breed conservation - sustain

D. PHILLIP SPONENBERG, DVM, PHD

VIRGINIA-MARYLAND REGIONALCOLLEGE OF VETERINARY MEDICINE

VIRGINIA TECH, BLACKSBURG, VA

AND - THE AMERICAN LIVESTOCKBREEDS CONSERVANCY

long term

long term success depends on a secure commercial use for each breed

assures that breeders maintain the breed for their own economic benefit

breeds are made of predictable animalsbreeds are repeatable “gene packages”can choose specific breeds for specific

production goals in specific environments

purposes of breeds

purposes of breeds

high levels of genetic variation make populations that are unpredictable

low levels of genetic variation are not viable

need to compromise between the two in order to have useful genetic resources

breed management

managing breeds assures a useful and successful role for them

without planning ahead usually have inbreeding and the problems that come with it

inbreeding arises more rapidly in rare breedseventually affects all breeds without careful

managementwell-planned management avoids problems

breed management

breed management

management has various purposes1. maintain variation and genetic health2. selection for enhanced production3. sssure economic return for owners

breeds must have good population structure to have a secure future

genetic relationships between the animals are important

bloodlines, families, and population structure are all important

breeds with high numbers can have inbreeding problems if breeders ignore genetic structure

more than numbers

population structure

all breeds need to have planned selection and reproduction to avoid inbreeding

without this planning selection causes a long, narrow bottleneck

a pyramid

elite

multipliers

commercial

standardized breed

“a bag of marbles”

no real heirarchy

landrace

both types of breeds need planned strategies for selection and breeder animal replacement

without planning it is easy to lose the genetic variation that is needed for viability

maintain variation

maintaining variation

to maintain maximum variation each animal should eventually replace itself

each sire produces a son used for breedingeach dam produces a daughter used for

breeding

little or no selection for improved production

no population growth

maintaining variation

this strategy does not work for selection for improved production

without selection the variation stays highpredictability can be too low for the breed to be

useful in practical production settings

maintenance

at the other extreme is the model used for modern industrial poultry or dairy cattle

artificial insemination with a single male and thousands of females

predictability of production is highgeneral health and resistance are low because

genetic variation is low

maintenance

need to compromise between selection and management of inbreeding

can assure the use of many sires, and that all of them contribute to the next generation

goal is an adapted population that is viable and productive

using several sires that have different grandparents minimizes bottleneck

using several sires that all have the same sire or grandsire assures a bottleneck

maintenance

important to assure that all herds contribute to the next generation

if all sires come from a single herd, this is similar to having all sires come from the same family

maintenance

maintenance

each sire produces a sire

one sire produces next sires

dramatically decreases genetics

maintenance

difficult to assure that all herds are providing sires

breeders usually have culture where a few breeders are powerful, most others have little influence

powerful breeders provide sires for most othersrare breeds need to have a much wider genetic

base than occurs with this strategy

the same strategies can work well within a single herd

ALBC has developed a “conservation breeding program” for long-term management of breeds

within a herd

conservation breeding program

the herd is divided into three groups (bloodlines) within a single herd (a, b, c) on the basis of genetic relationships

one sire at a time is used over the entire herd

the herd maintains crosses between the three groups (crossbred or linecrossed), as well as animals that have a majority genetic influence from each of the three groups (linebred)

conservation breeding

dams: A B CYear 1

sire A A/A=A A/B A/C

year 2sire B A/B B/B=B B/C

B/AB=B B/ACyear 3

sire C A/C B/C C/C=CC/AB C/AB C/

BC=CC/BAC

conservation breeding

A B Cyear 4

sire A A/A=A A/B A/CA/AC=A A/BC A/BCA/AB=A A/AB=A A/

ABC=Alikewise into the futurekey is to move of genetic material from linecrosses back

into the lines from generation to generationthe genetic material is moderately inbred in alternate

generations, and outbred in the others

conservation breeding

every step has opportunities for selection for performance

in cattle this works well, because a single two year old bull can be used in any one year

multiple bloodlines assures that there will be crosses among them, as well as moderately linebred animals within each bloodline.

these are replenished in each year depending on the sire used

conservation breeding

using linebred sires from each bloodline assures that these will be distantly related to the females of the other bloodlines

assures that linecrosses are always possibleusing linecross sires assures that few matings

are linecrosses, so inbreeding increasescomplicated in the beginning stagesafter it is started it is easy to continue

select a linebred replacement sire each yearuse when two years old

conservation breeding

in one sample year these are the males:a two year old bull (or two), used over the herd,

from bloodline “A”a yearling bull (or two or three), from bloodline “B” to use next yearbull calves from bloodline “C” to use in two years

conservation breeding

sires are selected from those linebred to the bloodine of the year

dams are selected from two sorts of femaleslinebred to the bloodline of the yearlinecross between the bloodline of the

yearand the other two bloodlines

conservation breeding

assures that the genetic material is in a linecross condition in some animals/generations, and a linebred condition in other animals/generations

permits selection in both conditions

shapes a strong genetic structure

conservation breeding

can be tailored for different situations

herds can be split to use multiple males each year

include both linebred and linecross matings in each group

multiple herds can cooperate by periodic exchange of males

managing landraces

in landraces it is nearly impossible to discover all animals of the breed

nearly always pure animals or herds that have escaped documentation

the breed will be changed from including animals that are not pure

also important to include all pure ones in order to keep the breed strong genetically

landraces

most landraces have an inspection process in order to include new animals into the registry

landraces

always better to inspect an entire herd for purity than it is to inspect individual animals

mistakes less likely with a herd than with individual animals

genetic management

every breed has a few animals in it that have great importance for the genetic health of the breed

usually animals with rare bloodlines or from rare families

important to discover and document these to not lose their genetic influence

important individuals

unique or important sires can be used relatively widely in the breed

unique or important dams can be mated to their own sons, trying to get a son that is 3/4 the genetic influence of the original dam, and then use the son widely