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Quantitative Genetics ANS 512 Introduction Purpose Texts By T.N. Gondwe, PhD Lecture 1 Course Aims • To equip students with knowledge of population genetics and principles of animal breeding as applied to livestock improvement • To enable students to apply theory of quantitative genetics to improve livestock performance through breeding in all sectors Course outcome • By the end of the course, students should be able to •demonstrate an understanding of principles of quantitative genetics •show an understanding of how to apply the principles in livestock improvement through breeding practices Topics of study • Background to animal breeding • Genetic constitution of a population, a review • Quantitative traits and measures of quantitative traits • Principles of selection • Response to selection and its prediction • Inbreeding and relationship • Effect of population size on inbreeding and genetic drift • Crossbreeding and heterosis Topics of study • Practical on • Calculation of gene and genotype frequencies • Performance recording including data processing • Estimation of heritability • Prediction of selection response • Computing inbreeding and crossbreeding parameters Texts Prescribed • Falconer, DS and Mackay, TCF (1996). Introduction to Quantitative Genetics • Wiener, G. (1994). Animal Breeding. CTA, The Tropical Agriculturalist. Macmillan Press Ltd., London. • Simm Geoff (2000). Genetic Improvement of cattle and sheep. CABI Publishing, Wallingford, Oxon OX10 8DE, UK Recommended • Legates, JE and Warwick, EJ (1990). Breeding and improvement of farm animals • Chapman, A.B. (Ed) 1985: General and quantitative genetics. Elsevier, Amsterdam. Assessment • Course Work 40 % • End of Course Exam 60 Topic 1: Genetic approach to animal improvement Aim • To introduce to students quantitative genetic approach to livestock improvement Objectives • Upon completion of the topic, students should be able to 1. Recall the roles of keeping livestock 2. Discuss the need to improve animal performance 3. Explain the genetic and non-genetic (environmental) approaches to livestock improvement 4. Discuss advantages and disadvantages of each approach 5. Discuss potential of genetic improvement in developing countries Objective of Genetic Approach To improve animal performance through breeding By applying principles of genetics Review roles of animals / livestock ~ how can you measure these roles? Source of food (eggs, meat, milk, etc) Animal power (draught power) Provide organic fertilizer, chicken manure, 5 % N, 21 % Ash Hides and skins Income and coping against hunger Cultural, leisure, prestige, etc. These roles of livestock Constitute animal performance That is shown physically (Qualitative) or through measurement (Quantitative) And need to be improved Animal performance Is expressed as Phenotype What we observe (e.g. hair coat) or measure (e.g. milk yield). In general, external expression of an animal That constitutes Genetic (internal factors), and Non – Genetic (external factors) components P = Phenotype G+E Genetic Environment Animal performance levels depend on Genotype Housing Climate Sex Age Health Nutrition Management Animal performance Phenotype Environment Genotype Basic approaches towards improving performance There are two Environmental approach Genetic approach These can work separately but works better when combined Environmental approach This works by improving the animal environment This exploits the E component that is non – genetic (external factors) You manipulate the environment to make it more favourable for animal growth, reproduction P = G + E Environmental approach involves Climate / housing conditions Nutrition Health conditions Management (handling and care of animals) Environmental approach You improve animal performance through Good feeding (Nutrition) Quality of feeds, frequency of feeding Improving animal health You prevent and control animals from diseases and parasites By vaccinations, prophylaxis, antibiotics, sanitation, treatment, clean water Environmental approach Through growth hormones That make animals grow bigger And all aspects that enhance better environment for the animals Good animals can be produced from good environment Advantages of environmental approach Quick response is obtained e.g., change from bad to good feeding Results get realised within a week Problems with environmental approach Improvement tend to be temporal Once you withdraw the manipulation, performance goes down Such as withdrawing drugs, feeding The potential of an animal to produce is determined by its genetic make up If genetic potential of zebu is 320 kg, that is the maximum it can achieve, no matter what environmental manipulation ~ liken to capacity of a car tank Problems with environmental approach P = G Limit + E Problems with environmental approach Local and Ross Four week old, Intensive At 8 wks, 2.0 kg Eight weeks old chicks, free range At 8 wks, .8 kg Problems with environmental approach 600 Live weights (g) 500 400 300 BA Local 200 100 0 1 2 3 4 5 6 7 8 Age (wks) Comparing BA and Local chickens at 8 weeks, under similar management Genetic approach to animal improvement In order to change the limit of an animal, there is need to use this approach You manipulate the genes or genetic makeup of an animal This elevates the genetic potential of an animal With this approach, you exploit the Genetic component P = G + E Genetic approach to animal improvement Goodness is that once you manipulate the genes, that tend to be permanent With this approach, the improvement is therefore, permanent You increase an animal potential by concentrating desirable genes Using various theories and means that will be discussed in the course Problems with genetic approach Despite having permanent gain, the improvement is very slow It may take four generations for the improvement project to be successful This may be > 15 years in Zebu Cattle It is shorter periods with smaller animals Due to high and fast reproductive rates and generation intervals Problems with genetic approach Despite the permanent improvement, you also need to improve the environment so that improved genes could fit in and express their potential Hence simultaneously improve feeding, management, housing, disease control etc. Problems with genetic approach Good feed Poor feed Problems of Genetic approach, Malawi case Most project in Malawi run for 4 – 5 years And later get abandoned due to lack of personnel, funds, proper planning of breeding goals and programmes There is high labour turn over in universities and government research institutes Hence genetic progress does not seem to make progress Potential of genetic improvement in SADC Is quite high Through existence of indigenous breeds That have not been exploited yet And possess a biodiversity of genotypes In almost all species Different livestock improvement approaches Basic farm practical in feeding, management, disease control facilitates better environment, hence improvement through environmental approach Understanding genetics, keeping records enable knowing the animal you work with in terms of its performance, feed consumption, reproduction, products and this facilitates genetic improvement of livestock