Interpreting the Sire Summary - CCA Breed Improvement

Three multiple trait animal models were used to predict carcass, scrotal circumference and calving ease EPDs.
The carcass evaluation is generated using a seven trait model (three growth and four carcass) Lean yield EPD were
predicted indirectly using EPDs for the seven traits in the carcass evaluation and their genetic correlation with lean
yield. For each trait in the carcass evaluation, a direct genetic (animal) effect was fit, but maternal genetic effects
were not included. Instead, a dam effect which includes both maternal genetic and maternal permanent
environmental effects was included for birth and weaning weights. All other aspects of the growth portion of the
TGE were the same as in the North American (NA) growth evaluation, including contemporary groups and
adjustments for age of dam and sex of calf. For carcass traits, the model accounted for contemporary group effects
(herd ! sex ! date on test), breed of dam and slaughter date. Carcass traits were adjusted to a slaughter age end point
of 425 days.
Scrotal circumference EPDs are calculated in a four trait animal model which included weaning weight, yearling
weight on farm and test station scrotal circumference measurements. The scrotal circumference EPD presented is
the on farm result.
The calving ease EPD is also the product of a multiple trait animal model. The three traits in the calving ease model
are birth weight, gestation length, and calving ease score. The calving ease EPD is presented as a standardized score
with a population mean of 50 and population standard deviation of 25. A larger number represents a higher
percentage of unassisted calves.
It is important to note that all records used in carcass, scrotal and calving ease evaluations were from CCA. No
performance records from the American International Charolais Association (AICA) were included. Although
growth EPDs were generated in the TGE, those from the NA growth evaluation are generally more accurate because
data from both CCA and AICA were used in the NA growth evaluation. Also, carcass, scrotal circumference and
calving ease EPD from the CCA are not directly comparable to carcass, scrotal and calving ease EPD published by
AICA.
Genetic Parameters - Heritability Estimates and Correlations
Heritability may be defined as the proportion of the observed differences among sire progeny groups that is due to
genetic variation. For example, since weaning weight is 25% heritable, 25% of the observed variation is attributable
to genetics while the remaining 75% of the variation is due to environmental (non-genetic) influences.
The higher the heritability, the easier it is to make genetic change in one specific trait. Since heritability is already
considered in the EPD calculation, EPDs reflect actual genetic differences.
Genetic correlations indicate how traits vary together and indicate the effect that selection for one trait can have on
other traits. Correlations may range from -1.0 to +1.0. A correlation of +1.0 indicates that the traits vary quite
closely together and that as one trait increases the other trait would be expected to increase as well. A correlation of
–1.0 also indicates that the traits are closely related; however as one trait increases it is expected that the other trait
will decrease. A correlation of 0 indicates that the traits have no covariance at all and that as one trait increases the
other trait may increase, decrease or not change at all.
For example the correlation between Birth Weight and Weaning Weight in this evaluation is +0.47. This indicates
that as weaning weight or birth weight is increased one would expect the other trait to increase as well. However
since this relationship is not +1.0, it means that it is possible to select for increased growth to weaning and lower
birth weights.