Within this special genetics issue, experts from around the country discuss many different breeding technologies. Here’s a list, in no particular order:* Cloning* Marker-assisted selection (MAS)* Genetic prediction* Gene transfer* Sex control* Systematic crossbreeding and composites* Animal identification (DNA and biometric methods)* In vitro fertilization and embryo transfer* Marker-assisted mating*
Rick Bourdon | Mar 01, 1999
Within this special genetics issue, experts from around the country discuss many different breeding technologies. Here’s a list, in no particular order:
* Marker-assisted selection (MAS)
* Genetic prediction
* Gene transfer
* Sex control
* Systematic crossbreeding and composites
* Animal identification (DNA and biometric methods)
* In vitro fertilization and embryo transfer
* Marker-assisted mating
* Multibreed evaluation
* Selection indexes
These tools can be categorized in a number of ways. They could, for instance, be categorized by field of research – conventional (statistical/mathematical) animal breeding, molecular genetics or reproductive physiology.
In terms of their impact on genetic improvement, however, it’s more revealing to group the technologies by what they might accomplish. These are my three general categories (note that some technologies fit in more than one category):
1. Technologies designed to improve selection (to increase the rate of genetic change through more efficient selection of sires and replacement females);
2. Technologies designed to improve mating (to help us decide which males to breed to which females and in so doing manage both complementarity and hybrid vigor);
3. Technologies designed to evaluate the relative importance of traits.
Technologies To Improve Selection * Cloning – Clones provide breeders easy access to the best, most thoroughly evaluated animals, increasing accuracy and intensity of selection.
* Marker-assisted selection (for both simply inherited and polygenic traits).
* Genetic prediction (statistical models, new traits, etc.).
* Gene transfer – A long shot perhaps, but infusion of new genes could increase genetic variation, producing more radical genotypes than are available today.
* Sex control – Consistent production of daughters out of two-year-old dams, themselves out of two-year-old dams, is a clever way to decrease female generation interval.
* Animal identification – DNA fingerprinting allows more information to be harvested from multiple-sire pasture data. In combination with other identification technologies like retinal imaging, it could increase the amount of data available from commercial animals, most notably for carcass traits.
* In vitro fertilization and embryo transfer – These technologies could put females on a par with males in terms of number of offspring.
* Ultrasound – This technology gives us more information on hard-to-measure carcass traits.
* Multi-breed evaluation – With multi-breed evaluation, we get better genetic prediction for crossbred seedstock and composite breeds.
Technologies To Improve Mating * Cloning – F1 (terminal breed terminal breed) market clones raised by F1 maternal cloned females – could it be the ultimate mating system?
* Genetic prediction – Researchers are developing methods for predicting non-additive or gene combination value. This may allow us to better predict progeny performance for specific matings.
* Sex control – Maternal/terminal crossbreeding systems are more attractive with a practical method of sex control. Fewer cows are needed to produce replacements so more cows are available to produce market steers.
* Systematic crossbreeding and composites.
* Animal identification – DNA fingerprinting techniques have the potential to identify breed composition, allowing breeders to more closely manage heterozygosity and hybrid vigor.
* Marker-assisted mating – Marker information does not add much to selection accuracy if accuracy is already high (as it is for growth traits for popular AI sires), but knowing what major genes an individual carries could be helpful in designing matings.
Technologies Designed To Evaluate The Relative Importance Of Traits * Selection indexes
Most of the technologies discussed help us select animals, typically by increasing the accuracy of selection, sometimes by increasing selection response in other ways. A number of technologies, however, help us make mating decisions. Just one technology helps us determine which traits are most important. More on that later.
Rating Breeding Technologies To rate breeding technologies, we need information on each technology’s effectiveness, practicality, cost and availability.
Effectiveness simply means the technology’s potential to increase income or decrease costs. Practicality refers to the “pain” factor. Some technologies may be effective but involve such intense management that few will use them. Cost and availability are likely to change over time, so we must know not only how available and costly a technology is today but how available and costly it is likely to be in the future.
A truly organized thinker would rate technologies with a table like the following one (Table 1). We can’t fill in the table at this point because there are too many unknowns, particularly in the cost and availability columns. Instead, let’s consider a couple of informative examples.
* Marker-assisted selection for polygenic traits is a practical technology. It’s no more difficult for a commercial producer to use than a sire summary, and no more expensive for the commercial producer, either.
It’s also quite practical for the seedstock producer. He’ll need to collect some tissue on his animals and send it to a laboratory. The cost to him may not be too great on a per head basis but, with many animals being tested, can add up. Remember, the cost of research to develop the technology is considerable.
The effectiveness of marker-assisted selection isn’t immediately clear. Effectiveness depends on whether consistently important major genes are segregating for traits of economic importance, whether reliable markers or direct tests for these genes are found, and whether alternative sources of information are available in quantity. The jury is out, but evidence suggests marker-assisted selection will be useful for traits related to disease resistance and carcass quality.
* Cloning. The availability and cost of cloning are in question, but there’s no doubt about its effectiveness in commercial production – at least short term. The “genetic lift” created by the use of superior clones is substantial.
Cloning is especially interesting from the standpoint of practicality. In most cases, the higher tech a technology is, the more intensive management must be to make the technology effective.
Take artificial insemination, for example. For most commercial operations, the inconvenience of concentrating cattle, heat detecting, and breeding artificially outweigh (at least in the minds of commercial producers) the advantages of AI.
The same is true of embryo transfer, only the effect is multiplied. And cloning, when it involves large-scale embryo transfer, fits the same pattern. But what about cloned bulls?
It is not inconceivable that commercial producers will soon be able to buy, at $2,000 to $3,000, a copy of a highly superior, high-accuracy herd sire in the form of an embryo in a test tube, a fetus in a recipient cow or a yearling bull in the flesh.
Packaged in the latter form, this technology is the ultimate in convenience – just turn the bull out with the cows. Cloned bulls represent a rare commodity – a high-tech solution that doesn’t require intensive production practices to implement.
The Importance Of Trait Evaluation The third category in the list of breeding technologies is for technologies designed to evaluate the relative importance of traits. Just one technology is listed in this category, selection indexes, and that suggests, perhaps, that this is not an important category.
I think it suggests something quite different: that we are not paying enough attention to evaluating the relative importance of traits. By using the technologies in the other categories we can create rapid genetic change in the national cowherd. But there is no guarantee that we will change the cowherd for the better.
Charging ahead with new selection and mating technologies without evaluating traits is like building a new jet, complete with the most powerful and fuel-efficient engines, but without a navigation system. Trait evaluation technology is that navigation system.
In truth, there are more technologies in the trait evaluation category than selection indexes. I like to lump them under the heading of multiple-trait selection technologies.
Selection index technology is a start. Having general indexes for terminal sires and maternal breeds would be instructive. More useful, however, are customized multiple-trait selection technologies, techniques that allow individual commercial producers to derive indexes (or alternatives to indexes like sire sequences) specific to their environment, management practices and market.
Bioeconomic simulation has great potential in this respect and has the advantage of helping producers make not only breeding decisions but management decisions of all kinds.
As we learn more about new and changing breeding technologies, we will begin to fill in the table on page 43. It will become clear which technologies to get excited about, which to dismiss, and which to watch closely. And, (I hope) we will see more technologies, particularly multiple-trait selection technologies, appearing in the table, catching people’s imaginations, and finding success.