agricultural production guidelines
dairying in kwazulu-natal
Dairying in KwaZulu-Natal
Dairying 6.2 1995
COMPOSITION AND THE FACTORS INFLUENCING IT
Nutritional influences on milk protein
Since the establishment of
the quality purchase scheme for fresh milk on the basis of the fat and protein content,
interest in the factors influencing these two components has increased enormously.
Absolute consistency regarding the composition of milk cannot be expected from different
cows or even from the same cow at different times, because milk is a product of a
biological process with an inherent natural variation. The average composition of
Holstein-Friesland milk is given in Table 1.
The fat content of milk
usually shows bigger variations than do the other ingredients.
It must be accepted that
within certain limits, daily variations in the fat and protein percentages of milk, as
well as the milk yield of individual cows, are normal (see Table 2). The more the
environmental conditions vary however, the bigger the variation in the composition of milk
Table 1. General
composition of cow's milk
Table 2. Daily
variations regarding production and the protein and butterfat content of milk in
Table 3. Differences
between the dairy breeds regarding total production, and the protein and the butterfat
content of milk
The positive correlation
existing between the fat and protein content is not valid for all breeds or for all cows
within a breed, as is shown in Tables 2 and 3. Stage of lactation, infection of the udder,
and feeding may influence this correlation.
FACTORS INFLUENCING THE
BUTTERFAT CONTENT OF MILK
Butterfat percentage is
partly a hereditary characteristic, and this causes the difference in average butterfat
percentage between different breeds, as shown in Table 3.
There is a common tendency,
within breeds, for high producing cows to produce milk with a low fat content. The
composition of milk of individual cows of a particular breed can differ greatly; for
instance, poorly-bred Jerseys may provide milk with 3% fat, while well-bred
Holstein-Friesland cows may give milk with a fat content of 4,3%.
The milk production of cows
increases after calving, to reach a maximum (peak) level during the second month of
lactation. It then decreases again gradually as lactation progresses.
The butterfat percentage
decreases during the first three months after calving, and then stays constant for three
months. After this period of five to six months, more noticeable increase occurs at the
end of the lactation period. Therfore, if a great number of cows in the herd calve
simultaneously, the fat content of the herd milk may be as much as 0,5% lower two months
afterwards, after which it will increase again to a percentage that can be higher than it
was during the calving season.
As the cows grow older an
increasing reduction of the fat content of milk occurs, as is shown in Table 4.
Feeding can influence the
fat content of milk within the genetic yield potential. Adequate protein and energy in the
ration are of primary importance in the effort to increase the fat content of the milk to
the inherited maximum.
Rations with a low-fibre
content will result in a reduction of the butterfat content. Research has shown that the
complete ration should contain at least 18% fibre. Young, lush pastures, high
concentrates, low-roughage rations, and finely-milled roughage (where physical fibrousness
is lacking) are examples of rations which produce milk yields with low fat contents. The
highest fat percentages occur in autumn and early winter, while the lowest fat percentages
are found during spring and early summer.
rations are fed, an intake of 2,5 to 3,5 kg long hay per cow per day is necessary to
prevent a decrease in the fat percentage. Cows normally have about 60 to 67 parts acetic
acid and 15 to 20 parts propionic acid in the stomach. In the case of high concentrates
and low-roughage rations, the ratios change to 40 to 45 parts acetic acid against 35 to 45
parts propionic acid. Propionic acid reduces the fat content and increases the protein
content of milk, while acetic acid has the opposite effect.
The use of buffers in diets
with a low-fibre content can make a small contribution to increase butterfat percentage.
Table 4. Influence of age
of cow on the fat percentage of milk
An increase in the number
of concentrate feedings from two to four or six per day can increase the fat content of
milk to a certain extent.
Malnutrition in the dry
period and/or at the onset of lactation reduces the milk yield and fat content of the
total lactation period.
Oestrus and gestation
Results show that, once the
foetus has reached the age of four to five months, the butterfat percentage in the milk
shows an abnormal increase. Gestation suppresses high milk-production after five months,
and therefore promotes a higher butterfat percentage.
The effect of oestrus on
the butterfat content of milk shows no definite pattern. In some animals the fat content
increases while in the case of others it shows a decrease.
Disease normally has a
disadvantageous effect on both milk production and milk composition. In cases of mastitis,
the fat content decreases, while an increase in the whey protein and chloride content is
The fat content of the
first milk extracted is 1,95% and that of the last milk 10%. Therefore, if a cow is not
milked out fully, some of the fat remains behind and the fat test will be low.
An inefficient milker who
cannot win the trust of the cow often causes her to be nervous and is not able to milk out
a cow completely. This causes the milk flow to be retarded, and the butterfat test to be
Incomplete milking also
occurs when the cow is upset during the milking process, if the milking machine hurts her,
or if the last milk is left for the calf to drink.
Number of milkings per
Where the milking intervals
are uneven, the cows give less milk after the shorter interval, but this milk will have a
higher fat content.
Where cows are milked twice
a day at regular intervals, there will be little difference between the fat percentage and
milk production of the different milking times, even if the milk yield of the morning is a
little greater with a slightly lower fat percentage. Where cows are milked three or four
times per day, the milk which is milked in the middle of the day will contain a little
Over-exercise causes a
considerable decrease in milk production. The higher butterfat percentage which is
obtained as a result of exercise does not justify the loss in total butterfat.
The fat content may show a
slight increase in warm weather (temperatures above 30° C) or when temperatures drop
NUTRITIONAL INFLUENCES ON MILK PROTEIN
Milk protein content is not
affected by the composition of the diet to the same extent as is milk fat content. It is
more affected by the amounts of the major nutrients (energy and protein) in the diet. Milk
protein is synthesised from feed protein (amino acids) absorbed from the gut and from
those amino acids synthesised within the body.
The propionic acid that is
produced in the rumen is the major precursor of glucose and hence lactose. The milk
protein content is partly related to propionic acid, although the precise mechanism
involved remains unknown. Thus one might expect diets which stimulatepropionic acid
production in the rumen to increase milk protein and hence SNF content. Cows normally have
about 60 to 67 parts acetic acid and 15 to 20 parts propionic acid in the rumen. However,
a decrease in the milk fat percentage may be expected when the propionic content in the
rumen is high and acetic acid low. In the case of high-concentrates and low-roughage
rations, the ratios change to 40 to 45 parts acetic acid and 35 to 45 parts propionic
acid. Propionic acid reduces the fat content, while acetic acid has the opposite effect.
A ration which is
formulated to give the maximum milk production and protein content is not always the best
ration for the production of milk fat.
Adequate energy is required
for the production of milk protein. Energy deficiency reduces both milk protein and SNF
content of milk, but an oversupply of energy produces relatively small increases.
The effect of energy
concentration and change in energy concentration of a complete diet on milk protein is
shown in Table 5.
Table 5 shows that in weeks
3 to 10 milk protein concentration and yield were respectively 0,16 percentage units and
0,07 kg/day higher in animals given diet H than those offered diet M. Changing from diet H
to M, and from M to L in week 11 decreased the protein concentration and the yield
recorded in weeks 11 to 20.
During the complete
experimental period the animals remaining on diet H had a milk protein concentration of
3,41% and yield of 0,67 kg/day both higher than those animals which were initially on diet
M and then subsequently changed to diet L.
In conclusion, it appears
that, seen from a milk protein point of view, the energy concentration in the total diet
should be in the order of 10,5 MJ ME/kg.
Malnutrition in the dry
period and/or at the onset of lactation reduces SNF over the total lactation period, viz.,
a decrease of 0,10 to 0,15% in the SNF percentage may be expected. Therefore, the aim must
be to attain satisfactory body condition at calving (3,5 body condition score) and limit
live-mass loss in early lactation by supplying sufficient energy to meet requirements.
Where excessive energy is
provided (25% above normal level), the protein and the SNF contents of milk can increase
by about 0,2% to 0,3% within genetic limits. A decrease of 0,4% in the SNF can be expected
if the energy provision is 25% under the normal level.
Table 5. Mean values for
concentration (%) and yield (kg/day) of milk protein for cows fed diets containing
different energy levels, for weeks 3 to 10, 11 to 20 and 3 to 20 of lactation (Phipps,
Bines, Weller & Thomas, 1984; J. Agric. Sci. 103, 323)
and stage of lactation (weeks)
( 3 to 10)
H (11 to 20)
( 3 to 10)
M (11 to 20)
( 3 to 20)
M (11 to 20)
( 3 to 10)
L (11 to 20)
Weeks 3 to 10
Weeks 11 to 20
Weeks 3 to 20
Weeks 3 to 10
Weeks 11 to 20
Weeks 3 to 20
H (65% concentrates: 35%
grass silage; 10,5 MJ ME/kg; 16,2% protein).
M (50% concentrates: 50% grass silage; 10,1 MJ ME/kg; 15,9% protein).
L (35% concentrates: 65% grass silage; 9,6 MJ ME/kg; 15,5% protein).
Dietary protein may affect
milk protein content directly, and hence that of SNF. At a fixed energy intake, increasing
dietary protein intake increases milk protein percentage. It is important to discriminate
between non-protein and protein nitrogen, with increasing dietary protein, amino acid
supply is increasing microbial protein synthesis in the rumen and the passage of non-rumen
degradable protein to the small intestine. Once microbial protein synthesis has been
maximised, an increase in the amino acid supply is entirely dependent upon undegradable
A relatively undegradable
protein source, with an optimal amino acid composition is expected to increase the milk
protein content. For high-producing dairy cows, diets high in degradable protein tend to
decrease the protein percentage in the milk when compared to diets with lower protein
Where rations show
severe protein deficiencies (40% under the normal level) a decrease of up to 0,4% of the
milk protein content can occur. Excessive protein in rations does not result in an increase in the protein
content of milk.
purposes the total diet should contain 16 to 17% protein during early lactation (0 to 120
days) after which the protein content can be decreased to 12 to 13 percent.
INFLUENCES ON MILK PROTEIN
It is usually found that
the higher-yielding breeds produce milk with a lower content of both fat and protein. In
addition, variation exists within a breed. The average protein content of milk of
Holstein-Friesland and Ayrshire cows varies between approximately 3,3 and 3,5% compared to
3,6 and 3,9% for Guernsey and Jersey cows.
Fortunately the correlation
between butterfat percentage and protein content is fairly high (0,48 to 0,62), and the
selection for higher butterfat content has also improved the protein content. The
butterfat and protein content of ensuing lactations of a specific cow are highly
repeatable (55 to 80%), with a high heredity (55 to 60%). Selection progress can therefore
take place if the composition of milk is purposefully emphasized in a selection programme.
The SNF content of milk
shows a gradual decrease during successive lactations. The total decrease over the first
five lactations is about 0,4% units.
Stage of lactation
The protein content
decreases during the first or second month of lactation after which it shows a gradual
increase. If a great proportion of the cows within the herd calve within the space of a few months, the
variation in milk protein, which is correlated with the stage of lactation, can have a
marked influence on the seasonal fluctuation of the protein content.
The lowest protein
values of milk are found during the late summer and early autumn, while the highest values
occur during spring. Deviations from this pattern can be attributed to stage of lactation
as well as feeding conditions, climate and temperature.
Mastitis decreases both
yield and SNF.
A decrease in the
protein content of 10 to 20% may be expected at temperatures above 27° C while an
increase may occur at temperatures under 0° C. Climate, rainfall and temperature exert an
influence on the growth and the composition of plants, and consequently also influence the quality of the roughages.
Nutrition is but one of
the many factors influencing milk quality. In the short term it is perhaps the easiest
means of improving milk quality, provided basic husbandry is sound. In the long term,
however, attention must be paid to breeding policy to improve the genetic potential for
enhanced milk quality as well as for yield.
NEITZ, M.H. &
ROBERTSON, N.H., 1991. Composition of milk and factors that influence it.
(Bulletin 421). Pretoria: Directorate of Agricultural Information, Department of
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