There are basically two kinds or patterns of selective breeding.  One is line breeding and the other is outcross breeding.  Line breeding involves breeding to fairly close relatives and thus is a kind of inbreeding, whereas outcrossing involves breeding to non relatives or to very distant relatives, those to which there is no known genetic link.

Each of these breeding patterns has its advantages and disadvantages.  Line breeding can accomplish several goals:  1)  produce a more consistent and uniform offspring;  2) identify breeding populations that have no genetic flaws, or identify existing flaws so they can be eliminated;  3)  accentuate and sustain more consistent excellence; 4)  develop linebred progeny that will provide a "genetic kick" or hybrid vigor when they are outcrossed with non relatives.

The advantage of outcrossing is basically what people call hybrid vigor.  This gives a genetic kick to offspring that are from parents that are as genetically distant from each other as possible within a given species.  This is essentially the advantage derived from cross breeding, but that advantage declines in each successive generation.  It is not as sustainable as the strengths developed from line breeding.

The difference between line breeding and outcrossing within a species can be illustrated on the macro level by the differences between breeding purebreds in one breed as opposed to breeding across breeds in the bovine species.  At the macro level, all Herefords are linebred and any breeding of Herefords to other breeds is outcrossing or cross breeding.

Within the Hereford breed or line of purebred Herefords, there are two types of line breeding possible.  One is to create a closed line of Herefords whose offspring are all bred to other animals or their linebred descendents in the original genetic pool.  This pattern concentrates on accentuating the best traits that exist in the original genetic population, and the goal of this closed line pattern of breeding is to develop a very consistent and uniform group of excellent cattle.  On the macro level that is how the "breeds" we have today came into existence.  All Herefords trace to a small group of similar type of cattle developed in Herefordshire, and all registered Herefords trace to those animals in the original Herdbook.  That is why Herefords of today that are purebred or closed line have the unique color patterns and composition associated with purebred Herefords.  Those patterns have been "locked in" by closed line breeding.

In America, two universities are best known for the closed lines of Herefords they developed.  These are Montana State University and Colorado State University.  These schools selected particular original groups of herefords as their base genetic pool, and then developed them as closed lines, meaning they never bred any of them to animals outside the original group or linebred descendents of the original group.  The most famous of these are the Line Ones developed at MSU and the Prospectors developed at CSU.  Each of these breeding programs had 8 or 10 other closed lines but they did not develop the overall excellence and popularity that the Prospectors and the Line Ones did.  That could be both due to the original animals selected and the success of the selection program within those lines.  This would be considered closed line breeding.

One of the great individuals produced from the line bred Prospectors was Prospector 7558.  He was bred to over 110 of his own daughters without producing any genetic flaws.  He is possibly the purest genetic package ever produced in the Hereford breed.  The successes of the Michigan State herd, the Frank Felton herd and Witherspoons Nizhoni Herefords all trace in part to the influence and impact of this great sire.  He was born in 1967, and was still being used 25 years later.  We still have semen on this great sire and many of his descendents.  Over half of the bulls in our 2000 Semen Sale Catalog are descendents of this great line bred sire.

Dr. Harlan Ritchie of Michigan State University had this to say about Prospector 7558:  "We have used many of the top horned and polled Hereford bulls in our breeding program and, based on two years of natural service, we have found that Prospector 7558 sired more merchantable bulls and excellent replacement females than any other bull we have ever used.  7558 added frame size and muscle composition while also strengthening maternal traits as his daughters are standout females and exceptional milkers.  The fact that he is 42% inbred makes him genetically very predictable which he has proven through his progeny.  Prospector 7558 may have more superior performance genes without evidence of defect than any other known bull."
 

In the Spring 2000 North American Sire Summary, 7558 has a scrotal EPD of +2.1 with an .89 accuracy.  There is not another bull in the breed today with an SC accuracy above .70 that has any higher scrotal EPD.  And most of the high SC EPD bulls of today, like Feltons 517, all trace to Prospector 7558 in multiple lines.  He is the premier bull of all time for fertility, and through line breeding that excellence was locked inand continues in his progeny and grand progeny today.  And fertility has been shown to be economically by far the most important production trait.

Back when breed associations wisely limited the AI use of unproven bulls, Prospector 7558 was the the first ever Hereford bull to attain Class AAA status, meaning his AI use was unlimited.  Of 7558 Dr. Richard Williams of Iowa State University stated:  "A progeny test of a sire bred to his own daughters checks the entire gene package for deleterious recessive genes.  This bull (7558) has little or no chance of carrying deleterious recessive genes.  As such, he is an excellent candidate for a sound line breeding program.  To double up on a sire's genes is a sound way to develop sons that will be superior to him, and thus have a creative breeding program based on this individual as a starting point."  How prophetic he was!

Using a line bred son of 7558, Prospector 0716, Frank Felton created just such a breeding program, and the result is Feltons 517, probably the most complete bull ever produced in the breed.  And 517 did not come about by accident, he was creatively produced with a plan and a discriminate selection program, the basis of which were superior line breeding patterns that were realized over long periods of time.

The other form of linebreeding is the line breeding of a particular individual.  In this case, one selects a particular sire or dam to line breed, as is done in 7558's pedigree below.  In this case the bull selected for line breeding is Prospector 4126.  The line breeding is created initially by breeding 4126's sons to 4126's daughters.  To achieve the best results of this form of line breeding, one should select only the very best son or sons of the bull to be used on only the very best daughters of the bull.  This produces half brother/half sister matings.  The resulting pedigree has two lines tracing to the choosen bull who is the grandsire on both sides of the pedigree.  Then one can extend the line breeding by selecting the best linebred sons to be bred to the best linebred daughters, producing a pedigree that makes the original bull the grandsire on all four lines of the pedigree, as is found in the pedigree of Prospector 7558 below.
 

And, of course, one can keep going with this pattern of line breeding.

The result of this pattern of line breeding will be a more and more uniform offspring but slower and slower progress toward higher levels of performance.  However, the progress made will be sustainable in future generations within the line, and will really provide a genetic kick when those linebreds are outcrossed with non relatives.

Line breeding narrows the normal genetic distribution curve, producing a more consistent offspring and thus more consistently generating the progress made.  Outcrossing widens the normal distribution curve, producing more inconsistency but, through the advantages of hybrid vigor, the overall progress will be more rapid.  This rapid progress, however, is not sustained in additional generations unless it is, so to speak, locked inby linebreeding.

This is why I emphasize a combination of line breeding and line crossing or outcrossing, building on the advantages of both and overcoming the disadvantages of each.