Predicted
Transmitting Ability (PTA)
PTA is a way of ranking animals for their genetic merit. This
is achieved by using an animal model. To achieve this, environmental
effects must be removed and 3 sources of information are used.
These include:
1. The parents genetic merit
2. Performance of the animal itself (when applicable)
3. Progeny test information
Genetic
Base
It is the reference point for evaluation of genetic merit
of animals for a trait. It sets the average PTA to zero for
a group of animals. Frequency of changes varies from one country
to the other for example in the US, genetic base changes within
5 years, and in Canada Breed Class Average is computed annually.
The current US genetic base for the Holstein breed is a breed
average production of 23,248 lbs produced over 305 day lactation.
Reliability: The
equivalence to confidence of determination for each factor.
Its determined by the Sires' number of daughters evaluated
and spread under different environments. Reliability is low
in young sires and high in older ones.
Choosing
the right bull
Sires are selected based on PTA for the traits important in
the herd. Reliability should be not part of criteria for selection.
The two ways to achieve this are:
 Independent
culling - this
sets limit for PTA levels. Small shortfall for a trait cannot
be compensated by
better performance in another trait.
Selection
index - Farmers should develop or use selection indices
most relevant to milk pricing structure. |
