USDA’s Beltsville
MD research farm did Dairy crossbreeding experiments in the 1940s-
1950s. Once that was concluded, the Animal Improvement Programs Laboratory
decided to enter into Genetic Evaluation
for purebreds (originated by the individual purebred Breed Associations).
The Predicted Difference was born in the 1960s. While purebred associations were publishing
sire daughter averages and daughter vs dam (“intergenerational”) comparison
proofs, the AIPL produced daughter vs herdmate (“intragenerational”) comparisons,
then introduced the idea that we could “rank” sires on the size of those
deviations, named “Predicted Differences”.
This
evolved into the Modified Contemporary Comparison. Purebred breeder criticism of the PD concept revolved around
the lower national DHIA breed averages compared to the “official” (supervised
testing) HIR lactation averages from which Breed Association “proofs” were
based. Could bulls proven in
below-average environments be equally useful for the highly preselected
breeding herd? MCC factored in the
rankings of herdmates’ sires and pedigree indexes on the sires evaluated to produce
what they now called Predicted Transmitting Ability. The first index “composite trait ranking”
was introduced, named Net Merit $, a term that has carried forward to the
present time (although its formula has been repeatedly changed).
Through this
entire period, into the beginnings of Genomic (DNA-based) ranking
indexes, one thing remained the same: Mature
Equivalent factoring of young cows’ lactation records. ME
was used by the purebred associations to allow “intergenerational”
comparison of first lactation cows to their matured and maturing dams with
multiple age lactations. We used MEs
because in every tested dairy breed
in the USA cows were observed to milk 30% to 40% more milk in their mature-age
lactations than they did in first lactation.
MEs created “parity” over a range of age.
ME factors
got carried over by AIPL into USDA “intragenerational” comparison of cows to
same age contemporaries. Anyone who
understood high school mathematics could have seen that the only effect of
using MEs instead of actual records was to inflate the deviations. Yet the AI industry continued using ME
data, perhaps thinking it would prove “the new bulls are better”.
The
primary goal of dairy genetics has been to “accelerate” the age of maximum cow
yields. The initial premise of the “PD” was
that those heifers with the highest deviations were faster at maturing their
production than the average of their contemporaries. In fact as you broke down lactations (as the
“Test Day Model” did later do) the key aspect of high PTA Milk sires was their
daughters set the highest peak test yields in their first lactations. The linear type trait appraisal system (used
by all breeds today) was later based on the appearance of high-peaking cows.
Geneticists
have succeeded in transforming cows to be faster maturing (and faster
aging).
Being
mathematicians (rather than biologists) they never anticipated that making cows
mature quicker would just accelerate the physical aging process, until three
calvings wears them out.
Where are
we today with all of this genetic evaluation ranking emphasis ?
The Council
on Dairy Cattle Breeding (CDCB), successor to AIPL in index formulation and DNA
application to Genomic ranking, has declared that ME factors are no longer
used for calculating PTA values. It
seems that Genetic Selection for faster maturity has succeeded; we no longer have any mature cows! Why add 30% to every heifer lactation
if only 20% of them will still be alive at the species age of maturity (five
years)? Just compare actual
production.
Basically,
today’s average cow will die before the end of her third
lactation. Cows no longer improve by
30% to 40% over their first lactation, because 80+% of all cows only
complete two lactations. It now takes as many days to raise a heifer calf
to milking as we expect to milk her after her first calving! Financial experts will tell you the average dairy cow wears out before you
have recovered her cost of raising.
There is currently a shortage of replacement cows so we are seeing
prices APPROACHING $4000 to buy a replacement fresh heifer—and this in spite of
technologies that were supposed to solve this, starting with PTA “Productive
Life” indexes, and leading to the gender sexing of semen to favor 90% heifer
calves.
In short, dairy
industry application of 1960s genetic theories, as applied through AIPL’s index
calculations and various ranking indexes, has changed the dairy cow’s
lifetime epigenetically. All
the genes in modern Genomic cows’ DNA were existent in the cows from the 1960s
, but in today’s environment they no longer help cows to live a full productive
life. Breed averages for realized PL
today (after ten generations of measuring it) are essentially unchanged since
1990.
Getting entire populations to focus on one “selection path” (the ideal Genomic
genotype) will, over time, virtually eliminate all heterosis for functional
length of life.
Linear
trait evaluation has taught us to admire cows with “frail” physiques. Following show type selection paths frequently builds cows
who are out of functional proportions, but may still possess more desired
“femininity” as it relates to natural fertility and will to milk. Genomics on the other hand, has confused
“beefiness” with health support traits and in spite of all the “talk” about how
the latest trait emphasis is on feed efficiency and reducing methane emission,
none of this will come to fruition; the basic, underlying physical
construction of high Genomic cows is grain and oilseed dependent and lacks
the capacity to use low-cost perennial forages effectively.
Finding a
genetic solution to this historical inbred genetic selection path
Start paying attention to sires from cow lines
recognized for “longevity” that show multiple lactations of consistent maturing
performance over many generations. In today’s sire populations, these are the only
true “outcross” sires. They will offer
the ability for more “even” body conditioning and flatter, more persistent
lactation curves reducing total feed costs.
They will give you cows with better natural fertility characteristics. These will include the highest combined
butterfat% and protein% bulls, especially if you are seeking A2A2 Beta Casein
alongside BB Kappa Casein to qualify for future premium milk marketing options.
