Livestock breeding systems
-straightbred
-composites managed as straightbred
-rotations
-terminal sires
-combo terminal sire and other
downsides of straightbreeding
-no hybrid vigor
-no production system complementarity
-must adapt to local conditions
what is grading up(back crossing)
crossbreeding where each progeny is bred back to the same parental breed
T/F back crossing is inherently inbred
FALSE
main advantage of composite breed managed as straightbred
you get some heterosis but have the simplicity of a straightbred program
what amount of sires should be used in a base population to minimize inbreeding
15-20
why are foundation animals for composites so influential
they provide most of the DNA
what is the amount of hybrid vigor retained dependent on
-number of breeds in composite
-amount of hybrid vigor base breeds have with each other
-proportions of base breeds
best ways to increase hybrid vigor in composites
-more foundation breeds
-foundation breeds of different types
-equal distribution of breeds
-avoid inbreeding
what is the dominance model
heterosis is due to dominance at many loci
what is a two breed rotation
crossbreed 2 breeds, back cross to alternating breeds depending on which is lowest in the progeny until a 2/3, 1/3 equilibrium is established
advantages of rotations
-HV in offspring and in dams
-replacement females produced within the system
-retention of hybrid vigor in advanced generations
limits of rotations
-reduced production system complementarity
-fluctuations in calf productivity due to difference in sires
-cattle have long generations
-bulls of different breeds will all be used in a given year
-requires more fencing/pastures
methods to improve ease of management for rotations
time period of breed usage
(ex. breed 1 for 3 years, breed 2 for next 3, F1 for next 3, back to breed 1)
what is rotational grading up
backcross to one breed until they are majority that breed, then switch to back crossing to the other breed in the rotation
what is the purpose of a modified 3-breed rotation
ensure that significant levels of one particular breed is stable in the program
what is the purpose of terminal sire systems
create high levels of hybrid vigor and production system complementarity
disadvantage of terminal sire system
replacement females are not produced(F1 females are expensive)
possible risks of terminal sire program with pigs
pigs in confinement spread diseases easily, must take care when bringing in outside animals
terminal vs continuous crossbreeding
Terminal
-progeny genetically different than either parent
-most potential for heterosis and complementarity
Continuous
-progeny can b e replacements for at least one parent
–generally less heterosis and potential for complementarity
combo system with terminal sires
females are kept as replacements, and terminal sires are bred to some females in the herd
-requires atleast 2 sires at a time
self-contained terminal sire F1 production system
-all females are straightbreds
-some females can be bred to the same breed to produce replacements
-remainder of females bred to terminal sire
