Crossbreeding theory

Commercial pig, beef cattle and sheep

production has relied on crossbreeding for

more than 50 years to improve survival,

fertility, growth and disease resistance.

Heterosis

The effects of heterosis are the opposite of the

effect of inbreeding depression. At each location

of the pairs of chromosomes the two genes are

much less likely to be identical with crossbreeding

than with same-breed matings. Therefore, genetic

recessives of both major and minor consequence

are not expresses. Research indicates that heterosis

is greatest for traits related to vitality, fertility, health

and survival.

Heterosis is not everything – the addititve breed

effect are important in crossbreeding as well as in

all breeding. The heterosis will be an extra benefit

on top of the parent average. So one critical point is

to always use the best bulls from breeds that suits

your conditions. A crossbreeding program needs to

be well planed and organized to produce benefits.

The breeds you pick must be unrelated, competitive

and have a efficient breed improvement program

– and remember to use the best bulls for the best

results.

Why three breeds?

Capturing and sustaining heterosis is a key part

to a efficient cross breeding program. Once you

have gotten used to the extra bonus of heterosis

you do not want it to drop below 75%. For 2-breed

crisscrossing the extent of heterosis drops to 50%

in the second generation – levelling of at 67%.

A system of 4 breeds results in a high heterosis

on average – 93% but it is very hard to find 4

competetive, unrelated breeds for most production

systems. A 3-breed rotation is the optimum and

results in average heterosis of 86%.

Colour tagging

To make your crossbreeding system as easy as

possible colour tagging is a good option. You

simply use 3 different colour ear tags on the calves.

Calves sired by Holstein get, for example, a blue

tag. Calves sired by Swedish Red get a red tag and

the calves sired by your third breed (for example

Jersey or Montbeliarde) get a yellow tag. When you

see a blue tag you know that that animal will be

inseminated with Swedish Red semen etc. When

you have your 3-breed crossbred you just begin the

circle once again by inseminating with Holstein.