There is more to success in breeding than just genetic rankings.

This article will expand your vision of herd mating for economic progress.

Y= BV + GCE + GEI

This is the sort of formula you will see in a college undergrad course on cattle breeding.   The Y stands for "Yield", as in volume of production, type score, calving interval, length of life, ie, any measurement in real terms that is the result of inherited traits and qualities.   The BV stands for "Breeding Value", ie, genetic evaluation trait measurements (as assigned to the dam and sire).    The GCE stands for "Gene Combination Effect", ie, the result of the specific mating tendencies of the dam and sire, also called a "mating effect" in some discussions.   The GEI stands for "Gene/Environment Interaction", which is an essential reminder that all measureable output is dependent upon the levels and limitations of inputs offered, and the geophysical environment within which the living organism must function successfully-- a domesticated animal's version of "survival of the fittest", otherwise called "adaptation" by biologists.

In the context of dairy cattle breeding in the USA, the BV figures used are PTA values published for production yields, health and fitness traits by USDA's AIPL department;  and for type scores and traits published by each breed association; these appear three times yearly, updated both by new progeny and added contemporary comparisons.     Breeding Values measure what are known as "quantitative" gene traits, ie, traits that are both measurable (for volume or direction) and accumulative.      While people call this data "proofs", the more proper term is "evaluations" due to recognition that the values are not fixed, but will fluctuate given more progeny and the elapse of time needed to fully measure long term traits.

GCE involves the area of "mating effects", above and beyond what we collate under genetic evaluation procedures.    Gene Combination Effects represent the cause of the individual variation between siblings that produces the "bell curve" of individual responses, from which the trait average for the parent is calculated.    The individual phenotype appears to follow patterns definable by broad qualities that exert a higher level of "pull" upon the physique than will be exercised by any trait measured singly.   This covers a type of gene action known as "qualitative", ie, not linearly measurable, not accumulative, having impact on the specific mating.

   In dairy breeding, the most successful attempt to impact upon GCE has been from the "aAa" breeding guide, as developed by William A Weeks between 1948 and 1974, from thorough and continuous study of both male and female dairy cattle physiques and the cause-effect relationship between trait weaknesses and the relative presence or absence of various physical and developmental qualities he defined from his deep understanding of dairy cattle form relative to its daily use function.

  GEI-- gene/environment interaction -- represents all variables (both humanly defined and randomly occurring) that will impact upon an animal's performance, once genetic selection and mating effects have produced the individual animal.    Genetic potential is only realized as an interaction of the animal with the environment within which it grows, develops, and tries to produce and reproduce.    For instance, an individual animal may be injured by human error, thus ending what promised to be a long productive life.   The actual realized yield from that animal will be less than what either genetics or mating balance would predict.    But another animal may survive longer than typical of her genetic background, as a result of timely and frequent veterinary intervention.

GEI recognizes that most gene activity is like a light switch-- the environmental stimulus turns it on or off.     Thus behavior under confinement housing and TMR feeding with induced heats for reproduction, can (and will) be different from behavior under pasture housing, rotational grazing, seasonally-adjusted supplementation, and naturally observed heats for reproduction.   Also, and more importantly, whenever a major aspect of the limiting environment changes, animal behavior will change-- and from a "genetic" standpoint, rerank relative performance.

    When the issue is breeding improvement we have to be fairly certain we are selecting ancestral genetics that can survive any environmental limitations we are unable to change, or both the positive BVs and GCE efforts will be negated/wasted by negative GEIs.    Animals selected from an external population (as sires for replacements) have to answer the question the surviving cows in a herd have already answered: are my genes "adaptable" to the limitations of this new environment?

To summarize

Do not select sire genetics in a vacuum of ignoring the mates available, nor of ignoring any or all environmental limitations that may make preferred genetics ineffective in your dairy herd.  In spite of the best efforts of populaiton geneticists at AIPL and elsewhere, that design evaluation procedures to minimize the errors resulting from management effects, it is impossible to totally separate the overall environment (genetics of mates + nutrition + behavior + human intervention + climate) from the range of deviation in performance traits that are summarized as the [statistical] "genotype" approximations.  

The approach at Mich Livestock Service

 We believe the practical approach is to (first) identify the traits most needed to make gains in the profitability and productivity of your herd.    Once identified, genetic selection of sires needs to focus upon [prioritize] those traits, rather than to randomly use a "one size fits all" genetic ranking system.

   We believe the "aAa" breeding guide offers you (second) the ability to avoid making undesirable replacement females from the desired sires.    It will aid you in avoiding the replication of weaker phenotypic traits present in your cows, at the same time it will aid you in avoiding acquisition of the weaker traits possessed by every bull for which your selection preference is the result of the narrowed trait selection focus desired by and common to genetic evaluation procedures.

We believe that (third) the dairyman should consider all ways in which his current environment could be improved so as to fully harvest the genetic and phenotypic improvement that will result from this careful selection of mating sires and matching of cow faults to sire qualities.

When all three of these elements are employed, a dairyman finds (first) that his calves are born stronger-- there will be less calf raising difficulty.    His heifers will grow more uniformly allowing a consistent age of first freshening.    The physical causes of early involuntary culling will be reduced, allowing both a longer breeding life and longe rproductive life for his replacements.    As a result of better fertiltiy and longevity, the ability to sell surplus usable replacements is increased, and at the same time, the "total genetic value" of the retained herd also increases, which is another way to improve our equity value of the herd.