., S. J. Folley, S. J. Rowland, D. H. Curnow, and S. A.
Simpson. Oestrogens in grass and their possible effects on milk
secretion. Nature 162:845. 1948.
10. Becker, R. B., and P. T. D. Arnold. Abnormally low butterfat tests in
a survey. Proc. So. Agr. Workers. Page 77. 1949.

11. Becker, R. B., and P. T. D. Arnold. Subnormal butterfat tests affected
by roughage supply. Guer. Br. J. 90 (1) : 16-17. Jan. 1, 1954.
12. Becker, R. B., P. T. D. Arnold, J. M. Wing, J. T. McCall, and G. K.
Davis. Subnormal milk. Its production and correction. J. Dairy Sci.
38:618-619. 1955.
13. Breirem, K. Norwegian experiments regarding the effects of the feed
on the composition and quality of the milk and milk products. XII
Internal. Dairy Congr. 1:28-60. 1949.
14. Burt, A. W. A. The influence of level of feeding during lactation up-
on the yield and composition of milk. Dairy Sci. Abstr. 19:436-454.
1957.
15. Burt, A. W. A. The effect of variations in nutrient intake upon yield
and composition of milk. I. Variations in the amount and type of
concentrates fed in winter rations. J. Dairy Research 24:283-295.
1957.
16. Campbell, I. L., D. S. Flux, and M. R. Patchell. Factors affecting
the non-fatty solids in milk, with particular reference to the New
Zealand town milk supply. Proc. N. Zeal. Soc. Animal Prod. 15:132-
139. 1955.
17. Danielli, J. F., G. Popjack, T. H. French, and S. J. Folley. Utilization
of acetate for milk fat synthesis in the lactating goat. Biochem.
J. 48:411-416. 1951.
18. Eckles, C. H., and L. S. Palmer. Influence of plane of nutrition of
the cow upon composition and properties of milk and butterfat. In-
fluence of underfeeding. Mo. Agr. Exp. Sta. Research Bull. 25:3-
107. 1916.







34 Florida Agricultural Experiment Stations

19. Emery, R. S., and L. D. Brown. Effect of feeding sodium and potas-
sium bicarbonate on milk fat, rumen pH, and volatile fatty acid
production. J. Dairy Sci. 44:1899-1902. 1961.

20. Flux, D. S., and M. R. Patchell. The effect of undernutrition after
calving on the quantity and composition of milk produced by dairy
cattle. J. Agr. Sci. 45:246-253. 1954.

21. Gorrie, C., and W. R. Harvey. Some causes of variation and covaria-
tion in fat and solids-not-fat percent of milk from Holstein cows.
Proc. 34th Ann. Meet. Western Division ADSA. Page 71. 1953.

22. Holmes, W., R. Waite, D. S. MacLusky, and J. N. Watson. Winter feed-
ing of dairy cows. I. The influence of level and source of protein and
of the level of energy in the feed on milk yield and composition.
J. Dairy Research 23:1-12. 1956.

23. Jack, E. L., F. H. Abbott, E. B. Boessler, and A. W. Irwin. Relation-
ship of solids-not-fat to fat in California milk. Calif. Agr. Exp.
Sta. Bull. 726:2-12. 1951.

24. Jacobson, M. S. Butterfat and total solids in New England farmer
milk as delivered to processing plants. J. Dairy Sci. 19:171-176. 1936.
25. Jordan, W. H., and C. G. Jenter. The source of milk fat. N.Y. (Geneva)
Agr. Exp. Sta. Bull. 132. 1897.
26. Kay, H. D. The solids-not-fat problem. Agriculture 62:369-373. 1955.
27. Krienke, W. A., L. E. Mull, and E. L. Fouts. Some properties of "sub-
normal" milk. J. Dairy Sci. 38:592. 1955.
28. Loosli, J. K., H. L. Lucas, and L. A. Maynard. The effect of roughage
intake upon the fat content of milk. J. Dairy Sci. 27:147-153.
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36 Florida Agricultural Experiment Stations

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