This message is from: "Janet" <[EMAIL PROTECTED]> John F Lasley's book, 'The Genetics of Livestock Improvement' is a classic text on selection and improvement of livestock. The definitions used there in are quite universal. Lasley's work is one of the foundations of modern principles used in animal breeding and selection.
he defines inbreeding as: 'a mating system in which progeny are produced by parents more closely related than the average of the population from which they come.' which sounds very close to the definition of a breed with one exception, when defining breed we are looking at the amount of relatedness of a group of animals to the whole species, and with inbreeding we are looking at the relatedness of an individual to a subset within the species from which it came. he defines linebreeding as: 'a system of mating in which the relationship of an individual or individuals is kept as close as possible to some ancestor in the pedigree.' (for which I appologize for my previous definition, which missed the heart of what linebreeding truly is about. But I redeem myself with Lasley's quote later in the chapter 'Linebreeding is often looked upon with favor by breeders, but inbreeding is not, probably because linebreeding is usually not so intense, and when it is used, the inheritance of truly outstanding individuals is concentrated in the pedigree). he defines crossbreeding as: 'the mating of animals of two or more different breeds.' he defines outcrossing as: 'the mating of unrelated animals within a breed.' and then goes on to say that: 'Although crossbreeding is more extreme than outcrossing the genetic effects of both are similar'. [in a separate, more recent text "Genetic Improvement of Cattle and Sheep" by Geoff Simm, defines inbreeding depression as 'The decline of performance, especially in traits associated with functional fitness , such as reproduction rate and disease resistance) which is a consequence of inbreeding'. I add to this that the more prolific the species (i.e. dogs) the easier it is to overcome inbreeding depression because the reproductive rate is naturally very high thus assuring at least one offspring will survive to carry on the next generation. In less prolific animals (i.e. the horse is very low) it is more difficult to overcome inbreeding depression because it may become impossible for each parent to put at least one viable offspring on the ground before it is removed from the breeding population. this same text also states that, 'It (inbreeding) is also an inevitable consequence of long term selection in a closed population.' By forbidding close inbreeding, the NFHR is slowing the rate at which inbreeding impacts the Fjord breed.] I was not aware that the phrase 'out cross' was considered vulgar language, or otherwise inappropriate language for a discussion list consisting of some folks who are active horse breeders.... especially since outcross refers to matings that take place -within- a pure breed. Since the NFHR forbids inbreeding, I would hope a discussion on the definition and merrits of outcrossing is welcomed and can be included here in a mature and sensible way. Janet
