Major Systems of Crossbreeding

Question 1

What are the three major systems of crossbreeding?

Answer 1

terminal, rotational, and rotaterminal

Question 2

What is terminal crossbreeding?

Answer 2

all offspring are sold, none are retained as replacement parents

Question 3

What is an example of a 2 breed terminal cross?

Answer 3

Rambouillet ewe x Suffolk ram

Question 4

What are genetic benefits of terminal cross?

Answer 4

direct heterosis in F1 crossbred lambs and breed complementation

Question 5

Why are rambouillet crossbred?

Answer 5

maternal traits, adaptability to physical and managerial environment

Question 6

Why are terminal sire breed crossbred?

Answer 6

growth rate and carcass merit

Question 7

What kind of limitations does 2 breed terminal crossbreeding have?

Answer 7

genetic and management

Question 8

What genetic limitations does 2 breed terminal crossbreeding have?

Answer 8

does not benefit from maternal heterosis

Question 9

What management limitations does 2 breed terminal crossbreeding have?

Answer 9

• provision of replacement females
• must purchase
• need reliable, healthy, and economic source

Question 10

What terminal crossbreeding occurred in the 1950s?

Answer 10

herefords bred with Angus

Question 11

What are the two main types of terminal cross breeding?

Answer 11

2 breed and 3 breed cross

Question 12

Which type of terminal crossbreeding is better?

Answer 12

3 breed

Question 13

Why is 3 breed terminal crossbreeding better?

Answer 13

maximization of maternal heterosis, genetically superior

Question 14

Why were Herefords bred with Angus?

Answer 14

angus produce low birth rate cattle, decrease in dystocia

Question 15

What problems had arose from Hereford breeding?

Answer 15

because of selection of bulls for growth rate, Herefords had dystocia

Question 16

What were the results of terminal breeding of Hereford and Angus?

Answer 16

direct heterosis for growth and survival of crossbred calves

Question 17

What happened after Angus and Hereford were bred?

Answer 17

in 2nd and subsequent matings, Hereford cows were mated to Hereford bulls

Question 18

What is 3 breed terminal crossing?

Answer 18

F1 crossbred females from 2 maternal breeds mated to males of sire breed

Question 19

What does 3 breed terminal crossing utilize?

Answer 19

maternal and direct heterosis

Question 20

What 3 breed terminal cross use increased?

Answer 20

increased breed complementation because both maternal breeds chosen for maternal traits

Question 21

What are maternal traits?

Answer 21

• adaptability to environment
• high merit for reproduction
• milk production
• mothering ability

Question 22

What is a drawback of 3 breed terminal cross?

Answer 22

purchase replacement females or keep separate herd for seedstock

Question 23

What is rotational crossbreeding?

Answer 23

production of herd replacements

Question 24

What happens after several generations of rotational breeding?

Answer 24

all dams and offspring will be crossbred

Question 25

What results from rotational crossbreeding?

Answer 25

direct and maternal heterosis

Question 26

What happens to original purebred dams in rotational crossbreeding?

Answer 26

will be replaced by crossbred descendants

Question 27

What do offspring and dams benefit from in rotational crossbreeding?

Answer 27

both direct and maternal heterosis

Question 28

What do offspring and dams not benefit from in rotational crossbreeding?

Answer 28

maximum potential heterosis

Question 29

What do offspring inherit in rotational crossbreeding?

Answer 29

some proportion of non-heterotic gene combinations

Question 30

What do 4 breed rotational crossbreeding systems retain more than 3 breed?

Answer 30

more heterosis

Question 31

Why are 4 breed rotational crosses less popular?

Answer 31

• more complex to manage

- easier to find 3 breeds that compliment well

Question 32

How does terminal crossbreeding choose breeds?

Answer 32

choose maternal and paternal breeds for sire and dam

Question 33

How does rotational crossbreeding choose breeds?

Answer 33

each breed is used as sire and dam

Question 34

How do terminal crossbred offspring compare to rotational?

Answer 34

more uniform

Question 35

What overlap is in rotational crossbreeding?

Answer 35

• overlap of generations within herd at any one time

- different aged females belonging to different generations

Question 36

What is needed in rotational crossing to make appropriate matings?

Answer 36

2 sire breeds each year

Question 37

What must happen with each female in rotational crossing?

Answer 37

must be mated to appropriate sire breed and she needs permanent ID

Question 38

What is a result of females needing permanent ID and needing to be mated to an appropriate sire for rotational?

Answer 38

increased labor and management

Question 39

What is rotaterminal?

Answer 39

a compromise between rotational and terminal crossbreeding systems

Question 40

What does rotaterminal use?

Answer 40

use rotational among maternal breeds to produce replacement gilts for terminal matings

Question 41

How many breeds are involved in rotaterminal?

Answer 41

rotational crosssbreeding among 2-3 maternal breeds

Question 42

What is produced from rotaterminal crossbreeding for the rotational crossing segment?

Answer 42

replacement females and also males

Question 43

What are the males produces from the rotational segment of rotaterminal?

Answer 43

not good market animals

Question 44

What is done with the first few cycles of females in rotaterminal?

Answer 44

breed to sire of maternal breeds and then terminal sire breeds

Question 45

Why are females bred to maternal breed sires in rotaterminal?

Answer 45

to reduce dystocia

Question 46

Why are females bred to terminal sires after a few matings to maternal sires in rotaterminal?

Answer 46

to produce large offspring, selected for growth rate

Question 47

How does breeding occur in rotaterminal?

Answer 47

breed females to terminal sires after a few matings to maternal sires