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FEEDING THE LACTATING DAIRY COW TO EXPRESS ITS
GENETIC POTENTIAL
L.J. Erasmus1, W.A. Smith
2, and P.B. Cronje
3
1 ARC-ANPI, Irene
2 Meadow feeds, Randburg
3 Dept Animal and Wildlife Science, Univ. of Pretoria
1. FEEDING ACCORDING TO STAGE OF LACTATION
Nutrient requirements vary with the stage of lactation and gestation. Figure 1 illustrates
the shape and relationship of curves for milk production, fat percentage, protein
percentage, dry matter (DM) intake, and change in body weight during lactation. Five
distinct feeding phases can be defined to attain optimum production, reproduction and
health of dairy cows:
* Early lactation - 0 to 70 days after calving (postpartum), characterised by peak
milk production and negative energy balance
* Peak DM intake - 70 to 140 days postpartum, milk production starts to decline,
DMI continues to increase and cows are in energy balance
* Mid- and late lactation - 140 to 300 days postpartum, milk production and DMI
decline and cows are in positive energy balance (replenish body reserves)
* Dry period - 60 to 14 days before the next lactation, cows non-lactating and 7
months pregnant
* Transition or close-up period - 14 days before parturition. Some define this
2
period as 3 weeks prepartum to 3 weeks postpartum
Fig 1. Lactation cycle phases with corresponding changes in milk production and
composition, dry matter intake and body weight. See attached pdf
2. PHASE 1 - EARLY LACTATION: 0 TO 70 DAYS POSTPARTUM
Milk production increases rapidly during this period, peaking at 6 to 8 weeks after
calving. Feed intake does not keep pace with nutrient requirements for milk production,
especially for energy, and body tissue will be mobilised to meet energy requirements for
milk production. Adjusting the cow to the milking diet is an important management
practice during early lactation. Increasing concentrates by about 0.5 kg per day after
calving will increase nutrient intake while minimizing off-feed problems and acidosis.
Excessive levels of concentrate (over 60% of the total DM) can cause acidosis and a low
milk fat percentage. Fibre level in the total ration should not be less than 18% ADF (acid
detergent fibre), 28% NDF (neutral detergent fibre). Roughage should provide at least 21
percentage units of NDF or about 75% of the total NDF in the diet. Physical form of the
fibre is also important. Normal rumination and digestion will be maintained if more than
20% of the roughage is 5 cm in length or longer. Chopping (less than 10 cm theoretical
length of chop - TLC), grinding, and/or pelleting all reduce the physical form of fibre and
its effectiveness in stimulating rumination.
Protein is a critical nutrient during early lactation. Meeting or exceeding crude protein
(CP) requirements during this period helps stimulate feed intake and permits efficient use
of mobilized body tissue for milk production. Diets should contain at least 19% CP to
meet requirements during this period. The type of protein (degradable or non-degradable,
RDP or UDP) and amount of protein to be fed will depend on dietary ingredients, method
of feeding, and milk production potential of the cow. A guideline for the rate of
concentrate feeding for cows fed roughage that varies in quality is provided in Table 1.
3
Low peak production and ketosis problems occur when nutrient levels are not met. Low
peak production results in low total lactation yield. A decrease of 1 kg in peak milk
production equates to a 220kg loss over the entire lactation. If concentrate intake is
increased too rapidly or is too high, loss of appetite, acidosis, and displaced abomasum
are possible.
TABLE 1: Rate of concentrate feeding1 for various milk production levels by dairy
cows weighing 600 kg and fed roughage of low, medium or high quality
Milk production when forage quality is:
Milk fat (%) Poor
2
Medium
3
High
4
3.0
3.5
4.0
-
-
-
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
-
-
-
-
-
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
-
-
-
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
51
53
55
57
59
-
-
.2
1.0
1.7
2.4
3.2
3.9
4.6
5.4
6.1
6.8
7.6
8.3
9.0
9.8
10.5
11.2
11.9
12.7
13.4
14.1
14.9
15.6
-
-
.5
1.2
2.0
2.8
3.6
4.4
5.2
6.0
6.8
7.5
8.3
9.1
9.9
10.7
11.5
12.3
13.0
13.8
14.6
15.4
16.2
17.0
-
-
.7
1.5
2.4
3.2
4.0
4.9
5.7
6.6
7.4
8.3
9.1
9.9
10.8
11.6
12.5
13.3
14.1
15.0
15.9
16.7
17.5
-
4
1 Dairy meal with energy concentration of 11.7 MJ ME/kg DM and 17% CP.
2 Poor: Cows eating 1.5% of body weight of poor quality roughage (e.g. full bloom
Eragrostis, veld hay, wheat straw, maize stover). 3 Medium: Cows eating 2.0% of body weight of medium quality roughage (e.g. good non
legume hay, lucerne hay and Eragrostis hay, maize silage). 4 Good: Cows eating 2.5% of body weight of good quality roughage (e.g. lucerne hay early
bloom, fresh early vegetative pastures). 5 Amounts of concentrate in bold typescript should be fed with caution because of possible
health problems (rumen acidosis, low milk fat percentage).
To increase nutrient intake:
* Feed top quality roughage.
* If possible, feed a total mixed ration (TMR)
* Make sure the diet contains adequate amounts of CP, RDP and UDP
* Concentrate intake should be increased at a constant rate after calving when fed
separately.
* Consider adding fat (450 - 700 kg/cow/day) to diets
* Allow constant access to feed
* Minimize stress conditions
* Add water to the TMR, not exceeding 45% moisture in the total diet
* Many feed additives are available today and have been used with varying degrees
of success during this period of lactation. Due to the cost implications it is
advisable to discuss the merits of each additive with a nutritionist. The following
additives are commercially available: buffers, fungal and yeast cultures,
ionophores, protected amino acids, probiotics, fats, choline, niacin, chelated
minerals, bacterial silage innoculants and enzymes.
3. PHASE 2 - PEAK DM INTAKE: >70 – 140 DAYS POST-PARTUM
Cows should be maintained at peak production for as long as possible. Feed intake is
near maximum and can supply nutrient requirements. Cows should no longer be losing
body weight, and are either maintaining weight or gaining weight slightly (Figure 1).
5
Concentrate intake can reach 2.5% of body weight but should not exceed this (600kg cow
can consume up to 15 kg of DM from concentrate). Adding concentrate or feeds high in
digestible fibre content to the diet may be necessary to help maintain an optimal rumen
environment when these high levels (55 to 60% of the diet DM) of concentrate are being
fed. In general, rations should not contain more than 40% NSC (non structural
carbohydrates). Roughage quality should still be high with intakes of at least 1.5% of the
cow's body weight (DM basis) to maintain rumen function and normal fat content. See
Table 2 for guidelines on daily DMI
TABLE 2: Dry matter intake requirements to fulfil nutrient allowances for
maintenance, milk production, and normal live weight gain during
mid- and late lactation
Live Wt:
(kg)
400 500 600 700 800
FCM (4%)a
(kg)
% Live Wt b.c
10
15
20
25
30
35
40
45
50
55
60
2.7
3.2
3.6
4.0
4.4
5.0
5.5
-
-
-
-
2.4
2.8
3.2
3.5
3.9
4.2
4.6
5.0
5.4
-
-
2.2
2.6
2.9
3.2
3.5
3.7
4.0
4.3
4.7
5.0
5.4
2.0
2.3
2.6
2.9
3.2
3.4
3.6
3.8
4.1
4.4
4.8
1.9
2.2
2.4
2.7
2.9
3.1
3.3
3.5
3.7
4.0
4.3
a 4% Fat-corrected milk (kg) = (0.4) (kg of milk) + (15) (kg of milk fat)
b DMI may be up to 18 % less during early lactation
c DMI as a percentage of live weight may be 0.02 % less per 1 % increase in diet
6
moisture content above 50 % if fermented feeds constitute a major portion of the diet
Potential problems during this period include a rapid drop or decline in milk production,
low fat milk content, silent heat (no observed heat), and ketosis.
To maximize nutrient intake:
* Feed roughage and concentrate several times a day
* Feed the highest quality feeds available
* Limit urea intake to 100 g per cow per day
* Minimize stress conditions.
4. PHASE 3 - MID- TO LATE LACTATION: 140 TO 300 DAYS POSTPARTUM
This phase is the easiest to manage. Milk production is declining, the cow is pregnant,
and nutrient intake will easily meet or exceed requirements. Concentrate feeding should
be at a level that will meet milk production requirements and will begin to replace body
weight lost during early lactation. Lactating cows require less feed to replace one kg of
body tissue than dry cows. Young cows should receive additional nutrients for growth
(2-year-old, maintenance plus 20%; 3-year-old, maintenance plus 10%). Consider NPN
(non- protein nitrogen) as a source of supplemental protein.
There are few potential problems during this phase. Milk production should decline
slowly at a rate of 8 – 10% per month. Avoid over-conditioning cows.
7
5. SUMMARY - PHASE 1, 2 AND 3
Compare your current feeding program with the following guidelines:
1. Protein: 18 to 19% CP (DM basis) in early lactation decreasing to 13% in late
lactation. Non-degradable or bypass protein (UDP) should be 35 to 40% of CP
in early lactation and 30 to 35% of CP in late lactation. About 30% of CP should
be soluble protein (SIP).
2. Metabolizable energy: 11.3 MJ ME per kg of DM or greater in early lactation
decreasing to 10.7 MJ ME/kg in late lactation, and 8.5 MJ ME/kg during the dry
period.
3. Roughage: Minimum of 1.5 kg of roughage DM per 100 kg of body weight.
High quality legume roughage should be the major source of roughage fed during
early lactation.
4. Fibre: A minimum of 18% ADF in the dietary DM during early lactation
increasing to 21% or more in late lactation. Roughage should provide a minimum
of 21% NDF in the dietary DM.
5. Non-structural carbohydrates (NSC): 35 to 40% of the dietary DM.
6. Fat: Maximum of 7% of the total diet DM with no more than 4% from
supplemental fat. Limit fat from oilseeds to 2% of the diet DM.
7. Salt: 0.5% of the diet DM or 1% of the grain mix.
8. Mineral: Approximately 1% of the concentrate mix should be a calcium-
phosphorus mineral mixture.
8
9. Urea: Maximum of 180 g of urea per day or 1% of the concentrate mix.
10. Vitamins: Supplement with vitamins A, D and E in diets to meet requirements.
11. Diet form: Roughage and concentrates should not be chopped or ground too
fine.
6. PHASE 4 - DRY PERIOD: 60 TO 14 DAYS BEFORE PARTURITION
The dry period is a critical phase of the lactation cycle. A sound dry cow program can
increase milk yield during the following lactation and minimize metabolic problems at or
immediately following calving.
A dry cow feeding program that is separate from the lactating cows program is required.
Diets should be formulated to specifically meet the nutrient requirements of dry cows:
body maintenance, foetal growth, and replacement of any body weight not replaced
during phase 3. DM intake will be approximately 2% of the cow's body weight.
Roughage intake should represent a minimum of 1% of body weight or 50% of the
dietary DM. Concentrate feeding should be according to needs, but should not exceed
1% of body weight. One half of 1% of body weight fed as concentrate per day is usually
sufficient for most dry cow feeding programs. It may be necessary to limit the amount of
feed DM offered to less than 2% of body weight to avoid over conditioning of cows when
rations contain only maize silage or other high energy feeds. Feeding low quality
roughage such as maize stalks or grass hay is preferable to restricted feeding. If restricted
feeding is necessary, the diet should be balanced to supply all nutrients in their correct
amounts. A minimum of 12% CP in the DM is recommended.
Meet calcium and phosphorus requirements, but avoid large excesses. Calcium intakes of
60 to 80 grams and phosphorus intakes of 30 to 40 grams are sufficient for most cows.
Dry cow diets containing more than 0.6% calcium and 0.4% phosphorus (DM basis) lead
to an increased incidence of milk fever. Provide adequate amounts of vitamin A, D and E
9
in diets to improve calf survival and reduce the incidence of retained placenta and milk
fever. Trace minerals, including selenium for most producers, should be adequately
supplemented in dry cow diets.
Problems such as milk fever, displaced abomasum, retained placenta, fatty liver
syndrome, fatty liver formation and poor appetite are common in fat cows at freshening.
Key management factors include:
* Observe body condition of dry cows and adjust energy feeding as necessary
* Meet nutrient requirements and avoid excessive feeding
* Change to a transition diet 2 - 3 weeks before calving
* Avoid excess calcium and phosphorus intakes
* Limit salt intake to 28 g/cow/day and limit other sodium-based minerals in the
dry cow ration to reduce udder edema problems.
7. PHASE 5: TRANSITION PERIOD - 14 DAYS BEFORE PARTURITION
Nutrition and management during this period is critical and determines the profitability of
the cow for the remainder of the lactation. During this period dry cows and heifers are
adjusting to the lactation diet and emphasis should be placed on the prevention of
metabolic disorders. Some concentrate, if not previously fed, should be fed starting two
weeks before freshening. Introduction of concentrate is necessary to begin changing the
rumen bacteria population over from an all-roughage digestion population to a mixed
population of roughage and concentrate digesters. Addition of some ingredients used in
the lactation diet during this period also minimizes the stress of dietary changes after
10
calving. Some suggested management strategies during this period include:
* Provide 2.5 to 5 kg concentrate daily to adapt rumen microbes to fermentable
carbohydrates and stimulate rumen papilla formation. Ingredients of the
concentrate, fed individually or as part of a lactating TMR, should be the same as
those that the fresh cow will be receiving
* Increase protein content of the diet to 14 and 15 % of the diet DM. Feeding some
of this additional protein in the form of UDP protein may be beneficial in
supplying amino acids for foetal growth
* Limit fat intake to 115 g. High fat feeding will depress DM intake
* Maintain 2.5 to 5 kg of long hay in the ration to stimulate rumination. If maize
silage or a lactation TMR is fed, limit DM to 1 % of body weight
* Remove salt from the diet if edema is a problem
* If niacin (to control ketosis) and/or anionic salts (to help prevent milk fever) are
to be used, they should be included in the ration during this period
* Other feed additives such as yeast cultures and ionophores (to reduce subclinical
ketosis) can be considered
Anionic salts are used to manipulate the dietary cation-anion difference (DCAD) in order
to feed close-up dry cows a diet with a negative DCAD. This increases blood pH at
calving by increasing bone mobilisation of Ca and absorption of Ca from the intestine in
response to changes in acid-base status. The DCAD of a diet is most commonly
described as follows:
DCAD = [(% Na / 0.023) + (% K / 0.039)] - [(% Cl / 0.0355) + (%S / 0.016)]
11
The recommended DCAD for closeup dry cows using this formula is - 100 to -150
meq/kg DM
The following strategy, when using anionic salts, is recommended by Beede & Pilbeam
(1988):
* Analyse all ingredients for Na, K, Cl and S content
* Select feeds, particularly roughage with low K content.
* Calculate DCAD and consider anionic salts
* First include magnesium sulphate: total Mg should be 0.35 - 0.4%
* Next supplement enough calcium chloride or ammonium chloride to achieve the
desired DCAD of -100 to -150 meq/kg DM
* Determine if the urine pH of cows has changed (see below)
* When the desired DCAD has been achieved, raise Ca content to 1.5 - 1.8 % of
DM. Calcium chloride can be used. Calcium intake should be 180 - 210g/cow/d
and P intake 45 - 50g/d for Holsteins and 35 - 40g/d for Jerseys
Urine pH of cows is still the best indicator of the appropriate DCAD. In herds
experiencing milk fever, the urine of close-up cows will be very alkaline with pH above
8. For successful control of milk fever the average pH of the urine in close-up Holstein
12
cows should be 6.0 - 6.5 and 5.8 - 6.2 for Jerseys. If the urine pH is between 5.0 and 5.5
too much anions have been added and DMI will be depressed.
8. FORMULATING DIETS
Most nutritionists, dairy producers and feed companies use the American Nutrient
Requirements of Dairy Cattle (NRC, 1989) when formulating diets. A new version, NRC
2001 will be released early in 2001. The total diet nutrient requirements are presented in
Table 3. If not familiar with diet formulation it is advisable to utilize the expertise of
animal scientists, consultants or technical advisors from feed companies. A register of
members of the SA Association of Professional Animal Scientists is available from the
website of the SA Society of Animal Science (www.sasas.co.za)
Various low cost feed formulation programs are available. In addition nutritional models
such as the CNCPS (Cornell Net Carbohydrate and Protein Systems) and CPM Dairy are
becoming increasingly important in the nutrition of the high yielding dairy cow and can
be used supplementary to the conventional formulation programs. These prediction
models provide additional information such as estimates of microbial protein production,
amino acid requirements, body weight loss, rumen pH, milk urea N and also take into
account the effect of environment on DMI and maintenance requirements.
13
TABLE 3: Guidelines for the total diet nutrient content (DM) for dairy cattlea
Item
Lactating cows Dry cows
Calf starter
Growing heifers and bulls
Freshb Early Mid-late Early Close-up
c 3-6 mo 6-12 mo 712 mo
CP, %
Soluble CP, %CP
UDP, %CP
ME, MJ/kg
ADF, % (min)
NDF, % (min)
Effective NDF (%)
NSC (%)
Fat (%)
Ca
P
Mg
K
Na
Cl
S
N:S ratio
18-20
30-35
34-38
11.3
21
28
24
35-38
<5
0.8-1.0
0.45
0.35
>1.4
0.25
0.3
0.27-0.31
10-12:1
16-18
30-35
34-40
11.5
19
28-32
20-24
35-40
5-7
0.8-1.0
0.38-0.42
0.25-0.3
1-1.5
0.2-0.25
0.25-0.3
0.24-0.28
10-12:1
13-16
30-40
34-38
10.5
19
28-35
23-27
35-40
4-6
0.7-0.8
0.34-0.38
0.25-0.3
1-1.5
0.2-0.25
0.25-0.3
0.22-0.24
10-12:1
12-13
30-40
30-35
8.5-9.0
30-35
35-40
27
30-35
3-4
0.5-0.7
0.24-0.28
0.2-0.25
<1.5
0.1-0.15
0.2-0.25
0.16-0.2
10-12:1
14-15
28-33
33-38
9.0-9.6
21
31-38
27
34-38
3-4
0.6-0.75
0.28-0.32
0.35-0.4
<1.3
0.1-0.15
0.2-0.25
0.2-0.25
10-12:1
18
-
-
12.0
-
-
-
-
3
0.60
0.40
0.10
0.65
0.10
0.20
0.20
-
18
-
40-45
10.4
16
23
-
-
3
0.52
0.31
0.16
0.65
0.10
0.20
0.16
-
16
-
35-40
9.9
19
25
-
-
3
0.41
0.30
0.16
0.65
0.10
0.20
0.16
-
12
-
25
9.2
19
25
-
-
3
0.29
0.23
0.16
0.65
0.10
0.20
0.16
-
TABLE 3 (continued)
14
Item
Lactating cows Dry cows
Calf starter
Growing heifers and bulls
Freshb Early Mid-late Early Close-up
c 3-6 mo 6-12 mo 712 mo
Fe, ppm
Zn, ppm
Cu, ppm
Mn, ppm
Co, ppm
I, ppm
Se, ppm
Vit A, IU/kg
Vit D, IU/kg
Vit E, IU/kg
100
80
15-20
80
0.4-0.6
0.8
0.3
4000
1000
15
100
70-80
10-20
60-80
0.2-0.4
0.6-0.8
0.3
3200
1000
15
100
70-80
10-20
60-80
0.2-0.4
0.6-0.8
0.3
3200
1000
15
50-100
70-80
10-15
60-80
0.3
0.5
0.3
4000
1200
15
50-100
70-80
15-20
60-80
0.4
0.5
0.3
4000
1200
15
50
40
10
40
0.1
0.25
0.3
2200
300
25
50
40
10
40
0.1
0.25
0.3
2200
300
25
50
40
10
40
0.1
0.25
0.3
2200
300
25
50
40
10
40
0.1
0.25
0.3
2200
300
25
a
Adapted from NRC (1989) and Stone et al., (1999). This table provides general guidelines and your
nutrition advisor may adjust these for your herd situation
b First 30 days in milk or until cows are increasing DMI rapidly
c If fed an anionic ration calcium should be increased to 1.1 - 1.4% Magnesium and sulphur should be
increased to 0.4 - 0.45 % and chloride up to 0.85 %
15
9. FEEDING SYSTEMS
Extensive Grazing
The quality of typical South African summer veld in the summer, rainfall in Gauteng,
Northern Province, NW Province, Mpumalanga and Free State areas is such that it would
only support daily milk production of 5-7 litres per 500kg cow. The protein and ME
contents of summer veld grass are 11 % and 9,5 MJ/kg DM respectively. Green summer
veld must be supplemented at least with a phosphorous/calcium, salt and trace element
mixture.
Winter veld grass with a protein content of less than 5 % and a ME content of less than 8
MJ/kg DM is not adequate to meet maintenance requirements and will have to be
supplemented with grains, protein and minerals.
Forage and concentrate feeding
Forages (pastures, silages, hays) form the basis of dairy cow diets. Forage quality and
often also quantity is probably the major obstacle for successful dairy cattle feeding in
Southern Africa. Dairy farmers should focus on producing adequate amounts of good
quality forages all year round. Concentrates only supply the balance between nutrients
required and that provided in the forage. High quality forage a large saver of concentrate.
All forages contain low concentration of ME, UDP, essential fatty acids, minerals, trace
elements and vitamins.
The energy level of concentrates should be as high as possible (>11.5 MJME/kg DM) in
order to feed a minimum amount of concentrate with ad libitum high quality forage to
meet the cow’s total energy requirement. In order to achieve high energy levels in
concentrates, grains must be included at high levels (70 % +). Maize is the most readily
available grain for dairy cows in Southern Africa. However grain sorghum or small
16
grains (wheat, barley, triticale) can also be utilised successfully in concentrates. Fats
(plant oils, animal fats or commercial fats) can also be included in concentrates to supply
the necessary fatty acid and to increase the energy contents even further.
The protein content of a concentrate is formulated to complement the protein content of
the forage base being fed to the cows. Forages are low in UDP, therefore 40% or more of
the protein in concentrates should be rumen non-degradable. Fishmeal, gluten 60,
cottonseed oilcake and soybean oilcake are protein sources with high UDP contents that
could be used in concentrates. When forages are low in total protein contents and
therefore also in RDP content e.g. (maize silage, small grain hays) urea can be included in
concentrates up to a maximum of 1,5 %. Low protein concentrates (12 %) are usually
supplemented to high-protein roughage such as good quality legume hay or clover
pastures. Medium protein concentrates (15-17 %) supplement medium quality lucerne
hay or silage and rye grass or kikuyu pastures while high protein concentrates (20-24 %)
are utilised to supplement maize silage, small grain hay or ammoniated straw.
Minerals (calcium, phosphorus, magnesium and sulphur), trace elements and vitamins
must also be included at adequate levels to ensure optimum immune system activity and
satisfactory reproduction.
The quantity of concentrate fed per cow per year (±1-3 tons) depends on forage quality,
milk yield potential and concentrate cost. Most dairymen will supplement
0.5 kg concentrate per kg milk produced during early lactation with lower levels (0.3
kg/kg milk produced) during mid- and late lactation. See also the guidelines in Table 1.
Cows are fed concentrate in many different ways. These can be classed into two main
categories, namely group or individual feeding.
Group feeding
17
Cows should be grouped according to milk yield. Yield should not vary by more than 5
kg. between groups. The daily allocation of concentrate for a group of cows should be
fed in two or three meals, after milking.
Trough space (65-75 cm/cow) is of great importance when group-feeding concentrates in
order to prevent dominating cows from consuming more that their allocated amount.
Individual feeding
Concentrate is allocated per cow according to yield. Individual concentrate feeding in the
milking parlour can only be recommended when cows can consume the required amount
during milking. Post-parlour feeding will increase feeding efficiency when required
amounts cannot be consumed readily during milking.
Computer-controlled out-of-parlour feeding stations, with cows wearing identification
transponders, can feed the required amount of concentrate in 6-8 portions per day which
will optimise rumen fermentation and the utilisation of nutrients.
Total mixed rations
Total mixed rations are the ideal diet type for lactating dairy cows. It is a mixture of all
dietary ingredients, blended thoroughly to prevent separation and sorting, formulated to
specific nutrient content according to production level, and offered ad libitum.
Total mixed rations can be more accurately formulated because forage intakes are known
and a wide range of good value alternative feeds can be used, resulting in more cost-
effective rationing, better performance and higher overall margins.
The physical structure and proper mixing of total mixed rations is as important as the
correct formulations. Roughage, especially grasses should be ground to a particle length
18
of 3-4 cm, while grains should be ground or rolled. Cottonseed should be fed whole,
while full-fat soybeans should be cracked.
The blending of mixed ingredients with sugar cane molasses (8 %) will prevent
separation. It is recommended that the moisture content of a total mixed ration should be
increased to 40 % by adding water. This will further prevent separation and also increase
dry matter intake.
Load- cell mixer wagons are recommended for the mixing of total mixed rations and
most of them are able to grind hay to the desired length.
Milk yield and factors influencing it
The milk yield potential of any dairy herd is firstly set by the genetic standard of the herd.
The genetic standard of South African dairy herds has increased dramatically during the
last two decades due to imported high standard semen from several overseas countries.
The challenge is to manage and feed these herds to the extent that their genetic potential
is fully exploited. Therefore, the most important factor influencing milk yield is probably
management, of which feeding and feed management is an absolute intrinsic part.
Management of dairy herds
The management and feeding of dairy cows is the most vital factor influencing milk
yield. Dairy managers must therefore be well skilled in all aspects of dairy management.
They must know the genetic potential of their herd and feed and manage it accordingly.
One of the vital management decisions a dairy manager often has to take is whether to
milk two or three times daily. It is known that increasing milking from two to three times
daily could increase production between 10 and 15 %. The increase will be greatest in
well managed and well fed herds.
The environment
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Daily temperatures, humidity, rain and mud play vital roles as factors influencing milk
production. It has been shown that the provision of shade, fans and water-cooling
systems in warm and humid environments can increase milk production by up to 20 %.
The availability of clean drinking water within easy walking distance of the cows is also
extremely important. Lactating dairy cows need larger proportions of water relative to
body weight than most livestock species because water comprises 87% of milk. With
temperatures ranging from -17°C to 27°C the estimated water requirement for cattle is 3.5
- 5.5 kg of water for each kg of DM consumed. Research in the USA has shown that
milk production will start decreasing if the water trough is further than 16m from a cow
in an intensive housing unit where total mixed rations are fed.
The effect of rain and mud on dry matter intake and milk production of dairy cows is far
more than is usually recognised. In the following table the effect of mud depth on dry
matter intake and milk production is given.
TABLE 4: The effect of mud depth on the daily dry matter intake and milk
production of high producing dairy cows
Mud depth (cm) Dry Matter Intake (kg) Milk production (kg)
0 24,2 45,0
5 23,0 41,4
10 21,9 39,4
15 20,7 37,3
20 19,6 35,3
25 18,4 33,1
30 17,3 31,1
Bovine somatotropin (bST)
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The correct use of bST as a tool to decrease the condition of over-conditioned cows and
also to increase milk production of cows with a condition scores of 2,5 and higher can
increase milk production by up to 15 %. It is of utmost importance that bST treated cows
must be well fed and well managed and that their condition score should never be below
2,5.
10. PHYSIOLOGICAL CONSIDERATIONS IN THE FEEDING OF
DAIRY COWS
Contrary to popular belief, the biological efficiency of the dairy cow of high genetic merit
for milk production is no different to that of a cow of low genetic merit. The higher
economic efficiency of the high producing dairy cow stems from the fact that the energy
costs of maintaining other body functions not directly associated with the production of
milk must be offset against the income derived from milk: thus, the higher the milk yield,
the lower the maintenance cost per liter of milk produced and the higher the economic
efficiency of milk production. High producing cows do not digest or absorb feed or
produce milk constituents from absorbed nutrients any more efficiently than cows of low
genetic merit; the higher milk yields of genetically superior cows are due to the fact that
these animals subsidize the nutrients required for milk production with nutrients
mobilized from body reserves to a greater extent than cows of low genetic merit. While
this increases economic efficiency, enhanced breakdown of body tissues during lactation
also increases the risk of metabolic disorders and the probability of reproductive failure
when nutrition or management is less than optimum. The degree of risk is exacerbated by
the fact that several of the metabolic disorders associated with increased milk yield can be
fatal.
Ketosis and fatty liver
21
High producing cows draw extensively on body fat reserves as an energy source during
early lactation. Much of the fatty acids released by the breakdown of fat reserves are
transported to the liver and converted to ketones which can be used as an alternative fuel
for body tissues during this period when many other nutrients are being used for milk
production. A certain amount of proteins are needed to transport fatty acids, and glucose
is needed to convert the ketones to energy. If the dietary supply of protein or glucose
precursors is insufficient to replace that lost in the milk, fatty acids will accumulate in the
liver and ketones will accumulate in the blood. Fat accumulation in the liver will impair
the functioning of this vital organ leading to decreased efficiency of digestion and
utilization of nutrients. Accumulation of ketones in the blood affects the acidity of the
blood which decreases the efficiency of utilization of nutrients and ultimately the
utilization of energy by the brain, leading to nervous symptoms and death. Ketosis usually
occurs during the first month after calving. Early-onset symptoms include a drop in milk
production and decreased feed intake, later symptoms include nervous disorders,
disorders in locomotion, defective vision and ultimately death. The main causes of ketosis
are all associated with incorrect diet formulation and include low energy content, low
Vitamin A content, either inadequate or excess protein content, high fatty acid content
and poorly made silage.
Fat cow syndrome
Whilst ketosis is commonly caused by a deficiency of nutrients during early lactation, an
excess of nutrients prior to calving can also cause metabolic disorders. Fat cow syndrome
commonly occurs in cows fed diets during the dry period that contain too much energy.
Displacement of protein and fibrous feed ingredients by energy substrates further
imbalances the diet and gives rise to secondary deficiencies. Fat cows typically show a
high incidence of difficult and premature calving, retained placenta, uterine infections,
mastitis, and displaced abomasum. Fat cows may refuse to eat during early lactation, and
this can precipitate both ketosis and milk fever. An excess of energy during pregnancy
results in fast growth of the fetus, but the imbalanced nature of the diet soon results in
22
fetal stress that induces calving at an early date. While the maturation of the fetus is
speeded up, the maturation of the placenta is not, and it is still relatively immature when
the cow gives birth. As a result, it is unable to detach from the uterus as would normally
occur after birth of the calf. Retention of the placenta can easily lead to uterine infections.
As a consequence of the nutritional stress imposed by an imbalanced diet, the immune
system of both the cow and calf are compromised, leading to increased susceptibility to
mastitis in the cow and to neonatal diseases in the calf. When the inclusion of excess
energy-containing feedstuffs (concentrates) has replaced and lowered the fibre content of
the diet, gas is formed in the abomasum (true stomach) of the animal and can cause it to
be displaced and even twist, leading to pain and ultimately death. Fat deposition in the
liver can lead to liver damage and as a consequence, impaired secretion of the hormones
and nutrients needed to ensure early re-conception. Fat cow syndrome is most often
observed in systems where cows are not grouped according to production state and where
the same diet is fed to both dry and lactating cows. In order to avoid this metabolic
disorder, high-producing cows should be fed a balanced diet during the dry period at
levels that result in a condition score of 3.5 at calving.
Milk fever
Milk fever is typically caused by a combination of a dietary excess before calving, a
deficiency after calving and an imbalanced diet. The immediate cause of milk fever is a
sudden decrease in blood calcium concentration caused by a loss of calcium in colostrum
during the first few days after calving. Because calcium is essential for nerve functioning,
symptoms include excitement, in-coordination, weakness, and eventually the classical
symptom of a cow that is unable to rise and lies with her head swung back onto the side
of the chest. Between 60 and 70% of cows die if left untreated. Because calcium is
necessary for muscle tone, teats fail to close tightly after milking resulting in a higher
incidence of mastitis, impaired contraction of the uterus results in uterine prolapse and
retained placenta, and impaired contraction of the abomasum (stomach) may give rise to
displaced a abomasum. In addition, feed intake decreases, making cows with clinical or
sub-clinical milk fever more susceptible to ketosis. High levels of dietary calcium in the
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period before calving decrease the activity of hormones necessary to mobilize calcium
from bone reserves making them relatively ineffective when the sudden demand for extra
calcium arises with birth of the calf and colostrum secretion. During early lactation, a
dietary imbalance between minerals classified as cations and anions also increases the
alkalinity of the blood and impairs the secretion of hormones responsible for absorption
of calcium from the gut and mobilization of calcium from bone reserves. Scientifically
formulated diets for the dry (anionic diets) and the lactating cow, containing the correct
levels of calcium in the correct balance with other minerals, together with a professionally
designed feeding schedule for the transition period just before and after calving are
essential to realise the genetic potential of the high producing dairy cow.
Acidosis and laminitis
Acidosis is a common cause of low milk production in cows fed high energy diets. Signs
of chronic acidosis are easily seen as ridges on the hooves of animals and an increased
incidence of lameness or hoof problems in the herd. High energy diets, particularly when
insufficient roughage is consumed, increase the acidity of the rumen (first stomach). The
rumen is inhabited by millions of micro-organisms that are responsible for the breakdown
of fibrous plant material into end-products that can be absorbed and used as energy
substrates by the cow. These micro-organisms begin to die when the rumen becomes acid,
and undesirable acid-tolerant species take their place. Eventually the lining of the rumen
becomes damaged and toxins enter the blood stream, leading to liver abscesses and
damage to the tissues of the hoof. As high energy diets are necessary to realise the
potential of dairy cows of superior genetic merit, it is essential that the formulation,
physical characteristics and feeding regime of the diet fed to these animals is designed by
a nutritionist.
11. REFERENCES
24
BEEDE, D.K. AND PILBEAM, T.E. 1998. Anion, Vit. E and Se supplementation for
close up dairy cows. In: Western Canadian dairy seminar,1998, page 19. J.J. Kennelly
ed. Univ. Alberta, Edmonton, Alberta, Canada.
LINN, J.G., HUTJENS, M.F., SHAVER, R., OTTERBY, D.E., HOWARD, W.T. AND
KILMER, L.H., 1994. Feeding the dairy herd. University of Minnesota Extension, St
Paul, MN
NATIONAL RESEARCH COUNCIL (NRC), 1989. Nutrient requirements of dairy
cattle. 6th
Rev. Ed. Natl. Acad. Sci., Washington, DC.
STONE, B., CHASE, L.E. AND OVERTON, T.R. 1999. Feeding high producing herds.
A supplement to Hoards Dairyman, Sept. 25. W.D. Hoard and Sons Co., Fort Atkinson,
Wisconsia, U.S.A.
WATTIAUX, M.A. AND HOWARD, T.W. 1994. Nutrition and feeding technical guide.
The Babcock Institute, University of Wisconsin, Madison, Wisconsin, USA.
