Lec 28

• Mating type


  Outbreeding - Mating of unrelated or distantly related individuals<|>Crossbreeding - Mating of individuals of different breeds<|>Terminal crossbreeding - Mating of individuals of specific breeds of sire which are mated to specific breeds of dam and no replacements are produced<|>Rotational crossbreeding - Mating of individuals of two or more sire breeds in a cycle where replacement females are kept for a generation
• Heterosis


  Advantage of the crossbred compared to the average of the parental purebreds
• Breed Complementarity


  Optimum combination of breeds using strengths of breeds, especially in choosing dam and sire breeds
• Trait


  • Heritability
  • Heterosis, %
• Traits of importance in choosing breeds for crossbreeding

  • Dam breed - Reproduction, Maternal ability, Milk production, Mature size
  • Sire breed - Fertility, Longevity, Weaning weight, Growth rate, Carcass traits
• Heterosis or Hybrid Vigour (H)


  Heterosis due to dominance effects expressed in heterozygotes
• Approaches to genetic improvement through crossbreeding

  • Terminal crossbreeding system to produce market animals
  • Rotational crossbreeding system to produce market animals while producing own replacements
  • Synthetic breed development to produce market animals and at the same time generate and maintain own replacement herd
• Synthetic breed


  Composite - Technically all breeds started as synthetics/composites, later evolved into stabilized breeds upon adaptation to the local environment
• Reasons to develop a new breed:
• Requirements to be successful in building a new breed:
• Examples of Composite Breeds of Beef Cattle

  • Santa Gertrudis
  • Brangus
  • Beefmaster
  • Simbrah
  • Brahmousin
  • Brahmaine
• Generation


  • Individual Heterosis
  • Maternal Heterosis
• After a breed is developed, selection to improve and increase uniformity will result in some heterosis being lost
• How to build a 5/8 A: 3/8 B composite breed

  1. A x B - 1/2 A : 1/2 B

  2. A x AB - 3/4 A : 1/4 B

  3. AB x A(AB) - 5/8 A : 3/8 B
• Breed


  A group/population of individuals belonging to the same species sharing common phenotypic characteristics and genome, stabilized after several inter se matings (usually F4 or later)
• Developing a Composite breed

  1. A x B - Hybrid AB

  2. Hybrid AB x AB - Composite AB
• Crossbreeding programme for ruminants in Malaysia:
• Breeding objectives - Traits to consider

  • Adaptability of dam - Fertility, Fitness, Disease & Parasitic resistance, Low feed quality
  • Longevity of dam - Reproductive efficiency, Maternal ability
  • Maintenance cost of dam - Mature size
  • Growth and carcass merit of sire - Targeted for specific production environment
• Breeds of beef cattle

  • Bos indicus - Kedah-Kelantan, Bali, Brahman, Nellore, Yellow cattle
  • Bos taurus - Herefords, Angus, Shorthorns, Limousin, Charolais, Simmental, Maine Anjou
• Individual Heterosis (IH) in Beef Cattle

  • Bos taurus x Bos taurus < Bos indicus x Bos taurus (Florida environment)
  • Calving difficulty when using small size dam breeds to breed to bigger size sire breeds
  • Bos indicus heifers bred with Bos taurus bulls have little calving difficulty
• Maternal Heterosis (IM) in Beef Cattle

  Calving rate, Calf survival, Birth weight, Weaning weight - Bos taurus x Bos taurus < Bos indicus x Bos taurus
• Retained Heterosis in Composite Breeds
• Traits associated with carcass merit (rib eye area, marbling, meat tenderness) not affected by crossbreeding
• Differences in mature size of crossbred cows due to differences in breed additive effects or breed complementarity
• If traits are solely controlled by additive gene effects then Average F1 = Average parental breeds
• More heterosis results from Bos indicus x Bos taurus crosses than from Bos taurus x Bos taurus crosses
• 1. breed Terminal Crossbreeding in Beef Cattle

  1. Charolais bulls x Brahman bulls x Red Angus cows = Brangus

  2. F1 cows bred back to Angus sires to reduce dystocia

  3. Replacement heifers purchased from outside
• 1. breed Rotational Crossbreeding in Beef Cattle


  Charolais - Brahman - Angus in a cycle
• Each approach (terminal, rotational crossbreeding and breed development) has its own merits and demerits
• Crossbreeding in Goats - Similar approach as with beef cattle
• Crossbreeding in Swine
• Composite breed to produce range chickens
• Summary: Breed or Composite Development from Crossbreeding