Sheep - AgRIS

Selection on this basis means that we estimate the breeding value of an individual through
a study of the traits or characteristics of its offspring. In other words, the progeny of different
individuals are studied to determine which group is superior, and on this basisthe superior
breedingdms given preference for future breeding purposes. If information is complete, this is
an excellent way of identifying superior breeding animals.
Progeny tests are very useful for determining characteristics that are expressed only in one
sex, such as milk production in cows or egg production in hens. Even though the bull does not
produce milk nor does the rooster lay eggs, they carry genes for these traits and supply one-half
of the inheritance of each of their daughters for that particular trait.
Progeny tests are also useful in measuring traits which cannot be measured in the living
individual. A good example ofthis is carcass quality in cattle, sheep, and hogs.
Progeny tests are also being used at the present time by experiment stations in studies of
reciprocal recurrent selection. This type of selection is used to test for the ―nicking, ability‖ of
individuals and lines and is based on the performance of the line-cross progeny. Selection of
this type is for traits that are lowly heritable and in which nonadditive gene action seems to be
important.
In comparing individuals on the basis of their progeny, certain precautions should be taken
to make the comparisons fair and accurate. In conducting a progeny test, it is very important to
test a random sample of the progeny. It would be more desirable if all progeny could be tested,
but where this cannot be done, as in litters of swine, those nearer the average of the litter should
be tested. It is also important that the females to which a male is mated should be a nonselected
group. One would expect the offspring of a sire to be superior if he is mated to the outstanding
females in the herd. Such a practice would be misleading in comparing males by a progeny test,
since much of the superiority of the offspring of one male could come from the dams and not
from the sire. Some breeders prefer using a rotation of different dams when testing males, but
this is practical only in swine, where two litters may be produced each year.
Using a large number of offspring in testing a sire increases the accuracy of the test rule.
Where the number of females in a herd is limited, the number of males that may be progenytested
will be less as the number of matings per sire is increased. The point is, then, that the
breeder must make some decision as to how many sires to test and how many progeny must be
produced to give a good test. The number of offspring required for an accurate progeny test will
depend upon the heritability of a trait, with fewer offspring being required, when the trait is
highly heritable, and more being required when it is lowly heritable.
To make accurate progeny tests, it is also important to keep the environment as nearly as
possible the same for the offspring of the different sires. In progeny-testing swine, for instance,
confusion would result when the progeny of one sire were fed in dry lot during the summer and
the progeny of another were fed on pasture. This would be particularly true in progeny-testing
for rate of gain, where pigs fed modern rations often grow considerably faster in dry lot than on
pasture. when this environmental condition were not controlled, the inferior sire might actually
be thought to be superior.
Progeny tests in most of our farm animals have certain definite limitations. In cattle,
especially it takes so long to prove an animal on a progeny test that he may be dead before the
test is completed and his merit actually known. Progeny tests may be tnow easily in swine than
in other farm animals, but even in this case the males are usually disposed of by the time they
are thoroughly progenytested.
The process of progeny-testing may be speeded up by testing males at an earlier age than
they~would ordinarily be used for breeding purposes. By hand-mating them to a few females,
or by using them on a larger number of females by artificial insemination, harmful effects that
might occur from overuse at too early an age may be prevented.
Too often, farmers send their old sires to market just as soon as their daughters are old
enough to breed, in order to prevent inbreeding. This practice has resulted in much loss of good
genetic material for livestock improvement. Actually a sire is not proved until his daughters
come into production. Rather than being slaughtered, a sire that has proved himself to be of
high genetic merit should be used more extensively. It is true that his usefulness in a particular
herd may be finished when his daughters are of breeding age, but he should be sent to another
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