Designer
Cows for Your Future
by L.B. HANSEN
University of Minnesota
Poor fertility
and shortened herd life are two traits of dairy cows that cause
dairy producers much frustration. Cow comfort is also a problem
for many dairy producers because stalls were typically designed
for cows with more moderate size than the cow of the 21st century.
How should dairy producers select sires that transmit decent fertility,
extra longevity, and moderate body size to their daughters? Designing
cows with these attributes has become easier because of the traits
Productive Life (PL) and Daughter Pregnancy Rate (DPR). New in February
2003, the trait DPR ranks sires for the ability of their daughters
to become pregnant. Some pointers to get you started:
-
Begin
your sire selection by starting at the top of the Net Merit ranking,
which is updated every four months by the U.S. Department of Agriculture.
Net Merit appropriately weights traits for commercial settings.
Those traits are production, SCS (lower is better), PL, udder,
feet & legs, and body size (which receives a slight negative
weight).
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Cows
must become pregnant to stay in herds. Look at the genetic evaluations
for DPR for sires, and eliminate sires from your breeding program
that rank poorly for this new trait. Within one year, DPR will
be included in Net Merit. In the mean time, you will need to look
at this trait separately from Net Merit. Unfortunately, the majority
of active A.I. sires are negative for DPR, because of the unfavorable
genetic trend for daughter fertility. Request DPR evaluations
from AI organizations if they are not forthright in providing
evaluations for this new trait.
-
Continual
selection for cows with dairy character ("sharpness")
in addition to selection for milk production has had a negative
impact on the fertility and, consequently, the longevity of cows.
Adequate body condition aids reproduction. The new trait of DPR
has a substantial negative relationship with sharpness of cows.
The designer cow of the future will have very high production,
but she will maintain some body condition to aid reproduction
and health.
-
Cows
that are more moderate in size (due to genetics, not to poor growth
because of bad health) have advantages for fertility, longevity,
and cow comfort compared with larger cows. Cows become larger
every year because of genetic trends, yet stall sizes are often
inadequate. When selecting for type, look at functional type traits
(udder and feet & legs) rather than final score type, which
strongly favors large cows that are very sharp.
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Inbreeding
depression is a contributor to depressed fertility and decreased
health. Pedigrees of cows must be compared to pedigrees of alternative
sires. This is a job made for computers, and all AI organizations
offer computerized mating programs. Be sure to furnish the pedigree
information on your cows to the program, and check to see that
the program looks for common ancestors at least five generations
back in pedigrees.
-
Some
dairy producers are turning to crossbreeding to improve fertility
and longevity of cows. New research is needed to determine the
effects of crossbreeding, and research is underway to document
the effects of crossbreeding using numerous dairy breeds from
the United States and Europe.
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