While inbreeding is a form of line-breeding and the two are related, no pun intended, they are different.
According to Jim Lents, owner of the Anxiety 4th line of horned Hereford cattle in Oklahoma, a line not outcrossed since the 1870’s, the difference between inbreeding and line-breeding is the amount of genetic influence any single animal plays in any descendent’s genetic makeup.
For instance, any individual is made up of 50% of each of its parent’s nuclear DNA (Mitochondrial DNA plays a role here; however, they are passed down only through the egg. In order to keep things simple we’ll ignore mitochondrial DNA for the time being). Â In other words, the sire and dam of your “best” cow each contributed 50% to that cow’s DNA. Â A daughter to that cow receives 25% each from her dam’s parents and 25% each from her sire’s parents, potentially watering down the quality and predictability of subsequent offspring.
In line-breeding the idea is to always keep the amount that any one animal contributes to the DNA of any descendent at or below 50%. Â With inbreeding you regularly will find a higher degree of influence. Â For instance, a sire/daughter mating will result in an offspring which carries 75% of it’s DNA from the sire and only 25% from the maternal dam. Â Interestingly, before the advent of genetic testing for recessive traits the only way to statistically ensure genetic “purity” of a bull/ram/buck etc. was to breed that bull to 35 of his own daughters concurrently. Â If no genetic defects show up in any of the offspring, the bull is 99.7% likely to be genetic defect free.
In any case, mating two full siblings together does not qualify as inbreeding because the level of influence any one of the grandparents exercises is still only 50% on the individual resultant calf from that full-sib mating.
In conversation with Dr. tatiana Stanton (yes, she spells her given name entirely in lower case) from Cornell University, the optimal level of relationship across a given herd/flock of animals is 12.5%. tatiana is the NY State Small Ruminant Specialist with Cornell Cooperative Extension and she is a breeder of goats and a goatherd in her own right. This 12.5% relationship ensures consistency of type and kind, uniformity of animals, while also allowing for enough diversity to avoid inbred suppression across the herd.
Wye Angus is a herd, really a program, owned and operated by the University of Maryland Foundation. Â The herd has had no new introductions of genetics since 1957. Â Many of the cattle within the herd will have individuals occurring hundreds of times in a given pedigree, yet the individual whose pedigree we are looking at may only carry an inbreeding coefficient of six or seven percent.
For my purposes, having certain extremely high quality individuals appearing multiple times up close in a pedigree is important. Â Most of my bull customers have completely heterogeneous herds of cows. Â By using a high quality bull that has been selected from proven lines of maternal efficiency, good disposition, longevity and phenotypic correctness, they imbue far more predictability and consistency into their subsequent calf crops.
One key component to any breeding program is culling. Â As a breeder of registered parent stock which I sell to commercial cattlemen and women, it is incumbent upon me to identify and remove any faults that may be hidden within my herd of cattle. Â I sincerely hope never to sell problems into someone else’s herd, especially genetic problems which are insidious in a total outcross environment.
If you have not read the book, Battle of Bull Runts, I highly recommend it. Â This is the story of how the simple recessive, lethal defect of snorter dwarfism (colloquial, I know) was not just propagated within the Hereford breed, but nearly brought the breed as a whole to commercial irrelevance from the 1920’s to the 1960’s. Â Through much investigative work looking through reams of pedigree documents the “index” animal was identified as a bull born in 1901. Â That bull was used in a complete outcrossing program for eight or nine years, only by natural service. Â Yet, the results of his offspring never being purposely and purposefully bred to one another allowed this simple genetic defect to go undetected until the 1920’s and unrecognized for what it was until the 1940’s.
Interestingly, the Anxiety 4th Herefords were one clean repository of genetic material from which the Hereford breed was able to  rebuild.  Why? The cattle in the herd have never been outcrossed.  Any defects that might be present are detected early and culled.
These same breeding principles, including heavy culling, are found in every breed and species of animal currently in domestication. Â The principles are actually quite close to what happens in isolated populations of wild animals, as observed and pondered by Charles Darwin. Â Also interestingly, Mr. Jim Lents, the current owner/breeder of the Anxiety 4th Herefords, is a devout Christian who looks to the Book of Genesis for his guidance in breeding. Â So whichever side of that particular discussion you come at breeding your own animals from, line-breeding works.
Check out the whole series on breeding matters by Morgan Hartman:
Line Breeding is Good for Profit
Breeding Matters III – Inbreeding vs. Linebreeding
Part IV – Culling for Fertility
Mr. Emenheiser, I was surprised when I was told of the low level of line breeding in antelope and such. As I now think of this it appears to be an outlier with a different genetic adaptation that can save a population when environmental extremes threaten their existence.
Mr. Hartman, I must disagree with one portion of your article, which by the way, is very good. You stated, “was not just propagated within the Hereford breed, but nearly brought the breed as a whole to commercial irrelevance from the 1920’s to the 1960’s.” The Hereford breed continued with without a drop in numbers during that period, and in fact, it wasn’t until the 1970’s that Hereford registrations began their downhill slide.
The Hereford problems began with their continued emphasis on the show ring and not the genetic problems they allowed to build and not confront, which were cancer eye, prolapses and bad uddders. Then they compounded on this with the assumption that bigger and faster was better. Their complete disregard of reality has brought them down. As an old Hereford man I have tracked this destruction of a breed that owes its problems to man, not the breed. I have discussed this with Jim Lents.
There is good information here, but I’d like to clear up a few things.
First, linebreeding is a form of inbreeding, not the other way around. Inbreeding is the mating of any two individuals that are related. If they have at least one individual on both sides of their pedigree, no matter how far back, they are related. Linebreeding is a strategic use of inbreeding, with attention given to the degree of relationship to a superior ancestor.
The maximum level of inbreeding “allowed” in linebreeding isn’t an arbitrary number as presented here, however. Some herds can tolerate a much higher level of inbreeding (i.e., pedigree relationship) than others and still be productive. A lot depends on the purity of the founder population, and the rate at which that high level of inbreeding was achieved.
The percentages described in the third paragraph are simply not how genes work. Genes don’t mix like colors of paint, they segregate at random. We might expect an individual to receive 25% of its genes from each of its grandparents, but the reality is that that number can range from 0 to 50%. That is further reason why the quality of linebreeding programs should be defined by more than just arbitrary limits for inbreeding and relationship estimates.
Even in isolated wild populations, adaptation requires variation, and so the greatest fitness usually lies in heterozygotes. Heterozygotes don’t breed true, but they preserve the genetic diversity that the species needs to survive in a changing environment. Our goals in artificial breeding are a bit different, because the most valuable use for that heterozygote advantage is in the F1 cross, and we must maintain predictable purebred populations in order to produce it consistently.
Joe Emenheiser, PhD
University of Vermont Extension Livestock Specialist
Hello Readers,
Morgan Hartman and Joe Emmenheiser have been conversing by email and wanted us to share it with you. Here you go:
From Morgan:
Thank you for your clarifications, Dr. Emenheiser.
Through this series of articles I’ve been trying to keep things as simple as possible in relation to the discussion of genetics. In using general assumptions, like the “expected” inheritance of 25% of an individual’s genes from each of its grandparents, there will of course be technical errors made. I do understand genes don’t mix like paint and there will be a range of inheritance from individuals from previous generations within a given pedigree.
But the main thing to remember here is exactly your point, and mine, that the quality and predictability of not only individuals but whole groups from within a given line breeding program is predicated upon the quality of foundation stock and the inherent selection required to eliminate undesirable traits. Once those populations of animals in the programs in question have moved past the Bulmer Effect and have been under continual selection for a suite of traits, the overall utility of those populations to both breeding stock and commercial cross breeding programs will be heightened relative to the breed as a whole.
Anyway, thank you. Most of why I write is to engage in conversation. For my own part, I really appreciate being corrected when I’m wrong about something. At the same time, when I’m trying to communicate a pretty complex concept I’m willing to generalize for the sake of pushing the conversation.
If you are interested, I encourage you to visit http://www.pinebank.co.nz for an interesting look at a breeding program with a lot of success and history. Their breeding program started with line breeding/inbreeding to provide a foundation, but then progressed into a more elaborate set of protocols designed by Dr. Ch’ang of Massey University in NZ.
I hope we can converse over time, Dr. Emenheiser. I know I have far more to learn. Thank you.
All the best,
Morgan
From Joe:
Morgan,
Thanks for your reply. I appreciate your efforts with the series of breeding articles, and I thought the discussion of maintaining purebreds for the purpose of making crossbreds was handled particularly well. It’s a tough subject to convey without getting too technical and without having our generalizations taken as gospel. The intentional gospel and technical inaccuracies spread by many linebreeding gurus increases the challenge of conveying science. But at the end of the day, I’m just as passionate about the subject, and I agree that the most important goal is to encourage thoughtful conversation. I hope you realize that my comments were intended as such, and I look forward to visiting with you more about this as some point.
By the way, I met you several years ago (and visited about Pinebank, etc.) at a Grazing Conference in West Virginia. I was in graduate school at Virginia Tech at the time. I’m sure our paths will cross regularly here in the Northeast, and I look forward to it.
Thanks again,
Joe