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Author: R. Parker, Dairy Cattle Specialist - Ontario - Ministry of Agriculture and Food -
Introduction
There are six key times during the yearly cycle when each cow should have her
condition evaluated. These occur: midway through the dry period, at calving, and
at approximately 45, 90, 180 and 270 days into lactation. The timing of the checks
coincides with the time for making important decisions about the future feeding,
breeding and health management of the cow. The following describes specific goals
with regard to body condition for each stage of the lactation cycle.
Dry Period
The goal for ideal body condition score for the dry cow is 3.5. To achieve satisfactory
health and performance early in the subsequent lactation condition score must
fall between a minimum of 3 and a maximum of 4.
It is a well accepted fact that cattle, replenish body fat reserves more efficiently
while lactating than during the dry period. Occasionally a cow must be dried
off before an acceptable condition score is reached. It will pay the manager
to continue to feed underconditioned dry cows for gain, to achieve a desirable
body condition score. Obviously, a well managed feeding program combined with
frequent observation is required to achieve condition gain without overfattening
the dry cow.
Average quality, long stemmed grass hay has proven to be the ideal forage for
the dry cow. Higher quality (energy and protein) forages, such as corn silage
and alfalfa haylage, must be limit fed to prevent excessive condition gain.
With correct forage quality and quantity, a low-energy high-fiber supplement,
containing appropriate protein, mineral and vitamin levels, could be fed in
controlled amounts to achieve the desired amount of gain.
Removing excess fat from overconditioned cows by limiting energy intake during
the dry period does not appear to seriously impair subsequent performance.
Early-Lactation
The cow should be evaluated frequently during early lactation. It is then that
body condition, as it reflects energy reserve, has its greatest impact on the
health, production and fertility of the dairy cow.
The cow freshening overweight, with a condition score of more than 4, is at
greater risk of fat cow syndrome problems such as difficult calving, retained
placenta, metritis, mastitis, displaced abomasum, ketosis and milk fever. Her
immune response is usually inadequate to combat the stress of calving and appetite
is less than ready to meet the demands of early lactation.
Another situation occurs when the cow starts lactation without enough energy
reserve, having a condition score of less than 3.
This cow may experience fewer health problems at calving but her later productive
and reproductive performance will be less than expected.
As shown in Figure 1, the average cow commonly peaks in milk production at
4 to 6 weeks into lactation. Her feed (dry matter) intake lags behind, normally
peaking at about 9 to 11 weeks. This situation puts the cow in a negative energy
balance for several months in early lactation. This means that feed energy intake
is less than milk energy output. The cow uses available body fat (tissue energy)
reserves to cover the shortfall.
Figure 1. - Typical Energy Curves for the
Lactating Dairy Cow
The cow starting lactation in thin condition lacks adequate energy reserve and
she will peak at a lower milk yield. Peak milk yield is directly related to
total lactation yield with mature cows. For each additional kilogram of milk
at peak there will be approximately 200 more kilograms of milk over the whole
lactation. Undercondition at calving is also a cause of low milk fat test. In
early lactation, a high proportion of milk butterfat precursors originate from
body fat stores.
The average mature cow calving in desired body condition, with a score of 3.5
(4 maximum), and in good health, can be expected to lose between one-half and
one kilogram of body tissue per day during the first 60 to 80 days in milk.
One kilogram of body tissue (mostly fat) can supply 4.92 megacalories of energy
(NEL) . At 3.5% butterfat, milk contains about .69 megacalories of energy (NEL)
per kilogram. Therefore, one kilogram of body tissue can provide the energy
to produce 7.1 kilograms of milk. The loss of 70 kilograms of fat by the average
mature cow translates into the production of nearly 500 kilograms of milk -
over than supported by feed energy intake.
During the first two months in milk the average mature cow will drop between
1/2 and 1 full point in condition score, stabilizing at a score near 3 by the
10th week and beginning to regain lost condition by the 90th day. At this time,
rising feed energy intake can satisfy the declining milk energy demand. This
coincides with the optimum period for observation of regular estrous activity,
breeding and conception.
Experience and research have shown that cows gaining weight (in positive energy
balance) at the time of service have a higher conception rate than cows losing
weight. A condition score between 2.5 and 3.5 would indicate adequate condition
for good reproductive efficiency.
Very high producing cows may drop to a score near 2.5 before stabilizing, having
lost up to 1.5 kilograms of tissue per day. They may be into the 4th month of
lactation when this occurs. The expression of estrus and fertility may be suppressed
in these cattle, resulting in delayed conception. Cows with good production
that demonstrate no or little condition loss in early lactation are most likely
very efficient feed converters. Cows that gain condition at this stage are probably
poor producers.
Low energy intake in early lactation can lead to excessively high rates of
fat mobilization of greater than 1.5 to 2.0 kilograms per day. This increases
the risk of the accumulation of fat in the cow's liver, and can lead to ketosis,
increased susceptibility to disease, a delayed return to estrus and reduced
fertility.
The feeding program for cows in early lactation must therefore be carefully
managed to achieve maximum dry matter intake and ration digestibility. Adequate
amounts of protein are critical to stimulate intake and provide nutrients (amino
acids) for milk production. The cow has limited body protein reserves to draw
from.
Cows in early lactation will consume about 10% less dry matter than cows at
the same level of production in mid-lactation. Therefore, providing enough protein
to meet the requirement for peak milk means that the ration protein content
will be in the range of 18 to 20% of the dry matter. Ideally, 40% of the protein
should bypass rumen degradation and provide the amino acids that are limiting
to milk production.
A compromise must be met between providing the fresh cow with large amounts
of highly digestible and rapidly fermented grain starch for energy and providing
adequate forage fiber to maintain rumen function and butter-fat synthesis.
The ration should be formulated to provide 72 to 75% Total Digestible Nutrients
(TDN) or 1.61 to 1.67 megacalories per kilogram of Net Energy for lactation
(NEL) . Total ration fiber levels should be between 19 and 21% acid detergent
fiber (ADF) and between 25 and 28% neutral detergent fiber (NDF). A minimum
of 21% of the total ration dry matter should come from forage NDF. Ideally some
of the forage should be in the form of hay to provide stimulation for optimum
rumen function.
Mineral and vitamin levels in the ration should be balanced to currently recommended
standards.
Following recommended feeding management practices will also help maximize
dry matter intake, eliminate the risk of cows going off-feed, and reduce the
cow's dependence on body fat reserves.
These practices include:
- lead feeding grain to the dry cow for 2 weeks, increasing to a maximum
of 1% of body weight at calving,
- challenge feeding grain and protein supplement to the fresh cow, increasing
gradually to the recommended maximum advised by ration formulation, by
three weeks into lactation,
- feeding concentrates in meals of less than 4 kilograms, more frequently
(i.e. 4 times) per day,
- feeding the highest quality forages available,
- following the feeding sequence of forage before grain and grain before
protein supplement, ideally with some time delay between, for optimum
ration digestibility,
- feeding more often when rapid feed spoilage is a problem,
- keeping mangers and water bowls clean and free of hazards,
- chopping forages to maintain adequate particle size (greater than 1
cm) and processing concentrates as coarsely in texture as possible to
stimulate rumen function and feed consumption,
- using molasses to improve the intake of unpalatable or dusty feeds,
- using buffers, such as sodium bicarbonate at .75 to 1.0% of total dry
matter intake, to improve the digestibility and intake of high concentrate
rations,
- adding .5 to .75 kilograms/day of rumen protected fat to the cow's ration
to increase the energy density while reducing the need to rely on starch
as the primary source of dietary energy. When adding fat to the ration,
calcium and magnesium levels need to be raised to 1.0% and .3%, respectively,
and attention must be given to providing adequate bypass protein and functional
fiber in the ration.
Adding 6 to 12 grams of niacin to the ration during the lead feeding and throughout
the early lactation period will help high producing cows that freshen in desired
or heavy body condition to use dietary fat and body fat stores more efficiently.
Mid-Lactation
At about 180 days in milk, a body condition appraisal should confirm that cows
are replenishing body fat reserves that were lost in early lactation. By this
stage of lactation, condition scores should be approaching 3 for the highest producing
cows in the herd and between 3 and 3.5 for the average producing cows. Below average
cows may have already exceeded a condition score of 3.5 and will need to be fed
carefully to prevent fattening. All cows being rebred should be confirmed pregnant
by mid-lactation.
Late-Lactation
The condition score check done at approximately 270 days in lactation should show
the average cow approaching a score of 3.5. During this period, low producing
cows tend to become over-conditioned, showing scores at or above 4. This occurs
more often where large amounts of corn silage are fed and where attention is not
paid to limiting access to concentrates. Cattle fed grain in milking parlors should
be allowed sufficient time to clean their share, leaving none behind for the next
cow that occupies the stall. In tie-stall barns, manger dividers may be needed
to prevent cows from stealing unneeded grain from immediate neighbors.
Overconditioning also happens in free-stall herds fed total mixed rations where
the cattle are not adequately grouped according to production. At least 4 and
perhaps 5 lactation groups; early, mid, late, first-calf, and dry may be needed
to prevent overconditioning.
In herds where extended calving intervals prolong the period of low production
and/or the dry period, many cows will become overfat. In this situation the
breeding management needs to improve.
Very high producing and persistent cows, like first-calf heifers, with normal
calving intervals, may be difficult to get to the goal of 3.5 in condition score
while still milking. With these cows, it may be necessary to continue to feed
for gain during the dry period to frilly recharge their energy reserves.
First-Lactation Heifers
The ideal condition score for the heifer calving for the first time is about
3.0. Heifers freshening with condition scores in excess of 3.5 have experienced
more calving difficulty.
First-calf heifers need to be managed somewhat differently from their older
herdmates. They will calve with 100 to 150 kilograms less body weight than the
older cows in the herd. Their daily concentrate amount must be adjusted accordingly
to maintain correct forage-to-concentrate ratios to prevent problems related
to digestive system malfunction.
The lactation curve of a first calver does not show the early high peak that
higher lactation number cows demonstrate. Therefore, the negative energy balance
occurring in early lactation will not be as demanding on body fat reserves as
it can be for older cows.
First-calf heifers do show greater persistency of lactation than older herdmates.
The first calver will show an average drop of 4% per month in mid-lactation
compared to 8% in older cows. In late-lactation, the first calver will fall
in milk at 6 to 8% monthly while the higher lactation number cows are declining
at 10 to 14%. This greater persistency means that the heifer cannot route as
high a proportion of energy intake as can her older herdmates toward the replenishment
of body fat stores.
First and second-calf heifers also have a major additional need for energy
- for growth - throughout mid-and late-lactation and the dry period. These cattle
must gain 50 to 75 kilograms during each of the first two lactations to reach
mature body weights.
To ensure that the additional nutrients needed for growth are provided, the
standard recommendation has been to feed more concentrates to these cattle.
During the mid-and late-lactation phase the first calver should get 10% and
the second calver 5% more concentrates than required for milk and body condition
gain.
Failure to provide these extra nutrients may be the cause of heifer "burn-out".
Today's genetically superior cattle can produce large volumes of milk, even
during their first lactation. If special care is not provided, they will begin
the second lactation stunted and/or lacking adequate energy reserve.
With the mature lactation curve, typical of second lactations, adequate tissue
energy reserves are critical to achieving desirable peak milk yields as well
as satisfactory butterfat synthesis. Body size is a major factor influencing
dry matter intake. Lack of sufficient growth will limit the improvement in feed
intake needed to support higher milk yields.
As a result of inadequate management the genetically superior heifer could
demonstrate poor second lactation performance or burn-out, and may be wrongly
culled.
Correct management of energy balance throughout the lactation and reproduction
cycles of the dairy cow can significantly improve her capacity to generate profit.
Author: R. Parker, Dairy Cattle Specialist - Ontario - Ministry of Agriculture and Food -
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