breed conservation - sustain

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

2. 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

3. purposes of breeds • breeds are made of predictable animals • breeds are repeatable “gene packages” • can choose specific breeds for specific production goals in specific environments

4. 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

5. 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

6. breed management • inbreeding arises more rapidly in rare breeds • eventually affects all breeds without careful management • well-planned management avoids problems

7. breed management • management has various purposes • maintain variation and genetic health • selection for enhanced production • sssure economic return for owners

8. more than numbers • 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

9. population structure • all breeds need to have planned selection and reproduction to avoid inbreeding • without this planning selection causes a long, narrow bottleneck

10. standardized breed • a pyramid • elite • multipliers • commercial

11. landrace • “a bag of marbles” • no real heirarchy

12. maintain variation • 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

13. maintaining variation • to maintain maximum variation each animal should eventually replace itself • each sire produces a son used for breeding • each dam produces a daughter used for breeding • little or no selection for improved production • no population growth

14. maintaining variation • this strategy does not work for selection for improved production • without selection the variation stays high • predictability can be too low for the breed to be useful in practical production settings

15. 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 high • general health and resistance are low because genetic variation is low

16. 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

17. maintenance • using several sires that have different grandparents minimizes bottleneck • using several sires that all have the same sire or grandsire assures a bottleneck

18. 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

19. maintenance • each sire produces a sire • one sire produces next sires • dramatically decreases genetics

20. 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 others • rare breeds need to have a much wider genetic base than occurs with this strategy

21. within a herd • the same strategies can work well within a single herd • ALBC has developed a “conservation breeding program” for long-term management of breeds

22. 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)

23. conservation breeding • dams: A B C • Year 1 • sire A A/A=A A/B A/C • year 2 • sire B A/B B/B=B B/C • B/AB=B B/AC • year 3 • sire C A/C B/C C/C=C • C/AB C/AB C/BC=C • C/BAC

24. conservation breeding • A B C • year 4 • sire A A/A=A A/B A/C • A/AC=A A/BC A/BC • A/AB=A A/AB=A A/ABC=A • likewise into the future • key is to move of genetic material from linecrosses back into the lines from generation to generation • the genetic material is moderately inbred in alternate generations, and outbred in the others

25. 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

26. 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 possible • using linecross sires assures that few matings are linecrosses, so inbreeding increases • complicated in the beginning stages • after it is started it is easy to continue • select a linebred replacement sire each year • use when two years old

27. 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 year • bull calves from bloodline “C” to use in two years

28. conservation breeding • sires are selected from those linebred to the bloodine of the year • dams are selected from two sorts of females • linebred to the bloodline of the year • linecross between the bloodline of the year • and the other two bloodlines

29. 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

30. 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

31. 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

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

33. 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

34. 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

35. 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