Inbreeding

My  post, “How We Decide: Listen To Your Gut,” explained how we had three littermate boars who all had the same abnormality in which they couldn’t extend their penis to breed.

Dad and I discussed possible causes for this condition.  He thought it may be an inbreeding problem.  I thought it had something to do with the increased use of artificial insemination, (AI), in swine.

When we started using AI fifteen years ago, maybe only 10% of the nation’s hogs were produced with AI.  Now, probably over 90% of the nation’s hogs are produced using AI.

Boars which would have been culled because of poor natural breeding ability are now being artificially collected and their genes are spread throughout the population.  I detailed the steps I am taking to combat this problem in my last post.

Dad recently read an article about inbreeding which discussed the deleterious effect it has on reproduction.  And he rightly assumed that the dam of the three boars may have been slightly inbred.  So, combining these two facts caused him to theorize the problem was inbreeding.

Good thinking.  Except I told him I knew the sire of the boars was completely unrelated to the dam.  So there is no chance of inbreeding.

But Dad thought if one of the parents is inbred, then inbreeding may be a problem in the offspring.  And that brings me to my point.

It doesn’t matter how inbred one or both parents are. As long as the parents are not related, the offspring will not be inbred.

Let me explain.  But first let me define two terms, homozygous and heterozygous.  Homozygous is when a pair of genes at any location, (locus), is identical.  Heterozygous is when a pair of genes at any locus is different.

Let’s use coat color in cattle as an example.  One parent is an inbred Black Angus and one parent is an inbred Red Angus.  The Black Angus is black and its pair of genes is represented by BB.  The Red Angus is red and its pair of genes is represented by bb.

Because we know one gene is inherited from each parent, the offspring will get one black, B, gene and one red, b, gene.  The offspring’s genes are heterozygous, Bb, even though its parents were inbred and homozygous.  A single mating between unrelated, inbred individuals wiped out all inbreeding in the offspring.

This example also illustrates how inbreeding and homozygosity is not necessarily a bad thing.  Just ask any Black Angus breeder if she is concerned that her cattle are homozygous black!

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