breed conservation - secure

D. PHILLIP SPONENBERG, DVM, PHD

VIRGINIA-MARYLAND REGIONALCOLLEGE OF VETERINARY MEDICINE

VIRGINIA TECH, BLACKSBURG, VA

AND - THE AMERICAN LIVESTOCKBREEDS CONSERVANCY

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1. Some populations are poorly defined and need definition, census and organization in order to persist

2. Some small populations need to be rescued to maintain their genetic variation in order to persist

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In either case, action is needed

action must be planned and intentional rather than letting events just unfold

rescue

rescue works best if carefully planned

always best to have a complete census

when all animals are in a single herd this is easy

for standardized breeds this is easyanimals that are typical purebreds even though

they have lost their identity or registration in the breed should be included

these animals are likely to have important genetic variation for the genetic health of the breed

this can be politically difficult with old, established breeders that have consistently registered animals

rescue

rescue

landraces with several herds present challengesneed to decide which animals to include, which

to excludebest to have a specific protocol to accept

animalsthe protocol should work into the futureit is common to discover typical animals even

after several years of active worknewly discovered animals/herds offer good

genetic variation to the breed

census

sexagerelationships between animals

information can guide a breeding plan to assure equal or balanced influence of founders

census

small herds need specific genetic rescue program

goal is a population with strong genetic structure

with this structure the population can advance to the future

assures future possibility for selection for production

assures the breed a role in future agriculture

rescue program

rescue program

goal is a herd that is large, diverse, and represents all of the founders

need to:increase numbersassure genetic variabilitymaintain / not lose breed characteristics

founders

many herds have females from an old linefew or no males available from that line

the majority of genetic variation is in the females

rescue program

use the females and one original male to produce males that are remotely related to one another

male Original females

Two or three sons

Two males from each sire

Two males from each sire

rescue programFirst generation – half brothersSecond generation – quarter brothersThird generation – eighth brothers

maleoriginal females

Two or three sons

Two sones from each sire

Two sons from each sire

rescue

eventually the herd develops males that are distantly related to the daughters of other sires

less related than the earliest generations

this strategy manages inbreeding at low levels despite a lack of males at the start

rescue

opposite to using a single male for several years

single male/ several years is common in many herds

using a single male for many years increases inbreeding rapidly and severely

rescue

sometimes only older females are availableno males of the same bloodlinemate sons to mothers, hoping for sonschanges the sex in which the genetic material

resides, so that it can be used more widely

rescue

mating son to mother is extreme inbreedingonly wise if unrelated animals in the breed can

then be mated to the inbred result

inbreeding generation after generation is especially damaging

inbreed for only one generationfollow with outbreeding the next generation

rescue

genetic management of a herdone sex is used for short breeding livesthe other is used for long breeding lives

usually more logical to use females for long lives, and males for short lives

avoids a genetic bottleneck

rescue program

use a single male for the first stepuse two sons from old females for the second

stepuse these two on different parts of the herd to

assure the production of relatively unrelated sons from each

next use three males from two different siresallows the beginning of a conservation program with three bloodlines in one herd

dynamics will be different in different species

rescue program

cattle and horses (long generations)use males over entire herdrotate through the bloodlines from year to year

sheep and goats (short generations)can split the herd into different breeding groups each year

rescue

using a single male for several years on entire herd of rare breed animals results in several problems

first generation, replaces half of original genetic material in the females with that of the one male

second cross (sire to daughters) the offspring only have one fourth of the original genes from dams

original genetic variation in the females is quickly reduced and lost

effective conservation requires planning and not actions without careful plans

examples

Randall cattle

landrace of northern European origin in the northeast USA

triple purpose:draft (oxen)milkmeat

Randall cattle

one herd rescued from extinctionbranch of landrace once widespread throughout

the northeast of the USA for centuries

Randall cattle

history of local use without crossbreedingorigin was northern European cattle

Randall cattle

founding population had few animalsherd management was to use a single bull over

the entire herd, and use him for several yearsall of the cattle born in a single year are half

siblingspotentially those from adjacent years are half

siblings as well

Randall cattle

founding population

one bull and five cows are offspring of a single bull (now dead) with six different cows as dams

two bulls and four cows that are younger resulted from the bull and cows of the previous group

one bull resulted from a younger bull and an old cow now dead

Randall cattle

in spite of the historical inbreeding in the herd, the phenotype of the cattle varied among three distinct types

this variation raised doubts that history was accurate

these might have been crossbred cattle

Randall cattle

blood types were used to validate history and importance of this herd for conservation

most blood type loci had minimal variation, in keeping with the history of isolation

one blood type (i103j’k’o’) is rare in other breeds, pointing to a unique, old population

two animals were negative for an old blood type “wisconsin” which is extremely unusual

Randall cattle

blood type evidence reveals the herd history was accurate, despite persistence of different types.

those types are likely due to only a few genes, which can happen in some breeds

the breed needed a conservation programa challenge was the high level of inbreeding

Randall cattle

breeding system changed from using one bull for years, to using two or three bulls each year

each bull used for only one yearThe matings had two distinct strategies:

1. minimize inbreeding2. maximize concentration of each

founder in some animalseach mating accomplished one or the other

Randall cattle

contribution of founders

founders 1 2 3 4 5 6 7 8 9 10 11 12

average % in all cattle

35 16 15 5.7 7 4 5.9 2.8 4.3 2.8 2 0.9

average % in cattle alive in 2005

33 16 15 5.7 7 4 5.9 2.5 4.6 2.4 2.1 1.5

minimum % in cattle alive in 2005

12 0 2 0 0 0 0 0 0 0 0 0

maximum % in cattle alive in 2005

48 50 25 38 25 50 25 19 25 13 25 50

Randall cattle

manage the % contribution of the founderssemen frozen on bulls that have a high %

contribution of an individual founderuse these “high %” animals to balance that

founder throughout the herdincreases the long-term possibility of matings

with a minimal level of inbreeding

Randall cattle

an extreme example of the potential for conservation of extremely small populations

currently the breed is 400 head (from 12 founders)

some cattle have reproductive problemsothers have good reproduction, growth rate, and

health

Java chicken

big, strong, productive chickenshad become weak small animals due to

inbreeding

Java chicken

two isolated bloodlinescrosses between these two resulted in larger,

strong birds more like the originals

both bloodlines had low numbers

the breed needs a careful breeding program

Java chicken

option one:maintain a single mixed population from the

original two

Java chicken

option one:

eventually this composite population based on the two founder lines will lose its ruggedness due to inbreeding

this strategy lacks an option to maintain variation and avoid inbreeding

Java chicken

option two:maintain a composite population as well as the

original two as isolated strains

Java chicken

option two:this strategy maintains almost all of the variation

in the original two populations, but in one strong and two weak populations

strong composite will eventually become weakerserves conservation fairly well, but lacks

strength in commercial usefulness because two of the populations are weak and only maintained as genetic reserves

Java chicken

option three:maintain composite population and original twowith the addition of one-fourth influence from the

composite population

Java chicken

this strategy assures that the populations remain well differentiated genetically in order to augment one with the other in the future should inbreeding depression arise

this provides an opportunity to have three reasonably strong and productive populations

Java chicken

option four:separate the composite population to produce

several new subpopulationsisolated except for crosses every three or four

generations

Java chicken

Java chicken

option four:this strategy divides the populationtends to maintain genetic variation for long termgenetic drift will occur in different directions in

each subpopulationoverall variation usually persists because what is

lost in one group is retained in another