Thursday, April 29, 2021

How to optimize your gains from genetic selection


CONCEPTIONS            Dairy route newsletter                       June-July 2020


The late Paul Harvey would say to this, “now for the REST of the story.”     All you hear in print and from semen salesmen is “genetic value [which implies high rank on a trait index].    This is the visible half of the story, because the money it has generated purebred breeders and AI bull studs has driven the industry’s selection focus for decades.

When you breed each cow, you want to see improvement from matings in future replacements.    Just staying “the same” means less future income to meet inflation in our future expenses.   The biggest reason for herd expansion in each generation is the need to increase income per farm if the net profit per cow in real spending power has not increased.    

The genetic evaluations and especially the Genomic data is NOT a calculation of what changed from one generation to the next (“intergenerational change”) but is a history of how the known progeny set compared to same generation “contemporaries” (same age herdmates) which they call “intragenerational deviation”.    Back in the 1960s, geneticists could not figure out how to compare daughters to dams in an era when herd averages were rising from newer equipment and better feeding, so they quit trying.   Since then the main factor added has been pedigree (“parent average”) which has compounded over generations to where “sire stack” now drives the Genomic bus (at 40% of the published values).

What is the true influence of “pedigree” on animal performance?

Last I checked, a pedigree starts with a sire and a dam (the bull you use on the cow you have).    ALL genes contributing to the resulting calf come only from those two mates.     Extending that pedigree out to grandparents, great-grandparents, et al may be more intellectual exercise than biologically determinant, but within Genomics, the extended “sire stack” is all weighted in to the calculated result.     The individual differences of the cow side of that ancestry are ignored.   Yet they have contributed 50% of the total genes passing down to your new heifers.    A strong maternal line (either in cows or bulls) can definitely change the result from the predictions of a sire stack, and we work with that variation in our herds every day – until we go to breed them.

Is there any usable system for managing “intergenerational change” in our favor?

I KNOW you get tired of me talking about the benefits of the “aAa” Breeding Guide, but this is exactly what the system does for you – (1) identifies the qualities your cows possess that will influence 50% of each mating you make; (2) identifies the qualities of bulls who will match up to her in a complementary way, so that (3) you harvest genetic potential that is only a prediction of average historical results in the data which genetic evaluation present you.

Simply put, “aAa” fills a void that genetic indexes were not designed to do – predict results from any individual mating.    This is why scientists call it “population genetics” and focus on progeny from bulls, rather than cows  ( “A cow doesn’t produce enough data for statistical accuracy”… )

What is the chief gain of using “aAa” breeding guide alongside sire selection concepts?

Genomics and genetic evaluation give “values” that depend on cows achieving “normal” length Productive Life.    The majority of GPTA- PL values are imputed from theoretical models because the bulls being marketed are not old enough to have tested progeny (or if they have any, their lives are still in progress, not completed for accurate measurement).     So again, historical data, pedigree sires, and a lot of other biased assumptions go into those calculations that may not fit your herd or the cow environment you have developed.

Users of “aAa” claim many benefits, but one of the most commonly mentioned is “aAa cows just last longer” [have less physical injury, less trouble calving, breed back well, stay healthy].     Zoetis has put out a lot of recent data to show that cows who remain functional at maturity produce 30% more milk than first-calf heifers – that is a benefit greater than even the highest GPTA Milk rated sires can produce.      You can benefit financially from a more mature herd.     

Looking at one of the first herds I ever analyzed, who still uses aAa, started with 80 cows at a 16,000 pound 3.2% bf herd average (ECM 14,000 pounds) 25 years ago.    Today there are 350 cows at a 25,000 pound 4.0% bf herd average [ECM 28,000 pounds] and a 13.5 month calving interval.    They had a cow reach 234,000 pounds lifetime from a first-generation aAa mating!     In 25 years they only ever bought 12 heifers and 1 cow when flirting with going registered … so this performance gain and expansion has all come from homebred natural increase.  

What proof can you offer that any of what you say here is true?

Toward the end of his life, Mr Weeks (founder of “aAa”) obtained data from Holstein USA to see how his concepts affected the results of dominant population genetics theories.    Looking at every Holstein heifer registered born in 1980 (nearly 250,000) they found 70% of these had production records that could be compared to their dams also on test.    On the average, these Holsteins of 1980 represented 41% “aAa use” (ie, how compatible on “aAa” was the sire vs the maternal grandsire?).     Sire selection preferences in the herds only using indexes were clearly the reason for only a 40% “match” (the industry loves breeding “likes to likes” which is where inbreeding depression starts).      

1980 cows that represented an 80% aAa match averaged 2500 pounds MORE than Momma did per lactation.  ( An 80% “percent use” average on aAa is the goal we use in herds that analyze. )

1980 cows that represented a 20% match averaged 4000 pounds LESS than Momma did in her lactations.     Most such cows had much fewer reported lactations than those at 80% match, and who her sire was (ie, how famous, how highly ranked) was no help to changing this data.

This simply demonstrates that making a complementary mating is as essential as using bulls who have genetic value according to your expected economic opportunities and production management system in place.     The “mating” side of the equation brings forward the prior adaptability of your cows to your environment.   The “genetic selection” side requires you to find bulls with the traits that can prepare for the financial value of your production.

No comments:

Post a Comment