Unit X: Principles of Selection and Assisted Reproductive Technologies PDF

Unit X: Principles of Selection and Assisted Reproductive Technologies Clarissa Therese M. Mordeno, DVM Objectives: 1.Evaluate the concepts of selection associated with herd environment. 2.Discuss the advantages and limitations of selection methods for multiple traits....

Unit X: Principles of Selection and Assisted Reproductive Technologies Clarissa Therese M. Mordeno, DVM Objectives: 1.Evaluate the concepts of selection associated with herd environment. 2.Discuss the advantages and limitations of selection methods for multiple traits. 3. Enumerate and discuss the common applications of assisted reproductive technologies in animal production. Outline: Recall patterns of selection Sexual Selection Artificial Selection Multiple Trait Selection Assisted Reproductive Technologies in Animals Recall: What is natural selection? What are the 3 patterns of natural selection? Directional Stabilizing Disruptive 4th Pattern: Sexual Selection - acts on traits that affect an individual’s ability to attract mates - powerful enough to produce features that are maladaptive to survival - Ex. Peacocks - Male peacocks adorn extravagant tails feathers to attract females - These extravagant and colorful tail feathers are likely to attract predators as well Mechanisms of Sexual Selection 1. Intersexual selection (mate choice) 2. Intrasexual selection (mate competition) 1. Intersexual Selection (Mate choice) involves individuals of one sex choosing among members of the opposite sex based on the attractiveness of certain traits that those individuals possess Example: long-tailed Manakin Males form pairs and perform dance displays in front of a female The female chooses among the different pairs The alpha male reproduce while the beta male does not 2. Intrasexual Selection (Mate competition) - involves one sex competing with members of the same sex for access to mates Male Deers Male Northern Elephant Seals Artificial Selection Artificial Selection Artificial selection is an evolutionary process in which humans consciously select for or against particular features in individuals The goal is to select superior animals  Artificial Selection Example: Pug What is the first step in selection of animals? Determine the selection objectives - which characters you aim to improve Selection is a multi-stage process 1. First stage (Initial): Phenotypic selection - physical attributes of phenotypic performance 2. Second stage (Final): Genetic selection - based on the breeding value of the animal 1. Phenotypic (Initial) Selection i. The selected animals should be free from any type of congenital defect ii. Functional reproductive system iii. The selected animals should be healthy and free from serious diseases. iv. Should be from the better performing dam or sire 2. Genotypic (Final) Selection Based on the animal’s breeding value Paternal Maternal Estimated on the basis of: Grand Grand Grand Grand i. Individual’s own performance Sire Dam Sire Dam ii. Performance of individual’s relatives Sire Dam Direct Collateral Collateral Individual relative Progeny Basis and Importance of Selection from Relative’s Performance (i) When the individual selection is not possible Sex-limited traits Traits that cannot be measured in living animals (ii) When selection is required earlier but the trait is expressed in later life of the individual Examples: lactation milk yield in dairy animals egg production Mature weight (iii) When the h2 of the trait under selection is low Multiple Trait Selection Multiple Trait Selection A selection program which usually focus on several traits of economic importance 3 methods: 1. Tandem selection 2. Independent culling levels 3. Total score or Selection index 1. Tandem Method The selection in which several traits are improved in succession Focuses on one trait at a time Trait A is improved first, then trait B, and so on. Less efficient than other methods Requires more time for improvement in all the traits The efficiency of this method depends on the genetic correlation among the traits under selection. 2. Independent Culling Levels (ICL) Involves selection for two or more traits at a time Cull independently and simultaneously for each trait A minimum standard (level) for each trait is fixed Every animal to be selected must meet the minimum level for each of the trait under consideration An animal with s poor performance in one trait is rejected despite being exceptionally good in one trait Traits Standard Buffalo No. 1 2 Age at first calving or AFC (months) 42 40 44 Milk yield (kg) 1900 1950 2100 Fat (%) 7 7 6.5 Which buffalo will be selected and which will be culled? 2. Independent Culling Levels (ICL) Advantages: Selection for more than one trait at a time Culling at early age Disadvantages: No compensation for other traits Culling level More emphasis on early expressed traits Effectiveness of this method depends on the level kept for each of the traits 3. Total Score or Selection Index Selection is practiced for several traits simultaneously but with a net merit Differs from ICL in that: 1. Culling levels are flexible 2. Each trait is weighted by a score and summed to a total score (index value) for each animal, which is taken as selection criterion 3. Superiority in some traits can make up deficiency in others Sample Problem: A swine breeder is selecting for increased number of pigs weaned (NW) and reduced backfat (BF) in her pigs. She plans to choose three out of the following eight boars based on EBVs for these traits. Which boars would she initially select using tandem selection: i. when NW is the first trait under selection? ii. when BF is the first trait under selection? Sample Problem: A swine breeder is selecting for increased number of pigs weaned (NW) and reduced backfat (BF) in her pigs. She plans to choose three out of the following eight boars based on EBVs for these traits. Which boars would she select using independent culling levels if the levels were set at 0 pigs for NW and -0.1 in for BF? Sample Problem: A swine breeder is selecting for increased number of pigs weaned (NW) and reduced backfat (BF) in her pigs. She plans to choose three out of the following eight boars based on EBVs for these traits. Which boars would she select using independent culling levels if the levels were set at 0 pigs for NW and -0.1 in for BF? Sample Problem: A swine breeder is selecting for increased number of pigs weaned (NW) and reduced backfat (BF) in her pigs. She plans to choose three out of the following eight boars based on EBVs for these traits. Applying this index value to all eight boars, which boars would she select? Assisted Reproductive Technologies in Animals  Artificial Insemination (AI) and Cryopreservation AI is the manual deposition of sperm suspension, fresh or frozen- thawed, into the female reproductive tract Improvements in methods to cryopreserve (freeze) and store semen have made AI accessible to more livestock producers Multiple Ovulation and Embryo Transfer (MOET) reproductive technique that primarily aims to fertilize several oocytes in a shorter period to produce more viable embryos, which are transferred into the recipient, resulting in a higher birth rate In Vitro Fertilization Accomplished by generating embryos from elite cows called donors and transferring them into cows with less genetic merit called recipients Sex Determination of Sperm Process of determining which sex chromosome a sperm carries Using a specific dye that binds to DNA and a flow cytometer/cell sorter, the DNA content of individual sperm is measured In cattle, for example, the X- bearing sperm contain 3.8 percent more DNA than the Y-bearing sperm. Nuclear Transfer or Cloning Since the mid 1980s, technology has been developed to transfer the nucleus from either a blastomere or a somatic cell to an enucleated oocyte This produces multiple copies of animals that are themselves nearly identical copies of other animals To date, somatic cell nuclear transfer has been used to clone cattle, sheep, pigs, goats, horses, mules, cats, rabbits, rats, and mice. Nuclear Transfer or Cloning  References Chapter 14. Bourdon, R. (2014). Understanding Animal Breeding. 2nd ed. Pearson Education Ltd. UK. pp155-165. Tomar, S.S. (2004). Textbook of Animal Breeding. Kalyani Publishers. IND Sexual Selection. https://evolution.berkeley.edu/evolution-101/mechanisms-the-processes-of- evolution/sexual-selection/ Evolutionary fitness. https://evolution.berkeley.edu/evolution-101/mechanisms-the-processes- of-evolution/evolutionary-fitness/ The Amazing Long-tailed Manakin Courtship Display. https://www.youtube.com/watch?v=dysuZHnwv3Y&t=11s Sexual Behavior of Male Northern Elephant Seals: I. Lethal Injuries to Adult Females. https://www.jstor.org/stable/4534913?seq=2 Cloned endangered horse ‘thriving’ at San Diego Safari Park. https://ktla.com/news/california/cloned-endangered-horse-thriving-at-san-diego-safari-park/ Research in Assisted Reproductive Technologies. https://www.nifa.usda.gov/grants/programs/animal-programs/research-assisted-reproductive- technologies