Major Systems of Crossbreeding Flashcards
What are the three major systems of crossbreeding?
terminal, rotational, and rotaterminal
What is terminal crossbreeding?
all offspring are sold, none are retained as replacement parents
What is an example of a 2 breed terminal cross?
Rambouillet ewe x Suffolk ram
What are genetic benefits of terminal cross?
direct heterosis in F1 crossbred lambs and breed complementation
Why are rambouillet crossbred?
maternal traits, adaptability to physical and managerial environment
Why are terminal sire breed crossbred?
growth rate and carcass merit
What kind of limitations does 2 breed terminal crossbreeding have?
genetic and management
What genetic limitations does 2 breed terminal crossbreeding have?
does not benefit from maternal heterosis
What management limitations does 2 breed terminal crossbreeding have?
- provision of replacement females
- must purchase
- need reliable, healthy, and economic source
What terminal crossbreeding occurred in the 1950s?
herefords bred with Angus
What are the two main types of terminal cross breeding?
2 breed and 3 breed cross
Which type of terminal crossbreeding is better?
3 breed
Why is 3 breed terminal crossbreeding better?
maximization of maternal heterosis, genetically superior
Why were Herefords bred with Angus?
angus produce low birth rate cattle, decrease in dystocia
What problems had arose from Hereford breeding?
because of selection of bulls for growth rate, Herefords had dystocia
What were the results of terminal breeding of Hereford and Angus?
direct heterosis for growth and survival of crossbred calves
What happened after Angus and Hereford were bred?
in 2nd and subsequent matings, Hereford cows were mated to Hereford bulls
What is 3 breed terminal crossing?
F1 crossbred females from 2 maternal breeds mated to males of sire breed
What does 3 breed terminal crossing utilize?
maternal and direct heterosis
What 3 breed terminal cross use increased?
increased breed complementation because both maternal breeds chosen for maternal traits
What are maternal traits?
- adaptability to environment
- high merit for reproduction
- milk production
- mothering ability
What is a drawback of 3 breed terminal cross?
purchase replacement females or keep separate herd for seedstock
What is rotational crossbreeding?
production of herd replacements
What happens after several generations of rotational breeding?
all dams and offspring will be crossbred
What results from rotational crossbreeding?
direct and maternal heterosis
What happens to original purebred dams in rotational crossbreeding?
will be replaced by crossbred descendants
What do offspring and dams benefit from in rotational crossbreeding?
both direct and maternal heterosis
What do offspring and dams not benefit from in rotational crossbreeding?
maximum potential heterosis
What do offspring inherit in rotational crossbreeding?
some proportion of non-heterotic gene combinations
What do 4 breed rotational crossbreeding systems retain more than 3 breed?
more heterosis
Why are 4 breed rotational crosses less popular?
- more complex to manage
- easier to find 3 breeds that compliment well
How does terminal crossbreeding choose breeds?
choose maternal and paternal breeds for sire and dam
How does rotational crossbreeding choose breeds?
each breed is used as sire and dam
How do terminal crossbred offspring compare to rotational?
more uniform
What overlap is in rotational crossbreeding?
- overlap of generations within herd at any one time
- different aged females belonging to different generations
What is needed in rotational crossing to make appropriate matings?
2 sire breeds each year
What must happen with each female in rotational crossing?
must be mated to appropriate sire breed and she needs permanent ID
What is a result of females needing permanent ID and needing to be mated to an appropriate sire for rotational?
increased labor and management
What is rotaterminal?
a compromise between rotational and terminal crossbreeding systems
What does rotaterminal use?
use rotational among maternal breeds to produce replacement gilts for terminal matings
How many breeds are involved in rotaterminal?
rotational crosssbreeding among 2-3 maternal breeds
What is produced from rotaterminal crossbreeding for the rotational crossing segment?
replacement females and also males
What are the males produces from the rotational segment of rotaterminal?
not good market animals
What is done with the first few cycles of females in rotaterminal?
breed to sire of maternal breeds and then terminal sire breeds
Why are females bred to maternal breed sires in rotaterminal?
to reduce dystocia
Why are females bred to terminal sires after a few matings to maternal sires in rotaterminal?
to produce large offspring, selected for growth rate
How does breeding occur in rotaterminal?
breed females to terminal sires after a few matings to maternal sires
