breed conservation - secure
D. PHILLIP SPONENBERG, DVM, PHD
VIRGINIA-MARYLAND REGIONALCOLLEGE OF VETERINARY MEDICINE
VIRGINIA TECH, BLACKSBURG, VA
AND - THE AMERICAN LIVESTOCKBREEDS CONSERVANCY
secure
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
secure
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