Tuesday, April 13, 2021

Selection for “Longevity” leads to greater profitability

 CONCEPTIONS   Dairy Route newsletter                           Winter 2019-20


We have now had “Productive Life” (GPTA-PL) genetic values on both Progeny Evaluated and Genomic imputed sires for three decades, which were to guide us into more profitable, lower turnover rate herds for the 21st century.    We are now 20 years into that new century, and the genetic base for “Productive Life” has barely gained three months from 1990.    The average US cow still only produces milk for a bit over two lactations, barely exceeding the length of time we rear them.

What are we losing from short cow herdlife?    Mostly, we lose the extra 30% gain of production from first lactation yield to mature age lactations, observed (says Zoetis in the studies for their “Wellness” health traits) in those cows who do calve a third, fourth, fifth time.    To put this into perspective, 70 pound heifers should become 100 pound cows when they mature (five years of age).    

Why are we not achieving the extra 1.5 lactations promised by the theory supporting “PTA-PL”?   Because at the same time, we have “accelerated” the genetic potential for faster maturity of production (calve earlier, milk harder) – and alongside of that, biology gave us “faster aging”.    Cows still continue to grow and develop after their first calving, but their physical quality has less “constitution” to stay healthy and functional into maturity.

Productive Life has basically screened out the sires who sired the shortest herdlifes—usually a generation after they have been widely used through AI—but has not identified sires who will have an impact on lengthening functional life.    In effect, the range of “plus” PL that exists in those sires who rank the highest on ranking indexes (even though PL is included in calculations for Net Merit and other indexes) is not significant at its estimated 15% heritability as a “trait”.

Heterosis vigor, Compensatory mating effects, Genetic selection effects

Calculations for “expected future inbreeding” began around the same time as “productive life”.   Until Genomic selection superceded pedigree and phenotye selection for AI contract matings, human intervention kept efi% below the supposed “danger” level of 8.5% inbreeding.    As we progress into our fifth generation of Genomic selected sires, utilizing full sibling females as ET donors for the elite ranked males, this control is gone.    As a result, individual herds are now experiencing “inbreeding depression” basically as a glass ceiling on new heifer production.

“Heterosis (Hybrid) Vigor” is observed when animals of differing genotypes are cross-mated to generate a production generation of milking females.    You accomplish this either by outcross mating within your breed, or crossbreeding with a different breed.     What is observed within Genomic selection is, the opportunity to find outcross mates at the elite level has disappeared.  Virtually all Genomic matings for future sires and donors are well above the 8.5% ibc level. 

Genomic selection and avoiding inbreeding at this point are basically incompatible goals.   The process of mating “by numbers” to accelerate the index values requires “likes to likes” matings

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The landmark Dutch study of Holstein sires used on Dutch Friesian cows published in 1997 is still definitive in explaining inbreeding depression a result, not of pedigree ancestors shared in common, but of “single trait” selection over a multiple (three or more) generations.    Whether a single trait (in their case, PTA Pounds Protein) or an unchanged composite index (TPI, NM$, JPI, LPI, BW), the underlying genotype that produces the single response loses many desired genes that counterbalance the “marker” genes on which we focus, after each generation.   The desired “heterosis” effect within pour matings just disappears.

 As for compensatory (phenotype characteristic) mating, its contribution to avoiding inbreeding effects has been proven by generating as much production gain intergenerationally as has been documented through sire summaries intragenerationally.    The largest study of the “aAa” effect (across 240,000 Holstein cows born in a single year) showed that “likes to likes” mating caused an average of 5,000 pounds loss per lactation (thus a shorter herdlife) for these cows compared to their dams—and irregardless of their sires’ PTA Milk values.   

So what is the solution?

First—if not already doing so, have your cows “aAa” analyzed to identify the physical genotype for each of your cows.     Grouping those results into patterns of needs in common, you will end up with six to eight “types” of sires needed to provide effective “compensatory mating”- which will provide the heterosis response needed for physical vigor and environmental adaptability.

Second—establish your “trait matrix” of the Genetic “traits” you wish to increase in your herd, based on current “real time” analysis of your herd records for production and reproduction, and the current economic trends in the milk market (for example, favor bulls +bf% and +pr%).  

Third—for each of the six to eight “aAa” groups, find bulls to fit that possess the trait values you established for genetic selection, and use them accordingly.

Fourth— evaluate each generation for progress on your genetic goals.     I do not mean average GTPI or GNM$ values, as Genomic testing would do (and which will act to cull your best mature cows from your breeding herd) but ACTUAL REALIZED production and fertility.     Save future replacements from the cows who are really doing it for you—sell all others as surplus to your needs, thereby reducing your cost of replacement rearing.

As your cow herd matures (in age and productivity) you will find that fewer replacements are needed.   You will have an ACTUAL gain in “Productive Life” in your herd, as the scientists had predicted when they dreamed up the measurements.    They only erred (and continue to err) in only accepting one “IDEAL” genotype as necessary to sustained progress.    You will need to find “outcross” genotypes for those “aAa” groups that do not match the one “ideal” phenotype that Genomics is producing—but this will maintain your herd heterosis vigor well into the future.

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