Performance Line
genetics for growth that she passes on (1/2 the weaning
weight EPD). Because it includes both direct and maternal
impacts on growth, TM is the best predictor of how daughters
of a bull will perform in terms of weaning heavier calves. his daughters probably produced more Milk than Sire A’s
daughters, but that “better” maternal environment provided by
Sire B’s daughters was not enough to overcome the genetics
for growth that were passed on by Sire A’s daughters.
Even if Total Maternal is not published in a sale catalog,
it can be calculated by simple arithmetic: ½ WW EPD +
Milk EPD = Total Maternal. To illustrate the differences
in WW, MILK and TM, let’s use the example below. In the BOLT-powered national cattle evaluation that NALF
participates in through International Genetic Solutions, WW,
MILK and TM EPDs are a product of a multi-trait evaluation.
This evaluation uses all performance information on the
growth traits (Birth through Yearling) along with pedigree
and genomic information. For most young sires, pedigree
along with their own birth, weaning and yearling weights
may be all that is available for the evaluation, though
many now also have genomic results. It is important to
note that in the current evaluation, a negative correlation
is used between direct and maternal growth. This means
that young animals who are outliers for direct growth traits
(WW and YW) may have lower-than average Milk EPDs until
and unless they have maternal grand-progeny weaning
weights that suggest they are curve benders for the traits.
Table 1: Weaning growth EPD example.
WW EPD Milk EPD Total Maternal
EPD
Sire A 72 15 51
Sire B 55 21 48.5
Assuming Sire A and B are used in the same
environment and bred to genetically similar females,
we would expect Sire A’s calves to average 17
pounds heavier at weaning that Sire B’s calves.
Now, let’s assume that we retain daughters from both bulls in
the herd and they are bred to genetically similar bulls. When
weaning time rolls around, we’d expect Sire A’s daughter’s
calves to weigh 2.5 pounds more, on average, than Sire B’s
daughter’s calves. Indeed, Sire B had a higher Milk EPD, and
18 | FEBRUARY 2019
A benefit of the IGS partnership is that the quantity of
data generated by the partner breeds has made possible
new research to update the variance components of the
growth EPD model, which will give us new and more
reflective correlations between direct and maternal
growth. We anticipate results from this research to
be implemented sometime in the new year. I