The Benefits of Inbreeding
Inbreeding is little understood by most people, including many livestock breeders. But if you know what you’re doing, it’s the surest way to improve your stock.
There are two methods of breeding: inbreeding and out breeding. The closest inbreeding possible is self-fertilization. It is the union of the egg and sperm of the same individual to form a new individual, and it is practiced to a great extent among certain plants and to a very small extent in the animal kingdom. In the higher animal forms this kind of breeding cannot take place due to the separation of the sexes.
The nearest approach to self-fertilization is the mating of brother to sister, of son to mother and of father to daughter. In these cases the germ cells, although not from the same individual, are very similar in structure.
Inbreeding has been condemned by nearly all breeders on the grounds that it tends to decrease size, vigor and fertility of the strain. Let us look for a few moments at the biological evidences we have, and see whether inbreeding is really harmful.
We find that many of our most important cereal grains such as wheat, oats, and rice regularly reproduce by means of self-fertilization. This process has been carried on in these forms for centuries with no apparent weakening. On the other hand, attempts to produce many other forms, such as Indian corn, by means of self-fertilization have always resulted in the production of small unproductive plants. Experiments carried out by Darwin and later by Shull show that if two of these small unproductive plants obtained by inbreeding are crossed, a plant of normal vigor and productiveness is again obtained.
In the animal kingdom, similar results have been obtained. Close inbreeding, when it is not accompanied by careful selection, always results in weakening effects. It is for this reason that the practice is condemned by most animal breeders. Experiments carried on by some early researchers resulted in animals with decreased size and lack of fertility, but then other experiments had exactly the opposite results.
Dr. Helen King of Wistav Institute inbred rats for 40 generations. Her inbred rats were not only as large and as vigorous as other rats, but were far superior to the average. Some of them weighed over 600 grams, being the largest on record. This weight was obtained as a secondary characteristic, as none of them were selected on the basis of size alone.
Dr. King attributed her success to three things: 1. Good foundation stock 2. proper care; and 3. careful selection.
The importance of good foundation stock cannot be over-emphasized as most of the breeding stock found in this country is not worth the room it occupies. The animals are sold for high prices because of their show qualities and the pedigrees which accompany them regardless of their vitality. On the other hand, high vitality should he the fundamental thing to consider when purchasing stock. No matter how near the standard an animal may be it is worthless as far as breeding qualities are concerned if it is of low vitality. Our standards in many instances are at fault.
The importance of proper feeding and care is recognized by every successful breeder. The rations must he well balanced so as to meet the conditions of the animals. The accessory food products known as vitamins must be present in sufficient quantities. These vitamins are found in the outside coverings of all grains, in milk and in many other natural foods. The surroundings of the animals must also be the very best. They must not he subjected unnecessarily to disease germs and they must be kept in clean, sanitary hutches.
By far the greater part of the success obtained by anyone in inbreeding depends on the proper selection of the stock to be used for breeding. Only the strong, vigorous animals carrying the desired characteristics should be selected. Inbreeding tends to bring together factors which are similar, while cross breeding tends to bring together factors which are different.
Continued inbreeding thus reduces the number of different combinations it is possible for the factors to form in fertilization and thus it enables the breeder to more easily produce the desired characters. Cross breeding on the other hand tends to introduce new possibilities and thus it draws the characters of the stock away from a certain specialized standard into the more general character of the race.
It has been found that by inbreeding, all the bad qualities of the strain crop out in the first few generations. This is the reason so many breeders have become discouraged with it and have been advocates against its use. However, if the breeder would persist through this discouraging period, he would he able by careful selection to eliminate all the bad qualities and thus produce a superior strain. When these defects have once been eliminated they will never reappear provided no new blood is introduced.
Cross breeding keeps the defects of a strain hidden and it also keeps continually introducing more hidden weaknesses. Inbreeding does not create defects as is generally supposed. It brings to the surface defects that have always been present. Cross breeding, on the other hand, does not exterminate defects, it merely hides them.
It is therefore a decided advantage to the animal breeder to practice close inbreeding, provided he is willing to stick to it and practice careful selection, if he desires to produce purebred stock. Any breeder who is not willing to carry it through to the finish should never attempt inbreeding except in the more modified form of linebreeding.
Cross breeding produces stock of increased vigor because it brings together germ cells which differ in their chemical composition. They are therefore more active chemically after fertilization. Cross breeding may be practiced by the breeder who is breeding only market stock, but should never be practiced by the breeder who is trying to produce stock in certain specialized characters.
-Countryside & Small Stock Journal,
Vol. 83 No. 5, Sept. Oct. 1999
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 tin 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