Managing the High Genetic Merit Cow
Limin
Kung, Jr., Ph.D.
Ruminant Nutrition & Microbiology Laboratory
Department of Animal & Food Sciences
University of Delaware
Newark, Delaware
U.S.A.
Introduction
In many areas of the world, producing milk economically has
become a major challenge for many reasons that include over-production,
inadequate distribution of the end product, low and/or volatile pricing,
competition from other countries, quota systems and inadequate pricing
and marketing schemes. Fluctuations
in milk prices have caused havoc in the U.S.
For example, in 1999 producers were paid as much as 22 to 25
pence/kg of milk but at the time of writing this article, milk prices
were less than 16 pence/kg. In
developed countries, the trends for fewer farms, more cows per farm, and
increased milk production per animal has been occurring.
In the U.S., between 1988 and 1998, the total number of dairy
farms decreased from about 205,000 to 118,000 (> 40% decrease) and
the number of milking cows decreased from over 10 million to about 9.1
million (9% decrease). However,
during the same time, average milk production per cow has increased from
6400 kg to more than 7900 kg/yr. (>20% increase).
It is not uncommon to find herds in the U.S. that average more
than 1,000 milking cows that produce on average more than 11,000 kg per
305-d lactation. Top
producing herds produce in excess of 14,000 kg of milk/cow/year.
Meeting the nutrient requirements for such high levels of milk
production coupled with low milk prices demands attention to details and
increased management of nutrition and environmental factors.
The aim of this paper will be to highlight some management
strategies that have taken place in the U.S. that address these needs.
Not all of the practices may be applicable in the U.K. due to
climate or market structure. However,
it is the hope of this author that this paper will stimulate dairy
producers to think about the multitude of management tools that are
available to them to improve the efficiency and production of milk and
to implement appropriate strategies for their particular situations.
Debates have taken place comparing the wisdom of striving for
high levels of milk production compared to striving for the most
efficient (and greatest profit returning) production of milk.
In areas of the world where milk production is based on pasture,
certainly striving for efficiency has been a winning strategy.
However, where pasture based dairying is limited because of
weather (e.g., North America and Europe) and significant amounts of
concentrates are fed, achieving high levels of production usually
results in efficient dairying. Thus,
a high level of production is efficient.
Efficiency increases because of a dilution in maintenance. As an example, a cow producing 40 kg of milk has only a
single maintenance requirement and thus requires less feed and produces
less manure than two cows that produce a total of 20 kg of milk per day.
Dunklee et al. (1994) compared the efficiency of a low producing group
of cows (5753 kg milk/yr.) to a high producing group (6694 kg/yr.). The high cows produced 15.7% more milk, but had 5.6% higher
feed costs and 29.8% higher health costs.
However, total net income over the lifetime of the cows was 17.4%
greater for the high genetic merit cows.
In countries where milk production is on a quota system, high
levels of production can still be a major goal because the same amount
of milk can be produced with fewer cows.
Keeping and Utilizing Good Records
Utilizing a good record keeping system to pinpoint weak points in
a dairy operation is invaluable because evaluation of records provides
feedback to management strategies.
In the U.S., cows in herds that participate in record keeping
through the Dairy Herd Improvement Association program average
approximately 1,000 kg more milk per cow per year compared to cows in
herds that do not keep records.
Raise Healthy Replacement Heifers
Calves and heifers are frequently overlooked on farms because
they are not producing milk. However,
they are the future of each dairy farm.
On many large dairy farms in the U.S. yearly cull rates average
between 35 and 45%. In some
areas of the country, bred replacement heifers cost over 1,000 £ per animal.
In
order to raise healthy replacement heifers, cows should calve in clean
and comfortable areas. The
timing of feeding first colostrum and amount of fed are key management
tools for reducing health problems in calves.
Colostrum is high in energy, protein, vitamins (especially
vitamins A, D, E and B12) and minerals.
Colostrum also contains proteins and peptides that have potent
biological activity. For
example, quality colostrum with high concentrations of antibodies is
also high in trypsin inhibitor. Trypsin
inhibitor probably helps by inactivating enzymes that would predigest
the antibodies before absorption. Colostrum also contains a
proabsorptive factor that stimulates pinocytotic activity in the
intestinal epithelial cells, a factor responsible for lipid mobilization
that increases the concentrations of circulating free fatty acids in the
newborn calf, and insulin and insulin-like growth factors.
Researchers have also identified molecules in colostrum that have
immunomodulating activities; for example, lactoferrin.
Most importantly colostrum contains high levels of
immunoglobulins that transfer passive immunity to the calf and enables
it to fight off infections. Immunoglobulin concentration in colostrum is
highest in the first milking and decreases to 50-70% at the second
milking, to 30 to 50% by third milking and is almost zero by the fourth
milking. To ensure optimal
transfer of antibodies from dam to calf, 3 liters (2 liters for high
quality colostrum and for smaller framed cows) of first colostrum must
be fed to the calf within the first 2 to 4 hr of life and may be
administered by an esophageal tube.
This process should be repeated 12 hours later.
This should result in a calf consuming about 100 g of the
antibody IgG. Immunoglobulins
are absorbed by pinocytosis by specialized cells in jejunum and ileum of
the calf. However, with
age, these cells are replaced by basal nuclei incapable of pinocytosis.
This process is also known as "gut closure" and it
begins as rapidly as 12 hr after birth if no colostrum is fed.
When gut closure is complete, immunoglobulins cannot be absorbed.
Calf mortality increases as the interval between birth and
ingesting colostrum increases to more than 6 hours.
The environment where calves are raised is also crucial for
raising healthy calves. Calves
raised in groups are prone to passage of disease among penmates and
calves raised indoors are often subject to high rates of respiratory
infections. Raising calves individually in hutches or in pens where
contact among animals is prohibited can reduce health problems. Hutches should be faced away from the prevailing winds and
bedded with clean straw. Hutches
should also be placed on a bed of gravel and slopped away from the
entrance to assist in drainage. Calves
in hutches should not be able to physically touch one another.
Sanitation of feeding equipment will also reduce spread of
disease in young calves.
Understanding Rumen Function
The
rumen is an environment with a diverse population of microorganisms.
Bacteria and protozoa dominate the fermentation both in terms of
numbers and metabolic processes. Of
the bacteria present in the rumen, several general types of bacteria can
be described based on metabolic functions.
For example, amylolytic bacteria specialize in fermenting starch
(from concentrates) while fibrolytic bacteria ferment fiber.
Different populations of bacteria will dominate the rumen
fermentation depending on the type of diet being fed.
Cattle fed diets solely of forage with high fiber will have a
ruminal bacterial population that is high in fibrolytic bacteria.
Simplistically, the fermentation of fiber (cellulose and
hemicellulose) results in the production of acetic acid that is used by
the cow for energy and is the primary precursor of fat in milk.
In contrast, digestion of sugars and starches yields propionic
acid that is converted to glucose in the liver of the cow and used for
energy.
The
amount and size of fiber particles in the diets of lactating dairy cows
is important to maintaining optimal rumen function.
Long fiber in the rumen forms the rumen “mat”. The mat is where fibers are entangled because they are too
long to pass to the lower gut. Fiber
from the mat is regurgitated and chewed producing large amounts of
saliva that naturally buffers the rumen.
When large feed particles are chewed, the surface area for rumen
bacteria to attach and then digest the feed is increased.
In order for a feed particle to pass out of the rumen and into
the lower gut, it must attain a size of about 1-mm!
Passage of particles from the rumen is important because without
digestion and passage, food would fill the rumen and depress intake.
There must also be a balance between retention time in the rumen
for microbial digestion and passage.
For example, grinding fiber to extremely small particles may
assist in passage from the rumen but ruminal digestion of that fiber
particle may actually be decreased if it passes too quickly.
The normal process of particle size reduction in the rumen leads
to increased surface area for microbial attachment and digestion.
The pH of the rumen has
profound effects on the growth of rumen microbes and the digestion that
takes place in this forestomach. A
pH of 7 is considered neutral, where the amount of acid and base are
equal. When pH falls below
7, we consider the medium to be acidic in nature.
The lower the pH falls below 7, the more acidic it is. A number of different factors can affect ruminal pH.
Lack of sufficient fiber or fiber that is chopped too finely,
reduces chewing times and thus reduces saliva production causing a
decrease in ruminal pH. Cows
fed a diet with long fiber particles chew for more than 10 hours,
ruminate for about 6 hours, and can produce as much as 50 gallons of
saliva per day! The ratio
of forage:concentrate in the diet of lactating cows also affect ruminal
pH. As concentrates
increase in the diet, total acid production in the rumen increases
causing a decrease in pH. In
contrast, feeding buffers, especially in high acidity silage-based
diets, can increase ruminal pH. The
type of concentrate can also affect ruminal pH as the starch in barley
is more readily fermented to acids in the rumen than the starch from
maize. Besides requiring
carbon skeletons, ammonia-N and energy for growth, fibrolytic bacteria
in the rumen grow best when the pH of the rumen is between 6.2 and 6.8. If rumen pH falls below 6.0-6.2, fiber digestion in the rumen
begins to decline. As rumen
pH decreases, fibrolytic bacteria in the rumen become less active and
fiber digestion is decreased. When
ruminal pH falls below 5.8-5.9, the rumen is mildly acidic and fiber
digestion in the rumen ceases completely. When rumen pH drops below 5.2
to 5.5, animals can succumb to acidosis.
Common signs of acidosis include laminitis (cows with swollen
feet and hocks), low milk fat tests (< 3.1% fat), cycling intakes, a
high incidence of displaced abomasums, loose manure, reduced cud
chewing, and excess consumption of free choice buffers.
Because the digestion of fiber in the rumen leads to acetic acid
production, and because acetic acid is a major precursor for milk fat,
reduction in ruminal fiber digestion leads to a decrease in milk fat
test. Thus, any factor that
helps to maintain ruminal pH above 6.0 is generally beneficial.
For example, feeding a total mixed ration (TMR) helps to moderate
decreases in ruminal pH that occur after feeding.
Ration Balancing
Working with nutritionists to balance the nutrient requirements
of animals should be done on a regular basis.
The DM content of silages should be monitored frequently
especially when silage in the clamp is not uniform or when changing to
new silage. On some farms,
the DM content of the silages is done on a weekly basis using a
microwave or other DM determining device and adjustments made as needed.
Energy. Every
1-kg increase in peak lactation results in a 200 kg increase in milk
over the entire lactation. Thus,
in order for cows to maximize their peak milk in early lactation,
attention must be paid to meet all of the nutrient requirements for milk
Specifically, energy density of the diet is crucial because
intake of energy and protein is less than required in early lactation.
High genetic merit cows may require 1.7 to 1.8 Mcal of Nel
per kg of DM (7.1 to 7.5 MJ/kg of DM).
To ensure adequate rumen energy, fermentable nonfiber
carbohydrates (NFC) should be between 35 and 40%.
Fat should be limited to about 4 to 5% of the DM during very
early lactation because some research has shown that higher levels
actually depress intakes. The
concentration of fat in the diet can be increased to 6 to 7% with the
use of rumen inert fat after about 6-7 weeks in milk but in many
instances the economics of this practice becomes questionable if milk
production is less than 25 to 30 kg/day.
When feeding high levels of fat, the calcium and magnesium
content of the diets should be increased to about 1.0 and 0.35%,
respectively because fat tends to tie up some of these minerals.
Protein.
Crude protein for high genetic merit cows producing more than
35 to 40 kg of milk/day may have to be as high as 18 to 20% of the
dietary DM. Undegradable
protein should be between 35 and 40% of the total CP but rumen
microorganisms still have requirements for nitrogen so adequate amounts
of soluble protein (30 to 35% of CP) must be present.
Ruminally protected amino acids, specifically lysine and
methionine, have been tested but except in very obvious conditions,
models that predict their shortages have not been very accurate.
More refining of the models will be needed before these products
can be broadly recommended. Current
recommendations suggest balancing for a lysine:methionine ratio of 15:5
(Schwab, 1995).
Fiber. Unfortunately, fiber is an ingredient in diets that is not
well defined. The National
Research Council (1989) recommends a minimum dietary ADF content of 19
to 21% and NDF content of 25 to 28% (dry matter basis) for lactating
cows (NRC, 1989). However,
these fiber requirements do not account for the form of fiber, particle
length, rate or extent of digestibility, or interactions of fiber with
other dietary components. To
account for this lack of knowledge, the NRC suggested that 75% of the
dietary fiber should be from traditional forage sources (e.g. maize
silage, lucerne or grass hay or silage).
Forage NDF should equal 1.2% of BW.
The assumption is that traditional forage sources should consist
of large particles that would encourage chewing.
However, many nonforage fiber feeds have high fiber contents but
because particle size is small, they are chewing is decreased, resulting
in low production of saliva. For example, imagine grass silage that may be 4 to 8 cm long
compared to a piece of soyhull that is perhaps 1 cm or less long.
Which feed would stimulate more chewing and saliva production?
Having 75% of the fiber requirement in a diet from traditional
forage fiber does not always insure that cows will chew and produce
sufficient saliva for good rumen function because the length of chop may
be highly variable. Silage
can be chopped too finely at harvest and/or reduced in size due to over
mixing in a TMR.
Because chemical fiber (what is analyzed
for and usually balanced for) does not take into account particle size,
the term “effective fiber” has been used to better define the fiber
requirements of dairy cows. The
need for effective fiber becomes critical for high genetic merit cows
that are fed high proportions of concentrates.
Effective fiber stimulates rumination, chewing, and saliva
production. It also
maintains a normal fat test, normal rumen pH, and normal rumen mat.
Balancing diets for effective fiber becomes more important as
cows increase their productive levels and therefore require more
concentrate and less forage in their diets.
General guidelines have been proposed to maintain adequate
effective fiber in the diets for lactating dairy cows.
Maize silage and lucerne silage should be chopped at a
theoretical 0.95 cm (3/8-inch). For
kernel processed maize silage, the theoretical chop length can be
increased to 1.90 cm (¾ inch). Several
methods exist to quantitatively measure effective fiber in dairy cattle
diets. Most of these
methods are based on separation of particles by size.
The Pennsylvania State Separator is commonly used in the
Northeast region of the U.S. and consists of three boxes with several
screens (Heinrichs et al., 1999). After
shaking a measured sample, forage is separated into 3 fractions: top
screen, middle screen and bottom box.
I believe that the most important time for use of a particle size
separator is before harvesting of forage for silage in order that proper
settings can be made for chopping.
Next, separator boxes are useful for assessing what cows are
actually receiving at the feed bunk.
For consulting nutritionists and extension agents, the separators
are good teaching tools when used on farm.
Water. Water is an often over looked nutrient requirement but
remember that milk is 87% water and thus when a cow produces 40 kg of
milk, she is excreting about 35 kg of water.
The most important factors affecting water consumption include
quality, accessibility, and flow rates, DM intakes and ambient
temperatures. Very few
farms routinely check water quality but should because high levels of
nitrates (> 500 PPM N03), sulfates (> 1,000 - 5,000 PPM), and
coliform counts can have negative effects on milk production.
Cows should have access to a waterer about every 15 m and
preferably near feed. Cows like to drink and eat intermittently.
For best consumption, there should be at least 1 waterer per 20
cows. Water should be
available immediately after milking since cows will drink about 30% of
their water requirements within an hour after milking.
Water temperature of between 15°
and 27°C
appears to be most acceptable.
Forage Quality
Excellent
quality forage stimulates DM intakes, promotes good rumen fermentation,
and thus results in high levels of milk production. The benefits of good quality forage cannot be fully
substituted by increasing the nutrient density of the concentrate (Kawas
et al. 1991).
Attention
must be paid to harvest forages at the optimal stage of maturity to
attain the best mixture of nutritive value and yield.
Processing maize silage has improved its nutritive value and
improvements appear to be greater as the plant matures.
Because a significant amount of forage is stored as silage, silo
management is also important to achieve and maintain high quality
silage. Where weather
permits, wilting to appropriate DM levels, rapid filling, good packing,
and sheeting of clamps can have profound affects on silage quality.
Research has also shown that use of an proven microbial inoculant
can improve silage quality, increase DM and nutrient recoveries, and
increase milk production (Kung and Muck, 1997).
An impressive number of animal experiments have been conducted
using a single silage inoculant containing Lactobacillus
plantarum MTD1. A
summary of 14 lactation studies conducted in University and
government research institutes in North America and Europe showed that
DM intake was increased by 4.8% and that milk production was increased
by 4.6% when cows were fed inoculated silage (Moran and Owen, 1994).
On
newer dairy farms, care must be taken when planning the size of clamps
to ensure adequate daily removal of silage in order to prevent heating
in the silo. When
conditions lead to poor-quality silage, measures should be taken to
minimize their contribution to the diet.
Avoid feeding moldy silage to cows at all costs!
Feed Additives
A number of feed additives have been useful in dairy herds to
achieve high levels of production.
Supplementing 6 to 12 g of niacin in the dry period and early
lactation have been shown to reduce the incidence of ketosis.
Feeding glucose precursors in some cases has been shown to
improve metabolic status and milk production in early lactation.
For example, cows fed 114 g of a calcium propionate based
additive 10 days prior to calving and into early lactation, produced 5.6
kg more milk per day than did control cows (Lopez et al., 1999).
Research is needed to assess whether mode of feeding (bolus
drenching versus feeding in the diet) is critical to achieving a
response. Christensen et al. (1995) reported that feeding propylene
glycol as part of the feed was not as efficacious as when it was fed as
an oral drench or part of a small grain mix.
More research is needed to prove that these practices are
economically feasible.
Feeding 150 g of sodium bicarbonate and 50 g of magnesium oxide
during early lactation has helped to keep the rumen pH in a zone for
optimum fiber digestion (see previous discussion).
This practice has been most useful in diets based primarily on
maize silage or in diets high in concentrates.
In the
rumen, feeding yeast has been shown to stimulate fiber-digesting
bacteria and possibly increase the metabolism of lactic acid.
Although added yeast do not multiply quickly enough to establish
a population they are metabolically active in rumen fluid (Kung et al.,
1995). In a review of 32
lactation studies conducted with yeast (Saccharomyces
cerevisiae) between 1986 and 1997, feeding cows a yeast supplement
increased milk production on average by more than 1.13 kg/day (Kung,
1998). During the same
period there were 26 comparisons where fungal extracts (from Aspergillus oryzae) were fed to lactating ruminants, but the
increase in milk production averaged only 0.45 kg/day.
Total
Mixed Rations and General Feeding Practices
The method of feeding cows TMR has become a common practice
especially in larger herds. The concept suggests that offering feed as a
TMR supplies a "balanced" bite of the diet with every mouthful
consumed and minimizes fluctuations in the rumen environment (primarily
pH) that can occur when grain is fed in large slugs thereby improving
rumen fermentation and animal production.
Feeding a TMR does have the advantage of masking unpalatable
ingredients.
Fresh feed should be available for cows at
all times. On many dairy
farms, feeding 2-3 times per day with additional "pushing up"
of uneaten feed is common practice.
It is especially important that feed be available immediately
after milking since this is when cows tend to have good appetites.
Eating after milking will also keep cows standing while the teat
sphincter muscle has time to close after milking and that will lower the
incidence of mastitis. At
the end of a 24-hour period, uneaten feed should be removed and replaced
with fresh feed. Mixing left over feed with fresh feed is not acceptable
especially during hot weather where feed may spoil in the bunk.
(Eating from a "clean plate" is more enticing than
eating from a dirty one!) Feedbunk
surfaces should be smooth and not rough to encourage eating.
Cows fed in a group must have adequate feeding space to prevent
excessive competition from pen mates.
Although research data varies, supplying at least 0.2-0.3 m of
feed space per cow is a good starting point and 0.6 to 0.7 m/cow is
better. Certainly at any
one time, at least 70 to 80% of cows in a group should have access to
feed. Grouping cows
according to milk production and feeding TMR matched to requirements are
key factors to maximize nutrients to high genetic merit cows and to
avoid overfeeding of lower producers in later lactation.
Balancing for the nutrient requirements of the top 30% of a group
ensures that nutrients are not limited for high producers.
Physically moving cows among production groups has posed problems
on many large dairies because of pecking orders and social interactions
among cows. Thus, in many dairies nutrient densities of the TMR are
changed within groups. As
milk production increases on dairy farms where milk production is in
excess of 11,000 kg of milk/cow/yr., cows are being fed a one group TMR
for the entire lactation. Providing
a separate group for first calf heifers is an increasingly common
practiced because these animals are smaller in stature and less
competitive. Although the
concept of feeding a TMR is well established, several problems still
exist. Recently, sorting of
feeds from a TMR has been shown to result in an increase in the
proportion of long particles left in the feed bunk throughout the day
suggesting that cows were not consuming balanced bites of feed.
Whether the rumen is able to compensate for such fluctuations
must be determined in future studies.
Another problem that is common is that excessive mixing in the
TMR can result in significant particle size reduction.
Load cells on TMR mixers should be checked for operation and
calibrated on a regular basis.
When a TMR is not fed, consider feeding forage before grain and
limiting the amount of grain that can be consumed in any one meal to
about 2 to 3 kg. In
addition, grain should not be too finely ground or processed when fed
separately from forages.
Managing the Environment
Managing the environment
around the cow can help it to reach its genetic potential for high
levels of milk production. For
example, at about 21°C,
milk production declines about 0.7 to 0.9 kg for about each 0.5°C
rise in temperature. Thus,
in areas where relative humidity is low and temperatures are high,
evaporative cooling has improved milk production and reproduction
(Armstrong, 1994). Newer
freestall barns are being designed to maximize ventilation (no solid
walls), and include fans and misters above the feeding areas and in the
holding pens at the entrances of the milking parlors.
Good air quality free from ammonia and stale odors is
recommended. In humid
climates, care must taken so that added water used for cooling does not
aggravate the temperature- humidity index.
Freestall
design should also be optimize to ensure that cows have stalls that
maximize cow comfort and minimize leg and hoof problems.
Eighty to ninety percent of cows should be lying and chewing
their cuds within two to three hours after milking.
Cows that do not use freestalls will lie in alleys with manure
that may result in higher incidences of mastitis.
The flooring of barns must also be designed to ensure good
footing for animals. This
will maximize mounting behavior and minimize damage to feet and hocks.
Also, cows should not spend more than 45 to 60 minutes in the
holding pen before milking. During
times of heat stress, adequate movement of air through the holding pen
area improves cow comfort.
A significant amount of research has
documented the fact that increasing the photoperiod above that found
from natural day length during the fall and winter months, resulted in
increased milk production. Although
the exact mechanism is unknown, light stimulates the pineal gland that,
in turn stimulates the liver to produce the hormone insulin like growth
factor-1 that may be responsible for improvements in milk production
(Dahl et al., 1998). A long photoperiod (14 to 18 hours of light providing 10 to
30 footcandles of light at the eye-level of the cow) improved milk
production by an average of 10% from seven published studies. Feed intake also increases by about 6% when photoperiod is
increased. The production
response to light is gradual and takes about 4 weeks.
In order to maximize the effect of prolonged photoperiod, cows
must have a 6-8 hour period of "darkness" (a low level of
lighting may be maintained for safety and cow movement).
In low ceiling barns (4 to 5 m), fluorescent lighting can be
economical, but in barns with high ceilings (> 10 m), high-pressure
sodium or metal halide are the preferred source of light.
Based on the increases in milk production and feed intake cited
above, milk at 17 pence/liter, and energy costs of about 10 pence/kWh,
the net return is about 20 pence per cow/day.
Considering the initial cost of installation, improving lighting
can pay back within a year to a year and a half.
In addition to production increases, improved lighting can
improve the detection of estrus, increase the quality of labor, and
facilitate human and animal movement through the barn.
Milking Frequency and Procedures
Certainly, high levels of milk can be
achieved when cows are only milked twice daily, but as milk production
increases, pressure and other factors within the mammary gland increases
and may limit production of milk is not removed at regular intervals.
In the state of Arizona, the top five farms (average of 11,900 kg
of milk/yr.) milk three times a day (Ax and Loper, 1999).
Similarly, four of the top six herds in the state of Wisconsin
(average of 14,170 kg of milk/yr.) milk three times a day (Gunderson et
al., 1999). Increasing to
three times a day milking typically results in an increase of 8 to 15%
more milk but increases as high as + 30% to actual negative effects (-2%
decrease in milk) have been observed.
These findings indicate that there are strong interactions
between increased milking frequency and management factors (Gisi et al.
1986). When switching to three time a day milking, remember that
cows will have increased nutrient requirements and DM intakes should be
adjusted to meet production needs.
Special attention must be given to body condition scores or cows
will dry off in poor flesh and not milk well in the next lactation.
Consistency
in prepping the cow before milking and the milking procedure will also
help to minimize somatic cell counts and maximize production. Machine attachment should be made within 1 to 1.5 minutes
after stimulation. Routine
checks of inflations and pulsation ratios must be part of a
comprehensive maintenance plan.
Managing the Transition Period
Consumption of dry matter (DM) is relatively low in the dry
period and decreases dramatically about 1-3 days prior to calving.
Coupled with high levels of milk production and low dry matter
intakes in early lactation, cows are in negative energy balance.
Thus, methods to maximize energy intakes during the transition
period (about 2-3 weeks prior to calving) may be helpful (Grummer,
1995). In a unique
experiment, Bertics et al. (1992) force fed a diet to cows during the
transition period through the rumen fistula to prevent the anticipated
decrease in intake that occurs before calving.
Upon calving, these cows produced more milk than companion cows
that were not force fed. Although
not always supported by research studies, "steaming up"
(increasing the energy density of the diet) in the transition period
(about 2 to 3 weeks prior to calving) has been an advisable practice for
several years. During steam
up an increase in concentrates to 5 to 6 kg/day with forage may help to
improve energy balance, stimulate absorptive function of the rumen
papillae, stimulate, and adapt rumen microbial populations to more
starchy feeds, and accustom cows to the milking diets.
Dietary components in the ration for cows in the transition
period with DM intakes of about 10 to 11 kg/day should be 1.5 to 1.6
Mcal Nel/kg of DM (0.62 to 0.68 MJ/ kg of DM), 14 to 15% CP,
33 to 38% undegradable intake protein (% of CP), 3 to 4 % fat, and a
minimum of 31% NDF.
Many
metabolic diseases in early lactation also have a start during the dry
period. Adjusting the
dietary cation-anion balance during the transition period has been used
successfully in some diets to prevent milk fever in early lactation
especially when diets have been high in calcium or potassium (Joyce et
al., 1997). Feeding diets
that are slightly anionic may help to mobilize calcium during early
lactation. The dietary
cation-anion difference (DCAD) should be approximately –10 to –15
milliequivalents per 100 g of dietary DM.
The DCAD can be calculated by the following equation:
milliequivalents of [(% K in DM/0.039) + (% Na in DM/0.023)] –
[(% Cl in DM/0.0355) + (% S in DM/0.016)].
Because a negative DCAD is an indication of acidification, urine
pH can be measured to assess the DCAD balance.
In the week prior to calving, urine pH in Holstein cows should be
between 5.8 and 6.8. If
urine pH is below 5.5 to 5.7, this is an indication of over
acidification that can lead to depressed intakes.
Monitoring Cow Parameters
Several
tests have recently helped to identify general feeding problems in the
herd. Strict guidelines
should be followed when evaluating such tests because there are numerous
factors that can affect the specific values for a cow and they could be
easily misinterpreted. Rumenocentesis,
or collecting ruminal fluid via a small needle puncture into the rumen,
can be done on farm to measure ruminal fluid pH.
Rumen pH values should average between 5.8 and 6.5.
Consistent ruminal pH values of less than 5.5 to 5.6 suggest
excessive intake of fermentable carbohydrates that could lead to
acidosis.
Milk
urea nitrogen (MUN) has also been used as a tool to identify problems
associated with nitrogen and/or degradable nonfiber carbohydrates (NFC)
in the diet (Jonker et al., 1998).
Although not measured on farm, many milk-testing labs offer MUN
testing as a service. Normal
herd average MUN values range from 12 to 18 mg/dl of milk.
Excessively high MUN may indicate that protein is too high, that
rumen fermentable NFC is too low, or that the percentage of degradable
protein is too high. In
contrast, a low average MUN for a group of cows indicates inadequate
protein in the diet, or too high a percentage of undegradable protein.
Some
nutritionists and veterinarians have measured the non esterified fatty
acid (NEFA) concentration of blood after calving, but no on farm test
kit is available. The NEFA
concentration is a measure of fat mobilized from the body tissues. After calving, NEFA levels should be less than 700 micromolar
seven days after calving and less than 300 micromolar three weeks after
calving. High levels of
NEFA indicate excessive deficits in energy balance (Drackley, 1999).
Body scoring can be recorded on farms to
manage high genetic merit cows. Fat
cows are prone to many metabolic problems in early lactation including
poor appetites and ketosis. Thin
cows have minimal body reserves to mobilize during times of negative
energy balance and thus are also prone to many metabolic diseases.
In the U.S., we recommend drying cows off in a body condition
score of about 3.25 to 3.5 (1 = too thin; 5 = too fat).
Adjustments to the diet to meet condition targets should be made
during the lactation and not the dry period.
During lactation, the goal is to minimize the loss in body score
to not more than 0.5. Cows
should be condition scored at calving, 4 to 6 weeks after calving, in
mid lactation, and at dry off.
Creatures of Habit and the Human Factor
The picture of a "contented cow" is always a pleasing
one, and in fact does have some real basis for discussions.
Cows are creatures of habits and when content, can produce large
amounts of milk. If
calves are handled when they are young, they will be easier to control
in their adulthood and less nervous around people and equipment.
Cows that are skiddish in nature are more stressed.
Avoid harsh physical treatment of your cows; treat them with
kindness and respect.
Summary
In developed countries where the average milk production of cows
continues to increase, attention to management and nutritional details
becomes increasingly important in order to maximize the efficiency of
milk production. There are certainly other aspects of managing dairy
cows that can have large impacts on production that were not covered by
this review. In conclusion, traditional aspects of nutrition management
will help to improve the efficiency of dairy production but dairy
producers should also consider managing the environment to enhance cow
comfort and analyzing cow behavior to better understand the cow.
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