breed conservation - secure

1. breed conservation - secure • D. PHILLIP SPONENBERG, DVM, PHD • VIRGINIA-MARYLAND REGIONAL • COLLEGE OF VETERINARY MEDICINE • VIRGINIA TECH, BLACKSBURG, VA • AND - THE AMERICAN LIVESTOCK • BREEDS CONSERVANCY

2. secure • Some populations are poorly defined and need definition, census and organization in order to persist • Some small populations need to be rescued to maintain their genetic variation in order to persist

3. secure • In either case, action is needed • action must be planned and intentional rather than letting events just unfold

4. 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

5. rescue • for standardized breeds this is easy • animals 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

6. rescue • landraces with several herds present challenges • need to decide which animals to include, which to exclude • best to have a specific protocol to accept animals • the protocol should work into the future • it is common to discover typical animals even after several years of active work • newly discovered animals/herds offer good genetic variation to the breed

7. census • sex • age • relationships between animals

8. census • information can guide a breeding plan to assure equal or balanced influence of founders

9. rescue program • 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

10. rescue program • goal is a herd that is large, diverse, and represents all of the founders • need to: • increase numbers • assure genetic variability • maintain / not lose breed characteristics

11. founders • many herds have females from an old line • few or no males available from that line • the majority of genetic variation is in the females

12. rescue program • use the females and one original male to produce males that are remotely related to one another Original females male Two or three sons Two males from each sire Two males from each sire

13. rescue program • First generation – half brothers • Second generation – quarter brothers • Third generation – eighth brothers original females male Two or three sons Two sones from each sire Two sons from each sire

14. 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

15. 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

16. rescue • sometimes only older females are available • no males of the same bloodline • mate sons to mothers, hoping for sons • changes the sex in which the genetic material resides, so that it can be used more widely

17. rescue • mating son to mother is extreme inbreeding • only 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 generation • follow with outbreeding the next generation

18. rescue • genetic management of a herd • one sex is used for short breeding lives • the 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

19. rescue program • use a single male for the first step • use two sons from old females for the second step • use 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 sires • allows the beginning of a conservation program with three bloodlines in one herd • dynamics will be different in different species

20. rescue program • cattle and horses (long generations) • use males over entire herd • rotate through the bloodlines from year to year • sheep and goats (short generations) • can split the herd into different breeding groups each year

21. 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

22. examples

23. Randall cattle • landrace of northern European origin in the northeast USA • triple purpose: • draft (oxen) • milk • meat

24. Randall cattle • one herd rescued from extinction • branch of landrace once widespread throughout the northeast of the USA for centuries

25. Randall cattle • history of local use without crossbreeding • origin was northern European cattle

26. Randall cattle • founding population had few animals • herd management was to use a single bull over the entire herd, and use him for several years • all of the cattle born in a single year are half siblings • potentially those from adjacent years are half siblings as well

27. 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

28. 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

29. 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

30. 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 program • a challenge was the high level of inbreeding

31. 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 year • The matings had two distinct strategies: • 1. minimize inbreeding • 2. maximize concentration of each founder in some animals • each mating accomplished one or the other

32. Randall cattle • contribution of founders

33. Randall cattle • manage the % contribution of the founders • semen frozen on bulls that have a high % contribution of an individual founder • use these “high %” animals to balance that founder throughout the herd • increases the long-term possibility of matings with a minimal level of inbreeding

34. 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 problems • others have good reproduction, growth rate, and health

35. Java chicken • big, strong, productive chickens • had become weak small animals due to inbreeding

36. Java chicken • two isolated bloodlines • crosses between these two resulted in larger, strong birds more like the originals • both bloodlines had low numbers • the breed needs a careful breeding program

37. Java chicken • option one: • maintain a single mixed population from the original two

38. 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

39. Java chicken • option two: • maintain a composite population as well as the original two as isolated strains

40. 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 weaker • serves conservation fairly well, but lacks strength in commercial usefulness because two of the populations are weak and only maintained as genetic reserves

41. Java chicken • option three: • maintain composite population and original two • with the addition of one-fourth influence from the composite population

42. 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

43. Java chicken • option four: • separate the composite population to produce several new subpopulations • isolated except for crosses every three or four generations

44. Java chicken

45. Java chicken • option four: • this strategy divides the population • tends to maintain genetic variation for long term • genetic drift will occur in different directions in each subpopulation • overall variation usually persists because what is lost in one group is retained in another