Breeding sistem

• Breeding System


  Two basic systems: 1. Straight breeding, 2. Crossbreeding
• Factors that determine the system used

  • Kind of livestock
  • Size of the herd
  • Amount of money available
  • Goals of the farmer or rancher
• Straight breeding systems


  • Purebred breeding
  • Inbreeding
  • Outcrossing
  • Grading up
• Crossbreeding systems


  • Two-breed crosses
  • Three-breed crosses
  • Rotation breeding
• Purebred animal


  Animal of a particular breed with characteristics of that breed, where both parents were purebred
• Purebred animals


  • Color markings is the most common disqualification
  • Not necessarily better than non-purebred
  • Undesirable recessive characteristics may appear due to homozygosity
• Inbreeding


  Mating of related animals, increases genetic purity but exposes undesirable and desirable genes
• Types of inbreeding


  • Close breeding (most intensive)
  • Linebreeding (distantly related animals)
• Outcrossing


  Mating of animals of different families within the same breed, to bring in desirable traits
• Grading up


  Mating of purebred sires to grade females, to improve the grade of the offspring
• Crossbreeding


  Mating of two animals from different breeds, producing a hybrid with hybrid vigor
• Methods of selection


  • Individual selection
  • Family selection
  • Sib selection
  • Selection by progeny test
• Individual selection


  Based on own performance records, most simple
• Family selection


  Based on average performance of family, more complicated and expensive, used for low heritability traits
• Simultaneous improvement of traits

  • Tandem method (one trait at a time)
  • Independent culling level (based on pre-determined performance)
  • Selection index (each trait weighted by coefficient)
• Inbreeding


  Increases homozygosity, leading to inbreeding depression and reduced fitness
• Inbreeding depression


  • Reduced juvenile survival, adult survival, mate acquisition, social dominance, fertility, fecundity, growth, proper development, disease resistance, environmental stress resistance, metabolic efficiency, sensory acuity
• Non-inbred crested wood partridges had 8% higher egg volume, 10% higher egg weight, 20% higher hatchability rate, and 41% fewer medical notes compared to inbred counterparts
• Linebreeding


  Mating system to maintain high relatedness to a particular ancestor, a mild form of inbreeding
• Linebreeding very quickly loses the gene combinations that defined the superior ancestor
• Crossbreeding


  Crossing animals from different breeds
• Breed


  Subpopulation of a species inter se mated with the objective of maintaining particular characteristics
• Differentiation in breeds


  • Different objectives using artificial selection (e.g. Holstein for milk, Hereford for beef)
  • Originate in different environments and influenced by natural selection (e.g. Brahman vs Hereford)
• Breeds represent different reservoirs of genes, with different alleles and frequencies
• Reasons for crossbreeding


  • Complementarity (combine best characteristics)
  • Method of migrating new genotypes
  • Creating synthetic breeds
  • Rapid change in performance