Genetic Selection has longer-term consequences

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.