1. SELECTION SCHEMES

2. SELECTION SCHEMES
There are three procedures used in selection schemes:
Performance testing
Progeny testing
Nucleus breeding schemes
Group breeding schemes
MOET breeding schems

3. PERFORMANCE TESTING / OWN PERFORMANCE TESTING
Definition: The recording of economically important performance traits and evaluation with a view to identifying genetically superior animals.
Procedure
It involves data collection by participating farmers or a responsible agent and submission to a data processing centre.
The data is analysed at the centre to obtain estimates of BVs of tested animals.
These estimates are returned to the farmer and thus form the basis of selection within the herd.

4. PERFORMANCE TESTING / OWN PERFORMANCE TESTING
Performance testing can be done on farm, ranch or on central testing stations.
It is important to ensure that animals being compared are given equal opportunities to perform under uniform feeding and management conditions.
These conditions should also represent nutritional and managerial regimens which are practical and comparable to those under which the progeny are expected to perform.

5. PERFORMANCE TESTING / OWN PERFORMANCE TESTING
The formula used to rank (compare animals) is:
EBVi = HA + h2(Pi – HA)
Where:
EBVi = the estimated breeding value of animal i;
HA = Herd average;
h2 = the heritability of the trait; and
Pi = the record of the ith animal.

6. PERFORMANCE TESTING / OWN PERFORMANCE TESTING
Example: A breeder has a herd average of 450kg for yearling weight. He has a bull which has a yearling weight of 550kg. Heritability for yearling weight is 0.4. What is the EBV for the bull?

7. PERFORMANCE TESTING / OWN PERFORMANCE TESTING
Solution:
EBVi = HA + h2(Pi – HA)
= (550 – 450)
= 490kg
What will be the EBV of a bull of 550kg yearling weight in a herd average of 500kg?
Based on the EBV, which bull will you buy for your herd?
Do you think this can be done for cows?

8. PERFORMANCE TESTING / OWN PERFORMANCE TESTING
Own performance testing which is based on the individual’s phenotype is called INDIVIDUAL SELECTION.
It is the most common type of selection practised.
The accuracy of individual selection is rGP = h.
Hence, when h2 is low, accuracy is low

9. PERFORMANCE TESTING / OWN PERFORMANCE TESTING
For effective performance test:
Treat all animals the same i.e. provide equal opportunity and manage them in contemporary groups (a group of animals of the same age and sex raised on the same farm and managed alike).
Adjust for predictable environmental effects;
Accurately measure traits of interest.

10. PERFORMANCE TESTING / OWN PERFORMANCE TESTING
Disadvantages of individual selection or performance testing:
Several traits are sex-limited, and hence, performance tests cannot be conducted in both sexes;
Some traits can only be measured late in life or after slaughter;
Individual merit is a poor indicator of BV at low heritabilities;
It may over-emphasize type appraisal.
It does not allow for between herd comparisons.

11. Performance testing on Central Test Stations
Procedure:
Farmers bring animals which were born and raised for some time in different herds to a common environment to test certain performance traits, primarily growth traits.
Advantages
This helps remove some of the environmental differences between herds; though one cannot entirely remove pre-test environmental differences between herds.

12. Performance testing on Central Test Stations
Heritability of test station performance is probably lower than that of within herd performance.
Central test station results can be a valuable educational and marketing tool in that the concept of performance testing is a big thing for performance-minded breeders. It can also provide a forum for discussion.

13. Performance testing on Central Test Stations
Disadvantages
The major weakness is that test station results do not allow comparisons among animals tested in different seasons, years and (or) locations.

14. National Performance Testing Programmes in Zimbabwe
Beef Performance Testing Programmes include those:
Conducted by AGRITEX;
Recorded by farmers-participating farmers record cow and calf records. Weights are taken at weaning (205 days) and 18 months (550 days)
Registered – registration records from the Zimbabwe Herd Book (ZHB) especially on birth weights also serve as data

15. National Performance Testing Programmes in Zimbabwe
Dairy Cattle Recording:
conducted by ZHB and Zimbabwe Dairy Herd Improvement Association; and
Obtained from regular own performance records like ZDHIA production records

16. National Performance Testing Programmes in Zimbabwe
Pig Performance Testing conducted by PIB
Central performance testing is done, where farmers send their animals for testing soon after weaning. At 35kg liveweight, they are put on test until 86kg. The animals are ranked on an index consisting of average daily gain, feed conversion ratio and ultrasonic backfat thickness.
PIB also conducts on-farm performance testing (often called a multiplication test) in which promising young boars and gilts are recorded on-farm by visiting PIB staff. They are assessed on an index comprising weight for day of birth and backfat thickness

17. National Performance Testing Programmes in Zimbabwe
Small ruminants (Sheep and Goats)
No performance recording scheme has been developed for sheep and goats in Zimbabwe. Recordings for small ruminants are conducted only by individual farmers and breed societies.
Poultry and Ostriches
Poultry and Ostrich recordings are conducted by individual farmers and Breed societies. Registration records serve as data.

18. PROGENY TESTING Progeny are offspring or children of animals.
Progeny testing is a method of selection widely applied in livestock improvement.
It is based on the principle that the mean performance of a progeny group should give a reliable indication of the breeding value of one or the other of its parents, since each offspring receives a random sample of genes from its parents (1/2 of them from each parent).

19. PROGENY TESTING
In progeny testing one attempts to predict the BV of one parent (usually the sire) on the basis of its offspring or progeny performance.
Dams are usually not progeny tested because of the limited number of offspring that she can produce in her lifetime.

20. PROGENY TESTING
In progeny testing, a group of potential parents (usually males) are mated to a random group/ samples of dams and their progeny performance measured.
Selection between the potential parents (sires) is on the basis of their progeny group average, weighted to take account of different numbers of progeny.
This is followed by mating of the selected parents to produce a second batch of progeny.
These are the next generation of potential parents which are then progeny tested.

21. PRINCIPLE OF PROGENY TESTING

22. PROGENY TESTING Advantages of progeny testing
AI has made it possible to select intensively and more accurately for the SS and SD pathways. More sires can be tested with each sire having many progeny spread across many herds. Progeny testing has been used widely in dairy cattle breeding.
Animals are tested in the environment in which they are going to be used later on.
The cow population is large hence a wide genetic base.

23. PROGENY TESTING Disadvantages of progeny testing
It takes long before a sire is evaluated since it has to wait for its progeny’s records to be collected. This is even worse if the trait is expressed late in life. For example, the earliest that milk records can be completed is when a heifer is 34 months old. Delays in evaluating sires result in long generation intervals hence slow rates of genetic progress.
Progeny of test sires should not be culled. They are kept till they reach producing stage and at a cost.

24. PROGENY TESTING
The offspring of test sires are usually found in different herds and are treated differently in these herds. The effect of different management in herds (herd effect) has been shown to account for about 60% of the variation in milk yield.
Selection is not controlled entirely by scientists. Farmers may have slightly different interests and therefore select for other traits other than those defined for the program thus resulting in slower rates of progress.
Animals to be recorded are in various herds and transport costs can be high.

25. NUCLEUS BREEDING SCHEMES
Rather than disperse breeding and selection over many breeders (herds) and units, it may be better to concentrate efforts in dedicated selection stocks and units.
These are called nucleus units and stocks.
This is the main system used by poultry and pig breeding companies and has also been used in sheep in Australia and New Zealand and; most recently in dairy cattle breeding.

26. The traditional breed structure

27. NUCLEUS BREEDING SCHEMES
The nucleus herd is set up by screening animals from the base population.
The top animals are moved to the nucleus herd.
This makes the nucleus herd genetically superior to the base population.
Selection is then practised within this nucleus herd.
The elite animals are used as sires and dams of the next generation in the nucleus.
The next top animals (particularly males) are sold to the base population and are sires of the next generation.

28. NUCLEUS BREEDING SCHEMES
Once the nucleus herd is established, it can either be kept closed or open.
A closed herd is one where no genetic material is allowed into the herd from outside.
An open nucleus allows some genetic material (mainly females) to be brought in from the base population. Occasionally, males (or semen) can be brought in from foreign populations or even from the base population.

29. NUCLEUS BREEDING SCHEMES
Advantages of nucleus breeding schemes
The selection objectives are clearly defined. It is easier to stick to the objectives since selection is practised in one herd. It therefore should be likely to achieve the theoretical rates of response.
Since the best animals are used to set up the nucleus, the herd benefits from this initial genetic lift.
Husbandry is controlled to ensure a fair test of genetic merit.
It is possible to take more frequent measurements since animals are all in one herd.

30. NUCLEUS BREEDING SCHEMES
It is possible to measure difficult traits, eg., feed efficiency.
The running costs of the scheme may be lower since all animals are in one herd.
It is possible to use more expensive or complicated technology.
Limited expertise can be concentrated in one herd.
Fast rates of genetic progress.

31. NUCLEUS BREEDING SCHEMES
Disadvantages of nucleus breeding schemes
The nucleus is a small breeding unit compared to a national breeding population.
The faster generation turnover of the nucleus herd tends to increase the rate of inbreeding per year. However, it is possible to have several nucleus schemes with exchanges of genetic material among them which will then decrease the inbreeding problem.

32. NUCLEUS BREEDING SCHEMES
Disease can wipe out the one herd. To avoid this, it is advisable to keep different age groups at different locations.
Possible G x E interaction in commercial production.
High initial capital.

33. NUCLEUS BREEDING SCHEMES
Examples of nucleus breeding schemes are:
Group breeding schemes; and
MOET nucleus schemes

34. Group breeding schemes
A group of farmers get together and form a group breeding scheme.
Interest in such schemes is generated by the basic genetic principle that it is possible to apply selection pressure in a large population than on a small one.

35. Group breeding schemes
Procedures:
Interested breeders join the group.
Members contribute top performing females to the nucleus herd.
Practise selection of females in the nucleus. Replacements can also be obtained from outside the nucleus herd (open nucleus).
Elite females are mated to top sires to breed sires for use within the nucleus.
Members of the group receive males from the nucleus.

36. Group breeding schemes
Group breeding schemes have been used mainly in New Zealand and Australia. The species for which they have been commonly used is sheep.
In addition to the advantages already listed for nucleus breeding schemes, group breeding schemes have the following additional advantages:
There is a great extension potential as group members usually gather annually to attend field days.
Financial resources are pooled and so are genetic resources resulting in an efficiently run program.

37. MOET NUCLEUS SCHEMES
MOET nucleus schemes are based on multiple ovulation and embryo transfer (MOET).
The MOET techniques make it possible to increase full sib family sizes to the point where information on collateral relatives (both full and sibs) can contribute significantly to the prediction of an animal’s breeding value.

38. MOET NUCLEUS SCHEMES Procedure:
The females identified as donor dams are grouped in one herd. The females can be selected at a young age (12 to 15 months) on the basis of parent and other relatives’ information (Juvenile MOET scheme). In an adult MOET scheme, selection decisions are delayed until the candidates themselves produce lactation records. Their own records and those of parents and other relatives are used to evaluate the animals.

39. MOET NUCLEUS SCHEMES
The selected females are given drugs to produce a lot of ova (superovulation). They are inseminated with semen from elite bulls. These elite bulls initially are from the base population. Later on, they are selected from within the nucleus. The embryos are collected from the cows and transferred to recipient cows.

40. MOET NUCLEUS SCHEMES
The elite offspring from the above matings are used as parents of the next generation in the nucleus. Some (males mainly) are sold to the base population and the low ranking ones are culled.
The nucleus herd can be open or closed.

41. MOET NUCLEUS SCHEMES Advantages of MOET nucleus schemes
The generation interval is reduced since sister records, rather than progeny records, are used to evaluate bulls.
Rates of genetic progress are faster for MOET schemes than for conventional schemes.

42. MOET NUCLEUS SCHEMES Disadvantages of MOET nucleus schemes
The technique of MOET is currently expensive.
The accuracy of evaluation is usually lower than when progeny information is used as a bull is likely to have more progeny than sisters. However, the accuracy of evaluation for females can be improved.
There are operational difficulties in implementing a MOET that are associated with embryo transfer. Some cows may fail to respond to superovulation and yield no embryos. This will result in the reduction of the female selection differentials.