Genetics- Animal Breeding

• Animal breeding


  Selection of the best parents for the next generation
• Animal breeding is not the same as reproduction
• Breeding goals


  • Select adapted animals (breeds) to a specific environment
  • Adapted animals = fertile / reproduce
  • Growth / products
  • Product quality
• Phenotype (P)


  How the animal looks, performance
• Genotype (G)


  Genetic composition of the animal, DNA
• Environment (E)


  All non-genetic factors that impact the animal, including nutrition, parasites, climate, age of dam, birth status, gender
• Phenotype = Genotype + Environment
• The best genetics will perform superior in a given environment
• Genetic variability is random in nature due to random segregation and independent assortment
• Variation is crucial for survival
• An animal's superior performance might be due to either superior genetics or a favourable environment
• In a given environment, the animal with superior genetics will always outperform the inferior genes
• Selection


  Choosing and growing specific individual animals with desirable characteristics
• Trait


  Observable / measurable characteristic
• Phenotype


  Measured level of performance for a trait
• Categories of traits


  • Fitness
  • Production
  • Quality
  • Type
  • Behavioral
• Fitness traits


  • Litter size, ovulation rate, calving interval, survivability
• Production traits


  • Weight, growth rate, milk yield, greasy fleece yield

  
• Quality traits


  • Meat tenderness, butterfat, fibre diameter
• Type traits


  • Udder conformation, legs, functional efficiency
• Behavioral traits


  • Temperament, learning ability, milk speed
• Traits may be species / breed specific
• Breed specific traits


  • Polled trait in cattle, fleece traits in goats and sheep, performance in race horses
• Animal recording


  Integrates animal identification and registration, animal traceability, animal health information and animal performance data
• Animal recording is an information tool to select the best parents for the next generation
• Animal recording process


  1. Identification system

  2. Recording of data (pedigree & performance & dates)

  3. Information system (manage data)

  4. Data analyses (on farm – index)

  5. Genetic evaluation (Breeding values)

  6. Application of the results (EBV and or selection indices)

  7. On Farm selection
• Recording starts with an identification number and pedigree
• Identification methods


  • Notching, tags, tattoos
• Practical example of animal recording

  Calf is born, weigh the calf, identify the calf and parents, send in birth notification, record cow info, record calf post-weaning

  
• Traits recorded


  • Reproduction data (conception rate, calving rate, number of offspring)
  • Production data (pre-weaning growth, post-weaning weight, quality traits)
  • Body measurements (height, length, scrotal circumference, udder conformation)
• Recording and storage of data can be paper-based, electronic devices, or specialized software
• What we do with the data

  1. Use contemporary groups for comparison

  2. Calculate genetic parameters

  3. Estimate breeding values

  4. Develop selection indices

  5. Breeders perform objective and accurate selection
• Selection is not a simple process, it requires setting objectives, animal recording, and statistical analyses
• Contemporary groups


  Groups of animals influenced by the same known and unknown environmental effects, used for objective comparison of traits
• Contemporary groups need to have at least 5 animals per group, and be correctly adjusted for sex, birth status, and age of dam
• Contemporary groups will differ depending on the species
• Sheep & pigs – birth status more important than in cattle
• Some production systems may have more than one breeding season – number of seasons may differ
• Additional management inputs e.g. feeding of preferential treatment will add to the contemporary groups
• Contemporary groups need to have

  • At least 5 animals per group (more always better)
  • Correct / adjust for sex, birth status
  • Use less levels for i.e. age of dam
  • Never form a group on a trait that you want to evaluate
  • Aim is to "compare green apples with green apples"