Chapter 14 Animal Science Larson
Chapter 14 Animal Science Larson ADS 1113
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This 3 page Class Notes was uploaded by Kaitlyn Notetaker on Monday October 3, 2016. The Class Notes belongs to ADS 1113 at Mississippi State University taught by Dr. Larson in Fall 2016. Since its upload, it has received 10 views. For similar materials see Animal Science in Animal and Dairy Science at Mississippi State University.
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Date Created: 10/03/16
Chapter 14 Animal Science: Mating Systems Learning Objectives o Describes the roles of animal breeders o Describe the advantages and disadvantages of inbreeding, linebreeding, outcrossing, and crossbreeding. o Describe heritability and heterosis o Calculate percent heterosis o Discuss the role of composite and hybrid breed formation. Mating Systems o We have already discussed seedstock and commercial producers Seedstock breeders often produce registered, purebred animals Commercial producers often produce crossbred animals for slaughter (non-breeding purposes) o Animals breeders make 3 critical decisions Choosing individuals that become parents Determining the rate of reproduction from each individual More on the sire side Deciding which mating system is most likely to yield beneficial results o Genetic improvement can be optimized by utilizing a combination of selection and mating systems o Inbreeding: mating of animals more closely related than the average of the breed or population o Outbreeding: mating of animals not as closely related as the average of the population o Inbreeding results in offspring with an increase homozygosity of gene pairs This discussion is a bit complicated in the book, I just want you to know the basic concepts Sometimes it (inbreeding) is good, sometimes it is bad o Two forms of inbreeding Intensive inbreeding: mating of closely related animals whose ancestors have been inbred for several generations Linebreeding: a mild form of inbreeding where inbreeding is kept relatively low while maintaining a high genetic relationship to an ancestor or line of ancestors Safer, middle road Intensive Inbreeding o Observations include: Increased inbreeding is usually detrimental to reproduce performance and pre and post weaning growth Inbred lines are more susceptible to environmental stressors Inbreeding may slow genetic improvement because there is no heterosis Inbreeding quickly identifies some desirable genes and some undesirable genes Superior inbred animals will create more uniform superior offspring Swine and poultry have had success in creating inbred lines o Seedstock producers may use inbreeding, but most commercial operations try to avoid it Linebreeding o Low risk form of breeding o Used most commonly by seedstock producers that cannot find more superior sires than the ones they raise in their herds (no selectional differential) o Inbreeding below 20% is considered low, whereas high when it reaches 50% or more. Outbreeding o Four types Species cross: crossing of animals of different species 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. Can involve some crossbreeding or it can be a type of outcrossing system o Two reasons Take advantage of breed complementation Benefit of crossing breeds for their strengths and weaknesses complement one another Heterosis The increase in productivity in the crossbred progeny above the average of breeds Most impactful on survival rates of newborns, longevity, and reproductive merit Calculating Heterosis o In book on page 230; table 14.2 Heritability and Heterosis Pg. 231 Table 14.3 Traits Heritability Heterosis o Reproduction o Low o High o Growth o Medium o Medium o Carcass o High o Low o Depending on the trait one is trying to improve, a producer should take into account this info o Crossbreeding is used commonly in swine, beef cattle, and sheep operations o Used much less commonly in dairy operations because milk yield is so important and the Holstein breed is superior in this trait Outcrossing o The process of mating unrelated animals within the same breed in an attempt to maximize heterozygosity Mask the expression of deleterious recessive alleles I think of this as trying to limit disadvantages to inbreeding while avoiding crossbreeding (incorporating other breeds) Grading Up o Continuous use of purebred sires of the same bred in a herd o Used mostly commonly in cattle and horses o A way to incorporate a new superior sire of a different breed into a “commercial” herd to generate offspring with those better qualities Generate ¾, 7/8, 15/16 breed animals o Figure 14.12 on page 233 was described in class so take a look at that New Breeds o Beef cattle Composite breeds Brangus, Beefmaster, Santa Gertrudis, MARC1 are examples of beef cattle o MARC stands for Meat Animal Research Center MARC1 consists of Crosses of Charolais, Brown Swiss, Limousin, Hereford, and Angus Breeds o Swine Hybrid boars development from crossing swine breeds but then inbreeding o Poultry Breeding for broiler or egg production Specific lines developed for highly productive birds Summary Points o Genetic relationship estimates the genes two animals have in common because the same ancestors appear in the first six generation of their pedigrees o Mating systems are identified by the genetic relationship of the animals being mated o Inbreeding is the mating of animals more closely related than the average of the population, while outbreeding is the mating of animals not as closely related as the average of the population o Inbreeding increases genetic homozygosity, while outbreeding increases genetic heterozygosity o Linebreeding is a mild form of inbreeding while maintaining a high genetic relationship to an outstanding ancestor o Outcrossing is the mating of unrelated animals within the same breed o Crossbreeding is the mating of animals from different breeds, resulting in heterosis (hybrid vigor) Review Questions: 1, 2, 3, 4, 5, 6 Possible Essay Questions: 2