[Jacob-list] Inbreeding and siblings

[Neal and Louise Grose]

"Neal: I thought the books said father/daughter or mother/son are okay, but bad, bad, bad is brother/sister.  You're saying just the opposite, right?"

Inbreeding is probably a bad idea in many cases, but it can be useful at times. Generally speaking, what we perceive as attractive is actually average: horns not too far forward, not to far back; markings not too black, not too white; body type not too large, etc. These are things that are most easily achieved by a high degree of heterozygocity: they are the result of crossing types and bloodlines. (A few years back, Newsweek did an issue on attractiveness in people. A composite photo of an average female face looked very much like Hale Berry. ) The trick is that these don't always breed true because the offspring only gets 1/2 of these genes, and it may not get the balance of the genes needed to look like much. For example: crossing Lincoln and merino will produce a fabulous long and soft fleece in the offspring, but the next generation may be short and course.

Inbreeding is not as severe in sibling crosses as it is in parent offspring crosses. A sister and brother will each carry 1/2 of the genes from each parent, but they may not be the same 1/2. With flocks, there will be several sets of genes from different ewes. At any rate, there is at least a chance for a new combination of these genes to occur.

Imagine if you would, that we start out with a starter flock of ten unrelated ewes and one ram, and move to an island off the coast and loose the phone number of the guy with the boat. 

If we use the ram for several years, the first year, all the lambs will carry 1/2 of his genes. If the ram is bred back to its offspring, then the resulting offspring will carry 3/4 of the genes of the sire. [1/2 + 1/2(1/2)] The next generation, the lambs will carry 7/8 of the genetics of the ram. The ram croaks at this point, and a new ram selected from this generation and used on his sisters would produce a high degree of inbreeding.

 Suppose instead, we use the original ram the first year and then have him for Winter Solstice dinner. The next fall, we choose his best ram lamb and use him back on the ewes and then eat him. He is only related to his sister and his dam. The next fall, we use a yearling ram from the first year's crop. Here again, HE is only related to his sister and his dam. Each year thereafter, we use only yearling rams, and vary the dams that these rams are selected from. The inbreeding influence on the flock as a whole is never as severe as it would be if we used the original ram back on his offspring. 

The important thing here is that we allow the genetic influence of the better ewes to be harvested for use in our breeding program. We have more information on our ewes than on our rams initially because we have more history with them. Concentrating on the rams means that we never know quite what we have until we see a few dozen of their offspring.

Neal Grose
North Carolina, where inbreeding is no big deal

"Invention does not consist in creating out of void, but out of chaos" Mary Shelly




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