Strategies to maintain genetic diversity in rare breeds of livestock
Mark Knauer, PhD
North Carolina State University Swine Extension Specialist
ALBC 11-8-13
Why is genetic diversity important?
Genetic diversity and inbreeding are inversely
related
Therefore, we work to keep inbreeding at a
minimum
– What is inbreeding? Mating together animals that are related by ancestry
Inbreeding is unfavorable
Impaired reproduction
7.58.08.59.09.5
10.010.5
0 10 20 30 40 50 60Inbreeding of dam, %
litter size
Adapted from Bereskin et al. (1968)
Inbreeding is unfavorable Impaired survival
Adapted from Bereskin et al. (1968)
7.58.08.59.09.5
10.010.5
0 10 20 30 40 50 60Inbreeding of litter, %
litter size - birth
litter size - market
Inbreeding is unfavorable
Impaired growth performance
Adapted from Bereskin et al. (1968)
232
234
236
238
240
242
0 10 20 30 40 50 60
lb.
Inbreeding of litter, %
weight at 180days of age
Inbreeding is unfavorable
Largest reproductive issue
– Getting females bred & continuing the
population
Inbreeding is unfavorable
Increased incidence of genetic defects
– hermaphrodites
Calculating inbreeding
Where
– t = generation and
– ∆F = 1/2Ne
Where Ne = the effective population size
Ft = 1 – (1 - ∆F)t
Maintaining genetic diversity
Reduce the rate of inbreeding
Ft = 1 – (1 - ∆F)t
Avoid mating close relatives
Avoid mating – in order of importance
– Parents and offspring
– Full siblings - brothers and sisters
– ½ siblings – ½ brothers and sisters
Increase the number of herd sires used
Important to use as many males as possible
Using a couple or several males, instead of
just 1, significantly reduces inbreeding
favorable unfavorable
Bring in outside genetics – live animals
If boar is too small
– Collect semen off of the sow in heat Inseminate sow with collected semen
– Use a breeding crate
If boar is too big
– Train to mount an AI dummy
– Use a breeding crate
What if your new boar is too large/too small for your females?
Bring in outside genetics – semen
Develop a grade up program
½ heritage
×
×3/4 heritage
×
×
7/8 heritage
Maintaining genetic diversity
Lengthen the generation interval
Ft = 1 – (1 - ∆F)t
Generation interval
Where L = generation interval
L = Lm + Lf
2______
__
Lengthen the generation interval
Do not keep offspring out of gilt litters
Keep offspring out of old boars and old
sows
Keep offspring out of older parents
Age of boar (yr) Age of sow (yr) Generation interval
Scenario 1 2 1 1.5
Scenario 2 5 4 4.5
Rate of inbreeding is 3 times less in scenario 2 vs. 1.
Strategies to maintain genetic diversity
Avoid mating close relatives
Increase your population size
Increase the number of males used for breeding
Bring in outside genetics
– Live animal introductions
– Semen
Develop a grade up program
Lengthen the generation interval
Thank you all for your hard work!
Maintaining heritage breeds can be
challenging
– Important to maintain the genetic diversity
associated with heritage breeds
Strategies to reduce inbreeding
Sample outside genetics
– At least once every 3 years
Lengthen your generation interval
– Retain old sows
Avoid mating
– Brothers and sisters
– ½ brothers and sisters
– Parents and siblings
Strategies to reduce inbreeding
Sample outside genetics
– At least once every 3 years
Lengthen your generation interval
– Retain old sows
Avoid mating
– Brothers and sisters
– ½ brothers and sisters
– Parents and siblings
Strategies to reduce inbreeding
Sample outside genetics
– At least once every 3 years
Lengthen your generation interval
– Retain old sows
Avoid mating
– Brothers and sisters
– ½ brothers and sisters
– Parents and siblings
Other benefits of using AI
Genetic improvement
– Only one “best” herd
Genetic cost - may be less expensive to use AI than
maintain a boar
– How many sows do you have?
Increase number of potential matings
– How many of you have had a boar that was too big or too
small to breed a desired female?
Other benefits of using AI
Genetic improvement
– Only one “best” herd
Genetic cost - may be less expensive to use AI than
maintain a boar
– How many sows do you have?
Increase number of potential matings
– How many of you have had a boar that was too big or too
small to breed a desired female?
Other benefits of using AI
Genetic improvement
– Only one “best” herd
Genetic cost - may be less expensive to use AI than
maintain a boar
– How many sows do you have?
Increase number of potential matings
– How many of you have had a boar that was too big or too
small to breed a desired female?
Summary
Multiple potential benefits to adopting AI
– Maintain genetic diversity!
– Genetic improvement
– Reduce genetic cost
– Increase boar usage
You are taking a positive step today towards
the benefits of AI technology
Why should you use AI?
1# reason – genetic diversity
Inbreeding causes inbreeding
depression which is characterized by
reduced fitness
Why should you use AI?
Inbreeding - the breeding or mating of
related individuals within a closed group
animals
When is the last time you introduced
outside genetics into your herd?
