How
many bulls should be used in a herd?
1. The number and strategy of selecting bulls may differ as
a result of:
 Herd size
Bull
reliability
Inclinations
of the farmer to take measured risks |
2. The Golden rule is that the number of sires to select for
AI should not be less than three (3) for every 50
cows in a herd.
3. Limit the use of young sires with low reliability only to
few units per sire
Inbreeding
This is the mating of animals with a common ancestry. It's
a result of too much gene similarity (homozygosity).
It has the largest impact on traits such as production and
conformation. Generally, inbreeding levels for cattle should
be kept below 6.25 %. Inbreeding levels above 6.25% manifest
in poor performance including: calf mortality, reproductive
performance, growth milk and fat yield.
The formula for calculating inbreeding is:
Where :
ns- the number of generations
to the common ancestor on the sire side
nd- the number of generations
the common ancestor on the dam side
Outbreeeding
This is the mating of animals that are members of the same
breed, but are less related than average animals in the breed
would be. This occurs when the animals are from separate "lines"
of descent.
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