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| Linebreeding by Dr. Fred C. Homeyer, 1999 Antelope Creek Ranch Linebreeding and inbreeding are subjects that most folks talk about in quiet whispers as if they were "dirty words." In truth, however, what may be considered incestuous for humans is accepted practice in the production of high quality breed stock in many animal species. Since this subject has captured my attention lately, I decided to do some research and reading about linebreeding and how one uses this concept to improve the genetic base for a group of animals. Quite a lot has been written about linebreeding and some of the information that was written over 50 years ago is just as valid today as it was when it was first written. One of the books that I read in this area was "Aids to Goatkeeping" by Carl A. Leach. This book was first copyrighted in 1926 and the edition that I had was copyrighted in 1971. It is important to note that the ideas expressed in this book has been around for some time and have gained considerable acceptance, especially in the dairy goat world. Mr. Leach was the editor of Dairy Goat Journal for many years and has a way of explaining a complicated idea in simple terms. Animals can be bred for purposes other than for producing offspring. For example, dairy cows are bred primarily to produce milk rather than calves. Sometimes a person uses great care in studying and considering particular animals in order to improve the genetic case of a specific herd of animals and sometimes a person has the goal of improving an entire breed of animals. "Grading" is a term given to the breeding program when the goal is to improve the offspring by taking common or indigenous animals and breeding them with a high bred animal in order to produce an offspring that is an improvement on the common or indigenous parent. In most cases one of the mates in this type of breeding program is a purebred or pure blood animal. Sometimes one can experience what is known as hybrid vigor where the offspring is considerably better than expected and in some cases this hybrid vigor will be expressed in some quality that is even better than the purebred mate used in the breeding. Linebreeding and inbreeding are the terms that often crop up in a discussion of breeding practices. The two terms mean the same thing. Linebreeding has a positive connotation while inbreeding is negative. What is normally considered incestuous or forbidden in humans can actually be a good practice for animals. Many great herd sires from various breeds are in fact very highly line bred, that is, they are the product of carefully planned matings of animals that are closely related such as a father bred to a daughter or a mother bred to a son. The mating mentioned above is the "closest" or "tightest" for of linebreeding. Breeding grandparents back to grandchildren is still considered to be linebreeding although not as close as the "closest" form. Linebreeding is practiced in an effort to intensify desirable traits and characteristics of a particular ancestor in an animal's pedigree. The more this close breeding of relatives occurs, the more consistently good traits can be realized in the offspring. Desirable traits in goats might include strong feet and legs, good reproduction, great mass and muscle, good milk production and other desirable characteristics. Of course, with the good comes the bad and linebreeding can also cause very bad traits, weaknesses and defects to show up in the offspring including traits termed "lethal genes." One example of a lethal gene might be a situation where the large intestine does not meet with the rectum and the animal dies within 24 hours of birth. Other examples of bad traits might be overshot ("parrot mouth") or undershot jaw, crooked legs, etc. Linebreeding is also inbreeding in the strictest sense, but the main idea that perhaps differentiates the two terms is that linebreeding is inbreeding with very well-defined goals in mind. The goal of linebreeding is to get as much blood from a given line of animals into the offspring. Normally inbreeding refers to the indiscriminate breeding of related animals without paying attention to particular blood in the parentage, such as breeding brothers to sisters without specific goats in mind. Brother bred to sister is a close for of inbreeding and what one normally thinks of when you mention inbreeding. This practice is not considered to be linebreeding as no increase in blood from a particular ancestry is realized when mating brother to sister. Even though this is considered to be the worst case of inbreeding , it is possible that even brothers and sisters can be quite different biologically. This is according to the laws of nature as stated in something called Mendel's law. Carl Leach in his "Aids To Goatkeeping" book states that: "Linebreeding is the most powerful method known of making the most of the excellence of superior individuals. It is the method by which the highest possible percentage of the blood of an exceptional individual can be preserved to characterize an entire line of descent, with the same speed as shown by the law that governs grading. It is not a method of originating excellence, but of preserving and utilizing it. It is probably safe to say that all really great animals in every breed have been strongly inbred themselves, since closely bred animals are enormously prepotent over everything else." Linebreeding emphasizes bad characters as well as the good. If weaknesses and defects occur in linebred strains, it merely amplifies those already existent - it does not make them. This very amplification of defects makes linebreeding important to the breeder in demonstration the hereditary characters with which he must deal in his breeding program." The idea of always needing "new blood" or changing sires in a herd quite often can be harmful rather than helpful for many breeders. A sire with "new blood" can bring unknown undesirable traits to a herd. The chance of introducing the bad qualities from "new blood" is far greater then the dangers that may result from close or tight linebreeding where you are aware of the desirable characteristics and heritage of the sire you are using. The breeder should try to introduce the qualities of his very best animal throughout his herd by introducing the blood of a good sire in the offspring. This process should continue as long as improvement in the offspring is realized. Page 21 of Leach's "Aids to Goatkeeping" gave me a new view of the amount of contribution that a particular animal makes in the pedigree of an offspring. Pedigrees and registration papers have their greatest value when used to plan a breeding system to improve a given herd of animals. "Pedigree or ancestor worship" occurs when one gives some distant ancestor credit for the good qualities of the offspring under consideration. A distant relative may constitute only a very small part of the inheritance in an offspring. When mating two animals, the sire and his full pedigree of ancestors contribute one half or 50% of the inheritance in the offspring while the dam and her entire pedigree of ancestors contributes the other one-half. The actual sire and dam each contribute 1/4 of the offspring's pedigree while the grandparents of the sire and dam each contribute 1/8. The great-grand parents each contribute 1/16 and the great-great-grand parents each contribute 1/32. The fractional contribution of each ancestor that hoes further and further back in a pedigree gets less and less. In other words, the great-great-great grandparents each give 1/64 each and so on. It is sometimes very helpful to know the characteristics and qualities of a given animal's brothers and sisters as one can see the qualities of an entire family exhibited by examining as many siblings as possible. Knowing the good qualities of an entire family can be very beneficial in a study of pedigrees where the breeder is establishing a breeding system to improve his herd. Knowing the percentage contribution of a particular ancestor makes one realize that you can get more than the one-fourth contribution from the sire of an individual by having the sire appear in other places in other generation in the pedigree. This goes the same for the dam. There is term called genetic representation that gives an indication of the total contribution from a specific animal appearing in several places in the pedigree. It might be possible to get a high enough genetic representation from a particular sire of dam such that it is as if this specific sire or dam produced the offspring under consideration even though it wasn't actually the physical parent. " The idea of linebreeding and inbreeding really opened my eyes to some ideas I had never thought of before. You may have seen some pedigree where the same sire or dam appears several times in the background of a particular animal. Each time the ancestor appears a lot of time in both the sire's side and/or the dam's side we can get what is termed a high "genetic representation" for that ancestor. If the genetic representation for a given animal approaches 40% to 50% it would be as if that ancestry almost were able to clone himself in the offspring whose pedigree we are examining. -by Dr. Fred C. Homeyer, 1999 Antelope Creek Ranch |
Boer Goats in West Central Minnesota
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