ADSC 2010 Lecture 21 Outline of Last Lecture I Inheritance Continued A Co dominance B Epistasis C Over Dominance D Heterosis II Improving Quantitative Traits A Two Basic Methods 1 Selection a Methods of Selection b Selection Tools 2 Mating or Breeding Systems a Breeding Value i Transmitting Ability 1 Expected Progeny Difference EPD 2 Predicted transmitting Ability PTA Outline of Current Lecture I Mating Systems 1 Radom Mating 2 Inbreeding 3 Outbreeding a Relationship of heritability and heterosis for different traits b How do we combine selection and mating systems II Crossbreeding Systems 1 Two Breed Terminal Cross 2 Two Breed Rotational Cross 3 Three Breed Rotational Cross Current Lecture Requirements that make genetic progress 1 Trait must be heritable 2 Must be variation in population Problems cloning Genetic process h2 x SD H2 heritability SD selection pressure difference between the average of the individuals selected for mating and the population Ex Backfat BF x 0 8 Boar A 0 4in 0 5in h2 0 5 Boar B 0 6in SD 0 3in 0 5 0 8 GENETIC PROCESS 0 5x 0 3 0 15in Population if all come from A and B will have 65in go down 5in avg x I Mating Systems Organized manner of mating the selected animals 1 Random mating no selection 2 Inbreeding mating of animals that are more closely related than the average of the population Line breeding concentrate the genotype of one superior animal Mother to grandson Father to granddaughter Reduce genetic variation look like one another Cattle certain lines selected Negative issue with Inbreeding depression reduction of genetic variability and thus reduced vigor and fertility 3 Outbreeding mating of animals that are less closely related than average of population crossbreeding Ex Heterosis lowly heritable traits Duroc Boar 2 4lbs day X Yorkshire Sow 1 8lbs day V Cross bred pigs 2 3lbs day Absolutely heterosis 2 3 2 1 0 2 heterosis 0 2 2 1 095 9 5 Predictive of Duroc and Yorkshire for the specific trait II Complementarity moving forward of genetics of crossbred parents that would maintain superiority of offspring Ex Angus into crossbreeds genes for marbling into next generation HIGHLY HERITABLE TRAITS a Relationship of heritability and heterosis for different traits Trait Heritability Heterosis Carcass High 4 5 Low Growth Med 25 35 Med Repro Low 1 2 High Big influence of repro traits environment Carcass genotype lower role on environment environment also heterosis big impact b How do we combine selection and mating systems Suffolk male x merino x rambouillet female Highest quality cross bred heterosis Meat complem SELECTION PRESSURE ON MALE Crossbreeding Systems 1 Two Breed Terminal Cross End when crosses everything produced market Breed A Breed B Progeny AB Marketed Advantages simple o Maximized heterosis 100 A B at every gene loci a allele and b allele Replacement females Disadvantages have to maintain purebred herds o No heterosis in females o Used by small producers in cattle 2 Two Breed Rational Cross Always mating females to opposite breed of their sires Used a lot in beef cattle Ex Angus Hereford black belay Herd 1 Bull breed A Herd 2 Bull breed B Replacement females Steers Cull heifers Steers Cull heifers Market Advantages o Simple o Produce Females o Heterosis dam Disadvantages o 2 3 of offspring have heterosis 67 heterosis o 2 pastures needed 3 Three Breed Rotational Cross Used in Deseret ranches in FL Brangus Simbrah Braford 54 000 moms Advantages o 86 heterosis o Produce Females o Heterosis in dams Disadvantages o Large numbers needed o Multiple pastures o Labor intensive Replacemen t females Replacemen t females Replacemen t Herd 1 females Bull breed A 14 5 A 28 5 B 57 0 C Herd 3 Bull breed C 28 5 A 57 0 B 14 5 C Herd 2 Bull breed B 57 0 A 14 5 B 28 5 C
View Full Document
Unlocking...