Breeding Matters III – Inbreeding vs. Line Breeding

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).  In other words, the sire and dam of your "best" cow each contributed 50% to that cow's DNA.  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%.  With i

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4 thoughts on “Breeding Matters III – Inbreeding vs. Line Breeding

  1. 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.

  2. 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.

  3. 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

    1. 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 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,

      From Joe:

      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,

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