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scmn | It is not uncommon for a dairy to have the majority of their cows trace back to a few cow families that they started with. The same can be said for most cow-calf operations. This is inevitable in most any breeding operation since you tend to keep the heifers out of the cows that work best in your operation. Cows that are profitable tend to be those that are kept: they breed back quickly and milk/raise good calves generally keeps them from getting culled, having good feet/legs gets them to the feed bunk and keeps them from getting culled, etc, etc so you tend to keep them longer.
If you keep them longer you also tend to get more replacements from them which increases the influence in the herd. Essentially you start with several cows A, B, C, D, etc. Consider cow A breeds back every time on the 1st or 2nd breeding and raises nice big calves and has excellent mobility, cow B raises nice big calves but breeds back on the 4-6th breeding and has good mobility, cow C raises small calves and breeds back on the 1st or 2nd breeding with good mobility, and cow D has small calves and takes forever to breed back and has excellent mobility. What typically happens is cow family A tends to breed back quicker and thus produces more calves in less time than cow family B. As a result cow family B produces less calves in the first 10 years as cow family A. Cow family D tends to get culled first since calves are small and takes forever to breed back even though she gets around well she does not do much good when open. Cow family C breeds back but will often get culled after D but before B since B raises big calves and you can deal with a stretched out calving window if it means more money. After 10 years you heard is primarily cow families A & B so you begin to focus on size, fertility, mobility, and efficiency so you start culling cow family B cows at younger ages to make room for the ever increasing number of cow family A cows since they do so well for you. After 4-5 generations of cattle, the majority of you herd traces back to a few cow families that have done really well for you. Take this to the extreme of the Holstein breed and over the coarse of 30+ generations ( you end up with a few families that rise to the top and influence most of the breed.
If you were to trace the lineage on all the cows of a given breed you will see a similar trend of the gene pool narrowing to natural selection. It is easier to trace in the Holstein breed since the majority of dairies on milk test (i.e. DHIA) and are reporting milk, butterfat, protein, etc on a monthly basis which is used to calculate bull scores; since both sire and dam are entered in the database for most registered and grade animals there is a far more complete database of lineage for the breed as a whole. I am not aware of a national database that records EPDs for all breeds of beef both registered and commercial like there is for dairy; compound this with the greater use of multiple herd bulls (both commercial and registered) in the same pasture makes tracing lineage in the beef herd more difficult. Some of it is the differences in how records are kept and some of it is the willingness of the individual farmer to report data to a national database to track the breed and further improve his herd in the process.
I for the life of me will not keep a cow with poor milk, poor fertility, and poor mobility around just for the sake of keeping genetic diversity in our herd nor do I know any breeders (both beef and dairy) that would. So often you hear a dairyman say I wish I had a whole barn full of cows like xxxx, she is on her 7th lactation, has never needed assistance calving, breeds back within 80 days, milks 28,000 per lactation, and has beautiful daughters just like her; beef guys have the same view on some of their cows so claiming you want genetic diversity and a uniform herd are not exactly complimentary statements. As more and more undesirable traits are bred out of cattle, the gene pool will continue to shrink and it is the nature of the beast.
FWIW we try to keep our inbreeding coefficient below 8% whenever possible. I care about genetic diversity when mating cows, but it is not a concern when culling and ultimately culling is what narrows the gene pool, not breeding. I do not see a huge issue with a narrow gene pool since there are benefits that are realized in uniformity. Last year at the MN State Fair I watched Emily Griffith judge the FFA beef show. She made a comment that stuck with me while judging the dairy steer showmanship. She said when she worked for the beef council that restaurants would ask for Holstein beef since it had consistent size, texture, flavor, and quality; she also stated that no other breed produced as consistent of a product as dairy beef and that it what restaurants liked about dairy beef. I would say the uniform selection by dairymen to select cows with good milk, good fertility, and good mobility has led to a uniform breed that produces dairy steers that feed out uniform and produce a consistent product.
If you could get every cow-calf producer in this country to AIN tag and report sire/dam info on all the beef cattle in the country and then convince the processors to report scores on every beef slaughtered into a national database you could statistically analyze the entire population have more accurate EPDs and would likely find that the majority of the beef herd is influenced by a few cow families in every breed and the smaller the breed, the fewer the influential cow families.
The majority of Holsteins can be traced back to just a few cows in the original herd book. This is the result of selective breeding to keep animals that exhibit desirable traits. What is not considered in tracing lineage to just a few cow families is the distribution of the genes then (no genetic data available) and now and the effect of small mutations to those DNA sequences over the coarse of numerous generations. One must remember that those small genetic mutations are what causes evolution and genetic diversity in the first place. Some would argue all cattle trace to one cow and one bull that got on the ark.
Sorry for book.
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Are Angus the new terminal breed?
