Reproduction and Genetics Lesson 15 – Mating Systems Why use mating systems??? – Genetic Superiority – Have animals that are genetically superior to other animals in the same breed or class. Animals are superior based on traits selected by the breeder. – Hybrid vigor (heterosis) – Performance of offspring that is greater than the average of the parents. Mating Systems • • Inbreeding – The mating of animals more closely related than the average of the breed or population. There are two types of inbreeding called intensive inbreeding and linebreeding. – Intensive inbreeding – Mating of closely related animals for several generations. – Linebreeding – A mild form of inbreeding that maintains a high genetic relationship to an outstanding ancestor. Outbreeding – The mating of animals not as closely related as the average of the population. There are four types of outbreeding called species cross, crossbreeding, outcrossing, and grading up. – Species cross – Crossing of animals of different species. (Example: Horse to donkey) – Crossbreeding – Mating of animals of different established breeds. – Outcrossing – Mating of unrelated animals within the same breed. – Grading up – Mating of purebred sires to commercial grade females and their female offspring for several generations. Taylor, Robert E., Scientific Farm Animal Production, 4th ed. Intensive Inbreeding. Why would we want to do intensive inbreeding? *Increase homozygosity in order to make sure certain traits are passed on to offspring and that they will breed true. For example PP will always be polled. pp x pp will always have horns. PP x pp will always be polled. Since inbreeding increases homozygous pairs, we can better predict offspring will breed true to what we are breeding for. Line Breeding Three Bars Impressive Three Bars Three Bars Line Breeding Continued Why would we want to do linebreeding? • It is a mild form of inbreeding used to maintain a genetic relationship to an outstanding sire. • It is used mainly by pure breeders because they have a hard time finding sires that are genetically superior to the ones they are already producing. • They are able to take advantage of an outstanding sire and cross with other genetically superior animals. Species Cross Why would we want to do a species cross? If your desired outcome will merit a species cross Example – Horse bred to a donkey to get a mule. Taylor, Robert E., Scientific Farm Animal Production, 4th ed. Crossbreeding Why would we want to use crossbreeding? By crossing breeds the strengths and weakness of each breed will compliment one another. Also increases heterosis, which increases the productivity of the crossbred offspring above the average of breeds that are crossed. Outcrossing Why would we want to use outcrossing? Unrelated animals of the same breed are mated. In order not to inbreed, but have animals maintain characteristics of the breed. Example – Unrelated animals of the same breed are mated. Taylor, Robert E., Scientific Farm Animal Production, 4th ed. Grading Up Why would we want to use grading up? In order to make a commercial cow herd a purebred cow herd. Once an offspring has 7/8 or 15/16 of the genetic make up of the desired breed, it is considered a purebred. This would take several generations of breeding up, but may be profitable when purebred females of high quality are very expensive.