Selection Schemes By Muzvondiwa J.V.

Introduction Breeding Value is the worth of an animal for a specific trait. Breeders always attempt to identify those animals with the best breeding values for the trait(s) they are interested in. Several methods are used to estimate breeding value. Each method has strengths and weaknesses. NB* An animal with the best breeding value may not necessarily be the animal with the best phenotype. In almost all evaluations, breeding value is most commonly expressed as a deviation from the mean of some group. Difference in reproductive rates between sexes has had a significant effect on genetic improvement schemes Advent of frozen semen combined with AI has magnified the improvement of males in genetic improvement schemes

Objectives Draw comparisons between selection schemes Critically assess the effectiveness and application of the different selection schemes for various livestock species Outline the spread of the selection schemes throughout the world Identify the selection schemes most suitable for Zimbabwe

Performance Testing Is the recording of economically important performance traits and evaluation with a view to identifying genetically superior animals Is an important tool for the genetic improvement of farm animals Involve data collection by participating farmers or a responsible agent and submission to a data processing centre. Data is analyzed at the centre to estimate the BV of tested animals Estimate s are returned to the farmer forming the basis of selection within the herd. Can be done on farm, ranch, or on central testing stations. Sometimes called own performance testing.

Perfomance testing Formula used to rank animals is; EBV = HA + h2 (Pi –HA) where; EBV = Estimated Breeding Value of animal i; HA = the herd average h2 = the heritability of the trait Pi = the record of the ith animal 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? Answer EBV = HA + h2 (Pi – HA) = 450 +0.4(550 – 450) = 490kg

Performance testing Activity What will be the EBV of a bull of 550kg yearling and in a herd average of 500kg? Based on the EBV, which bull will you buy for your herd? This selection based on the individual’s phenotype is called individual selection Most common practised For effective performance test; Treat all animals the same i.e. provide equal opportunity and manage them in contemporary groups; adjust for predictable environmental effects Accurately measure traits of interest.

Performance testing Short-comings 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 breeding value at heritabilities May overemphasize type appraisal NB* the principles of performance testing are primarily based upon within herd comparisons.

Central Test Stations 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 Remove some of the environmental differences between herds; though one cannot remove pre-test environmental differences between herds; Heritabilities 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 Provides a forum for discussion NB* Do not allow comparisons among animals tested in different seasons, years and (or) locations

National Performance Testing Programmes Beef Performance Testing Programme Beef Performance Testing Programmes include those; Conducted by AGRITEX/LPD Recorded by farmers – participating farmers record cow and calf records. Weight are taken at weaning (205 days) and 18 months (550 days) Registered – registration from Zimbabwe Herd Book (ZHB) especially on birth weights also serve as data. Dairy Cattle Recording Dairy cattle recording are; Conducted by ZHD and Zimbabwe Dairy Herd Improvement Association (ZDHIA) Obtained from regular cow performance records like ZDHIA production records

National Performance Testing Programmes Pig Performance Testing Pig performance testing is conducted by Pig Industry Board (PIB); Central Performance testing for testing is done where farmers send their animals for testing soon after weaning. At 35kg live weight, 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 boras and gilts are recorded on farm by visiting PIB staff. They are assessed on an index comprising weight for day of age and backfat thickness

National Performance Testing Programmes 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 Recordings are conducted by individual farmers and Breed Societies. Registration records often serve as data Activity What are the major weaknesses of the current performance testing schemes in Zimbabwe?

Progeny testing Method of selection widely used in livestock improvement Based on the principle that the mean performance of a progeny group should give a reliable indication of the breeding value (B.V.) of one or other of its parents since each offspring receives a random sample of genes from its parents Progeny testing attempts to predict the breeding value of one parent (usually the sire) on the basis of its offspring or progeny performance. Dams are not progeny tested (limited number of offspring that she can produce in her lifetime) A group of potential parents (usually males) are mated to a random group/samples of dams and their performance measured Potential parents are selected (usually males) basing on the average performance of offspring Selected parents are mated

Progeny testing As A1 h P1 AD1 AD2 A2 h P2 P AD3 A3 h P3 As is the breeding value of the sire AD1-AD3 BV of Dams 1 to 3 mated to one sire A1- A3 are paternal half sib progeny H is the square of heritability P1 – P3 are performance records of progenies 1 to 3 P is the average performance of the three offspring

Progeny testing Activity 1. Discuss the biases that are associated with progeny testing. 2. Design a progeny testing scheme for dairy herds in the commercial areas of Zimbabwe.

Nucleus/Cooperative/Group Breeding Multiplier Commercial

Nucleus/Cooperative/Group Breeding Traditional breed structure is pyramidal with nucleus, multiplier and commercial Apex of the pyramid is the nucleus which should follow an efficient system for genetic improvement Animals in the nucleus are genetically superior to the multiplier herd which in turn is superior to the commercial sector Genetic improvement is disseminated from the apex downwards Sires are sold from the apex through the next stratum The whole concept is based on the assumption that the nucleus is making progress for the traits that are important for improvement in the whole country herd and is constantly released Nucleus controls the genetic makeup of the whole population because the direction in which the multiplier and commercial producers must move depends on the selection and migration of males from the nucleus

Nucleus/Cooperative/Group Breeding Principles underlying the nucleus breeding scheme is that in each herd (whether nucleus, multiplier or commercial), there is a small number of genetically very superior animals which if brought together will form a nucleus whose average genetic merit is far greater than that of any of the contributing herds. important element is therefore for a group of farmers to agree to pool their high performing animals The larger the number of animals in the cooperating herds, the more successful the programme is likely to be since sampling should produce genetically superior foundation stock containing a wide degree of genetic variability Initial screening process to form an elite group is the most important step Once the nucleus is assembled, an efficient system of recording and selection is implemented including selection of young males on pedigree information and progeny testing

Nucleus/Cooperative/Group Breeding Best males are kept for breeding in the herd while other selected males are given to the cooperating herds Nucleus may remain open or closed ‘open’ system – part of the annual female replacements and males in the nucleus originate from the base herds which are then compared with those in the nucleus ‘closed’ system – no addition of animals into the nucleus is permitted after the initial screening and selection A closed nucleus herd is an established herd of superior animals where no new genes are brought in from outside and where animals perform under very similar conditions Main advantage of this group breeding scheme is that the genetic superiority of sire replacements coming into the base herds is far greater than what is achievable in each of the base herds.

Nucleus/Cooperative/Group Breeding Advantages The genetic merit of animals in the central nucleus is higher than that of individual herd. These animals are also free of structural defects since they are screened. Animals are chosen on the basis of performance under practical farm conditions, therefore, G x E interactions will not occur Replacement sires for the cooperating farms come from the nucleus unit, so the improvement quickly spreads through the group A rapid generation turnover of breeding stock is maintained Inbreeding which can occur in small units is minimised Cooperating farmers benefit from a coordinated policy, shared facilities and from the improvements achieved.

Nucleus/Cooperative/Group Breeding Ideal structure of an open nucleus scheme Is as follow as; 10% of the female replacements should be in the nucleus 50% of the female replacements should come from the base population All surplus females born in the nucleus should be used for breeding in other flocks or herds Activity How could you set up a group breeding scheme for the genetic improvement of the indigenous Sabi sheep breed in Zimbabwe?

Nucleus/Cooperative/Group Breeding Nucleus herd can be combined with progeny testing Nucleus herds are used to produce the bull that will be progeny tested Proven bulls are then used in the commercial population The larger the nucleus breeding scheme, the higher the cost, the faster the genetic progress from the nucleus to the producer. The lower the inbreeding, the greater the genetic variance ( i.e. the greater the selection differential) In the smallholder sector of then Sub Saharan Africa, factors such as single sire flock/herds, communal grazing, small herd/flock sizes, mean that group breeding schemes with on station nucleus breeding will continue to dominate. Allied to a nucleus unit must be the effective dissemination of the improved stock selected in the unit AI has an important role in ensuring extensive dissemination of superior sires. MOET can ensure the rapid distribution of superior genotypes

MOET Schemes MOET Procedures Cows of high genetic merit are treated with hormones (superovulation) to release many eggs Cows are then mated by AI to the best proven bulls Fertilized eggs are transferred from donor cows and inserted into recipient cows Young heifers are used at 1 year of age as donors for embryo transfer (E.T.) their progeny reared as potential breeding animals. The best animals are ranked and selected based on their first lactation record Special nucleus herds are established with the use of MOET Infertile cows are made pregnant thus indirectly increasing conception rate of the herd

MOET Schemes Disadvantages Reduced accuracy Increase in the rate of inbreeding Very expensive due to the high costs of embryo transfer (E.T) which have to be met (financial constraints) Activity Zimbabwe is most suited to an open nucleus MOET goat breeding scheme. Discuss this statement Why is selection of males more effective than that of females? How would you set up a beef improvement programme in your district?