Breeding Issues (Conservation Genetics, Scrapie, et)

Howling Oak Ranch

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Breeding Issues

As breeders of livestock, we are responsible for maintaining the valuable traits of the animals within our care. Most of us also hope to improve the utility and / or beauty of the breeds we are working with.

The breeding of purebred animals is relatively new -- the concept of "pureblood" arose in the 1800s. Unfortunately, many breeds that are maintained with closed stud books have experience precipitous declines in quality and vigor. Modern scientific techniques, such as genotyping and sequencing of species' genomes, will increase breeders ability to change breeds to suite our purposes. There is some question, however, whether we have the wisdom to make good choices for the breeds of which we are stewards.

This page is an attempt to both provide information and promote discussion of these issues.

Conservation Breeding

Conservation breeding is a technique used to maintain genetic diversity within a population. Genetic diversity allows a breed or species to maintain reproductive vigor (i.e., avoid or reduce inbreeding depression) and provides breeders with the raw material needed to adjust the breed to changes in environment or circumstance. Many modern breeds have little genetic diversity due to over-use of popular sires, the ease with which artificial insemination can spread the popular type of the day, and for minor breeds, contraction in breed numbers. The genetic diversity that remains is an invaluable resource, and I hope this page will provide some useful guidelines on how it can be maintained.

Conservation breeding (link to part 1) by K. Gerhart (printable version)
Flock Improvement using Selection. Part 1: Calculations without weights, by K. Gerhart (printable version pdf)
Flock Improvement using Selection. Part 2: Calculations involving weights by K. Gerhart

Please see also:

Managing Breeds for a Secure Future: Strategies for breeders and breed associations. 2007. D.P. Sponenberg and D.E. Bixby. The American Livestock Breeds Conservancy, Pittsboro, NC
A Conservation Breeding Handbook. 1995. D.P. Sponenberg and C.J. Christman. The American Livestock Breeds Conservancy, Pittsboro, NC

Articles discussing loss of genetic diversity

Scrapie (an example of selection focused on one-trait)

Scrapie Primer: Selection for Resistance and Consequences for Genetic Diversity (An overview by K. Gerhart)
Does Q stand for Quality? (problems with selection for scrapie resistance in sheep by John Bare)
Breeding lambs for longterm scrapie resistance (a perspective from the UK)

Inbreeding Depression

Inbreeding: Its meaning, uses and effects on Farm Animals. by Vogt, Swartz and Massey. A technical disussion of inbreeding.