The fulfillment
of this objective requires dairy animals that can produce large
amounts of milk efficiently and with a minimum care, animals that
can compete at the manger, animals that will be strong and healthy
throughout the rigors of a long
productive life. This goal can be attained through a balanced
breeding program which utilizes the best genetic merit for
economically important traits available both in cow and bulls. The
attainment of this objective will result in a herd of animals with
outstanding genotype for total economic merit.
The ideal genotype may vary from
herd to herd because the relative
economic importance of different traits varies depending on the
herd's management program and the country or the region in
which it is located. Breeding towards the ideal genotype for a
particular herd environment
requires the evaluation of many alternatives in the selection
program and consideration of how many different traits affect the
herd's profitability status.
High Yielding Dairy Animals in a Breeding Program
Dairy Animals in
the Breeding Program:
The dairy animals for which most dairymen strive are usually
referred to as `foundation
animals'. These animals have following characteristics:
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They have outstanding phenotypes and have transmitted superior
genotypes to their progeny
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They are
valuable as breeding stock
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They possess
most of the qualities of a strong constitution.
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They have
high milk yield
Unfortunately, few animals possess
all the desirable qualities.
Therefore, genetic improvement should be evaluated in terms of the
economic importance of each trait for making an animal
profitable in a particular herd. One economically important end
result of a strong constitution is
the capacity for longevity. Longevity in dairy animals means length of
productive life and is usually measured in years of age or
number of completed lactations. In addition, the ability for
longevity is an ingredient of a profitable program in most herds.
Every animal that is culled because of a weakness or defect,
decreases the dairyman's opportunity for selection,
reduces the effectiveness of his
breeding program and costs him money. However, a high proportion of
old dairy animals in a
herd is a sign that the effectiveness of the breeding program has
decreased. An effective breeding program should produce a
steady flow of heifers that are genetically superior to older
animals, no matter how good they were.
Milk Yield and
Milk Components:
First lactation yield of each dairy animal is of primary importance
to her profitability. In
addition, initial selection of sires is mostly on the basis of first
lactation yields of their daughters. A number of studies have
shown that animals with higher first lactation yields tend to have a
longer productive life. Positive phenotypic and genetic correlations
exist between first lactation yield and lifetime, thus selection
mainly on the basis of first lactation yield will result in animals
with greater longevity.
The influence
that milk components have on a farmer's income is determined largely
by the milk pricing structure in a particular area. For a long time
milk fat has been the only component paid for directly in most parts
of Asia. The future, however, will be different since in many
advanced countries, emphasis seems to have shifted from fat content
alone to protein and solids-not-fat contents of milk as a basis for
milk pricing. At the present time, the most efficient way for
dairymen to increase income and
to follow the changing trend in milk pricing is to increase
milk yield while maintaining the level of components. It is possible
that after a few years as component pricing becomes more widespread
(especially with the arrival of western-based milk product
manufacturing companies), component differentials may increase in
importance, especially in areas where a high proportion of milk will
be used for manufacturing purposes. The heritabilities of level of
milk components are high, and yields are the same as milk yield.
There are high positive genetic correlations between yield of milk
and yield of milk components and strong negative genetic
correlations between component
percentages and milk yield. Therefore, it appears that dairymen
should select for component yields rather than component
percentages in genetic improvement programs.
Body Size and
Efficiency of Feed Utilization:
Average differences apparently exist among the major dairy breeds in
their efficiency of feed utilization. Within breeds, larger animals,
as judged by several measurements of size, are less efficient in
feed utilization than are smaller animals. These relations of size
and efficiency of feed utilization are essentially the same in
all breeds. The larger animals
that have lower efficiency of feed utilization also have, on the
average, lower income over feed cost and therefore lower
relative profitability.
It is suggested
that dairymen should not select directly for larger animals, rather
they should select for high yield. By doing so, they will breed
higher-yielding animals that on the average will also be larger in
size.
Reproductive
Efficiency:
Reproductive problems are often the second most frequent cause of
dairy animal losses, after culling for low yield. A high incidence
of reproductive problems reduces the opportunity for genetic
improvement of yield by increasing days open and days dry; as a
result the generation length is increased and the potential rate of
genetic improvement is decreased over a given period of time. An
unusual situation is probably due to the fact that higher yielding
animals are known to have more breeding value on an average than low
producers. An apparently positive genetic correlation exist
exists between breeding problems and level of yield and longevity.
Therefore, an effective herd program of diagnosis and
treatment of reproductive problems is very important for maximum
genetic progress.
Mastitis and Milking Rate:
Mastitis is probably the most costly disease afflicting dairy
animals in the world. The heritability of
resistance to mastitis is low (around 0.10).
Milking speed is
also an economically important trait of dairy animals. Slow-milking
animals require extra labour to milk and efficiency of labour
utilization is one of the most important factors of profitable
management. The heritability of milking speed is about 0.30.
The genetic
correlations indicate that higher yielding
animals have a tendency to
contract more mastitis. Some evidence also exists that
faster-milking animals tend to fall victim to mastitis,
probably due largely to the tone of the teat sphincter muscle. A
more relaxed sphincter muscle results in faster
milking, but a greater incidence
of mastitis since bacteria can enter the streak canal more easily.
However, there is essentially genetic correlation between
yield and milking speed. Therefore, one can select for higher yield
independent of milking speed.
These
relationships suggest that dairymen should select for high milk
yield but should exercise restraint in selecting for rapid
milking rate. Selection for both may result in animals with a higher
susceptibility to mastitis and a tendency to leak milk.
Importance of Superior Bulls in Dairy Animals Breeding Program
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The greatest opportunity for genetic
improvement in a herd is through the bulls that are selected for
use in the breeding.
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The selection differential within each
herd can be much higher for bulls than for cow, since bulls are
selected from among the outstanding bulls in the entire country,
especially when used by means of frozen semen, whereas the cows
selected must constitute the majority of those in the single
herd.
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The use of a
superior sire for several consecutive generations can improve
the genotype make up of a herd. In each generation, one-half of
the remaining portion of original genotypes is replaced by the
genes from the superior sires. Therefore, after only 3
generations of breeding to superior sires, seven-eighth of the
herd's genetic makeup comes from the sires and only one-eighth
of the original genotype remains.
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For most herds, the greatest potential for
genetic improvement is through bulls available for artificial
insemination.
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A dairyman who wisely selects bulls to be
used in his herd can gain much additional income.
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